Feb. 8, 2026
Theia's Fate, Galaxy Mergers & the Mysteries of Mars' Atmosphere | Q&A
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This episode of Space Nuts brought to you by Incogni.Reduce the volume of spam calls and emails. They can't spam you if the can't find you. To find out more and to take up our 60% off offer, visit incogni.com/spacenuts and use the cou[on code SPACENUTS at checkout.
Theia's Fate, Galactic Mergers, and the Mysteries of Hydrogen
In this captivating Q&A edition of Space Nuts, hosts Andrew Dunkley and Professor Fred Watson tackle a range of intriguing questions from listeners, diving deep into cosmic mysteries and scientific theories. From the fate of the former planet Theia to the dynamics of galaxy mergers and the origins of hydrogen, this episode is packed with insights that will expand your understanding of the universe.
Episode Highlights:
- The Fate of Theia: Rusty from Donnybrook poses a thought-provoking question about Theia, the planet that collided with Earth. Andrew and Fred discuss the most accepted theories regarding Theia's remnants and how they may have been absorbed into Earth's mantle, leaving behind intriguing geological evidence.
- Galaxy Mergers Explained: New listener Melina asks about the merging of spiral galaxies in an expanding universe. The hosts explain how gravity can overcome the universe's expansion on galactic scales, leading to fascinating interactions and eventual mergers between galaxies.
- Olympus Mons and Mars' Atmosphere: Kevin wonders if the colossal eruptions of Olympus Mons could have contributed to Mars' atmospheric loss. Andrew and Fred explore the volcanic activity on Mars and clarify that while Olympus Mons is impressive, the planet's lack of a magnetic field is a more significant factor in its atmospheric decline.
- Hydrogen's Cosmic Origins: Five-year-old Yuki asks why hydrogen is the only element not formed in stars. The hosts explain that hydrogen was created shortly after the Big Bang, making it the most abundant element in the universe, while other elements formed later through stellar processes.
For more Space Nuts, including our continuously updating newsfeed and to listen to all our episodes, visit our website. Follow us on social media at SpaceNutsPod on Facebook, Instagram, and more. We love engaging with our community, so be sure to drop us a message or comment on your favorite platform.
If you’d like to help support Space Nuts and join our growing family of insiders for commercial-free episodes and more, visit spacenutspodcast.com/about.
Stay curious, keep looking up, and join us next time for more stellar insights and cosmic wonders. Until then, clear skies and happy stargazing.
Become a supporter of this podcast: https://www.spreaker.com/podcast/space-nuts-astronomy-insights-cosmic-discoveries--2631155/support.
This episode of Space Nuts brought to you by Incogni.Reduce the volume of spam calls and emails. They can't spam you if the can't find you. To find out more and to take up our 60% off offer, visit incogni.com/spacenuts and use the cou[on code SPACENUTS at checkout.
Theia's Fate, Galactic Mergers, and the Mysteries of Hydrogen
In this captivating Q&A edition of Space Nuts, hosts Andrew Dunkley and Professor Fred Watson tackle a range of intriguing questions from listeners, diving deep into cosmic mysteries and scientific theories. From the fate of the former planet Theia to the dynamics of galaxy mergers and the origins of hydrogen, this episode is packed with insights that will expand your understanding of the universe.
Episode Highlights:
- The Fate of Theia: Rusty from Donnybrook poses a thought-provoking question about Theia, the planet that collided with Earth. Andrew and Fred discuss the most accepted theories regarding Theia's remnants and how they may have been absorbed into Earth's mantle, leaving behind intriguing geological evidence.
- Galaxy Mergers Explained: New listener Melina asks about the merging of spiral galaxies in an expanding universe. The hosts explain how gravity can overcome the universe's expansion on galactic scales, leading to fascinating interactions and eventual mergers between galaxies.
- Olympus Mons and Mars' Atmosphere: Kevin wonders if the colossal eruptions of Olympus Mons could have contributed to Mars' atmospheric loss. Andrew and Fred explore the volcanic activity on Mars and clarify that while Olympus Mons is impressive, the planet's lack of a magnetic field is a more significant factor in its atmospheric decline.
- Hydrogen's Cosmic Origins: Five-year-old Yuki asks why hydrogen is the only element not formed in stars. The hosts explain that hydrogen was created shortly after the Big Bang, making it the most abundant element in the universe, while other elements formed later through stellar processes.
For more Space Nuts, including our continuously updating newsfeed and to listen to all our episodes, visit our website. Follow us on social media at SpaceNutsPod on Facebook, Instagram, and more. We love engaging with our community, so be sure to drop us a message or comment on your favorite platform.
If you’d like to help support Space Nuts and join our growing family of insiders for commercial-free episodes and more, visit spacenutspodcast.com/about.
Stay curious, keep looking up, and join us next time for more stellar insights and cosmic wonders. Until then, clear skies and happy stargazing.
Become a supporter of this podcast: https://www.spreaker.com/podcast/space-nuts-astronomy-insights-cosmic-discoveries--2631155/support.
WEBVTT
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Hello again, thanks for joining us on a Q and
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a edition of Space Nuts. My name is Andrew Dunkley,
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and today we will be I won't Fred will be
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answering questions about the former planet known as Fear Galaxy.
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Mergers have come up. We go back to Mars with
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a theory about Olympus mons and why only hydrogen? That
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is a question that comes from a believer, a five
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year old. We'll deal with all of that today on
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this edition of Space Nuts fifteen in channel ten nine
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ignition sequence Space nuts or three two space nuts as
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can I reported Neil Goods. And to solve all of
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those little riddles, we're joined again by Professor Fred Watson,
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Astronomer at Large.
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Hello Fred, Hello Andrew, very good to see you again.
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Good to see you too. We've got a bit of
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weird noise on your line. I think it's probably just
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the Internet being the Internet, so hopefully that'll go away.
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In fact, it just did, so yeah, there you go,
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solved itself. It must have heard me winging all as well.
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I assume.
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Yep, we're doing fine. Thank you. It's good to join
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you on the questions episode of what's this called again?
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Oh Space Nuts?
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That's right, space idiots, space nuts. Yes, yeah, they're all
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good people. We might as well jump in straight away
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to our first question, and it comes from one of
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our regular contributors.
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It's Rusty today, Fred and Andrew, It's Rusty in Donnybrook.
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I've been listening to your latest episode where look at
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the relationship between Sea and the Earth before the collision,
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and I just want to make sure I've got the
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story glory straight, so I put it in my own words.
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The Earth had a buddy named THEA who came a
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little too near. She hit with a splash, then made
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off with a dash. But there's no mooning for THEA
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around here, So what happened to THEA after the collision?
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The theories prior to this revelation said THEA had enough
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kinetic energy to leave the Solar System all together.
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But if the orbits were so close, that doesn't seem likely.
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So it seems to me there's three possibilities that THEA
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fell into the Sun, which would be another amazing feat
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to get that sort of precision. After the collision, Sea
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picked up a little slingshot energy and moved out further
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and became Mars, and Mars is a Mars size object
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after all. And the third possibility I can think of
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is that it picked up an unlikely amount of kinetic
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energy and became planet nine. So if it did become
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planet nine, it would have a highly eccentric orbit because
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it's too far away from us to actually see at
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the moment. But would this orbit then at some stage
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bring it back to the Inner Solar System of its origin?
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That's it? How you guys? Well, jeez, thanks, Rusty, hope
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you're will two over there in w A. What happened
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to THEA? He's come up with some interesting theories, quite
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a few ideas. I'm guessing they can't all be true.
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I think that's right. There's actually a fourth possibility I
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did to the three that that Rusty has proposed, and
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I think that's the one that's usually accepted, and there's
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kind of evidence for that. The fourth possibility is that
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basically was absorbed into the Earth. The remnants of thear
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actually in the Earth's mantle, And in fact, there's something
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called and there are two of these, a large low
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sheer velocity province in the Earth's lower mantle. And the
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hypothesis is that that is the remnants of thear so
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that we still see the evidence of that collision by
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anomalies basically in the Earth's mantle, which we investigate, you know,
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with seismology. That's how we know about what's going on
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in the mantle of the Earth. It's how we know
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about large low sheer velocity provinces. I'm kind of just
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using the words here because I'm not somebody who knows
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about the inside of the planet other than you know,
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the sketchiest outline of a core, a mantle, and a crust.
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But the mantle we know has significant structure and in
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fact money. And I have a good friend who Nick Petford,
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who is a volcanologist, and he's somebody who looks at
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these velocity structures in the in the mantle of the
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Earth and you know, the upwelling of material to form
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volcanoes and things like that. Next time we see Nick,
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I will ask him about these large scale low velocity
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shear areas and their relationship to THEA. But I think
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that's the consensus, rusty that the impact basically resulted in
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an explosion which shed something like I think one of
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the suggestions is about seventy percent of the mass of
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the Moon may have come from THEA. I'm actually I
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think that might. Let's put it this way, THEA is
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responsible for seventy to ninety percent of the total mass
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of the Moon. Under the classic giant impact scenario, where
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THEA is considerably smaller than a proto Earth, which it
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would have been, the Earth was still kind of Earthish sized.
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THEA was Mars ish sized, but the Earth would have
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probably grown a bit by absorbing the debris from THEA.
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Remember that the mass of the Moon is about one
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eightieth of the mass of the Earth, so it's a
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significantly large body compared with the other moons in the
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Solar System, but it's clearly smaller than you know, it's
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not Mars sized, And so Rusty's right in that the
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you know, the remnants of THEAR had to do something,
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but the current theory is that they were absorbed by
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the proto Earth, and we can still see evidence for them.
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Yeah, okay, so yeah, definitely not likely to be P nine.
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That would be a very odd kind of occurrence, wouldn't it.
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Yeah, well, yes, I think that kinematics don't work. You
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you know, you can't give it enough velocity and you
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need you need a lot of velocity for it to
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fall back into the Sun as well, too much energy.
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That's quite an energetic process, is getting rid of the
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orbital velocity of a body to make it fall into
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the sub It's you know, you need as much energy
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as you do to get it pushed out to the
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outer planet.
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So, yeah, didn't we talk about it once before and
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suggest that remnants of it just probably speed off into
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space never to be So again.
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I'm sure there would have been an element of that. Yes,
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you know that that debris cloud that eventually formed the
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Moon probably lost some of its some of its material content,
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and there may even be stuff wandering around in the
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form of neuroth asteroids now that are bits and pieces
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that are left over from that. But remember this was
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you know, this was within the first couple of hundred
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million years of the history of the Solar System. So
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you're talking about things that happened a very long time ago. Yeah.
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Indeed, I'm wondering, Fred, why we've just got this sudden
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influx of people asking questions in POM. This is just
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I'm blaming Martin for that. Martin Berman Gorvine, you started
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this and now it's so I think.
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I really liked Rusty's one there about the thought that
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was very nice.
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Yeah, I don't know. I think he pushed it a
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bit on one of those one of those rhymes. Although
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there there was a regular guest, and I'm sure you
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know who I'm talking about, col Wilson, who used to
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join us on the radio once a week to do
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bush poetry, Blew the Shearer, and he often got asked
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to do shearing demonstrations and he had to tell them, look,
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I'm not a shearer. I can't the sheer a sheep
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that saved my life. It's just my show name. But
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he used to actually invent words to create rhymes. It
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was one of his wonderful traits. And yeah, I used
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to spend a lot of time with Collie as a
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terrific bloke. I think we've dealt with Rusties theories and
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they were all wrong. Thanks for Rusty. Takes Rusty great
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to hear from you. Let's take a break from the
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to our next question, and this one I've lost here
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it is. This comes from Lena. I am a new
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listener and not as hardcore as Spacenut as most of
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your audience. It's probably a good thing, but I saw
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an article today talking about merging spiral galaxies. If the
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universe is expanding, how does something as large as a
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galaxy move toward and merge with another galaxy? It seems
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they should be moving further away from each other. That
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comes from Lena in British Columbia in Canada. I think
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we've had questions of this ilk before, but it's always
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good to go over it again because there's a lot
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more going on in the universe than just you know,
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spreading out like school children playing what's that game where
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you don't know, I don't know what you call it?
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Something that you throw a ball and try and hit
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someone in the head. Anyway, go on, that's cricket, isn't it? Dodgeball? Dodgeball?
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And there's a bunch of games like that, like Red
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Rover Crossover. Did you ever play that? Oh no, we
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mustill have a lot of fun with that.
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Anyway. Look, Lina's question is a great one, and I
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guess the simplest answer here is that, yes, galaxies are big,
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but they're tiny compared with the universe, And so the
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expansion of the universe is something that we look at
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on very large scales. You know, you're looking out billions
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of light years and seeing this expansion. It's actually, with
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today's technology, it's one of the easiest observations that you
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can make that the universe is expanding, discovered back in
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nineteen twenty nine by Edwin Hubble. So, yes, So if
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the universe is expanding in space, is getting bigger and
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naturally carrying things further and further apart, why are some
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galaxies coming towards each other? And it's because on the
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scale of a galaxy, the expansion of the universe is miniscule,
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and that by far the dominant the dominant process is gravity.
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So galaxies, which yes, are being carried gradually apart by
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the expansion of the universe, when you put them close together,
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their own gravity gives them a force that pulls them
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together that's much greater than the expansion. And we actually
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give that a name. We call this the peculiar velocities
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of galaxies, because it's a velocity peculiar to an individual galaxy.
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And the usual way that we describe it, and I
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think we've talked about this before on Space Nuts, is
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if you imagine a river flowing, which represents the kind
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of expansion of the universe, and then somebody in a
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boat is moving around on the river. They're being carried
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downstream by the river's movement, but they've got their own
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movement provided by the boat on the water. And it's
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a bit like that with galaxies. They're being carried along
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by the expansion of the universe, but a far bigger
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effect is the way gravity pulls them together. So that's
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what's pulling our galaxy and the Andromeda galaxy together. It's
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the gravitational force between them. And on the scale of
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the distance between Andromeda and our own galaxy, which is
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about two and a half million light years, the expansion
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of the universe makes virtually no difference. You only start
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really noticing it when you get to much bigger, bigger scales.
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Yeah, they will come a point in time where all
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these galaxy mergers will finished, They'll be done and dusted,
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and the universe will keep expanding and eventually it'll just
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be darkness. There'll be nothing.
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Yeah. If that's assuming dark aage big crunch, right, yeah,
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I mean dark energy. We're now just starting to see
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the first signs that maybe over the last few billion
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years it's decreased. And so the acceleration of the universe
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it's still accelerating. The expansion is still getting faster, but
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it's getting faster at a slower rate, if I put
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it that way. So the acceleration itself looks as though
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it's declining. And that's why some people are still talking
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about the big crunch or they're going to have gibb again.
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It's it's because if the acceleration eventually goes away and
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becomes a deceleration, then yeah, you're going to get a
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big crunch.
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Yeah, yeah, it's you know, could go either way at
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this stage the way they're talking. We we have witnessed
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