Sept. 2, 2026
There's Something Molten Under Mars's South Pole
Today's episode — S05E183, Wednesday September 2, 2026: Main story: A thermal anomaly beneath Mars's south pole. Writing in Nature on August 27, a team led by Alexander Berne (Caltech PhD '26, now University of Arizona) reports that the interior of Mars's southern hemisphere is 200–400 °C hotter than the northern hemisphere and partially molten. The team used tidal tomography — measuring how much the solid body of Mars flexes under the Sun's tidal pull by tracking minute velocity changes in three orbiters (Mars Global Surveyor, Mars Odyssey and Mars Reconnaissance Orbiter) across roughly 25 years of radio tracking data. Hotter, softer rock deforms more, so the degree of flex reveals interior temperature. The result offers a deep-interior explanation for the Martian crustal dichotomy — the sharp division between the smooth low northern plains and the ancient, thickly crusted southern highlands, unexplained since the Viking era — and also accounts for the concentration of crustal magnetic anomalies in the south and the unexpectedly strong seismic-wave damping seen by InSight. The cause of the asymmetry remains open: a giant early impact, lopsided mantle convection, or a heat-trapping compositional layer. Co-authors span Brown University, NASA Goddard, the University of Arizona, Academia Sinica, the University of Rome, TU Delft, UCLA, UT Austin, CU Boulder and UC Santa Cruz. Crew-13 stands down. NASA and SpaceX announced on August 29 that an oxidizer leak had been found in the Dragon spacecraft's propulsion system during standard prelaunch processing, delaying the Crew-13 launch from its September 12 target. Teams are performing additional tests and data review and will complete any necessary rework before flight; a new target date will be announced once available. The crew is commander Jessica Watkins (NASA), pilot Luke Delaney (NASA), and mission specialists Joshua Kutryk (CSA) and Sergey Teteryatnikov (Roscosmos), flying an approximately seven-month increment with significant station maintenance and several spacewalks planned. Swift is observing again. NASA's Neil Gehrels Swift Observatory restarted science operations on August 26, with two of its three instruments back online and the third expected within weeks. Swift's telescopes had been powered down progressively — the ultraviolet/optical and X-ray telescopes in February, the Burst Alert Telescope in April — to reduce power draw and atmospheric drag while awaiting a boost from Katalyst Space's LINK spacecraft, launched in July. NASA announced on August 19 that LINK would not attempt the capture after developing attitude-control problems. With no rescue coming, NASA has restarted the instruments to extract as much science as possible. NASA expects Swift to fall below roughly 300 km (185 miles) — where telescope operations become impractical — within the next one to two months. Katalyst will still fly proximity operations to demonstrate in-orbit servicing techniques. An 80,000-year mission to Alpha Centauri. The Seattle-area nonprofit Fermi Explorer Mission announced plans to launch a 100–200 kg probe toward Alpha Centauri (4.4 light-years away) at the end of 2029, most likely on a SpaceX rideshare. Solar electric propulsion plus repeated perihelion pumping manoeuvres would build a cruise speed of 24.2 km/s (about 54,000 mph) — faster than New Horizons at Pluto — for a journey of roughly 80,000 years: 12 years of active operations followed by around 79,500 years of coasting. Budget is under $15 million, with $10 million verbally pledged. Payload is at least 1 kg in a shielded 10 cm cube, including a digitised Voyager Golden Record, messages from children worldwide, and cosmic-ray detectors. Co-founders Philip Johnston, Ezra Feilden and Adi Oltean are behind the space computing company Starcloud; the advisory board includes Rob Meyerson (former Blue Origin president) and Jeff Thornburg (former SpaceX propulsion lead). Johnston: "We'll be the first to leave, and the last to arrive." It would be the first spacecraft deliberately aimed at a specific star. Tonight's sky and the month ahead: Five naked-eye planets are in play through September. Venus dominates the early evening, low in the west/west-southwest about 14° up an hour after sunset (Sydney sunset ≈ 5:34pm AEST), still close to Spica after last night's conjunction, and building to maximum brilliance on September 18 — with a thin crescent Moon alongside on the 14th. Saturn is up most of the night at magnitude +0.4 with its rings tilted just 8° from edge-on, the narrowest in about a dozen years, and rides far higher for Southern Hemisphere observers than for northern ones. Mars rises around 1:40am and is slowly brightening; Jupiter rises east-northeast around 3:50am, and on September 8 the Moon occults Jupiter for much of North America. Mercury appears low in evening twilight in the final week, about 1° above Spica on the 25th. The Moon is a waning gibbous heading to last quarter on September 4. Also this month: International Observe the Moon Night on the 19th, the equinox on the 22nd, and a Harvest Moon near Saturn on the 26th. Standing reminder: any solar filter must be certified to ISO 12312-2. Links & sources: Caltech — Thermal Anomaly Discovered Below Mars's South Pole (Aug 28) Nature — "Tidal Tomography Reveals a Thermal Anomaly Beneath Mars's Crustal Dichotomy", Berne et al. (Aug 27) Phys.org — Thermal anomaly discovered below Mars' south pole Space.com — Scientists discover massive underground 'thermal anomaly' on Mars NASA Space Station Blog — NASA, SpaceX Adjust Crew-13 Launch Date (Aug 29) Space.com — SpaceX, NASA delay next astronaut launch to ISS due to leak on Dragon spacecraft NASA Swift Blog — NASA's Swift Restarts Science Observations (Aug 28) Space.com — NASA's Swift space telescope resumes observations after failed orbital rescue attempt (Aug 31) GeekWire — Fermi Explorer team plans 80,000-year trip to Alpha Centauri (Sept 1) Space.com — Nonprofit wants to launch 80,000-year mission to Alpha Centauri in 2029 (Sept 1) MIT Technology Review — How AI plotted an interstellar journey to Alpha Centauri (Sept 1) NASA Science — What's Up: September 2026 Skywatching Tips Space.com — 5 planets will light up the September sky Follow us: @AstroDailyPod
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This episode includes AI-generated content.
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Anna: Hey, everyone. Welcome back to Astronomy
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daily. It's Wednesday, September 2nd,
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series five, episode 183.
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Avery: And today we've got a genuinely lovely piece
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of planetary science to lead with, which
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doesn't happen every day.
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Anna: It really is a good one.
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There's something hot buried under Mars's
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south pole. And I mean that literally.
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Avery: Bolton.
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Anna: Even Bolton. A new Nature
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paper says the southern half of Mars's
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interior is hundreds of degrees hotter than
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the northern half. And it might finally
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explain the single weirdest thing about that
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planet.
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Avery: Then Crew 13 is standing down after a leak
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turned up in Dragon. NASA's Swift telescope
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is observing again, but now it's in a race
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with the atmosphere. And the Seattle
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nonprofit wants to launch a spacecraft to
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Alpha Centauri that won't arrive for
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80,000 years.
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Anna: They're aware of that, by the way. That's the
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pitch.
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Avery: That is very much the pitch. Then we'll get
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you sorted for tonight's sky. Five planets
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are in play this month. North and south.
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Anna: Let's get into it.
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Avery: Okay, Set this up properly for me because I
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want to understand what was actually found.
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Anna: So this is a paper published in nature on
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August 27, titled, and I love
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this title. Title. Tomography Reveals a
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Thermal anomaly beneath Mars's Crustal
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Dichotomy. Lead author is Alexander
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Byrne, who did this as his PhD work at
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Caltech and has just moved to the University
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of Arizona.
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Avery: And the finding, in one sentence, the
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Anna: inside of Mars's southern hemisphere is
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somewhere between 200 and 400
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degrees Celsius, hotter than the inside of
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its northern hemisphere and parts of it are
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partially molten.
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Avery: Two to 400 degrees is not a
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subtle difference.
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Anna: It's enormous. This isn't a hot spot or
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a plume. This is one half of a planet's
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interior running fundamentally hotter than
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the other half and staying that way over
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geologic time.
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Avery: Before we get to how they measured that,
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explain the thing it might solve.
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You said the weirdest thing about Mars,
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Anna: the Martian crustal dichotomy. If
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you've ever looked at one of those false
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colour topographic maps of Mars, you'll have
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seen it immediately, even if nobody named it
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for you. The northern third of the planet is
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smooth, low lying, young looking plains.
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The southern two thirds is high, ancient,
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heavily cratered highlands on crust that's
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substantially thicker. And the boundary
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between them is remarkably sharp, a step
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of several kilometres in elevation in places.
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Avery: How long has that been sitting there,
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unexplained?
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Anna: It's sitting there since the Viking orbiters
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mapped it in the 70s. 50 years
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it's genuinely one of the oldest open
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questions in planetary science.
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Avery: So it's not just a surface feature, it goes
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deep.
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Anna: That's the point of this paper. The dichotomy
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isn't paint on the outside. The it appears to
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have a matching structure hundreds of
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kilometres down in the mantle. The hemisphere
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that looks different on the surface is also
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the hemisphere that's hotter underneath.
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Avery: Okay, so how do you take the temperature of
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another planet? We've got exactly one
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seismometer that's ever operated on Mars and
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it's dead now.
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Anna: This is the part I find really clever.
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They didn't use seismology at all. They used
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the fact that Mars flexes. Lex's
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Howe the sun pulls on Mars the way
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the moon pulls on Earth's oceans, tides.
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Mars has no oceans. But the whole solid
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planet still stretches and relaxes
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very slightly on every orbit. And how much
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it flexes depends on what it's made of and
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critically, how hot and soft its interior
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is. Hot, partially molten rock
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deforms more easily than cold rigid rock.
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Avery: So the amount of squish tells you
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Anna: the temperature, the amount of squish tells
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you the temperature. It's a tiny effect, but
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a planet that changes shape has a gravity
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field that changes with it. And we've had
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spacecraft orbiting Mars continuously for
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decades, all tracked by radio from Earth.
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Avery: So the spacecraft are the instrument, the
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Anna: spacecraft are the instrument. Burns team
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went back through tracking data from Mars
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Global Surveyor, Mars Odyssey and Mars
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Reconnaissance Orbiter. 25 years of it,
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looking at the minute velocity changes as
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each one flew over different parts of the
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planet. Those wiggles map the gravity field.
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And the way that field breathes across a
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martian year maps the flex.
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Avery: And nobody had done that before, not
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Anna: to this resolution and not with the aim of
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separating one hemisphere from the other.
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That's what the tomography in the title is
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doing. Same word as a medical CT scan.
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Roughly the same idea. Lots of measurements
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from lots of angles reconstructed into a
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picture of the inside.
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Avery: 25 years of data collected by missions
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that weren't launched to do this.
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Anna: Mars Global surveyor launched in
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1996 and stopped talking to us in
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2006. And its tracking data is still
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producing new results 20 years later.
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It's a good argument for archiving everything
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forever. And this is a big international
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effort. Co authors across Brown,
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NASA Goddard, Arizona, Academia
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Sinica in Taiwan, the University of Rome,
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Delft, ucla, UT Austin,
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Colorado, Boulder and UC Santa Cruz.
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Avery: So what else does this hot southern interior
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explain?
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Anna: Two things that have been nagging at people.
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First, magnetism. Mars has no global
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magnetic field today. But the crust is
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magnetised in patches, frozen in evidence
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of a field that switched off billions of
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years ago. And those anomalies are
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overwhelmingly concentrated in the southern
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highlands. A hemisphere with a, uh, different
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thermal history from the start would
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magnetise differently and hold that record
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differently.
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Avery: And the second.
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Anna: The second seismic, when Insight was
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operating its seismometer, found waves
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passing through parts of Mars interior were
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damped from far more strongly than expected.
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Waves lose energy fast in hot soft
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material. Exactly what partially molten
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rock down there would produce.
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Avery: So it's not one line of evidence. It makes
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three separate puzzles line up.
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Anna: That's what makes it feel solid. Any one
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on its own you'd want it replicated. All, ah,
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three pointing the same way is more
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persuasive.
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Avery: Do we know why the southern half ended up
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hotter?
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Anna: Oh, and the team is upfront about that. Three
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families of explanation. One, a, uh, giant
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impact early in Mars's history. Something
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enormous hitting the northern hemisphere,
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blasting out the lowlands and rearranging the
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interior. Two, mantle convection that
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settled into a lopsided pattern and stayed
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there. Which planetary interiors genuinely
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can do. Three, something compositional.
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A layer enriched in radioactive elements
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generating its own heat.
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Avery: And this result doesn't pick between them.
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Anna: Not yet. What it does is hand you a hard
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number. Every explanation now has to
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reproduce. Before this, why is Mars
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lopsided? Was mostly a surface geology
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question. Now it's a question about the whole
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planet with a temperature constraint
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attached.
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Avery: Does this connect to the water storey? That's
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usually where Mars questions, um, end up.
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Anna: It does. And it's the line from the team I
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keep coming back to. The dichotomy matters
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because it tells you about the processes that
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shaped the hydrology of Mars, including the
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formation of the basins that may have held
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water. Those northern lowlands are exactly
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where you'd put an ancient ocean, if Mars
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ever had one. So whatever made the north low
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may also have decided where the water went.
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Avery: And, um, there's a nice bit of symmetry for
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us, isn't there?
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Anna: There is. We're a show made in the southern
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hemisphere that spends a lot of time
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explaining why the southern sky is the
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interesting one. Turns out Mars southern
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hemisphere is the interesting one too. It's
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just interesting several hundred kilometres
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down.
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Avery: Anything coming that would test this further?
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Anna: More of the same. The tracking data keeps
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accumulating as long as we keep flying
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orbiters. And the technique sharpens the
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longer the baseline gets. A second
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seismometer on Mars would help enormously.
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But there isn't one funded in flying in the
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meantime. This is a very good example of
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squeezing genuinely new physics out of data.
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Avery: We already had storey two and
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it's a stand down.
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Anna: Crew 13 was scheduled to launch to the
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International space station on September
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12th. It's not launching on September
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12th. NASA and SpaceX announced on
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August 29th that they'd found an oxidizer
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leak in the Dragon spacecraft's propulsion
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system during standard pre launch processing.
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Avery: Standard processing meaning caught on the
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ground doing the cheques you do?
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Anna: Exactly. And that's worth saying, clearly,
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because Leak found on crew spacecraft
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reads alarming in a headline. This was the
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process working the way it's supposed to.
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Teams are running additional tests and data
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reviews and will do any rework needed before
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flight. No new target date yet.
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Avery: Why is an oxidizer leak, specifically a, uh,
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stop everything item?
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Anna: Because of what the Dragon's propulsion
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system is for and what's in it. Dragon
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runs hypergolic propellants, a fuel and
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an oxidizer that ignite on contact with each
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other. No spark needed. Fantastically
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reliable, which is exactly why you use it on
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a crew vehicle. But the oxidizer side is
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aggressively corrosive and you handle it with
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enormous care. And that propulsion system
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isn't just for manoeuvring. The same broad
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system family is tied to the launch escape
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capability, the thing that pulls the capsule
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off a failing rocket.
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Avery: So the bar for signing it off is about as
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high as it gets.
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Anna: Nobody is flying this until they can explain
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precisely where the leak was and why it won't
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happen again. Who's on this Crew
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commander is NASA's Jessica Watkins,
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pilot is NASA's Luke Delany. And the two
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mission specialists are Joshua Kutryk from
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the Canadian Space Agency and Sergey
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Tetrietnikov from Roscosmos. It's
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a roughly seven month increment. A lot of
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station maintenance. Several spacewalks
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planned the usual science load
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Avery: and, um, they'd be walking into a station
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that's just had a very busy month. We talked
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Yesterday about Expedition 75 running
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four spacewalks inside four weeks,
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which is
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Anna: exactly the backlog Crew 13's own
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task list was built on top of.
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Avery: Does a delay cause knock on problems?
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Anna: Station handovers are a chain. Rotations
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overlap deliberately, so there's always
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experienced crew aboard and a slip at one end
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compresses things at the other. NASA hasn't
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flagged any concern beyond the launch date
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itself, so read that as manageable for
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now.
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Avery: When do we expect a new date?
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Anna: Unknown. And it depends entirely on what the
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inspections find, a fitting or A seal is a
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fix measured in days. Something in the
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plumbing that needs the system opened up is
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longer. NASA's line is that a new target will
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be announced once available, and we'll flag
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it the moment it lands.
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Avery: Storey three closes a loop. We opened a
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couple of weeks back and it's a better ending
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than I expected.
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Anna: It genuinely is.
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NASA's Neil Gehrels Swift Observatory is
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doing science again. Two of its three
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instruments came back online on August
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26, and NASA expects the third within
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weeks.
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Avery: Remind everyone how Swift got into trouble.
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Anna: Swift launched in 2004 to catch
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Gamma ray bursts, the brightest explosions in
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the universe, by slewing incredibly fast
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to point at one with within seconds of
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detecting it. Hence the name 22
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years of workhorse science. But it's in
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low Earth orbit, which has just enough
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atmosphere in it to slowly drag you down.
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And Swift has no propulsion at all.
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Avery: So it can't save itself.
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Anna: It can't. As the orbit decayed, NASA
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started shutting things off to buy time. The
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ultraviolet and optical telescope and the X
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ray telescope went dark in February. The
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Burst Alert telescope in April, partly for
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power and partly to hold an orientation that
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minimised drag, the space
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equivalent
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Avery: of tucking your arms in. And meanwhile,
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there was a rescue coming.
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Anna: Catalyst Space's Link spacecraft, launched
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in July, designed to rendezvous with Swift,
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grab hold and boost the orbit. The first
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commercial rescue of a NASA science mission.
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Then, on August 19, NASA called it off.
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Link developed problems controlling its own
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orientation, which, for a spacecraft whose
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whole job is a delicate close proximity
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capture, is disqualifying.
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Avery: So what changed to let Swift start observing
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again?
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Anna: The calculus. With no rescue coming, there's
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no point conserving altitude for a rendezvous
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that isn't going to happen. So NASA turned
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the telescopes back on to get every last
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observation out of it.
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Avery: How long have they got?
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Anna: NASA's estimate is that Swift drops below
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about 300 kilometres
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in the next one to two months. Below that,
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the drag makes precise pointing difficult
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and the telescopes stop being useful.
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Reentry follows.
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Avery: So weeks of real science left?
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Anna: Weeks. And given. Swift's specialty is
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catching things that appear without warning.
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Every day up there is a day it might catch
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something nobody else was pointed at.
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Avery: What happens to Link?
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Anna: The other decent bit of news? Catalyst isn't
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writing it off. They'll fly proximity
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operations anyway to demonstrate in orbit
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servicing techniques. So the mission that
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couldn't save Swift still generates data for
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the next one that tries. And there's a whole
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generation of productive science spacecraft
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in low orbit with no propulsion, all
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quietly losing altitude. Swift is the test
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case for whether we ever get good at going up
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after them.
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Avery: Last storey before the sky. And it's the most
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quietly audacious thing
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Anna: I've read in the While a nonprofit in the
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Seattle area called the Fermi Explora Mission
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announced this week that it intends to launch
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a, uh, spacecraft to Alpha Centauri at the
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end of 2029. Travel time, about
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80,000 years.
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Avery: That's not a typo.
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Anna: Not a typo. And the team's own framing is the
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best part. Their president, Philip Johnston,
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says we'll be the first to leave and the
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last to arrive.
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Avery: Meaning they fully expect to be overtaken
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completely.
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Anna: It's baked in. Somebody will build something
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faster in the intervening millennia and beat
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them there. His other line none of us will be
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here when this journey ends. And that is the
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point.
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Avery: So what actually flies 80,000 years
371
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suggests they're not waiting on exotic
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propulsion.
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Anna: Deliberately not Nothing that needs
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inventing. A spacecraft in the 100 to
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200 kilogramme range. Solar electric
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propulsion to proven technology. We fly today
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carrying at least a kilogramme of payload in
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a shielded 10 centimetre cube.
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Avery: How do you get to interstellar speed?
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Anna: With an ion thruster, a manoeuvre they call
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perihelion pumping. Instead of burning
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straight outward, you loop in close to the
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sun and thrust hard at closest approach,
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where you're moving fastest. That's the Obert
385
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effect. And it converts your fuel into far
386
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more speed than the same burn would out here.
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Repeat it and you build real Velocity.
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They're targeting 24.2
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kilometres a second at cruise, about
390
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54,000 miles an hour faster
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than New Horizons was moving at Pluto.
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Avery: And, um, still nowhere near enough for four
393
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and a bit late years.
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Anna: 4.4. That's the honest
395
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arithmetic of interstellar travel. 12
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years of active operations, then roughly
397
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79 and a half thousand years of
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coasting in the dark.
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Avery: Who's behind it?
400
00:16:18.300 --> 00:16:20.980
Anna: Donston founded it with Ezra Feldon and
401
00:16:20.980 --> 00:16:23.660
Adi Oltean. The three of them are behind the
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00:16:23.660 --> 00:16:26.180
space computing company Star Cloud. The
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00:16:26.180 --> 00:16:28.940
advisory board has real names on it. Rob
404
00:16:28.940 --> 00:16:31.660
Meyerson, who used to run Blue Origin, and
405
00:16:31.660 --> 00:16:34.220
Jeff Thornberg, formerly SpaceX's
406
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propulsion lead budgets under $15
407
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million, with one billionaire space founder
408
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verbally pledging 10 million of it.
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Avery: What's it carrying?
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Anna: A digitised Voyager golden record.
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Messages from children around the world and
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real instruments. Cosmic ray detectors among
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them. The 12 active years aren't nothing.
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You'd be measuring your way out through the
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heliosphere.
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Avery: And the name's doing Some work.
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Anna: The Fermi is Enrico Fermi and his
418
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paradox. If the galaxy should be full of
419
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civilizations, where is everybody?
420
00:17:08.310 --> 00:17:10.590
Johnston's argument is that one candidate
421
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answer is that interstellar expansion is
422
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so hard, nobody bothers to start.
423
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So you start even badly, even
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slowly.
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Avery: How is it different from breakthrough
426
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Starshot, which made a lot of noise in 2016?
427
00:17:24.950 --> 00:17:27.830
Anna: Starshot was the opposite bet. Laser
428
00:17:27.830 --> 00:17:30.790
pushed light sales. 20% of light speed
429
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arrive within a human lifetime. But needing
430
00:17:33.910 --> 00:17:36.890
technology that doesn't exist, it's stalled.
431
00:17:37.050 --> 00:17:39.850
Fermi Explorer inverts it. Use only what
432
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exists except an absurd travel time
433
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and actually launch. It'd also be the
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first spacecraft ever deliberately aimed at a
435
00:17:48.650 --> 00:17:51.250
particular star. The Voyagers are leaving,
436
00:17:51.250 --> 00:17:53.450
but they're not going anywhere in particular.
437
00:17:54.170 --> 00:17:57.050
Avery: I find this weirdly moving and I can't fully
438
00:17:57.050 --> 00:17:58.010
justify why.
439
00:17:58.410 --> 00:18:00.890
Anna: It's the honesty of it. Most space
440
00:18:00.890 --> 00:18:03.250
projects sell you a payoff you'll live to
441
00:18:03.250 --> 00:18:05.920
see. This one explicitly doesn't and
442
00:18:05.920 --> 00:18:07.600
asks you to fund it anyway.
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Avery: Right, let's get everyone sorted with today's
444
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sky watch. And September is a good month.
445
00:18:12.440 --> 00:18:15.000
There are five planets in play, all
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Anna: five naked eye ones spread across the night.
447
00:18:18.240 --> 00:18:20.160
Let's take them in order of when you'd see
448
00:18:20.160 --> 00:18:20.400
them.
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Avery: Start with the evening.
450
00:18:21.960 --> 00:18:24.320
Anna: Venus, and it's unmissable.
451
00:18:24.640 --> 00:18:27.160
Low in the west to west southwest after
452
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sunset, about 14 degrees up an hour after
453
00:18:30.160 --> 00:18:32.940
the sun goes down. For Sydney sunsets
454
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around 5.34pm AEST
455
00:18:35.780 --> 00:18:37.940
tonight, so you're looking from a quarter
456
00:18:37.940 --> 00:18:40.900
past six. Northern listeners get a similar
457
00:18:40.900 --> 00:18:43.660
window after their own sunset. The key
458
00:18:43.660 --> 00:18:46.620
either way is a genuinely flat western
459
00:18:46.620 --> 00:18:49.300
horizon because Venus is not high.
460
00:18:49.700 --> 00:18:51.780
Avery: It was next to Spica last night.
461
00:18:52.100 --> 00:18:54.540
Anna: That conjunction peaked yesterday and they're
462
00:18:54.540 --> 00:18:57.300
separating now, but Spica is still right
463
00:18:57.300 --> 00:18:59.540
there. Worth a look through binoculars while
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they're close. Venus builds to maximum
465
00:19:02.140 --> 00:19:04.500
brilliance on the 18th, so it only
466
00:19:04.500 --> 00:19:07.460
improves mark the 14th too, when a
467
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thin crescent moon sits beside it.
468
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Avery: Then Saturn.
469
00:19:11.420 --> 00:19:13.739
Anna: Saturn's the one to actually point a
470
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telescope at this month. Up for most of the
471
00:19:16.340 --> 00:19:19.020
night. Magnitude 0.4
472
00:19:19.180 --> 00:19:22.140
and the rings are tilted just 8 degrees from
473
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edge on the narrowest in about a dozen
474
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years. That's a genuinely unusual view
475
00:19:27.980 --> 00:19:30.340
and it won't look like this again for a long
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00:19:30.340 --> 00:19:30.700
time.
477
00:19:31.180 --> 00:19:32.740
Avery: And, um, there's a hemisphere difference
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00:19:32.740 --> 00:19:33.020
here,
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00:19:33.180 --> 00:19:36.180
Anna: a big one in our favour for once. From
480
00:19:36.180 --> 00:19:38.980
Sydney or Auckland or Cape Town, Saturn
481
00:19:38.980 --> 00:19:41.779
climbs high overhead. Less atmosphere to look
482
00:19:41.779 --> 00:19:44.660
through, so a steadier, sharper view from the
483
00:19:44.660 --> 00:19:47.620
northern US or the uk. It stays comparatively
484
00:19:47.620 --> 00:19:49.580
low and you'll be fighting turbulence.
485
00:19:49.900 --> 00:19:52.060
Northern listeners wait for it to get as high
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00:19:52.060 --> 00:19:54.220
as it gets. And be patient with the seeing
487
00:19:54.880 --> 00:19:57.040
morning sky. Mars rises around
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00:19:57.120 --> 00:20:00.040
1:40am that distinctive amber
489
00:20:00.040 --> 00:20:02.680
colour slowly brightening as Earth catches up
490
00:20:02.680 --> 00:20:05.280
to it. Then Jupiter up in the east
491
00:20:05.360 --> 00:20:08.280
northeast around 10 to 4 and easier to
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00:20:08.280 --> 00:20:10.000
catch before dawn every week.
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00:20:10.399 --> 00:20:12.600
Avery: And there's a Jupiter event for our North
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00:20:12.600 --> 00:20:15.360
American listeners, specifically a good one.
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00:20:15.600 --> 00:20:18.120
Anna: On September 8, the moon passes
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00:20:18.120 --> 00:20:20.760
directly in front of Jupiter, an actual
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00:20:20.760 --> 00:20:23.360
occultation visible from much of North
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00:20:23.360 --> 00:20:26.230
America. Jupiter winks out behind the
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00:20:26.230 --> 00:20:28.710
lunar limb and reappears on the other side.
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00:20:29.110 --> 00:20:31.430
Small telescope makes it spectacular.
501
00:20:31.670 --> 00:20:34.310
Binoculars will show it. Not for us down
502
00:20:34.310 --> 00:20:36.590
south. So northern listeners, that one's
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00:20:36.590 --> 00:20:38.070
yours. Put it in the calendar.
504
00:20:38.390 --> 00:20:40.710
Avery: And um, the fifth planet Mercury.
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00:20:40.870 --> 00:20:43.350
Anna: But you'll wait for it final week of
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00:20:43.350 --> 00:20:45.990
September. Low in the west southwest in
507
00:20:45.990 --> 00:20:48.470
evening twilight, magnitude minus
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00:20:48.470 --> 00:20:51.400
0.1 on the 25th. It sits
509
00:20:51.400 --> 00:20:54.120
about a degree above Spica, which is a handy
510
00:20:54.120 --> 00:20:54.880
way to find it.
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00:20:55.120 --> 00:20:56.560
Avery: What's the Moon doing tonight?
512
00:20:56.800 --> 00:20:59.760
Anna: Waning gibbous, past full heading for
513
00:20:59.760 --> 00:21:02.680
last quarter on the fourth. It's rising later
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00:21:02.680 --> 00:21:05.080
each night, so the early evening is getting
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00:21:05.080 --> 00:21:07.680
properly dark again. Good news for anything
516
00:21:07.680 --> 00:21:08.160
sane.
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00:21:08.480 --> 00:21:09.920
Avery: Anything else for the diary?
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00:21:10.160 --> 00:21:12.960
Anna: The 19th is international. Observe the moon
519
00:21:12.960 --> 00:21:15.440
night. The 22nd is the equinox.
520
00:21:15.520 --> 00:21:17.960
Spring for us, autumn for our northern
521
00:21:17.960 --> 00:21:20.750
listeners. And around the 26th the full
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00:21:20.750 --> 00:21:23.630
moon rises near Saturn with Neptune close
523
00:21:23.630 --> 00:21:26.390
by. If you've got binoculars and patience, if
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00:21:26.390 --> 00:21:29.350
you want the Milky Way itself. Mid month is
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00:21:29.350 --> 00:21:32.190
the window, roughly the 14th to the 20th
526
00:21:32.190 --> 00:21:34.789
when the moon's out of the evening sky. The
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00:21:34.789 --> 00:21:37.510
core and Harry's in Scorpius. The
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00:21:37.510 --> 00:21:40.070
teapot in Sagittarius sits high
529
00:21:40.070 --> 00:21:42.950
overhead. For us northern listeners get the
530
00:21:42.950 --> 00:21:45.570
same region but low toward the south. So
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00:21:45.570 --> 00:21:47.810
you'll want a dark site and a clear southern
532
00:21:47.810 --> 00:21:48.370
horizon.
533
00:21:48.850 --> 00:21:51.370
Avery: One standing reminder before we go, the
534
00:21:51.370 --> 00:21:53.690
Anna: one we never skip. If you're pointing
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00:21:53.690 --> 00:21:56.370
anything at or near the sun, whether
536
00:21:56.370 --> 00:21:58.930
that's sunspots, a ah, transit or just
537
00:21:58.930 --> 00:22:01.569
chasing Venus a bit too close to sunset.
538
00:22:01.730 --> 00:22:04.650
Any filter you use must be Certified to
539
00:22:04.650 --> 00:22:05.570
the ISO
540
00:22:05.650 --> 00:22:08.290
123122.
541
00:22:08.290 --> 00:22:11.050
Standard sunglasses are not solar
542
00:22:11.050 --> 00:22:13.970
filters. Welding glass off the shelf is not
543
00:22:13.970 --> 00:22:16.650
a solar filter. Improvised filters
544
00:22:16.650 --> 00:22:18.810
cause permanent damage in seconds.
545
00:22:19.050 --> 00:22:20.890
Certified or don't look.
546
00:22:21.290 --> 00:22:23.130
Avery: Never gets old, never should.
547
00:22:23.610 --> 00:22:25.610
And that brings us to the end of today's
548
00:22:25.610 --> 00:22:28.490
show. Molten anomaly under Mars southern
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00:22:28.490 --> 00:22:30.610
hemisphere. That may finally explain the
550
00:22:30.610 --> 00:22:33.570
crustal dichotomy. Crew 13 standing
551
00:22:33.570 --> 00:22:35.930
down over an oxidizer leak in Dragon.
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00:22:36.250 --> 00:22:38.810
Swift back doing science in a race against
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00:22:38.810 --> 00:22:41.570
its own orbit. An 80,000 year
554
00:22:41.570 --> 00:22:44.530
mission to Alpha Centauri and five planets
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00:22:44.530 --> 00:22:45.690
to hunt down this month.
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00:22:46.090 --> 00:22:48.250
Anna: If you enjoyed today's episode, the best
557
00:22:48.250 --> 00:22:50.570
thing you can do for us is leave a rating or
558
00:22:50.570 --> 00:22:52.930
review wherever you're listening and share it
559
00:22:52.930 --> 00:22:55.330
with a fellow space nerd. It really does help
560
00:22:55.330 --> 00:22:57.610
us out and makes a difference. Plus, you get
561
00:22:57.610 --> 00:22:59.810
featured on our new website, where you can
562
00:22:59.810 --> 00:23:02.450
also find full show notes, sources and
563
00:23:02.450 --> 00:23:05.210
links for every storey we covered today. Just
564
00:23:05.210 --> 00:23:07.530
point your browser to astronomydaily
565
00:23:07.770 --> 00:23:10.170
IO cheque out our new blog there too.
566
00:23:10.410 --> 00:23:12.410
Avery: We'll be back tomorrow with more space and
567
00:23:12.410 --> 00:23:15.330
astronomy news. Until then, keep looking up.
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00:23:15.570 --> 00:23:17.570
Anna: See you next time. Clear skies, everyone.
0
00:00:00.640 --> 00:00:03.040
Anna: Hey, everyone. Welcome back to Astronomy
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00:00:03.040 --> 00:00:05.602
daily. It's Wednesday, September 2nd,
2
00:00:05.718 --> 00:00:08.320
series five, episode 183.
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00:00:08.800 --> 00:00:11.400
Avery: And today we've got a genuinely lovely piece
4
00:00:11.400 --> 00:00:13.760
of planetary science to lead with, which
5
00:00:13.760 --> 00:00:14.960
doesn't happen every day.
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Anna: It really is a good one.
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00:00:17.040 --> 00:00:19.400
There's something hot buried under Mars's
8
00:00:19.400 --> 00:00:21.920
south pole. And I mean that literally.
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Avery: Bolton.
10
00:00:23.040 --> 00:00:26.000
Anna: Even Bolton. A new Nature
11
00:00:26.000 --> 00:00:28.320
paper says the southern half of Mars's
12
00:00:28.320 --> 00:00:30.920
interior is hundreds of degrees hotter than
13
00:00:30.920 --> 00:00:33.260
the northern half. And it might finally
14
00:00:33.260 --> 00:00:35.980
explain the single weirdest thing about that
15
00:00:35.980 --> 00:00:36.380
planet.
16
00:00:36.780 --> 00:00:39.660
Avery: Then Crew 13 is standing down after a leak
17
00:00:39.660 --> 00:00:42.660
turned up in Dragon. NASA's Swift telescope
18
00:00:42.660 --> 00:00:45.260
is observing again, but now it's in a race
19
00:00:45.260 --> 00:00:47.420
with the atmosphere. And the Seattle
20
00:00:47.420 --> 00:00:49.940
nonprofit wants to launch a spacecraft to
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00:00:49.940 --> 00:00:52.100
Alpha Centauri that won't arrive for
22
00:00:52.100 --> 00:00:53.420
80,000 years.
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Anna: They're aware of that, by the way. That's the
24
00:00:55.580 --> 00:00:55.900
pitch.
25
00:00:56.700 --> 00:00:59.420
Avery: That is very much the pitch. Then we'll get
26
00:00:59.420 --> 00:01:02.060
you sorted for tonight's sky. Five planets
27
00:01:02.060 --> 00:01:04.380
are in play this month. North and south.
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00:01:04.780 --> 00:01:05.900
Anna: Let's get into it.
29
00:01:06.140 --> 00:01:09.020
Avery: Okay, Set this up properly for me because I
30
00:01:09.020 --> 00:01:11.020
want to understand what was actually found.
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00:01:11.340 --> 00:01:13.740
Anna: So this is a paper published in nature on
32
00:01:13.740 --> 00:01:16.700
August 27, titled, and I love
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00:01:16.700 --> 00:01:19.540
this title. Title. Tomography Reveals a
34
00:01:19.540 --> 00:01:22.220
Thermal anomaly beneath Mars's Crustal
35
00:01:22.220 --> 00:01:24.940
Dichotomy. Lead author is Alexander
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00:01:24.940 --> 00:01:27.620
Byrne, who did this as his PhD work at
37
00:01:27.620 --> 00:01:30.060
Caltech and has just moved to the University
38
00:01:30.440 --> 00:01:31.240
of Arizona.
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00:01:31.240 --> 00:01:33.920
Avery: And the finding, in one sentence, the
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00:01:33.920 --> 00:01:36.600
Anna: inside of Mars's southern hemisphere is
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00:01:36.600 --> 00:01:39.360
somewhere between 200 and 400
42
00:01:39.360 --> 00:01:42.160
degrees Celsius, hotter than the inside of
43
00:01:42.160 --> 00:01:44.960
its northern hemisphere and parts of it are
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00:01:44.960 --> 00:01:46.040
partially molten.
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00:01:46.600 --> 00:01:49.560
Avery: Two to 400 degrees is not a
46
00:01:49.560 --> 00:01:50.360
subtle difference.
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00:01:50.760 --> 00:01:53.680
Anna: It's enormous. This isn't a hot spot or
48
00:01:53.680 --> 00:01:56.400
a plume. This is one half of a planet's
49
00:01:56.400 --> 00:01:59.000
interior running fundamentally hotter than
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00:01:59.000 --> 00:02:01.280
the other half and staying that way over
51
00:02:01.280 --> 00:02:02.580
geologic time.
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00:02:03.060 --> 00:02:04.980
Avery: Before we get to how they measured that,
53
00:02:05.140 --> 00:02:06.700
explain the thing it might solve.
54
00:02:06.700 --> 00:02:09.140
You said the weirdest thing about Mars,
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00:02:09.460 --> 00:02:12.220
Anna: the Martian crustal dichotomy. If
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00:02:12.220 --> 00:02:14.020
you've ever looked at one of those false
57
00:02:14.020 --> 00:02:16.780
colour topographic maps of Mars, you'll have
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00:02:16.780 --> 00:02:19.340
seen it immediately, even if nobody named it
59
00:02:19.340 --> 00:02:21.900
for you. The northern third of the planet is
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00:02:21.900 --> 00:02:24.580
smooth, low lying, young looking plains.
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The southern two thirds is high, ancient,
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heavily cratered highlands on crust that's
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substantially thicker. And the boundary
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between them is remarkably sharp, a step
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00:02:36.010 --> 00:02:38.930
of several kilometres in elevation in places.
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Avery: How long has that been sitting there,
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00:02:40.930 --> 00:02:41.650
unexplained?
68
00:02:41.970 --> 00:02:44.410
Anna: It's sitting there since the Viking orbiters
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00:02:44.410 --> 00:02:46.930
mapped it in the 70s. 50 years
70
00:02:47.330 --> 00:02:49.730
it's genuinely one of the oldest open
71
00:02:49.730 --> 00:02:51.490
questions in planetary science.
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Avery: So it's not just a surface feature, it goes
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00:02:54.410 --> 00:02:54.770
deep.
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Anna: That's the point of this paper. The dichotomy
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00:02:57.770 --> 00:03:00.360
isn't paint on the outside. The it appears to
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00:03:00.360 --> 00:03:02.680
have a matching structure hundreds of
77
00:03:02.680 --> 00:03:05.560
kilometres down in the mantle. The hemisphere
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that looks different on the surface is also
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00:03:08.080 --> 00:03:10.320
the hemisphere that's hotter underneath.
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Avery: Okay, so how do you take the temperature of
81
00:03:13.000 --> 00:03:15.120
another planet? We've got exactly one
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00:03:15.120 --> 00:03:17.840
seismometer that's ever operated on Mars and
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00:03:17.840 --> 00:03:18.720
it's dead now.
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Anna: This is the part I find really clever.
85
00:03:21.760 --> 00:03:24.640
They didn't use seismology at all. They used
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00:03:24.640 --> 00:03:27.590
the fact that Mars flexes. Lex's
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00:03:27.590 --> 00:03:30.470
Howe the sun pulls on Mars the way
88
00:03:30.470 --> 00:03:33.230
the moon pulls on Earth's oceans, tides.
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Mars has no oceans. But the whole solid
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00:03:36.510 --> 00:03:38.990
planet still stretches and relaxes
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very slightly on every orbit. And how much
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00:03:42.230 --> 00:03:45.030
it flexes depends on what it's made of and
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critically, how hot and soft its interior
94
00:03:47.830 --> 00:03:50.430
is. Hot, partially molten rock
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00:03:50.590 --> 00:03:53.470
deforms more easily than cold rigid rock.
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00:03:53.950 --> 00:03:55.830
Avery: So the amount of squish tells you
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00:03:55.830 --> 00:03:58.590
Anna: the temperature, the amount of squish tells
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00:03:58.590 --> 00:04:01.310
you the temperature. It's a tiny effect, but
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00:04:01.310 --> 00:04:03.950
a planet that changes shape has a gravity
100
00:04:03.950 --> 00:04:06.350
field that changes with it. And we've had
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00:04:06.350 --> 00:04:09.110
spacecraft orbiting Mars continuously for
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00:04:09.110 --> 00:04:12.030
decades, all tracked by radio from Earth.
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00:04:12.910 --> 00:04:15.550
Avery: So the spacecraft are the instrument, the
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00:04:15.550 --> 00:04:18.350
Anna: spacecraft are the instrument. Burns team
105
00:04:18.350 --> 00:04:20.550
went back through tracking data from Mars
106
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Global Surveyor, Mars Odyssey and Mars
107
00:04:23.550 --> 00:04:26.230
Reconnaissance Orbiter. 25 years of it,
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looking at the minute velocity changes as
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00:04:29.030 --> 00:04:31.230
each one flew over different parts of the
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planet. Those wiggles map the gravity field.
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00:04:34.310 --> 00:04:36.750
And the way that field breathes across a
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00:04:36.750 --> 00:04:38.790
martian year maps the flex.
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00:04:39.270 --> 00:04:41.830
Avery: And nobody had done that before, not
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Anna: to this resolution and not with the aim of
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00:04:44.470 --> 00:04:46.630
separating one hemisphere from the other.
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That's what the tomography in the title is
117
00:04:49.150 --> 00:04:51.910
doing. Same word as a medical CT scan.
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00:04:51.910 --> 00:04:54.520
Roughly the same idea. Lots of measurements
119
00:04:54.520 --> 00:04:57.200
from lots of angles reconstructed into a
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00:04:57.200 --> 00:04:58.600
picture of the inside.
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00:04:59.080 --> 00:05:02.040
Avery: 25 years of data collected by missions
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00:05:02.040 --> 00:05:03.640
that weren't launched to do this.
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00:05:04.040 --> 00:05:06.120
Anna: Mars Global surveyor launched in
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00:05:06.120 --> 00:05:09.000
1996 and stopped talking to us in
125
00:05:09.000 --> 00:05:11.840
2006. And its tracking data is still
126
00:05:11.840 --> 00:05:14.440
producing new results 20 years later.
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It's a good argument for archiving everything
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00:05:17.480 --> 00:05:19.880
forever. And this is a big international
129
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effort. Co authors across Brown,
130
00:05:22.630 --> 00:05:25.430
NASA Goddard, Arizona, Academia
131
00:05:25.430 --> 00:05:28.310
Sinica in Taiwan, the University of Rome,
132
00:05:28.470 --> 00:05:31.350
Delft, ucla, UT Austin,
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00:05:31.430 --> 00:05:34.150
Colorado, Boulder and UC Santa Cruz.
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00:05:34.630 --> 00:05:37.390
Avery: So what else does this hot southern interior
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00:05:37.390 --> 00:05:37.910
explain?
136
00:05:38.230 --> 00:05:40.390
Anna: Two things that have been nagging at people.
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00:05:40.790 --> 00:05:43.670
First, magnetism. Mars has no global
138
00:05:43.750 --> 00:05:46.310
magnetic field today. But the crust is
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00:05:46.310 --> 00:05:49.110
magnetised in patches, frozen in evidence
140
00:05:49.110 --> 00:05:51.510
of a field that switched off billions of
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00:05:51.510 --> 00:05:53.710
years ago. And those anomalies are
142
00:05:53.710 --> 00:05:56.190
overwhelmingly concentrated in the southern
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00:05:56.190 --> 00:05:58.430
highlands. A hemisphere with a, uh, different
144
00:05:58.430 --> 00:06:00.590
thermal history from the start would
145
00:06:00.590 --> 00:06:02.910
magnetise differently and hold that record
146
00:06:02.910 --> 00:06:03.550
differently.
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00:06:03.950 --> 00:06:04.990
Avery: And the second.
148
00:06:05.630 --> 00:06:08.310
Anna: The second seismic, when Insight was
149
00:06:08.310 --> 00:06:10.750
operating its seismometer, found waves
150
00:06:10.750 --> 00:06:13.390
passing through parts of Mars interior were
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00:06:13.390 --> 00:06:15.500
damped from far more strongly than expected.
152
00:06:16.060 --> 00:06:18.900
Waves lose energy fast in hot soft
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material. Exactly what partially molten
154
00:06:21.700 --> 00:06:23.180
rock down there would produce.
155
00:06:23.660 --> 00:06:26.220
Avery: So it's not one line of evidence. It makes
156
00:06:26.220 --> 00:06:27.980
three separate puzzles line up.
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00:06:28.300 --> 00:06:31.220
Anna: That's what makes it feel solid. Any one
158
00:06:31.220 --> 00:06:33.780
on its own you'd want it replicated. All, ah,
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00:06:33.820 --> 00:06:35.980
three pointing the same way is more
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00:06:35.980 --> 00:06:36.700
persuasive.
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00:06:37.100 --> 00:06:39.220
Avery: Do we know why the southern half ended up
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hotter?
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00:06:40.160 --> 00:06:42.960
Anna: Oh, and the team is upfront about that. Three
164
00:06:42.960 --> 00:06:45.760
families of explanation. One, a, uh, giant
165
00:06:45.840 --> 00:06:48.400
impact early in Mars's history. Something
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enormous hitting the northern hemisphere,
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00:06:50.560 --> 00:06:53.160
blasting out the lowlands and rearranging the
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interior. Two, mantle convection that
169
00:06:56.039 --> 00:06:58.360
settled into a lopsided pattern and stayed
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there. Which planetary interiors genuinely
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can do. Three, something compositional.
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A layer enriched in radioactive elements
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generating its own heat.
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Avery: And this result doesn't pick between them.
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Anna: Not yet. What it does is hand you a hard
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number. Every explanation now has to
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reproduce. Before this, why is Mars
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lopsided? Was mostly a surface geology
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question. Now it's a question about the whole
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planet with a temperature constraint
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attached.
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Avery: Does this connect to the water storey? That's
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usually where Mars questions, um, end up.
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Anna: It does. And it's the line from the team I
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keep coming back to. The dichotomy matters
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because it tells you about the processes that
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shaped the hydrology of Mars, including the
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formation of the basins that may have held
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water. Those northern lowlands are exactly
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where you'd put an ancient ocean, if Mars
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ever had one. So whatever made the north low
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may also have decided where the water went.
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Avery: And, um, there's a nice bit of symmetry for
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us, isn't there?
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Anna: There is. We're a show made in the southern
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hemisphere that spends a lot of time
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explaining why the southern sky is the
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interesting one. Turns out Mars southern
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hemisphere is the interesting one too. It's
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just interesting several hundred kilometres
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down.
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Avery: Anything coming that would test this further?
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Anna: More of the same. The tracking data keeps
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accumulating as long as we keep flying
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orbiters. And the technique sharpens the
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longer the baseline gets. A second
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seismometer on Mars would help enormously.
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But there isn't one funded in flying in the
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meantime. This is a very good example of
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squeezing genuinely new physics out of data.
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Avery: We already had storey two and
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it's a stand down.
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Anna: Crew 13 was scheduled to launch to the
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International space station on September
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12th. It's not launching on September
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12th. NASA and SpaceX announced on
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August 29th that they'd found an oxidizer
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leak in the Dragon spacecraft's propulsion
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system during standard pre launch processing.
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Avery: Standard processing meaning caught on the
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ground doing the cheques you do?
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Anna: Exactly. And that's worth saying, clearly,
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because Leak found on crew spacecraft
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reads alarming in a headline. This was the
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process working the way it's supposed to.
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Teams are running additional tests and data
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reviews and will do any rework needed before
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flight. No new target date yet.
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Avery: Why is an oxidizer leak, specifically a, uh,
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stop everything item?
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Anna: Because of what the Dragon's propulsion
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system is for and what's in it. Dragon
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runs hypergolic propellants, a fuel and
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an oxidizer that ignite on contact with each
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other. No spark needed. Fantastically
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reliable, which is exactly why you use it on
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a crew vehicle. But the oxidizer side is
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aggressively corrosive and you handle it with
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enormous care. And that propulsion system
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isn't just for manoeuvring. The same broad
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system family is tied to the launch escape
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capability, the thing that pulls the capsule
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off a failing rocket.
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Avery: So the bar for signing it off is about as
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high as it gets.
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Anna: Nobody is flying this until they can explain
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precisely where the leak was and why it won't
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happen again. Who's on this Crew
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commander is NASA's Jessica Watkins,
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pilot is NASA's Luke Delany. And the two
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mission specialists are Joshua Kutryk from
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the Canadian Space Agency and Sergey
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Tetrietnikov from Roscosmos. It's
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a roughly seven month increment. A lot of
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station maintenance. Several spacewalks
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planned the usual science load
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Avery: and, um, they'd be walking into a station
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that's just had a very busy month. We talked
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Yesterday about Expedition 75 running
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four spacewalks inside four weeks,
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which is
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Anna: exactly the backlog Crew 13's own
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task list was built on top of.
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Avery: Does a delay cause knock on problems?
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Anna: Station handovers are a chain. Rotations
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overlap deliberately, so there's always
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experienced crew aboard and a slip at one end
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compresses things at the other. NASA hasn't
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flagged any concern beyond the launch date
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itself, so read that as manageable for
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now.
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Avery: When do we expect a new date?
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Anna: Unknown. And it depends entirely on what the
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inspections find, a fitting or A seal is a
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fix measured in days. Something in the
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plumbing that needs the system opened up is
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longer. NASA's line is that a new target will
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be announced once available, and we'll flag
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it the moment it lands.
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Avery: Storey three closes a loop. We opened a
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couple of weeks back and it's a better ending
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than I expected.
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Anna: It genuinely is.
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NASA's Neil Gehrels Swift Observatory is
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doing science again. Two of its three
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instruments came back online on August
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26, and NASA expects the third within
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weeks.
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Avery: Remind everyone how Swift got into trouble.
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Anna: Swift launched in 2004 to catch
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Gamma ray bursts, the brightest explosions in
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the universe, by slewing incredibly fast
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to point at one with within seconds of
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detecting it. Hence the name 22
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years of workhorse science. But it's in
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low Earth orbit, which has just enough
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atmosphere in it to slowly drag you down.
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And Swift has no propulsion at all.
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Avery: So it can't save itself.
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Anna: It can't. As the orbit decayed, NASA
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started shutting things off to buy time. The
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ultraviolet and optical telescope and the X
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ray telescope went dark in February. The
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Burst Alert telescope in April, partly for
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power and partly to hold an orientation that
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minimised drag, the space
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equivalent
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Avery: of tucking your arms in. And meanwhile,
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there was a rescue coming.
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Anna: Catalyst Space's Link spacecraft, launched
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in July, designed to rendezvous with Swift,
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grab hold and boost the orbit. The first
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commercial rescue of a NASA science mission.
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Then, on August 19, NASA called it off.
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Link developed problems controlling its own
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orientation, which, for a spacecraft whose
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whole job is a delicate close proximity
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capture, is disqualifying.
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Avery: So what changed to let Swift start observing
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again?
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Anna: The calculus. With no rescue coming, there's
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no point conserving altitude for a rendezvous
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that isn't going to happen. So NASA turned
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the telescopes back on to get every last
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observation out of it.
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Avery: How long have they got?
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Anna: NASA's estimate is that Swift drops below
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about 300 kilometres
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in the next one to two months. Below that,
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the drag makes precise pointing difficult
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and the telescopes stop being useful.
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Reentry follows.
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Avery: So weeks of real science left?
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Anna: Weeks. And given. Swift's specialty is
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catching things that appear without warning.
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Every day up there is a day it might catch
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something nobody else was pointed at.
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Avery: What happens to Link?
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Anna: The other decent bit of news? Catalyst isn't
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writing it off. They'll fly proximity
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operations anyway to demonstrate in orbit
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servicing techniques. So the mission that
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couldn't save Swift still generates data for
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the next one that tries. And there's a whole
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generation of productive science spacecraft
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in low orbit with no propulsion, all
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quietly losing altitude. Swift is the test
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case for whether we ever get good at going up
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after them.
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Avery: Last storey before the sky. And it's the most
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quietly audacious thing
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Anna: I've read in the While a nonprofit in the
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Seattle area called the Fermi Explora Mission
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announced this week that it intends to launch
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a, uh, spacecraft to Alpha Centauri at the
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end of 2029. Travel time, about
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80,000 years.
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Avery: That's not a typo.
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Anna: Not a typo. And the team's own framing is the
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best part. Their president, Philip Johnston,
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says we'll be the first to leave and the
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last to arrive.
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Avery: Meaning they fully expect to be overtaken
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completely.
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Anna: It's baked in. Somebody will build something
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faster in the intervening millennia and beat
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them there. His other line none of us will be
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here when this journey ends. And that is the
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point.
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Avery: So what actually flies 80,000 years
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suggests they're not waiting on exotic
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propulsion.
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Anna: Deliberately not Nothing that needs
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inventing. A spacecraft in the 100 to
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200 kilogramme range. Solar electric
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propulsion to proven technology. We fly today
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carrying at least a kilogramme of payload in
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a shielded 10 centimetre cube.
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Avery: How do you get to interstellar speed?
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Anna: With an ion thruster, a manoeuvre they call
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perihelion pumping. Instead of burning
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straight outward, you loop in close to the
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sun and thrust hard at closest approach,
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where you're moving fastest. That's the Obert
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effect. And it converts your fuel into far
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more speed than the same burn would out here.
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Repeat it and you build real Velocity.
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They're targeting 24.2
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kilometres a second at cruise, about
390
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54,000 miles an hour faster
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than New Horizons was moving at Pluto.
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Avery: And, um, still nowhere near enough for four
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and a bit late years.
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Anna: 4.4. That's the honest
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arithmetic of interstellar travel. 12
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years of active operations, then roughly
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79 and a half thousand years of
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coasting in the dark.
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Avery: Who's behind it?
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Anna: Donston founded it with Ezra Feldon and
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Adi Oltean. The three of them are behind the
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space computing company Star Cloud. The
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advisory board has real names on it. Rob
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Meyerson, who used to run Blue Origin, and
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Jeff Thornberg, formerly SpaceX's
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propulsion lead budgets under $15
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million, with one billionaire space founder
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verbally pledging 10 million of it.
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Avery: What's it carrying?
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Anna: A digitised Voyager golden record.
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Messages from children around the world and
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real instruments. Cosmic ray detectors among
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them. The 12 active years aren't nothing.
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You'd be measuring your way out through the
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heliosphere.
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Avery: And the name's doing Some work.
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Anna: The Fermi is Enrico Fermi and his
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paradox. If the galaxy should be full of
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civilizations, where is everybody?
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Johnston's argument is that one candidate
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answer is that interstellar expansion is
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so hard, nobody bothers to start.
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So you start even badly, even
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slowly.
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Avery: How is it different from breakthrough
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Starshot, which made a lot of noise in 2016?
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Anna: Starshot was the opposite bet. Laser
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pushed light sales. 20% of light speed
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arrive within a human lifetime. But needing
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technology that doesn't exist, it's stalled.
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Fermi Explorer inverts it. Use only what
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exists except an absurd travel time
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and actually launch. It'd also be the
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first spacecraft ever deliberately aimed at a
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00:17:48.650 --> 00:17:51.250
particular star. The Voyagers are leaving,
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00:17:51.250 --> 00:17:53.450
but they're not going anywhere in particular.
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00:17:54.170 --> 00:17:57.050
Avery: I find this weirdly moving and I can't fully
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00:17:57.050 --> 00:17:58.010
justify why.
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00:17:58.410 --> 00:18:00.890
Anna: It's the honesty of it. Most space
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00:18:00.890 --> 00:18:03.250
projects sell you a payoff you'll live to
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00:18:03.250 --> 00:18:05.920
see. This one explicitly doesn't and
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00:18:05.920 --> 00:18:07.600
asks you to fund it anyway.
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00:18:08.080 --> 00:18:10.200
Avery: Right, let's get everyone sorted with today's
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00:18:10.200 --> 00:18:12.440
sky watch. And September is a good month.
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00:18:12.440 --> 00:18:15.000
There are five planets in play, all
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00:18:15.000 --> 00:18:17.840
Anna: five naked eye ones spread across the night.
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00:18:18.240 --> 00:18:20.160
Let's take them in order of when you'd see
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00:18:20.160 --> 00:18:20.400
them.
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00:18:20.880 --> 00:18:21.960
Avery: Start with the evening.
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00:18:21.960 --> 00:18:24.320
Anna: Venus, and it's unmissable.
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00:18:24.640 --> 00:18:27.160
Low in the west to west southwest after
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00:18:27.160 --> 00:18:30.160
sunset, about 14 degrees up an hour after
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00:18:30.160 --> 00:18:32.940
the sun goes down. For Sydney sunsets
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00:18:32.940 --> 00:18:35.380
around 5.34pm AEST
455
00:18:35.780 --> 00:18:37.940
tonight, so you're looking from a quarter
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00:18:37.940 --> 00:18:40.900
past six. Northern listeners get a similar
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00:18:40.900 --> 00:18:43.660
window after their own sunset. The key
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00:18:43.660 --> 00:18:46.620
either way is a genuinely flat western
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00:18:46.620 --> 00:18:49.300
horizon because Venus is not high.
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00:18:49.700 --> 00:18:51.780
Avery: It was next to Spica last night.
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00:18:52.100 --> 00:18:54.540
Anna: That conjunction peaked yesterday and they're
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00:18:54.540 --> 00:18:57.300
separating now, but Spica is still right
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00:18:57.300 --> 00:18:59.540
there. Worth a look through binoculars while
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00:18:59.540 --> 00:19:02.140
they're close. Venus builds to maximum
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00:19:02.140 --> 00:19:04.500
brilliance on the 18th, so it only
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00:19:04.500 --> 00:19:07.460
improves mark the 14th too, when a
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00:19:07.460 --> 00:19:09.580
thin crescent moon sits beside it.
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00:19:10.060 --> 00:19:11.100
Avery: Then Saturn.
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00:19:11.420 --> 00:19:13.739
Anna: Saturn's the one to actually point a
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00:19:13.739 --> 00:19:16.340
telescope at this month. Up for most of the
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00:19:16.340 --> 00:19:19.020
night. Magnitude 0.4
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00:19:19.180 --> 00:19:22.140
and the rings are tilted just 8 degrees from
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00:19:22.140 --> 00:19:24.980
edge on the narrowest in about a dozen
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00:19:24.980 --> 00:19:27.980
years. That's a genuinely unusual view
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00:19:27.980 --> 00:19:30.340
and it won't look like this again for a long
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00:19:30.340 --> 00:19:30.700
time.
477
00:19:31.180 --> 00:19:32.740
Avery: And, um, there's a hemisphere difference
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00:19:32.740 --> 00:19:33.020
here,
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00:19:33.180 --> 00:19:36.180
Anna: a big one in our favour for once. From
480
00:19:36.180 --> 00:19:38.980
Sydney or Auckland or Cape Town, Saturn
481
00:19:38.980 --> 00:19:41.779
climbs high overhead. Less atmosphere to look
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00:19:41.779 --> 00:19:44.660
through, so a steadier, sharper view from the
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00:19:44.660 --> 00:19:47.620
northern US or the uk. It stays comparatively
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00:19:47.620 --> 00:19:49.580
low and you'll be fighting turbulence.
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00:19:49.900 --> 00:19:52.060
Northern listeners wait for it to get as high
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00:19:52.060 --> 00:19:54.220
as it gets. And be patient with the seeing
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00:19:54.880 --> 00:19:57.040
morning sky. Mars rises around
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00:19:57.120 --> 00:20:00.040
1:40am that distinctive amber
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00:20:00.040 --> 00:20:02.680
colour slowly brightening as Earth catches up
490
00:20:02.680 --> 00:20:05.280
to it. Then Jupiter up in the east
491
00:20:05.360 --> 00:20:08.280
northeast around 10 to 4 and easier to
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00:20:08.280 --> 00:20:10.000
catch before dawn every week.
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00:20:10.399 --> 00:20:12.600
Avery: And there's a Jupiter event for our North
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00:20:12.600 --> 00:20:15.360
American listeners, specifically a good one.
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00:20:15.600 --> 00:20:18.120
Anna: On September 8, the moon passes
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00:20:18.120 --> 00:20:20.760
directly in front of Jupiter, an actual
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00:20:20.760 --> 00:20:23.360
occultation visible from much of North
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00:20:23.360 --> 00:20:26.230
America. Jupiter winks out behind the
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00:20:26.230 --> 00:20:28.710
lunar limb and reappears on the other side.
500
00:20:29.110 --> 00:20:31.430
Small telescope makes it spectacular.
501
00:20:31.670 --> 00:20:34.310
Binoculars will show it. Not for us down
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00:20:34.310 --> 00:20:36.590
south. So northern listeners, that one's
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00:20:36.590 --> 00:20:38.070
yours. Put it in the calendar.
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00:20:38.390 --> 00:20:40.710
Avery: And um, the fifth planet Mercury.
505
00:20:40.870 --> 00:20:43.350
Anna: But you'll wait for it final week of
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00:20:43.350 --> 00:20:45.990
September. Low in the west southwest in
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00:20:45.990 --> 00:20:48.470
evening twilight, magnitude minus
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00:20:48.470 --> 00:20:51.400
0.1 on the 25th. It sits
509
00:20:51.400 --> 00:20:54.120
about a degree above Spica, which is a handy
510
00:20:54.120 --> 00:20:54.880
way to find it.
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00:20:55.120 --> 00:20:56.560
Avery: What's the Moon doing tonight?
512
00:20:56.800 --> 00:20:59.760
Anna: Waning gibbous, past full heading for
513
00:20:59.760 --> 00:21:02.680
last quarter on the fourth. It's rising later
514
00:21:02.680 --> 00:21:05.080
each night, so the early evening is getting
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00:21:05.080 --> 00:21:07.680
properly dark again. Good news for anything
516
00:21:07.680 --> 00:21:08.160
sane.
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00:21:08.480 --> 00:21:09.920
Avery: Anything else for the diary?
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00:21:10.160 --> 00:21:12.960
Anna: The 19th is international. Observe the moon
519
00:21:12.960 --> 00:21:15.440
night. The 22nd is the equinox.
520
00:21:15.520 --> 00:21:17.960
Spring for us, autumn for our northern
521
00:21:17.960 --> 00:21:20.750
listeners. And around the 26th the full
522
00:21:20.750 --> 00:21:23.630
moon rises near Saturn with Neptune close
523
00:21:23.630 --> 00:21:26.390
by. If you've got binoculars and patience, if
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00:21:26.390 --> 00:21:29.350
you want the Milky Way itself. Mid month is
525
00:21:29.350 --> 00:21:32.190
the window, roughly the 14th to the 20th
526
00:21:32.190 --> 00:21:34.789
when the moon's out of the evening sky. The
527
00:21:34.789 --> 00:21:37.510
core and Harry's in Scorpius. The
528
00:21:37.510 --> 00:21:40.070
teapot in Sagittarius sits high
529
00:21:40.070 --> 00:21:42.950
overhead. For us northern listeners get the
530
00:21:42.950 --> 00:21:45.570
same region but low toward the south. So
531
00:21:45.570 --> 00:21:47.810
you'll want a dark site and a clear southern
532
00:21:47.810 --> 00:21:48.370
horizon.
533
00:21:48.850 --> 00:21:51.370
Avery: One standing reminder before we go, the
534
00:21:51.370 --> 00:21:53.690
Anna: one we never skip. If you're pointing
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00:21:53.690 --> 00:21:56.370
anything at or near the sun, whether
536
00:21:56.370 --> 00:21:58.930
that's sunspots, a ah, transit or just
537
00:21:58.930 --> 00:22:01.569
chasing Venus a bit too close to sunset.
538
00:22:01.730 --> 00:22:04.650
Any filter you use must be Certified to
539
00:22:04.650 --> 00:22:05.570
the ISO
540
00:22:05.650 --> 00:22:08.290
123122.
541
00:22:08.290 --> 00:22:11.050
Standard sunglasses are not solar
542
00:22:11.050 --> 00:22:13.970
filters. Welding glass off the shelf is not
543
00:22:13.970 --> 00:22:16.650
a solar filter. Improvised filters
544
00:22:16.650 --> 00:22:18.810
cause permanent damage in seconds.
545
00:22:19.050 --> 00:22:20.890
Certified or don't look.
546
00:22:21.290 --> 00:22:23.130
Avery: Never gets old, never should.
547
00:22:23.610 --> 00:22:25.610
And that brings us to the end of today's
548
00:22:25.610 --> 00:22:28.490
show. Molten anomaly under Mars southern
549
00:22:28.490 --> 00:22:30.610
hemisphere. That may finally explain the
550
00:22:30.610 --> 00:22:33.570
crustal dichotomy. Crew 13 standing
551
00:22:33.570 --> 00:22:35.930
down over an oxidizer leak in Dragon.
552
00:22:36.250 --> 00:22:38.810
Swift back doing science in a race against
553
00:22:38.810 --> 00:22:41.570
its own orbit. An 80,000 year
554
00:22:41.570 --> 00:22:44.530
mission to Alpha Centauri and five planets
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00:22:44.530 --> 00:22:45.690
to hunt down this month.
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00:22:46.090 --> 00:22:48.250
Anna: If you enjoyed today's episode, the best
557
00:22:48.250 --> 00:22:50.570
thing you can do for us is leave a rating or
558
00:22:50.570 --> 00:22:52.930
review wherever you're listening and share it
559
00:22:52.930 --> 00:22:55.330
with a fellow space nerd. It really does help
560
00:22:55.330 --> 00:22:57.610
us out and makes a difference. Plus, you get
561
00:22:57.610 --> 00:22:59.810
featured on our new website, where you can
562
00:22:59.810 --> 00:23:02.450
also find full show notes, sources and
563
00:23:02.450 --> 00:23:05.210
links for every storey we covered today. Just
564
00:23:05.210 --> 00:23:07.530
point your browser to astronomydaily
565
00:23:07.770 --> 00:23:10.170
IO cheque out our new blog there too.
566
00:23:10.410 --> 00:23:12.410
Avery: We'll be back tomorrow with more space and
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00:23:12.410 --> 00:23:15.330
astronomy news. Until then, keep looking up.
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00:23:15.570 --> 00:23:17.570
Anna: See you next time. Clear skies, everyone.
