The Hydrogen Map: How a Radio Telescope Heard Half the Universe

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Kind: captions
Language: en

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Hey everyone, welcome back to Astronomy


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Daily. And it's Saturday, so you know


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what that means.


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>> The weekend rap. One brand new story


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properly developed and then we run back


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through the week's biggest news in case


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you missed any of it.


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>> It's Saturday, September 5th, 2026. I'm


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Anna and this is series 5, episode 186.


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>> And I'm Avery. Anna, today's fresh story


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is one I've been waiting years for


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somebody to pull off.


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>> A radio telescope in the Ku Desert has


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heard hydrogen, not from one galaxy,


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from billions of them at once, 4 to 5


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billion lightyear away. And it did it


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without any help from an optical


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telescope, which sounds modest until you


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understand that this particular signal


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is buried under a foreground about


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10,000 times brighter than it is. It's a


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technique people have been trying to


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make work for 15 years. This week it


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worked and it's a South African


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instrument that did it with a strong


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Australian sequel coming.


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>> Then the week that was Roman opened its


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planet camera's eyes. Starship flight 14


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finally has a date on it. Mars turned


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out to be hotter underneath than anyone


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expected. Bey Columbo let go of the ride


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that got it to Mercury. A dark matter


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detector recorded one flash it cannot


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explain.


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>> And brand new this week and genuinely


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lovely. Astronomers have watched a comet


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switch on 3 billion miles away over 5


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years in real time.


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>> Plus the sky for the week ahead. Both


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hemispheres and it is a dark one in the


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good way.


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>> It's a big episode. Let's get into it.


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>> Right. Start me at the beginning. Who


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did what? a team led by Dr. Surro Paul.


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He's at the University of Manchester and


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the University of the Western Cape.


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Working with Laura Wols at Jawril Bank,


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Mario Santos at the Western Cape and


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Xiaoing Chen at Edinburgh. The paper is


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in the Astrophysical Journal letters and


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Manchester put the release out on


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Tuesday. It has been rolling through the


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international wires all week. Shinha ran


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it yesterday.


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>> And the instrument is Mircat. Mircat 64


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radio dishes standing in the Karu in


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South Africa's northern Cape one of the


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quietest patches of radio sky on earth


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which turns out to be the whole point


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and Mircat is not just a fine telescope


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in its own right it's a precursor it


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gets absorbed into SKA mid the


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mid-frequency half of the square km


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array


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>> okay now tell me what they detected


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because hydrogen on its own doesn't


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sound like news


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>> it isn't on its zone. Hydrogen is the


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most common thing in the universe. The


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news is how they detected it and at what


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distance. Neutral hydrogen, a lone


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proton with a lone electron, emits at a


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very specific radio wavelength, 21 cm.


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>> The famous 21 cm line,


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>> the famous one, and it's famous because


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it's reliable. Hydrogen doesn't care


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whether it's in a bright galaxy or a dim


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one. If it's neutral, it glows at 21 cm,


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which makes it in principle the perfect


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tracer for where matter actually is.


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>> In principle.


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>> In principle. In practice, the emission


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from any single distant galaxy is far


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too faint to pick out. So about 15 years


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ago, people proposed a workaround called


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intensity mapping. Stop trying to


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resolve galaxies. point the telescope at


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a big patch of sky, deliberately blur


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it, and measure the total 21 cm glow


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coming from that whole volume.


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>> So instead of a photograph of individual


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galaxies, you get what? A heat map.


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>> That's exactly the right image, a


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lowresolution map of where the hydrogen


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is piled up and where it's thin. And


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because hydrogen sits inside galaxies


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and galaxies sit inside the cosmic web,


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that blurry map traces the large scale


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structure of the universe cheaply and


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over enormous volumes.


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>> Why does cheap matter? We have galaxy


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surveys.


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>> We do, and they're superb, but they're


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expensive in telescope time. To map


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structure optically, you have to


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identify each galaxy and measure its


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distance one at a time, millions of


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them. Intensity mapping says I don't


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need to know which galaxy is which. I


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only need to know how much hydrogen is


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in this cube of space versus that one.


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And if you can do that out to high red


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shift you can measure how the universe


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has expanded which is the dark energy


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question.


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>> So why hasn't anyone done it?


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>> Because of the foregrounds. And this is


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the part I want to be precise about. The


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21 cm signal from those distant galaxies


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is extraordinarily faint. Sitting on top


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of it is radio emission from our own


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Milky Way. Synretron radiation,


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electrons spiraling in the galaxy's


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magnetic field. And that is roughly four


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orders of magnitude brighter than the


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thing you're trying to measure.


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>> 10,000 times.


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>> 10,000 times, give or take. then add


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human radio interference, satellites,


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aircraft, mobile networks, and then add


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the telescope's own quirks, which


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imprint themselves on the data in ways


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that look deceptively like signal.


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Paul's line in the release is the honest


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one. The signal is extremely faint and


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difficult to isolate from foreground


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emission, human-made radio frequency


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interference, and instrumental effects.


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>> So, how have people got around that


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until now? By cheating slightly, and I


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mean that admiringly, you take your


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radio map and you crossorrelate it with


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an optical galaxy survey of the same


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patch of sky. You already know where the


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galaxies are from the optical data. So


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you ask, does the radio map get brighter


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in the places the optical survey says


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galaxies live?


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>> And if it does, that's the hydrogen.


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>> That's the hydrogen. It's a legitimate


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detection, and Mircat and its


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predecessors have done it before, but it


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has a built-in limit.


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The foreground contamination and your


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instrumental noise don't know where the


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optical galaxies are. So they average


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away in the crossorrelation,


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which is wonderful for confidence and


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useless if what you actually want is a


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standalone survey. You're always


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tethered to an optical telescope.


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>> And this week they cut the tether.


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>> This week they cut the tether. This is


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the 21 cm signal measured in the radio


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data alone. No optical survey propping


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it up. The foregrounds had to be


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genuinely removed rather than


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statistically dodged. And what's left is


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a real measurement of the hydrogen


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distribution.


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>> How much observing time did that take?


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>> Here's the part that made me sit up.


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About 96 hours.


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4 days of telescope time. That's


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nothing.


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>> And it gets better. Santos's quote is my


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favorite line in the whole release. It


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is particularly remarkable that the data


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used in this study were taken in 2018


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when Mircat had only just started


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science operations.


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>> Wait, the data is 8 years old.


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>> The data is 8 years old. This is not a


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new observing campaign. This is a brand


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new analysis of some of the first


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science data Mircat ever took. And the


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advance is in the method, the foreground


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removal, the handling of the


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instrument's own systematics, the


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pipeline. The telescope was always


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capable. We weren't.


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>> How far back are we actually looking?


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>> The emission has been traveling 4 to 5


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billion years. So, we're seeing the


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hydrogen as it was when the universe was


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around 9 billion years old, roughly a


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third of its present age ago and well


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into the era when dark energy had taken


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over and the expansion was accelerating.


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That is exactly the epoch you want if


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you're trying to test how dark energy


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behaves over time.


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>> And the structures they're mapping are


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big,


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>> enormous. The scales involved are


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comparable to the gap between us and


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Andromeda, millions of light years,


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which is precisely the size range where


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the cosmic webs.


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>> All right. Southern hemisphere angle


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because I know there is one and I know


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you're saving it.


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>> I am. And it's not a footnote. It's the


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entire future of this field. The square


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kilometer array observatory is being


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built in two halves. Both of them in the


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south. SKA mid is going up in the KU


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alongside and incorporating Mircat


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itself. SKA low is going up at


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Inyuramana Ilgari Bundara, the CSRO


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Merchesen radioastronomy observatory in


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Western Australia on Wajari Yamamaji


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country.


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>> So this technique's proving ground and


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its future home are both in the southern


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hemisphere


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>> both. And that's not an accident of


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politics. its radio quietness and its


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geography. You cannot do this from a


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populated continent. The signal is too


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faint. You need somewhere with legally


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protected radio silence, and both the


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Karu and the Merchesen have exactly


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that. WS's line is the forward-looking


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one. Mircat continues to open new


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windows for cosmology, and the point of


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a precursor is that everything you learn


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on it, you carry across.


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So, what does the SKA do with a working


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version of this?


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>> Surveys of a size that simply aren't


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available any other way. If 96 hours on


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64 dishes gets you a detection, then


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thousands of hours on an array with


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vastly more collecting area gets you a


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map. A three-dimensional hydrogen map


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running across billions of years of


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cosmic time measuring the expansion


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history directly. That's a dark energy


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experiment done with radio waves from


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the southern half of the planet.


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>> And the honest caveat because you always


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have one.


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>> Two. First, this is a detection of the


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signal, not yet a precision cosmological


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measurement. The error bars are wide and


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turning this into competitive


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constraints on dark energy is a longer


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road. Second, foreground removal is the


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kind of problem that has embarrassed


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radio astronomy before. The 21 cm


00:10:37.040 --> 00:10:38.870
cosmology field has had claimed


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detections walked back. The reason this


00:10:41.600 --> 00:10:43.910
one is being taken seriously is the


00:10:43.920 --> 00:10:45.910
crossorrelation groundwork underneath


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it. They had already shown they could


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find the signal the safe way before they


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went looking for it the hard way.


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>> Which is the right order to do things


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in.


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>> It's exactly the right order and it's


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why Paul's summary is the sentence to


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take away. Detecting it directly with


00:11:02.079 --> 00:11:04.550
Mircat shows that this technique is


00:11:04.560 --> 00:11:07.750
becoming a practical tool for cosmology.


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Not a promising idea anymore, a tool.


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>> Right. Monday to Friday, the six stories


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that mattered. And three of them have


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moved since we covered them.


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>> We start where we ended last weekend.


00:11:21.120 --> 00:11:23.430
The Nancy Grace Roman Space Telescope


00:11:23.440 --> 00:11:25.990
launched on Sunday, August 30th on a


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Falcon Heavy out of launch complex 39A,


00:11:29.120 --> 00:11:31.990
and it was clean. No anomalies, straight


00:11:32.000 --> 00:11:34.470
up, right on the money. We led Monday's


00:11:34.480 --> 00:11:36.230
episode with it, and that closed an arc


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we'd been building since the 25th of


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August.


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>> But it hasn't stopped being a story.


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>> It hasn't. On Tuesday, NASA powered on


00:11:44.800 --> 00:11:46.710
the Roman coronagraph instrument for the


00:11:46.720 --> 00:11:49.750
first time. It came alive between 7:27


00:11:49.760 --> 00:11:52.550
and 8:22 in the morning, Eastern time.


00:11:52.560 --> 00:11:54.389
That's the technology demonstration that


00:11:54.399 --> 00:11:56.069
blocks the light of a star so you can


00:11:56.079 --> 00:11:58.150
photograph the planets around it.


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>> Which is the hard part.


00:11:59.519 --> 00:12:01.990
>> Absurdly hard. You're trying to see


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something a billion times fainter than


00:12:04.320 --> 00:12:06.389
the thing sitting right next to it. The


00:12:06.399 --> 00:12:09.590
coronagraph does it with masks, sensors,


00:12:09.600 --> 00:12:11.910
and mirrors that flex themselves in real


00:12:11.920 --> 00:12:14.470
time to cancel out scattered starlight.


00:12:14.480 --> 00:12:16.629
And what it's after is a class of planet


00:12:16.639 --> 00:12:19.269
we've barely photographed. Worlds that


00:12:19.279 --> 00:12:22.389
are older, colder, and in closer orbits


00:12:22.399 --> 00:12:25.110
than the hot, young super Jupiters that


00:12:25.120 --> 00:12:27.910
direct imaging has managed so far.


00:12:27.920 --> 00:12:30.310
>> How long before it produces anything?


00:12:30.320 --> 00:12:33.110
>> Months. It goes into a long calibration


00:12:33.120 --> 00:12:35.430
campaign, and its observing is spread


00:12:35.440 --> 00:12:38.230
across roughly 3 months of time inside


00:12:38.240 --> 00:12:40.870
the mission's first year and a half. So


00:12:40.880 --> 00:12:43.269
don't expect pictures soon. But the


00:12:43.279 --> 00:12:45.269
instrument is awake and that's the


00:12:45.279 --> 00:12:46.389
milestone.


00:12:46.399 --> 00:12:49.910
>> On Tuesday, we led on Starship flight 14


00:12:49.920 --> 00:12:52.550
and the news then was that booster 21


00:12:52.560 --> 00:12:55.590
had cleared its 33 engine static fire


00:12:55.600 --> 00:12:58.389
and ship 41 static fire was already


00:12:58.399 --> 00:13:00.790
done. What we could not give you was a


00:13:00.800 --> 00:13:01.509
date.


00:13:01.519 --> 00:13:02.949
>> And now there's one.


00:13:02.959 --> 00:13:05.590
>> There's one with a caveat I want to put


00:13:05.600 --> 00:13:08.790
up front. An FCC filing points to launch


00:13:08.800 --> 00:13:11.590
no earlier than September 15th. and the


00:13:11.600 --> 00:13:14.150
launch trackers have moved to that date.


00:13:14.160 --> 00:13:16.550
SpaceX itself has not stood up and


00:13:16.560 --> 00:13:20.870
confirmed it. So net the 15th from pad 2


00:13:20.880 --> 00:13:23.590
at Starbase and treat it as a strong


00:13:23.600 --> 00:13:26.069
indication rather than a promise.


00:13:26.079 --> 00:13:27.829
>> And this is the big one.


00:13:27.839 --> 00:13:30.550
>> This is the big one on two counts. It's


00:13:30.560 --> 00:13:32.710
build as the first genuinely orbital


00:13:32.720 --> 00:13:35.030
flight of Starship. Previous test


00:13:35.040 --> 00:13:36.949
flights have flown trajectories that


00:13:36.959 --> 00:13:38.949
deliberately stopped short of orbit, so


00:13:38.959 --> 00:13:41.670
the vehicle came down regardless. And it


00:13:41.680 --> 00:13:43.590
carries the first ever attempt to catch


00:13:43.600 --> 00:13:46.470
the ship itself. Not the booster, the


00:13:46.480 --> 00:13:49.110
upper stage back at the tower into the


00:13:49.120 --> 00:13:49.910
arms.


00:13:49.920 --> 00:13:52.310
>> They've caught boosters repeatedly now.


00:13:52.320 --> 00:13:54.310
>> They have. And it stopped being


00:13:54.320 --> 00:13:56.710
astonishing faster than it should have.


00:13:56.720 --> 00:13:59.189
But the ship is a different animal. It


00:13:59.199 --> 00:14:01.430
comes back from orbital velocity through


00:14:01.440 --> 00:14:03.670
the worst of the heating. and it has to


00:14:03.680 --> 00:14:05.829
arrive at a precise point with enough


00:14:05.839 --> 00:14:08.550
control authority left to be grabbed. If


00:14:08.560 --> 00:14:10.550
that works on the first try, it will be


00:14:10.560 --> 00:14:12.550
one of the more remarkable things this


00:14:12.560 --> 00:14:13.910
vehicle has done.


00:14:13.920 --> 00:14:15.430
>> And if it doesn't,


00:14:15.440 --> 00:14:17.750
>> then it's a test flight. And that's what


00:14:17.760 --> 00:14:20.790
test flights are for. 10 days out,


00:14:20.800 --> 00:14:23.030
weather and paperwork permitting.


00:14:23.040 --> 00:14:24.870
>> Wednesday's lead was the one I keep


00:14:24.880 --> 00:14:27.430
thinking about. A paper in Nature


00:14:27.440 --> 00:14:30.230
published on August 27th, led by Burn


00:14:30.240 --> 00:14:32.470
and colleagues, built out of years of


00:14:32.480 --> 00:14:34.949
accumulated radio tracking of three NASA


00:14:34.959 --> 00:14:38.310
spacecraft, Mars Global Surveyor, Mars


00:14:38.320 --> 00:14:40.629
Odyssey, and the Mars Reconnaissance


00:14:40.639 --> 00:14:41.590
Orbiter.


00:14:41.600 --> 00:14:43.990
>> And the technique was the clever bit,


00:14:44.000 --> 00:14:46.790
>> title tomography. The sun and Phobos


00:14:46.800 --> 00:14:49.350
flex Mars very slightly, and how much a


00:14:49.360 --> 00:14:51.350
planet flexes depends on how stiff it is


00:14:51.360 --> 00:14:53.910
inside. So if you track your orbiters


00:14:53.920 --> 00:14:56.310
precisely enough for long enough, the


00:14:56.320 --> 00:14:58.150
wobble in their orbits tells you about


00:14:58.160 --> 00:15:00.710
the rigidity of the rock beneath them.


00:15:00.720 --> 00:15:03.269
It's seismology without a seismometer.


00:15:03.279 --> 00:15:04.550
>> And what did it find?


00:15:04.560 --> 00:15:06.310
>> That the interior beneath the southern


00:15:06.320 --> 00:15:09.590
highlands is somewhere between 200 and


00:15:09.600 --> 00:15:12.870
400° C hotter than the north and


00:15:12.880 --> 00:15:15.910
partially molten, which is not a small


00:15:15.920 --> 00:15:19.189
asymmetry. That's one planet with two


00:15:19.199 --> 00:15:21.030
different interiors.


00:15:21.040 --> 00:15:23.110
Does that explain anything we've been


00:15:23.120 --> 00:15:24.150
stuck on?


00:15:24.160 --> 00:15:26.629
>> Potentially three things at once, which


00:15:26.639 --> 00:15:29.110
is why it's such a satisfying result.


00:15:29.120 --> 00:15:31.509
The crust dichotomy, why the southern


00:15:31.519 --> 00:15:33.590
highlands sit kilome above the northern


00:15:33.600 --> 00:15:36.389
lowlands. The crust magnetic anomalies,


00:15:36.399 --> 00:15:38.230
which are overwhelmingly a southern


00:15:38.240 --> 00:15:41.030
phenomenon, and a puzzle from insight,


00:15:41.040 --> 00:15:42.870
where seismic waves were damped more


00:15:42.880 --> 00:15:45.350
than the models predicted. A hotter,


00:15:45.360 --> 00:15:47.430
partly molten south is a candidate


00:15:47.440 --> 00:15:50.949
answer to all three. And what caused it?


00:15:50.959 --> 00:15:54.710
>> Open. A giant impact early on, lopsided


00:15:54.720 --> 00:15:56.870
convection in the mantle, or a layer


00:15:56.880 --> 00:15:59.189
down there trapping heat. The paper


00:15:59.199 --> 00:16:01.749
doesn't pick one, and I respect that.


00:16:01.759 --> 00:16:04.069
>> Moving on to Thursday, and one of those


00:16:04.079 --> 00:16:06.949
quiet, irreversible moments. Bey


00:16:06.959 --> 00:16:09.269
Columbbo, the joint European and


00:16:09.279 --> 00:16:11.590
Japanese mission to Mercury separated


00:16:11.600 --> 00:16:13.910
from its Mercury transfer module on


00:16:13.920 --> 00:16:15.670
Wednesday the 3rd.


00:16:15.680 --> 00:16:17.749
>> 8 years to get to that point.


00:16:17.759 --> 00:16:20.870
>> 8 years. and nine planetary flybys.


00:16:20.880 --> 00:16:23.430
Using gravity to shed speed, because


00:16:23.440 --> 00:16:25.910
falling toward the sun is the easy part,


00:16:25.920 --> 00:16:27.829
and arriving slowly enough to be


00:16:27.839 --> 00:16:30.710
captured is the hard part. The transfer


00:16:30.720 --> 00:16:33.430
module is the ion propulsion bus that


00:16:33.440 --> 00:16:36.069
did all that work, including working


00:16:36.079 --> 00:16:38.069
around a thruster power fault that


00:16:38.079 --> 00:16:40.949
forced the arrival to be redesigned. And


00:16:40.959 --> 00:16:43.430
once you let it go, you don't get it


00:16:43.440 --> 00:16:44.310
back.


00:16:44.320 --> 00:16:46.790
>> So, what's the timeline now? gravity


00:16:46.800 --> 00:16:50.069
capture at Mercury on November 21st.


00:16:50.079 --> 00:16:52.389
Then the two orbiters go their separate


00:16:52.399 --> 00:16:55.430
ways. Japan's MO is released around the


00:16:55.440 --> 00:16:58.310
9th or 10th of December. Europe's


00:16:58.320 --> 00:17:00.790
Mercury planetary orbiter reaches its


00:17:00.800 --> 00:17:03.189
final science orbit on the 10th of March


00:17:03.199 --> 00:17:06.150
next year, and routine science begins on


00:17:06.160 --> 00:17:07.829
the 6th of April.


00:17:07.839 --> 00:17:09.669
>> So, this is the start of the arrival,


00:17:09.679 --> 00:17:11.590
not the end of the cruise.


00:17:11.600 --> 00:17:14.230
>> Precisely. And there are follow-up beats


00:17:14.240 --> 00:17:16.710
all the way through. This is a story


00:17:16.720 --> 00:17:18.710
we'll be coming back to for the next


00:17:18.720 --> 00:17:20.069
seven months.


00:17:20.079 --> 00:17:21.829
>> And yesterday, the story with the


00:17:21.839 --> 00:17:23.429
biggest headlines and the smallest


00:17:23.439 --> 00:17:25.829
number attached to it. The LZ


00:17:25.839 --> 00:17:29.350
collaboration, Lux Zeppelin, 10 tons of


00:17:29.360 --> 00:17:32.310
liquid xenon a mile under South Dakota,


00:17:32.320 --> 00:17:35.110
reported a single nuclear recoil event


00:17:35.120 --> 00:17:37.830
they cannot explain. In a place where


00:17:37.840 --> 00:17:40.549
dark matter could plausibly show up


00:17:40.559 --> 00:17:43.029
>> in exactly that place with essentially


00:17:43.039 --> 00:17:46.630
zero expected background in 220 days of


00:17:46.640 --> 00:17:50.390
data from 2023 and 2024. It was


00:17:50.400 --> 00:17:52.630
announced at TEV particle astrophysics


00:17:52.640 --> 00:17:55.190
in Chiba. Brown University released it


00:17:55.200 --> 00:17:57.430
on Tuesday and the paper has gone to


00:17:57.440 --> 00:17:59.270
physical review letters


00:17:59.280 --> 00:18:00.630
>> and the number


00:18:00.640 --> 00:18:05.190
>> 2.6 sigma globally 3.4 locally. Physics


00:18:05.200 --> 00:18:07.750
calls something a discovery at five. So


00:18:07.760 --> 00:18:10.630
this is an anomaly. And to LZ's enormous


00:18:10.640 --> 00:18:12.230
credit, they have published it as an


00:18:12.240 --> 00:18:14.630
anomaly. Rick Gateskull's line was that


00:18:14.640 --> 00:18:16.710
with only one event, they are not


00:18:16.720 --> 00:18:18.390
claiming to have seen dark matter.


00:18:18.400 --> 00:18:20.150
>> If people take one thing from


00:18:20.160 --> 00:18:21.830
yesterday's episode,


00:18:21.840 --> 00:18:23.909
>> let it be the difference between local


00:18:23.919 --> 00:18:27.430
and global significance. Local asks how


00:18:27.440 --> 00:18:29.830
surprising the event is at one specific


00:18:29.840 --> 00:18:32.950
mass and energy. Global asks how


00:18:32.960 --> 00:18:34.470
surprising it is that you found


00:18:34.480 --> 00:18:36.310
something odd anywhere in the whole


00:18:36.320 --> 00:18:38.710
range you searched. Account for the size


00:18:38.720 --> 00:18:40.230
of the haystack and the surprise


00:18:40.240 --> 00:18:42.549
shrinks. That gap is the reason the


00:18:42.559 --> 00:18:44.789
honest number is 2.6


00:18:44.799 --> 00:18:47.029
>> and the southern angle briefly because


00:18:47.039 --> 00:18:48.470
it's a good one.


00:18:48.480 --> 00:18:51.270
>> CUPL the Stell Underground Physics


00:18:51.280 --> 00:18:53.750
Laboratory a kilometer down a working


00:18:53.760 --> 00:18:56.150
gold mine in Western Victoria and the


00:18:56.160 --> 00:18:57.990
only underground physics lab in the


00:18:58.000 --> 00:18:59.830
southern hemisphere. Its first


00:18:59.840 --> 00:19:02.950
experiment, Saber South, installs late


00:19:02.960 --> 00:19:05.110
this year to test a 20-year-old Italian


00:19:05.120 --> 00:19:07.909
claim from Reversed Seasons, which is a


00:19:07.919 --> 00:19:09.990
genuinely elegant piece of experimental


00:19:10.000 --> 00:19:10.870
design.


00:19:10.880 --> 00:19:13.110
>> And to finish, something new that we


00:19:13.120 --> 00:19:15.110
didn't get to during the week, and it's


00:19:15.120 --> 00:19:17.190
my favorite thing on the list.


00:19:17.200 --> 00:19:19.750
Astronomers have watched a comet switch


00:19:19.760 --> 00:19:20.710
on


00:19:20.720 --> 00:19:22.630
>> watched present tense


00:19:22.640 --> 00:19:26.950
>> over 5 years. The object is 450p


00:19:26.960 --> 00:19:30.470
Lonios. It's a centaur. And centaurs are


00:19:30.480 --> 00:19:33.510
the in between population. Icy bodies


00:19:33.520 --> 00:19:35.990
out among the giant planets that used to


00:19:36.000 --> 00:19:38.390
live in the Kyper Belt and are on their


00:19:38.400 --> 00:19:41.110
way over enormous time scales to


00:19:41.120 --> 00:19:43.430
becoming the short period comets we


00:19:43.440 --> 00:19:44.630
recognize.


00:19:44.640 --> 00:19:46.470
>> So they're comets in waiting.


00:19:46.480 --> 00:19:48.950
>> Comets in waiting. And normally we catch


00:19:48.960 --> 00:19:51.830
them at one end or the other. Catching


00:19:51.840 --> 00:19:55.190
one mid-transition is rare. The work is


00:19:55.200 --> 00:19:56.950
out of the University of Central


00:19:56.960 --> 00:19:59.510
Florida, Charles Shambo leading with


00:19:59.520 --> 00:20:02.470
Maria Wulmarmac, Yan Fernandez, and


00:20:02.480 --> 00:20:04.870
Aaron Beck. And it's been accepted by


00:20:04.880 --> 00:20:07.669
the Planetary Science Journal released


00:20:07.679 --> 00:20:09.110
on Tuesday.


00:20:09.120 --> 00:20:10.630
>> How far out is it?


00:20:10.640 --> 00:20:13.590
>> Over 3 billion miles. And using the


00:20:13.600 --> 00:20:16.150
James Webb Space Telescope together with


00:20:16.160 --> 00:20:18.789
Gemini North, they detected carbon


00:20:18.799 --> 00:20:22.070
dioxide gas, icy dust, and thermal


00:20:22.080 --> 00:20:24.549
activity around it. And a coma that


00:20:24.559 --> 00:20:27.350
grows visibly across observations from


00:20:27.360 --> 00:20:30.070
2019 to 2024.


00:20:30.080 --> 00:20:32.230
>> So what's turning it on? It's nowhere


00:20:32.240 --> 00:20:33.510
near the sun.


00:20:33.520 --> 00:20:35.750
>> It doesn't need to be. And this is the


00:20:35.760 --> 00:20:39.110
lovely bit of physics. Out in the cold,


00:20:39.120 --> 00:20:41.510
water ice freezes into an amorphous


00:20:41.520 --> 00:20:45.270
form. disordered glassy with other gases


00:20:45.280 --> 00:20:47.990
trapped inside the structure. Warm it


00:20:48.000 --> 00:20:50.549
gently and it rearranges into proper


00:20:50.559 --> 00:20:53.669
crystallin ice. That transition releases


00:20:53.679 --> 00:20:56.710
the trapped gas, carbon dioxide in this


00:20:56.720 --> 00:20:59.350
case, and that's what's blowing the coma


00:20:59.360 --> 00:21:00.149
out.


00:21:00.159 --> 00:21:01.590
>> And they can see that the ice has


00:21:01.600 --> 00:21:02.549
changed.


00:21:02.559 --> 00:21:04.950
>> They found crystallin water ice in the


00:21:04.960 --> 00:21:07.669
coma, which is the fingerprint. And a


00:21:07.679 --> 00:21:09.590
Saturn encounter appears to be what


00:21:09.600 --> 00:21:11.909
nudged the object onto the path that


00:21:11.919 --> 00:21:14.549
started warming it in the first place.


00:21:14.559 --> 00:21:17.190
So you get the whole causal chain. A


00:21:17.200 --> 00:21:19.909
gravitational nudge from a giant planet,


00:21:19.919 --> 00:21:22.710
a slow warming, a phase change in the


00:21:22.720 --> 00:21:25.430
ice, and a comet is born.


00:21:25.440 --> 00:21:27.430
>> 3 billion miles away. And we watched it


00:21:27.440 --> 00:21:28.310
happen.


00:21:28.320 --> 00:21:30.149
>> We watched it happen.


00:21:30.159 --> 00:21:32.230
>> Let's move on to our skywatch segment.


00:21:32.240 --> 00:21:33.909
And this is a good week to actually get


00:21:33.919 --> 00:21:36.070
outside because the moon is getting out


00:21:36.080 --> 00:21:38.789
of the way. Last quarter was yesterday.


00:21:38.799 --> 00:21:41.590
>> Last quarter yesterday. And new moon on


00:21:41.600 --> 00:21:44.470
Friday the 11th. So every night this


00:21:44.480 --> 00:21:47.110
week, the moon rises later and thinner


00:21:47.120 --> 00:21:50.149
and the evening sky is dark. If you have


00:21:50.159 --> 00:21:51.669
been putting off looking at something


00:21:51.679 --> 00:21:54.070
faint, this is the week.


00:21:54.080 --> 00:21:55.830
>> Southern hemisphere first.


00:21:55.840 --> 00:21:57.350
>> Southern hemisphere first because


00:21:57.360 --> 00:21:59.110
September is our last really good month


00:21:59.120 --> 00:22:01.590
for it. From Sydney, the sun sets just


00:22:01.600 --> 00:22:04.390
before a/4 to 6. And once it's properly


00:22:04.400 --> 00:22:06.310
dark, the center of the Milky Way is


00:22:06.320 --> 00:22:09.270
almost directly overhead. Sagittarius


00:22:09.280 --> 00:22:12.070
and Scorpius at the zenith. That means


00:22:12.080 --> 00:22:13.350
you're looking through the least


00:22:13.360 --> 00:22:15.909
atmosphere possible at the richest part


00:22:15.919 --> 00:22:17.270
of our galaxy.


00:22:17.280 --> 00:22:19.590
>> What do people actually point at?


00:22:19.600 --> 00:22:21.590
>> Find the teapot of Sagittarius with the


00:22:21.600 --> 00:22:24.310
naked eye and follow the steam up out of


00:22:24.320 --> 00:22:27.510
the spout. That's the galactic center.


00:22:27.520 --> 00:22:29.750
Binoculars turn it into star clouds and


00:22:29.760 --> 00:22:32.390
dark dust lanes. and the Lagoon Nebula


00:22:32.400 --> 00:22:34.870
and a whole run of globular clusters are


00:22:34.880 --> 00:22:37.750
sitting right there. Then later in the


00:22:37.760 --> 00:22:40.070
evening, the Magelanic clouds climb up


00:22:40.080 --> 00:22:43.190
in the southeast and 47 Tucan is


00:22:43.200 --> 00:22:45.590
arguably the finest globular cluster in


00:22:45.600 --> 00:22:46.549
the sky.


00:22:46.559 --> 00:22:47.909
>> Planets down here,


00:22:47.919 --> 00:22:50.310
>> Venus low in the west after sunset,


00:22:50.320 --> 00:22:52.549
brilliant, unmistakable, and building


00:22:52.559 --> 00:22:54.310
toward greatest brilliancancy on the


00:22:54.320 --> 00:22:58.630
18th at magnitude 4.8. Saturn is up most


00:22:58.640 --> 00:23:00.630
of the night in Aquarius, heading for


00:23:00.640 --> 00:23:03.110
opposition on October 4th. And from the


00:23:03.120 --> 00:23:05.270
south, it rides far higher than it does


00:23:05.280 --> 00:23:07.909
for northern observers. And Jupiter is


00:23:07.919 --> 00:23:10.310
the pre-dawn showpiece in the east.


00:23:10.320 --> 00:23:12.470
>> Anything to circle in the diary?


00:23:12.480 --> 00:23:15.350
>> Tomorrow morning, Sunday the 6th, a thin


00:23:15.360 --> 00:23:17.350
waning crescent moon sits a few degrees


00:23:17.360 --> 00:23:19.909
from Mars in the pre-dawn sky. A nice


00:23:19.919 --> 00:23:22.549
one for a phone camera. Monday, the moon


00:23:22.559 --> 00:23:24.230
moves on to Pollock


00:23:24.240 --> 00:23:27.350
>> and North America gets the proper event.


00:23:27.360 --> 00:23:29.750
Tuesday the 8th, the moon occults


00:23:29.760 --> 00:23:32.230
Jupiter. The planet passes behind the


00:23:32.240 --> 00:23:35.430
lunar disc. The footprint covers Canada,


00:23:35.440 --> 00:23:38.070
Greenland, the United States, Eastern


00:23:38.080 --> 00:23:40.789
Russia, and the North Pacific. And for


00:23:40.799 --> 00:23:42.630
much of eastern North America, it


00:23:42.640 --> 00:23:45.750
happens after sunrise in broad daylight.


00:23:45.760 --> 00:23:46.789
>> Daylight.


00:23:46.799 --> 00:23:49.029
>> Daylight. And that brings the standing


00:23:49.039 --> 00:23:51.909
reminder which applies directly here. If


00:23:51.919 --> 00:23:54.310
you are observing anywhere near the sun,


00:23:54.320 --> 00:23:56.710
hunting Jupiter in a bright sky, or


00:23:56.720 --> 00:23:58.390
looking at the sunspots I'm about to


00:23:58.400 --> 00:24:01.110
mention, any filter you use for direct


00:24:01.120 --> 00:24:03.350
solar viewing must be certified to the


00:24:03.360 --> 00:24:06.230
ISO12312-2


00:24:06.240 --> 00:24:09.270
standard, not sunglasses, not welding


00:24:09.280 --> 00:24:11.510
glass of unknown grade, not smoked


00:24:11.520 --> 00:24:16.950
glass, not a phone screen. ISO12312-2


00:24:16.960 --> 00:24:19.669
and check the certification is genuine.


00:24:19.679 --> 00:24:21.590
Sweeping binoculars or a telescope


00:24:21.600 --> 00:24:24.149
across a daylight sky is exactly how


00:24:24.159 --> 00:24:26.470
people injure themselves permanently and


00:24:26.480 --> 00:24:28.710
it takes a fraction of a second.


00:24:28.720 --> 00:24:29.750
>> Meteors,


00:24:29.760 --> 00:24:32.070
>> the September epsilon perciads peak on


00:24:32.080 --> 00:24:34.789
Wednesday the 9th, a modest shower,


00:24:34.799 --> 00:24:37.269
about 8 an hour at best, and it's a


00:24:37.279 --> 00:24:38.870
northern hemisphere event with the


00:24:38.880 --> 00:24:41.590
radiant in Perseus. But it falls two


00:24:41.600 --> 00:24:43.909
nights before new moon. So if you're up


00:24:43.919 --> 00:24:46.149
north and you're out anyway, conditions


00:24:46.159 --> 00:24:48.149
are as good as that shower ever gets.


00:24:48.159 --> 00:24:50.070
And the sun itself


00:24:50.080 --> 00:24:52.950
>> busier than last weekend. Active region


00:24:52.960 --> 00:24:56.390
4524 has come back around the limb and


00:24:56.400 --> 00:25:00.310
fired an M1.2 flare at 7:45 universal


00:25:00.320 --> 00:25:02.549
time yesterday with a brief radio


00:25:02.559 --> 00:25:06.310
blackout. Region 4523 is growing and


00:25:06.320 --> 00:25:08.789
throwing C-class flares. Nothing is


00:25:08.799 --> 00:25:11.269
aimed squarely at us. The strongest


00:25:11.279 --> 00:25:13.590
eruption went well away from Earth.


00:25:13.600 --> 00:25:15.269
>> Aurora chances.


00:25:15.279 --> 00:25:18.549
>> Honest answer. Quiet tonight, possibly


00:25:18.559 --> 00:25:21.830
unsettled Sunday into Monday. KP 3 to 4


00:25:21.840 --> 00:25:24.230
at best. That's a high latitude show


00:25:24.240 --> 00:25:26.789
only. Tasmania and southern New Zealand


00:25:26.799 --> 00:25:29.750
down here, Scotland and Alaska up there.


00:25:29.760 --> 00:25:31.510
Watch the space weather feeds rather


00:25:31.520 --> 00:25:32.870
than the headlines.


00:25:32.880 --> 00:25:35.269
>> And one for northern binoculars,


00:25:35.279 --> 00:25:37.510
>> the double cluster in Perseus while the


00:25:37.520 --> 00:25:40.470
moon's away. Naked eye, it's a smudge.


00:25:40.480 --> 00:25:42.789
In binoculars, it's two open clusters


00:25:42.799 --> 00:25:45.190
side by side in one field. and it's one


00:25:45.200 --> 00:25:47.190
of the best sites in the sky.


00:25:47.200 --> 00:25:49.029
>> And that's the weekend wrap for


00:25:49.039 --> 00:25:51.990
Saturday, September 5th. A radio


00:25:52.000 --> 00:25:55.110
telescope in the KU has mapped hydrogen


00:25:55.120 --> 00:25:58.549
across 4 to 5 billion lightyear using


00:25:58.559 --> 00:26:01.350
nothing but radio waves and proved out


00:26:01.360 --> 00:26:03.750
the technique the square kilometer array


00:26:03.760 --> 00:26:06.310
will use to measure dark energy from the


00:26:06.320 --> 00:26:07.830
southern hemisphere.


00:26:07.840 --> 00:26:10.470
>> Roman's coronagraph is awake. Starship


00:26:10.480 --> 00:26:13.110
flight 14 is penciled in for the 15th


00:26:13.120 --> 00:26:15.510
with the first attempt to catch a ship.


00:26:15.520 --> 00:26:17.510
Mars is hotter underneath its southern


00:26:17.520 --> 00:26:20.470
half than anyone expected. Bey Columbo


00:26:20.480 --> 00:26:22.549
has let go of its transfer module and is


00:26:22.559 --> 00:26:25.190
falling toward Mercury. A xenon detector


00:26:25.200 --> 00:26:27.269
under South Dakota has one flash it


00:26:27.279 --> 00:26:29.669
can't explain and is being admirably


00:26:29.679 --> 00:26:30.870
careful about it.


00:26:30.880 --> 00:26:33.990
>> And a centaur 3 billion miles away has


00:26:34.000 --> 00:26:36.470
spent 5 years quietly turning into a


00:26:36.480 --> 00:26:39.430
comet while we watched. Full show notes,


00:26:39.440 --> 00:26:41.350
links to every primary source, and the


00:26:41.360 --> 00:26:43.110
whole back catalog are at


00:26:43.120 --> 00:26:45.269
astronomyaily.io.


00:26:45.279 --> 00:26:47.909
>> You'll find us on X, Instagram, and Tik


00:26:47.919 --> 00:26:50.950
Tok at astroaily pod. And if you've got


00:26:50.960 --> 00:26:53.750
a question or a correction, we want it.


00:26:53.760 --> 00:26:56.149
There's a contact form on the website.


00:26:56.159 --> 00:26:58.549
>> If today's episode was useful, the


00:26:58.559 --> 00:27:00.950
single most helpful thing you can do is


00:27:00.960 --> 00:27:03.669
send it to one person who'd enjoy it.


00:27:03.679 --> 00:27:05.590
>> We're back Monday with the regular


00:27:05.600 --> 00:27:08.870
weekday format. Until then, the moon's


00:27:08.880 --> 00:27:11.190
out of the way all week. Get outside.


00:27:11.200 --> 00:27:12.470
Clear skies.


00:27:12.480 --> 00:27:14.710
>> Clear skies.


00:27:14.720 --> 00:27:16.950
>> Day


00:27:16.960 --> 00:27:20.760
stories told.