Astronomy Cast

Even though humanity has returned samples from a fraction of the worlds in the solar system, the cosmos has delivered many more without us having to lift a finger. Meteorites. We have meteorites from the Moon, Vesta and even Mars! What have we learned about these rocks from other worlds? Space missions to other worlds cost millions to billions of dollars, and if we want to know exactly where space rock samples come from, we need to spend the big bucks for sample return. But, if it's good enough to know "this rock came from somewhere on that world," space offers an amazing delivery system in the form of meteorites. Come learn about the search for, identification, and science of meteorites from other worlds.  

Show Notes

• Meteorites as samples: Natural delivery from Moon, Mars, Vesta, asteroids
• Impact ejection: Collisions launch rocks into space at escape velocity
• Scientific value: Reveal early Solar System chemistry & planetary history
• Limitations: Unknown exact origin, shock damage, Earth contamination
• Identification methods: Spectroscopy, composition matching, trapped gases
• Crater studies: Tektites, shock features, and local knowledge
• Life debate: Controversy over possible biosignatures (ALH meteorite)
• Sample return vs meteorites: Precision vs accessibility
• Possible sources: Mars, Moon, Vesta, Phobos, maybe beyond
• Interstellar material: Difficult to identify but potentially present
• Key takeaway: Meteorites = accessible clues to planetary and cosmic history

Transcript

Fraser Cain: 

Astronomy Cast, Episode 790 Meteorites from Other Worlds. Welcome to Astronomy Cast, your weekly facts-based journey through the Cosmos, where we help you understand not only what we know, but how we know what we know. I'm Fraser Keane, I'm the publisher of Universe Today.

With me as always is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hello, Pamela.

Dr. Pamela Gay: 

Hello, Fraser. I have a new favourite moment in Rule Breaking. Can I share it?

Yes. So, Astronaut Commander Reed from the Artemis II Integrity Capsule was supposed to leave RISE, the little round plushie that they had as a zero-g indicator. He was supposed to leave it on board Integrity as it floated in the ocean, hopefully to be rescued, and he couldn't do it.

He couldn't leave behind RISE. So he stole it.

Fraser Cain: 

You don't leave a crew member behind. Right.

Dr. Pamela Gay: 

Snuck it out. So RISE now is Commander Reed's, and he's been just like kind of carrying it around in lots of different... It is my favourite moment.

Fraser Cain: 

Isn't it supposed to end up at a school, though, at some point? Like it's going to end up with some... I forget how...

Dr. Pamela Gay: 

I don't know. I just know it wasn't left behind on the capsule, and there are so many adorable photos. And yeah.

Fraser Cain: 

Man, that mission was so great. I was just transported to a younger version of me watching sort of the one that actually felt most significant to me was the Mars Pathfinder Sojourner mission. That was the one that I was really just glued to the live streams, watching every moment.

And this brought me back to that world, watching all of these key moments, even just sort of switching back to see the live stream, the quiet view of the porthole of the Orion capsule to see either the Moon or the Earth. It was absolutely incredible. And it just shows us the best of what humanity can do.

And obviously, there are details about the $4 billion that it cost to launch these things, the delays in the launch, the potential competition from reasonable rocket companies and so on and so forth. But still, this was just... Humanity went farther than humanity has ever gone, and I was there for it, and it was incredible.

I think we should do an episode about Artemis 2 when we have a little bandwidth. Even though humanity has returned samples from a fraction of the worlds in the solar system, the cosmos has delivered many more without us having to lift a finger. Meteorites.

We have meteorites from the Moon, Vesta, and even Mars. What have we learned about these rocks from other worlds? Meteorites.

Meteorites. Which worlds do we have meteorites from that have fallen down here on Earth?

Dr. Pamela Gay: 

Mars, the Moon, Vesta series, a whole bunch of the other asteroids, but they come in families, which makes it a whole lot harder to say exactly which one they came from.

Fraser Cain: 

Right. They came from this family. Who knows if it was...

Which of the specific rocks?

Dr. Pamela Gay: 

I'm pretty sure we don't have any from Venus, but...

Fraser Cain: 

No, we don't.

Dr. Pamela Gay: 

Okay. You often prove me wrong, so I have learned to add caveats.

Fraser Cain: 

That would be wise, yeah. No. From what I understand, there are none from Mercury, none from Venus.

Dr. Pamela Gay: 

The energy from Mercury is not realistic, and Venus's atmosphere is just super thick.

Fraser Cain: 

Yeah. Nothing's getting out of either of those. Yeah.

Yeah. Okay. And that is incredible.

So how do they get here?

Dr. Pamela Gay: 

Well, when a rock hits a rock, transfer of momentum is expletive. So what ends up happening, and this is part of my favorite caption that has ever existed in a print magazine. There is this amazing caption that I believe based on the formatting of the page that I found on Reddit, came from Scientific American.

I've not been able to find the actual article. The caption basically reads that when the asteroid that killed the dinosaurs struck Earth, the shock wave flung at escape velocities, dirt, trees, and dinosaurs. And...

Fraser Cain: 

What a way to go.

Dr. Pamela Gay: 

Yeah. Yeah. So the first life forms to leave the planet Earth were very dead dinosaurs.

Fraser Cain: 

Right.

Dr. Pamela Gay: 

But...

Fraser Cain: 

I mean, probably very dead.

Dr. Pamela Gay: 

Many other things.

Fraser Cain: 

Many other things. Yeah. When you think about the giant impacts that have happened in the history of planet Earth, there was some early first astronaut.

Dr. Pamela Gay: 

So when space rock comes down, whether it be something tiny that just becomes a meteorite or something bigger where you just keep calling it an asteroid, when it collides, that kinetic energy from its motion ends up getting translated into heat, into noise, into compression waves moving through the ground. And that energy excavates the crater, melts a lot of stuff, flings boulders in all directions as it does its excavating. And some of those things that it flings are going to be going at escape velocities from whatever world is getting hit.

And those excavated chunks of world are then on their own orbits that could include a trajectory that heads them straight towards us. And this leads to all sorts of mixing of early solar system substances back when collisions were much more common between the early forming worlds that, well, Venus, Earth, and Mars were all settling into habitability at about the same point before Mars decided to become too cold and Venus decided to become way too hot.

Fraser Cain: 

So let's talk about some of the samples that have been found and some of the most interesting ones. And I mean, I think, I mean, this is not the same as a meteorite that is out in space. This is not the same as us retrieving a sample from an asteroid or from a comet.

When you think about, say, Hayabusa, Hayabusa 2, Cyrus Rex, they pulled a chunk, they pulled material off of these objects. And these were in a pristine state. I mean, obviously they're rubble pile asteroids, they've gone through, they've seen some things, but they haven't sort of experienced the same kind of shock and damage that has happened from something that was actually scoured out of another planet.

Dr. Pamela Gay: 

Yeah. We have three scientific problems with donated samples from other worlds. One is we don't know exactly where on that other world it came from.

Fraser Cain: 

But even, well, so hold on, I was going to bring that up, but actually they're starting to get a sense of where some of those samples came from.

Dr. Pamela Gay: 

For some worlds, but we can't consistently do it.

Fraser Cain: 

The Mars ones, they're getting a sense based on the kind of, I mean, we know so much about the rock on Mars that we can guess where those samples might've come from roughly.

Dr. Pamela Gay: 

But we can't do the kinds of things that we do with like collected lunar rocks where we take them into a lab, we measure exactly how old they are, and then we can use them to calibrate our understanding of how old different surfaces on the moon are. We can't do that.

Fraser Cain: 

No. And then like think about what's happening with Perseverance as it is going across the landscape of Mars, looking for the perfect rock and then drilling a sample, holding it closely inside its sample container, moving on. Like that is precision in what you get as opposed to what you get with just random rocks being hurled at the planet.

Dr. Pamela Gay: 

Right, right.

Fraser Cain: 

So that's the first challenge. You don't know where they came from.

Dr. Pamela Gay: 

Right. So first challenge is you don't know where they came from. Second challenge is they're getting altered by the space environment a whole lot.

So there was whatever excavated them was a high energy event. They traveled through space, which causes surface weathering. And then they went through our atmosphere, which causes its own form of challenge as it gets heated up and then smashes into whatever it smashes into.

Fraser Cain: 

Yeah. And that's probably not the worst part of the contamination. The worst part is that they then sit on the surface of the earth for an unknown amount of time being infested by our local life forms.

And that one of these meteorites can be hidden for hundreds, thousands, tens of thousands, hundreds of thousands of years.

Dr. Pamela Gay: 

Hundreds of thousands is pushing it because we do get them from places like deserts and ice flows and our planet has had weather cycles.

Fraser Cain: 

Right. But the point being that that's plenty of time for occupation to occur. Yeah.

I mean, what probably happens is that the various weathering process that we have on the earth dismantle the meteorites within that timeframe. So it's the ones that we get to them before they're completely faded away. But still we can do science.

What kind of science can we do with these samples?

Dr. Pamela Gay: 

So there's the straightforward, which is you take them into a lab, you cut them into very thin slices and you study what is the stuff inside them. What is the components? And this is useful for two different reasons.

One is we can also shine light at them and reflect the light off and match them to other worlds. This is actually how we figure out what meteorite came from, where, when it comes to the asteroids is we know the asteroids really well in reflected sunlight. You take a space rock, take it into your lab, reflect sunlight, sun, light off of it and see what it matches.

And that's its parent body. And then, because we don't have samples of Vesta, we don't have samples of Ceres, we don't have samples of like all but just the tiniest handful of asteroids. So then we take them apart and look at them to measure the various mineral structures, to measure the various, how does all of this stuff come together and then shred them completely in a mass spectrometer to get at the atom by atom understanding.

And some of the thin cuts that they do through these and then shine light through look like the most amazingly chaotic stained glass. So our solar system is out there creating chaotic stained glass and sending it our way.

Fraser Cain: 

But I think one of the most exciting things is that there is gas trapped within these rocks.

Dr. Pamela Gay: 

Yes, I have to admit that is one of the things I am, I am weirdly just less interested in. But we have found both liquid and gas trapped inside the crystalline structure of various minerals. It turns out things like diamonds in particular are very good at holding stuff in their inclusions.

So when we get particularly lucky, we're not looking for amber containing animals, we're looking for minerals containing gas, containing liquid, containing a moment in the history of another world.

Fraser Cain: 

Yeah, yeah. I mean, again, this is just incredible when you think about this, that a giant asteroid smashed into Mars, scoured out material, sent it into orbit. These rocks have been floating around in the solar system.

And then some part portion of them found their way to the Earth's atmosphere, enter the atmosphere, reached the ground, a scientist found it, and then sliced it open. And there were bits, there were tiny bits of trapped Mars atmosphere in that meteorite that you can then use to study the atmosphere of Mars at the time that the space rock was hurled into space. What have we learned, do you think, about being able to study these samples from other worlds?

Dr. Pamela Gay: 

One of the first things we've learned is what makes someone a scientist is when they find something cool, they report it. Because so many of the meteorites that have been found that weren't in Antarctica where we send groups of humans who have been trained to find meteorites to go find meteorites. A lot of the other ones that have been found are like someone's back pasture, someone's back 40.

So farmers are one of the great sources of meteorites. Yeah, all over the world, people find meteorites and when we're lucky, they report what they found and they share and we get to go get samples. We have learned that there are a whole lot of unique rocks that allow us to look at things and go, this is actually a crater right here.

Because when the impactor is big enough, it creates tektites, which are melty bits of the rock that was already there that now become new rocks. And it creates these shocked rocks where you can actually look at them and see through, they're called shock cones, go figure, we're not exciting in how we name things. So there's all these local ways geology gets wrecked when big things hit and it changes the landscape.

And there's this one really funny case of a winery in France that was creating meteorite wine. And they were claiming that their vineyard, which is in this cool circular indentation, was a meteorite crater and everyone was like, ha, ha, ha. And it turned out that some geologists who were traveling, who of course went because it was funny, were like, oh, oh, wait, this might be a crater.

And so they went back and it was actually a crater. And I'm super sad because you can't get this wine in the United States and I really want a bottle. So folks in France, I really want a bottle of this wine.

And so we have learned that we need to listen to the locals. We need to listen to their stories. We need to listen to like oral traditions are a great way to figure out where craters formed in the past at various points in history.

And then when we pick up these rocks, we also learn to be slightly afraid because they could be carrying stuff from a point in time where life existed on other worlds than this.

Fraser Cain: 

Right. And I think we need to talk about one of the most controversial rocks found from another planet, Allen Hills. So this is going to be a moment that is kind of seared into everybody's memory.

And this happened at roughly the same time that I was enthusiastic about watching the Mars Pathfinder mission complete its various operations. Shortly after that, we saw the announcement of life on Mars. Thanks to the Allen Hills meteorite.

Dr. Pamela Gay: 

Yeah. And back in 1984, this meteorite was found on Allen Hill in Antarctica. And it takes a while for them to get through all the different meteorites they find and do research on them.

And this particular one, they found it, they sorted it. And then Roberta Skor, who's the lab manager at Johnson Space Center, she was the one who found it. And it was claimed to be the oldest Martian meteorite that had been found to be 4 billion years old.

And when folks started studying it, one of the things that the research team did was they cut it, they gold plated it, they put it through an electron scanning microscope. So the gold plating was to make the electron scanning microscope work better. And when they looked at the images that came out of the electron scanning microscope, they saw what looked like little tiny nanobacteria nodules that were similar to what had been studied at places like Yellowstone.

And the claim was made that life had been found in the Allen Hills meteorite. Now this was super controversial for a number of different reasons. One was it turns out if you're not like the absolute nicest person on the entire planet, people are going to show more skepticism to your research.

And when we were all going to see the talks on this, the person presenting, whose name I'm not going to name, would show the meteorite, would then show pictures of his grad students in skimpy clothes next to where they collected the nanobacteria from field sites. And that didn't sit well with many of us. And so there's that underlying, blech, that just like kind of went into how you looked at the research.

And then there was like the knowledge that if you screw up your gold plating, you get artifacts that look exactly like what they were saying was nanobacteria. And then there's like the fact that just sometimes minerals do stuff. And they haven't really allowed the experiment to be replicated.

So you have this situation where no other means of exploration have been able to replicate what they found. Other work done on the same meteor didn't find indications of life. And there was just kind of this overall, blech, involved in the research.

So, yeah, they might have found something. But until it gets found in a more credible way, and likely until it's presented by someone that doesn't leave all of us feeling slightly creepy, it's life hasn't been discovered.

Fraser Cain: 

Yeah. And I mean, I think you've got to sort of compare this to what happened with, say, the Hayabusa and the OSIRIS-REx mission. You had these samples returned.

They were sent out around the world to dozens of teams with some of the world's best labs. And they've been trickling back their information, confirming each other's discoveries, finding all these amino acids and all of this sort of measuring the amount of water in these samples, and determining a lot of really interesting things about the early history of the solar system. And that this is, you know, partly that when a rock from space lands on Earth, it is just one rock.

And then it's up to the team who claims it to work on it to sort of decide how the information is sort of parceled out. And that if you have a really bombastic discovery, it is tricky to then put yourself to that level of scrutiny. And yet that's what science demands.

That's how science works. As opposed to this sort of top-down, hey, we've got all these samples, here you go everybody, get back to some of what you found. And then they're kind of double-checking each other.

So it's, yeah, it's, unfortunately, I mean, we have a lot of examples of this. We have the Viking, we have the Allen Hills meteorite, we have the discovery of phosphine in Venus, we have the detection of methane on Mars, we have Mono Lake, yeah, we have all these times where life was found, and yet it just didn't hold up to scrutiny. The wow signal, like it just, it goes on and on and on.

The discovery of satellites in orbit around the Earth before the first artificial satellites were launched.

Dr. Pamela Gay: 

The Japanese UFO on an archaeological thing, yeah.

Fraser Cain: 

Boyajian's sort of dust ring, like it goes on and on and on. And it just shows that when the potential consequences of the discovery are big, then the level of rigor and the amount of sort of ego setting aside needs to be done is astronomical. And few are up to that task.

Dr. Pamela Gay: 

And you really need to have no clear alternative answers because Occam's Razor is a thing. And when you can say, yeah, but if you gold-plated it not perfectly, that's exactly what it looks like. That is such an easy explanation for what they saw, and it's not like you can un-gold-plate the meteorite.

Fraser Cain: 

Right. Yeah. So let's talk about kind of hypothetical meteorites.

Yes. Could there be meteorites from Mercury, Venus, Phobos, Io here on Earth somewhere?

Dr. Pamela Gay: 

Phobos, yes, that's easy. Io, I mean, it could happen, but it's going to take a whole lot. And the idea of something being big enough, having come off of Io, traveled this way and made it through our atmosphere, my brain is going, but it's a gooey world.

I mean, it's not all gooey, but that's where my brain went is it's gooey. Yeah.

Fraser Cain: 

I mean, it's covered in rock.

Dr. Pamela Gay: 

Yeah.

Fraser Cain: 

You hit it with an asteroid, it's going to blow up rocky chunks into space. They're not going to remain lava.

Dr. Pamela Gay: 

Yeah. You just have to hit it really, really hard because of Jupiter's gravity.

Fraser Cain: 

Yeah. Yeah. You have to escape Jupiter.

Dr. Pamela Gay: 

Yeah. You have to escape Jupiter's gravity, which means that you have to somehow dig deep enough to get a whole lot of boulders sent out at a whole lot of velocity. So, Io is giant question mark of could it happen?

Well, a lot of things can happen, but I put the probability on that one super low. Venus.

Fraser Cain: 

What about? Oh, Venus.

Dr. Pamela Gay: 

Okay. Yeah. Venus depends on when.

So, Venus hasn't always had the atmosphere it currently has. And so, if you hit it really, really hard when it didn't have that super thick atmosphere, but had already solidified and before it got its prior atmosphere flung off, yes. So, I mean, it's always had an atmosphere.

It just hasn't always had its current atmosphere.

Fraser Cain: 

But it is tricky to climb up that gravitational well.

Dr. Pamela Gay: 

But if you can fling dinosaurs that escape velocity off of the planet Earth.

Fraser Cain: 

Yeah. But you not only have to fling them off of a world that is as much as.

Dr. Pamela Gay: 

You have to escape the sun.

Fraser Cain: 

Yeah. You have to escape the sun.

Dr. Pamela Gay: 

Yeah.

Fraser Cain: 

That is the challenge. You have to get, you have to climb, like people always sort of imagine Venus in this sort of, or these worlds in this sort of perfect balance and you just drift away from one to the other. But no, the sun is this giant gravitational well.

It is at the bottom of this gravitational well. Mercury has partially climbed out of this gravitational well. Venus is a little better and Earth is a little higher.

Dr. Pamela Gay: 

Yeah.

Fraser Cain: 

But to go from Venus up to Earth, it literally is up to you. You've got to climb a mountain and that is a challenge. Of course, it's also difficult to climb down the mountain.

Dr. Pamela Gay: 

Right.

Fraser Cain: 

Both are challenges.

Dr. Pamela Gay: 

And this is where you have to be looking for things that are on elliptical orbits that intersect both Venus's orbit and Earth's orbit because that is easier to accomplish. And as always, your friendly reminder that it is far easier to yeet things out of the solar system than to yeet them into the sun.

Fraser Cain: 

Right. What about an interstellar object?

Dr. Pamela Gay: 

Oh, yeah. I'm sure we have interstellar objects on our world. Yeah.

We just don't have a reflection spectrum to match them to. So it's probably like unlabeled mystery rock.

Fraser Cain: 

Right. But you can imagine someone doing, say, a sample of it, looking for the radioactive decay and then going, wait a minute, this sample is 8 billion years old. Right.

This rock is 8 billion years old. Like in theory that it's never been found. Right.

All of the meteorites ever been tested have always been exactly the same age, the age of the solar system. But out there somewhere, there is a meteorite that will, when you test it. Now, they've found pre-solar grains in meteorites that are older than the solar system.

Dr. Pamela Gay: 

But those are grains.

Fraser Cain: 

Grains. Not full meteorites. And yet you think, you know, we have, we've seen three interstellar objects passing through the solar system.

Dr. Pamela Gay: 

Models show there should be like 6 to 12 a year.

Fraser Cain: 

Yeah. And there should be probably 10,000 plus just going through the solar system at any one time. And so at some point in the past, an interstellar object has struck the earth and it's there somewhere on the planet for the finding.

Yeah. And then can you imagine what we could learn studying a rock that came from another planet in the galaxy?

Dr. Pamela Gay: 

The frustration of not knowing its provenance is the great frustration.

Fraser Cain: 

Yeah. Yeah.Yeah.

Yeah. Yeah. It's just like, you know, it's made of different stuff.

I mean, it would still be made of the same kinds of material. But the ratios will be different. Slightly different ratios.

Yeah. Yeah. And it's older.

Dr. Pamela Gay: 

Right.

Fraser Cain: 

Be like, oh, it formed a billion years ago. But we don't know where. Like maybe you could look at the chemistry of stars out there and find one that it's We can't even find our own siblings.

Dr. Pamela Gay: 

Yeah. We orbit the center of the galaxy, I think every 250 million years.

Fraser Cain: 

Yeah. Yeah. And so a lot of potential siblings of the sun have been found.

Dr. Pamela Gay: 

Right. But we can'tprove it because we've scattered to the four directions, inward, outward, forward and back. Yeah.

Fraser Cain: 

Yeah. Yeah. But that'll be that'll be incredible if there's some time like people have proposed that the trajectories of certain meteorites coming in, hit the atmosphere, that they were on an interstellar trajectory.

There was a search by Avi Loeb and others to try and find a meteorite, but the results were inconclusive. So we are still waiting for that. And then probably the best thing is to just chase down an interstellar object and sample it directly and bring a piece home.

That will be the greatest accomplishment of humanity, I think, is to be able to chase down.

Dr. Pamela Gay: 

And you just did a video on that. Have I? You just did a video on chasing down meteorites.

Fraser Cain: 

Yes. Yeah. Yeah.

Well, those are ones in the Earth's atmosphere.

Dr. Pamela Gay: 

Okay. That's true.

Fraser Cain: 

That's true.

Dr. Pamela Gay: 

So the meteor, meteorite, meteoroid set of words.

Fraser Cain: 

Yeah.

Dr. Pamela Gay: 

Just put all of this into your heads. Meteoroids, asteroids are space rocks still in space. Meteor is while they're going through the atmosphere.

Meteorite is once you've picked them up because minerals and an ite. Yeah. So these words are evil.

I just call them space rocks.

Fraser Cain: 

Yes. And people love to give you a hard time if you... Confuse them.

...don't get it perfectly right. But I think there's a lot of edge cases where you kind of wonder, you know, does a meteor hit the moon?

Dr. Pamela Gay: 

A meteoroid hits the moon.

Fraser Cain: 

Yes. But what if it's a kilometer across?

Dr. Pamela Gay: 

Then it's an asteroid.

Fraser Cain: 

It's not a meteoroid. I think, you know, I think meteors can hit the moon.

I think, you know, I think meteors can hit the moon. I think if they're on a collision course with the world, that that's when they become a meteor, in my opinion. But anyway, I think we've wrapped up this topic.

We're now starting to rabbit hole. So thanks, Pamela.

Dr. Pamela Gay: 

Thank you, Fraser. And thank you so much to all of you out there. Being able to continue doing science communications in this day and age where we're seeing NASA literally cancel the entire office of science communications.

It is an honor and a pleasure. This week, I would like to thank our patrons over on patreon.com slash astronomycast, who allow us to have Rich, Ali and others, Aviva, making sure we don't sound terrible. This week, we are pleased to thank the following people whose names I shall now mangle.

Our show wouldn't be here without the wonderful support of so many of you over on patreon.com slash astronomycast. This week, I'm going to thank you the best way I have, which is by probably mispronouncing your name. Thank you so much to Antisor, ArcticFox, AstroSets, Benjamin Mueller, Bob Zatzke, BoogieNut, Breznik, Brian Kilby, Cody Rose, Conrad Holling, Daniel Schechter, David, David Gates, David Green, Diane Philippon, G.

Caleb Sexton, Galactic President Scooper McScoopsalot, Glenn Phelps, Gold, Jared Heal, Janelle, Jason Kwong, Jeremy Kerwin, Jim Schooler, John M, Jordan Turner, Laura Kettleson, Lee Harbourn, Lana Spencer, Marco Irrasi, Matt Rucker, Michelle Purcell, Michelle Wichman, Nala, Nate Detweiler, Older, Patricia Hope, Paul D. Disney, Randall, Richard Drumm, Robert Palasma, Sachi Takaba, Sandra Stantz, Sean Matz, Siggy Kemmler, Slug, TC Starboy, Thomas Gutzeta, Tiffany Rogers, Timeroid Iroh, Tricor, Tricia McKinney, and Vettely. Thank you all so very much.

And I'm so sorry for my failure to pronounce things.

Fraser Cain: 

All right. Thanks, everyone. We'll see you next week.

Dr. Pamela Gay: 

Bye-bye, everyone.

Live Show

A star like the Sun only lasts about 10 billion years and it becomes a red giant and finally a white dwarf. This is catastrophic for some of the planets, consumed by the expanding red giant star. But most survive. What happens next in the long, slow cooling to the background temperature of the Universe?

Show Notes

• Stellar lifecycle: Sun → red giant → planetary nebula → white dwarf
• Fate of Earth: likely engulfed or stripped to a molten core
• Mass loss reshapes planetary orbits (planets may drift outward)
• Planetary nebula: gas, radiation, and drag affect surviving worlds
• White dwarfs: hot, dense cores supported by electron degeneracy
• Second-generation planets can form from debris disks
• Possible habitable zones near white dwarfs (tidally locked planets)
• White dwarf evolution: cooling, crystallization (“diamond core”)
• Observations: debris, planetesimals, and planets around white dwarfs
• Long-term future: shrinking habitable zone, fading system
• Ultimate fate: cold stars, lost planets, and a dark, cooling universe

Transcript:

Fraser Cain: 

AstronomyCast, episode 789, what happens to planets when the stars die? Welcome to AstronomyCast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. I'm Fraser Cain.

I'm the publisher of Universe Today. With me, as always, is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of Cosmic Quest.

Dr. Pamela Gay: 

Hey, Pamela, how are you doing? I am doing well, and I glitched it exactly the way it drives you crazy.

Fraser Cain: 

No, no, no, just to be clear, it does not drive me crazy at all. I never even noticed until one of our viewers mentioned this exact tick that you have. And now, as a supportive co-host, I had been mixing it up just to sort of kick you off of your routine, and clearly, we go back to the standard, and you're back on your routine.

So we need to go deeper, I think. I need to make the introduction and me asking you how you are more complicated. Things are going to get weird, and that's fine.

We need to pass through the valley of fire before we can come out the other side. New, reforged, refreshed. So we've both seen Project Hail Mary.

Dr. Pamela Gay: 

Yes, I found it deeply endearing. I am not going to buy the Lego set, but I may 3D print my own Rocky, because Rocky is the best.

Fraser Cain: 

I mean, when you see the making of, and you see them running that guy around as a puppet, that's crazy how much of that movie is practical. Are you going to love this movie? Yes.

Are you going to have some scientific quibbles if it runs across something that you're actually very good at? Yes. But that's fine.

It's a good movie. I really enjoyed it. Anywhere can do no wrong.

Keep it up, Andy. I hope you get your Star Trek series. A star like the sun only lasts about 10 billion years, and then it becomes a red giant, and finally a white dwarf.

This is catastrophic for some of the planets consumed by the expanding red giant star, but most survive. What happens next in the long, slow cooling to the background temperature of the Universe? Alright, the Sun.

Give us the future history of the Sun.

Dr. Pamela Gay: 

I love that concept. Our Sun, oh man, it's going to shed a whole lot of mass, and exactly what happens depends on how much mass gets shed. So we know for certain that it's eventually going to shed its outer layers, form a planetary nebula.

The remaining part of the core is going to collapse down, get supported through what's called electron degeneracy pressure, which is basically all of the electrons going, poly exclusion principle, poly exclusion principle, and pushing each other out.

Fraser Cain: 

You can hear them. Literally, you can hear them yelling out if you're close enough to a neutron star.

Dr. Pamela Gay: 

I don't recommend it. Not a neutron star. A white dwarf.

Neutron star have neutron degeneracy pressure, so they're yelling something different.

Fraser Cain: 

Different sound.

Dr. Pamela Gay: 

Yeah, yeah.

Fraser Cain: 

Exactly.

Dr. Pamela Gay: 

So one of the problems with the mass loss is depending on how much mass loss occurs, you have planets moving different amounts. So it is entirely possible that the Earth will be consumed when the Sun bloats up into a red giant star, or due to mass loss, it might move outward and escape that fate. Now the problem is you now have all of this material all over the place, and it's going to create drag.

And so now you have a new problem. You have hopefully escaped the red giant stage. You are now living within a planetary nebula.

You're now living within the shredded outskirts of your star. And what is left over is a white dwarf that shines very brightly in the ultraviolet. And ultraviolet can vaporize rock.

Fraser Cain: 

Right. And I know that the temperature, like when the, like the core of the Sun, the temperatures are in the millions of Kelvin. And then the star dies, blasts out those outer layers, bloats up as a red giant, consumes definitely Mercury and Venus.

Maybe Earth, we're still not sure. Mars will probably survive. The ice moons of Jupiter will enter the habitable zone, which I always think is so cool.

And then it will, you know, puff out a layer, shrink back down, and then it'll do it again, puff out a layer, shrink back down. And then, as you said, you get that planetary nebula that's around it that is always so cool. What sort of, what decides the final orbit of the planets?

Dr. Pamela Gay: 

It is a combination of what is the final mass of the white dwarf, what is the final velocity of each planet, and is their orbit stable or is it decaying as they interact with material around them?

Fraser Cain: 

Right. So if you, if you decreased the mass of planet Earth, like if you just opened up a wormhole and just started siphoning away mass from Earth to some other part of the Universe, what would happen to the orbits? Our orbit would not noticeably change.

No, no, but what happened to the orbits of the satellites? Because now they're orbiting something with less mass.

Dr. Pamela Gay: 

So it's GMM over R squared there, so the total force goes, hold on, you asked me a question and my brain just broke. So if their velocities stay constant, so they move outward.

Fraser Cain: 

Right, their velocities stay constant, so they move outward.

Dr. Pamela Gay: 

Yes.

Fraser Cain: 

Right, yeah. So there is less gravity that is pulling on them, or there is less distortion of space time that they are maneuvering through, and they still have that same velocity, therefore they will spiral outward.

Dr. Pamela Gay: 

Yes, and this is where the mass loss of the Sun means if it loses enough mass, we move far enough outwards that we escape the expansion. However, if there's drag on our system, depending on the amount of drag compared to the amount of mass loss, we can move back inward. This is one of the ways they consider for creating hot Jupiters, and so these are things we need to think about.

Now, in general, the interplay between mass loss and the orbital velocity of planets is considered second order to the amount of mass lost by that star, but these are still things that keep me awake at night.

Fraser Cain: 

Right, and I think it's really important to say that we are not unharmed. In the best case scenario, we are the planet Earth is mangled, believe, right? It is, you have spent maybe 4 billion years, 5 billion years in a temperature regime that is beyond the boiling point of water on the surface of the Earth, all of the oceans have boiled away, that you have now, you have spent time maybe in the atmosphere of the star as it was expanding as a red giant.

That wasn't fun.

Dr. Pamela Gay: 

Our world is a crispy critter.

Fraser Cain: 

Yeah, yeah. So it may still exist as a sphere of rock, but it is not unharmed. That's why we have all moved out to the ice moons of Jupiter to watch the mayhem unfold.

So then we settle into what is this long future balance, and what does that look like?

Dr. Pamela Gay: 

So that little tiny Earth-sized basically star in the center, dead star in the center, while it screams electron degeneracy pressure, it starts out super hot, but it's not generating heat any longer, which means that over time, it's going to cool off. And there's going to be this really neat evolution of what's going on close to that star. So some really cool work came out last year, I think.

Fraser Cain: 

I think I reported on this. I was going to bring this up, but you weren't going to.

Dr. Pamela Gay: 

Yeah, Jordan Stekloff led the work where a really hot white dwarf vaporizes the rock around it. But then as it cools, that rock reforms a new dust disk. And so you have this disk that ends up forming.

It's not like protoplanetary disk the way we think of protoplanetary disks. But as we look for objects around white dwarfs, we don't find anything around hot young ones. We find dust disks around medium-aged ones.

And as they cool, we start to find these planetesimals. And that is just super cool to me.

Fraser Cain: 

Right. It's planetary formation round two, that the material is following the same laws of physics that cause the dust to come together into larger and larger objects. And then eventually you get, as you say, planetesimals forming around the white dwarf.

And so it is another chance. So there's hope. One other piece of research that I found really interesting that I also reported on was that there appears to be this pause that white dwarfs go through in their cooling process.

Yeah. That kicks in. They crystallize.

Yeah. They crystallize. And then that sort of crystallization, it's changing.

I forget what exactly it is. It's like the boron in it is like changing the shape of the crystallization. And so it's cooling halts for billions of years before finally it kicks off again.

And so you actually end up with a long lived habitable zone that it does appear to match this sort of process of planets forming around it that will last you for quite a while. So it's interesting that you can, and like the habitable zone around the white dwarf is like four times the distance from the earth to the moon. So it is very close, like a million kilometers away from the star.

You will be tidally locked. Yes. And yet the habitable zone is there.

Dr. Pamela Gay: 

And what gets me about this process is we're starting to learn of all these weird crystalline things that go through metamorphic changes. And we see the same thing with water ice where there's different kinds of water ice and energy will go to phase changes in how the water ice is formed at various temperatures. And so this idea that you have to think through how does the crystalline structure mediate cooling processes is something that I never learned to wrap my head around.

Now, admittedly, I was in school as an astrophysicist, we have hydrogen, helium and everything else. But when we discussed white dwarf cooling, this wasn't something we were considering in the 90s. This is a new concept.

And it's really cool to see how it plays into our understanding of the evolution of stars around us.

Fraser Cain: 

And this isn't theoretical work at this point, like we are seeing examples of white dwarfs with the signs that we're talking about around them. We are seeing them with planetesimals. We are seeing there are white dwarfs with planets.

There are white dwarfs with clouds of debris around them that have been detected and observed with James Webb and others. So this is not just a theoretical possibility. This is confirmed in some of the white dwarf systems that have been observed so far.

So what do you think is kind of the best case scenario for the future of a star system like the sun?

Dr. Pamela Gay: 

I mean, it depends on best case to whom. If you're asking for humanity...

Fraser Cain: 

No, we're cooked.

Dr. Pamela Gay: 

We're cooked. Yeah. Yeah.

Fraser Cain: 

We've moved to Proxima Centauri. That's the best case for us.

Dr. Pamela Gay: 

Right. Exactly. Yeah.

And so, I mean, Proxima Centauri is tiny. It's going to have its own different issues, but it will live forever. But it's going to last five trillion years.

Yeah. Yeah. Yeah.

Yeah. I think massive amounts of mass loss making a truly beautiful planetary nebula that the remnants of humanity can study the formation of would be pretty cool.

Fraser Cain: 

From inside?

Dr. Pamela Gay: 

Yeah. Yeah.

Fraser Cain: 

Or from Proxima Centauri?

Dr. Pamela Gay: 

From Proxima Centauri. And what gets me about things like planetary nebulae is they can be huge. They can be light years across.

And so, this is a nebula that would reach out and touch someone. And Proxima Centauri will no longer be the closest star at that point. Our separations will radically change.

So, we could be on some completely different star, just to be entirely clear. But this idea of humanity getting to watch the evolution of a planetary nebula, and so all the mass you can possibly lose, please do it and let future scientists enjoy.

Fraser Cain: 

Yeah. I mean, we definitely have some questions about what are the conditions that are required to give you those really cool planetary nebulae. Is it a binary system?

Like, do you need a second star to whip up the material to create those interesting shapes? Or do you just get it with a single star that's just puffing out those outer layers?

Dr. Pamela Gay: 

And planets, what kinds of planets are necessary? And yeah, it's complicated. And we want to know all the things.

Fraser Cain: 

And what happens to the outer planets? I mean, we're obviously focused on Earth. It's cooked, crispy critter.

What happens to the outer planets, the Jupiters, the Saturns, Uranus, Neptunes?

Dr. Pamela Gay: 

So, they migrate outwards. And so, Jupiter will end up being stripped of some material because it's gassy. It doesn't hold on to its outer layers extraordinarily well when it's getting blasted and the temperatures are changing.

Fraser Cain: 

So, it might go through mass loss as well.

Dr. Pamela Gay: 

Yeah. Yeah. More like mass stripping.

Fraser Cain: 

Right. Which would have repercussions for its moons.

Dr. Pamela Gay: 

So, it's complicated. The outer planets are all gassy, icy objects that can undergo structural changes in the process. So, we will have asteroids that are probably okay.

They will just get melty on the surface. We have Mars, which any ices it's still got are going to be gone. It'll probably lose what little atmosphere it has left.

The icy moons will cease to be icy moons out at the distance of Jupiter. I'm not sure about Saturn. I'd have to run the maths to see just where Saturn lands in the equations.

Fraser Cain: 

Right. But this migration, and I mean, can this migration cause mayhem in the universe? We know early on in the solar system there appears to be a migration.

This is the Nice model. Do we go through this second phase where what was once this sort of perfect clockwork balance now gets out of balance again and there's another chance for mayhem?

Dr. Pamela Gay: 

There is another chance for mayhem. There will definitely be additional mayhem, but luckily there are fewer worlds available for that mayhem. So, early on we had at least a few extra planets that we no longer have.

The one that smashed into Earth to form the Earth moon as it is today.

Fraser Cain: 

Yeah, whatever happened to Uranus? Yeah, yeah.

Dr. Pamela Gay: 

Yeah. Venus is another one that had something bad happen. Jupiter's core is fluffier than it should be, so something creamed into it.

Fraser Cain: 

Yep. And who knows what went into the sun?

Dr. Pamela Gay: 

Yeah. And so there were a lot more objects around to create mayhem in the first iteration. In the second iteration we will have had a lot of stuff obliterated, we'll have a lot of stuff made smaller.

So yes, mayhem will occur at a smaller scale.

Fraser Cain: 

All right. So the sun has died, gone into its red giant phase, gone to its white dwarf phase. Now it is cooling down.

There's a cloud of debris around it that has maybe formed into some kind of planetesimal, maybe even within the habitable zone. And so a future Proxima Centauri expedition will be able to build a base and examine what it's like to live inside a white dwarf system down in the future. But the sun has died, but now what happens to the sun and what happens to the planets that are around it from this point on?

Dr. Pamela Gay: 

So anything that snuggled in at that kind of Earth-Moon distance to this new white dwarf will have formed there out of the dust debris cloud and is going to be tiny. So sure, that group from Proxima Centauri can set a cup of water on it and watch as it sublimates away into pure gas because there's no atmosphere on that little tiny world. Right.

So habitable only refers to the temperature. It doesn't pay attention to things like pressure that also matter if you want to have life outside of spacesuits.

Fraser Cain: 

They're solar system engineers. Okay. They drag something inward.

And are able to import, yeah, they've imported a whole bunch of comets and have dumped them onto the world and built up, thickened the atmosphere.

Dr. Pamela Gay: 

And added mass.

Fraser Cain: 

And added, well, I mean, I know that even, this was like a paper that I reported on that even like 1.5 meters per second is enough escape velocity for you to be able to hold on to an atmosphere. I'm not sure.

Dr. Pamela Gay: 

Right. But those planetesimals are probably smaller than that.

Fraser Cain: 

So as you say, they add mass, they mash a bunch of them together, they do some solar system engineering. I guess where I'm going with this is if you did have the right kind of world, would it be a stable, habitable place that you could live on for now billions of years?

Dr. Pamela Gay: 

I wouldn't say billions of years. These things do cool down over time where your ultraviolet heated white dwarf has to cool down to allow those planetesimals to form. But that cooling is just going to keep going and keep going until eventually you're no longer, that habitable zone is going to snuggle up closer and closer and closer until you can touch the surface of the star.

I do not recommend doing this.

Fraser Cain: 

Yeah.

Dr. Pamela Gay: 

Because the gravity is still there. Yeah, yeah. So, but ignoring the gravity, the white dwarf in the fullness of time will cool off and it will also evaporate in the fullness of time if we're correct about protons not being stable.

Fraser Cain: 

Right. Right. Or even Hawking radiation.

Right. We talked about that, right? Yeah.

That it appears that if Hawking radiation works for black holes, it probably works for anything and everything.

Dr. Pamela Gay: 

Yeah. That has energy.

Fraser Cain: 

And that in a roughly the same time scale, you'll get all of the white dwarfs evaporating away and, you know, any planet, anything, right, anything with mass will evaporate. But before that, like we've got this white dwarf that is cooling down, but you still have the interactions between the solar system and the rest of the galaxy. So what happens next?

Dr. Pamela Gay: 

So you're getting dragged around as you get colder and colder and you literally end up being a source of darkness except for gravitationally lensing things you happen to pass in front of.

Fraser Cain: 

Right.

Dr. Pamela Gay: 

And, and there's, I mean, this is as boring as it gets. You have cold planets orbiting a cold star. Everything is cold and your only ability to, to raise excitement and make your existence known is through gravitationally lensing background objects.

Fraser Cain: 

Well, so, so the thing that's, that I think people don't realize is that you're still experiencing these gravitational interactions with the other stars in the, in the galaxy and they are going to be plucking away your planets one by one. Yes. And it takes about a hundred billion years and you will lose all of your planets but one.

So whichever one, yeah, yeah, this was a, this was a paper that I report on. So you'll lose all your planet. It takes about 10 billion years, I'm sorry, a hundred billion years.

And then you're down to one planet. And this process is going to happen in all of the star systems. So they're all going to use up their star forming material.

They're all going to die. They're all going to then give up their planets. And then over even deeper time, all of those stars will be kicked out through three body interactions of the galaxy itself.

And so eventually you'll just be left with the supermassive black hole and all the stars have just been all kicked out and all of their planets have all been kicked out. And then it takes about five trillion years for the, for the white dwarf to just cool down to the background temperature of the universe.

Dr. Pamela Gay: 

I love this story of the universe building structure, building structure, building structure, removing the structure.

Fraser Cain: 

Yeah. And they're just, they're just dismantling it all. You built your Lego set and now you're, you're throwing all the pieces away and you're back to square one.

Dr. Pamela Gay: 

No, don't throw them away. Scatter them to the wind.

Fraser Cain: 

You scatter them to the wind. Yeah. You've thrown them all in.

You waited for wind gusts and you just throw pieces of Lego out into the wind and let them carry. This analogy is falling apart. But, but, but the point is that, that in the end there will be the sun and it will be a, a ball of material, right?

Roughly the size of the earth, the background temperature of the universe, it will probably have one planet that is tidally locked to it and, and it has been kicked out of the Milky Way and it is wandering the universe until Hawking radiation makes it dissolve into a, just a soup of particles and energy in the background temperature of the universe.

Dr. Pamela Gay: 

The exciting part is it will at least be a giant diamond.

Fraser Cain: 

So there is that. Yeah. Yeah.

For a while there, the sun will be the world, the, the universe's biggest diamond.

Dr. Pamela Gay: 

Well, I mean, there could be other ones out there.

Fraser Cain: 

There will be bigger diamonds. Yeah.

Dr. Pamela Gay: 

Yeah.

Fraser Cain: 

From other stars. Yeah. There's the theoretically largest possible carbon white dwarf.

Yes. But still. Yeah.

Dr. Pamela Gay: 

The future is weird.

Fraser Cain: 

It really is. Yeah. Yeah.

Isn't it weird? I always, I always remark on this, how when we think about deep time, we feel this, uh, this sense of sadness in our we about this future that we don't stand a chance of experiencing, right?

Dr. Pamela Gay: 

Well, it's, I, I think it's kind of like when important buildings are lost, even if we've never visited them, it's just sort of like energy went into the formation of that. Don't destroy it. And, and so in, in the end times, as we currently expect it to go, everything that we know will end up becoming nothing more than diffuse energy in, in this, this cold rip of space time.

But it's that intermediate point where things are getting flung hither and yon and all the spiral galaxies are getting taken apart. All the elliptical galaxies are getting taken apart. Galaxy clusters are, are just becoming lumps of diffuse glow.

Um, I mean, it's, it's, it's kind of both sad and silly at the same time. It really, your Lego analogy was excellent until you said you throw them out.

Fraser Cain: 

Okay, fine. You mail them off. You mail the pieces off to friends around the world.

Dr. Pamela Gay: 

Well, I really just like imagine this angry, small individual in the center of a room throwing with varying amounts of energy, all of the pieces until there's just this diffuse cloud of, of Legos.

Fraser Cain: 

So there you go. Uh, so what we're saying is there's a chance.

Dr. Pamela Gay: 

There is a chance. There's always a chance.

Fraser Cain: 

Yeah. All right. Thanks, Pamela.

Dr. Pamela Gay: 

Thank you, Fraser. And thank you so much to all of our Patreons out there. And I'm now going to mispronounce your name as my way of saying thank you.

Our show wouldn't be here without the amazing support of so many of you over at patreon.com slash astronomy cast. This week, I would like to attempt to thank by name the following people, and I'm sorry for what I'm about to do to the pronunciation of your names. This week, I'd like to thank Abraham Cattrell, Alex Cohen, Alexis, Andy Moore, Bore Andro Bart Flaherty, Benjamin Davies, Brian Breed, Brian Cagle, Claudia Mastroianni, Dan Fiennes, DeSastrina, Dwight Ilk, Ed, Eron Zegrev, Eric Lee, Evil Melky, Flower Guy, Jeff McDonald, Glenn McDavid, Helga Bjorkhag, Jarvis Earl, Jean-Baptiste Lamartine, Jim of Everett, Joe Holstein, John Esdraseth, Jonathan H.

Starver, Jonathan Poe, Justin Proctor, Justin S., Katie B., Kimberly Reck, Larry Zotz, Mark Scheer, Masa Herleyu, Michelle Cullen, Mike Dogg, Nick Boyd, Noah Albertson, Paul L. Hayden, Paul Lowell, Pauline Middlelink, Philip Grand, Philip Walker, Red Bar is watching, Rill, RJ Basque, Ryan Omery, Steven Coffey, Steven Miller, Tim Garish, Travis C. Porco, William Andrews.

Thank you all so very much.

Fraser Cain: 

All right. Thanks, everyone. And we will see you next week.

Dr. Pamela Gay: 

Bye-bye, everyone.

LIVE SHOW

Main sequence stars spend most of their time being… normal. Fusing hydrogen into helium in their cores. Producing radiation. But as their stockpiles of hydrogen run out they switch to other fuels, starting to climb the ladder of the periodic table of elements. And this is when things get weird. As we get more and more observations of the cosmos, our understanding gets more detailed. In this episode we look at all the ways a star can die and the updates that we've learned in the past 20 years of Astronomy Cast. 

Show Notes

• Origin of life theories: abiogenesis, warm ponds, ice chemistry, hydrothermal vents
• Astrobiology approach: studying extreme environments on Earth
• Discovery of organic molecules in space (amino acids, alcohols, PAHs)
• Spectroscopy: how astronomers identify molecules in space
• Cold molecular clouds as factories for complex chemistry
• Detection of amino acids in asteroids (Ryugu & Bennu)
• Role of comets & asteroids in delivering water and life’s ingredients
• Panspermia hypothesis: life’s building blocks may come from space
• Complexity of molecular formation beyond Earth
• Potential habitats: Europa & Enceladus
• Importance of sample return missions
• Key idea: ingredients for life are widespread in the universe

Transcript:

Fraser Cain:

Astronomy Cast, Episode 788 Life's Molecules in Space. Welcome to Astronomy Cast, our weekly facts-based journey through the Cosmos, where we help you understand not only what we know, but how we know what we know.

I'm Fraser Cain. I'm the publisher of Universe Today. With me, as always, is Dr. Pamela Gay, a Senior Scientist for the Planetary Science Institute and the Director of CosmoQuest. Hey, Pamela.

Dr. Pamela Gay:

Hey, Fraser.

Fraser Cain:

How you doing? I just keep mixing it up on you, and good, good. Just stay frosty.

These introductions, I may just start with other questions. Who knows what's going to happen, but clearly we have just fallen into a greetings rut. We need to clean this up.

Here we are. Is there any news that people can use, newsable news?

Dr. Pamela Gay:

They want to use?

Fraser Cain:

Have you seen Project Hail Mary? I have not, so we can't even talk about whether or not we liked it or not.

Dr. Pamela Gay:

I know.

Fraser Cain:

I guess you could say whether you liked it. Did you like it? I liked it.

I really, really liked it. Did you love it?

Dr. Pamela Gay:

I think so. Okay. I'm not sure I'm at the, I will buy the Lego of the Hail Mary spaceship stage love it, but I wouldn't buy the beer stein of it.

Fraser Cain:

That feels like it's a fairly low bar for you, though. You will Lego almost anything.

Dr. Pamela Gay:

I'm running out of shelf space, so the bar had to move.

Fraser Cain:

Oh, okay. All right. All right.

The theory of evolution explains how life takes on its wildly different forms, but how did life get started in the first place? It appears the universe has been making life's molecules in space for billions of years, setting up the conditions for life everywhere. All right, Pamela.

So the old school, the, the, the traditional idea, let's explain, explain this idea of a biogenesis. We'll start there as this, like, where did life come from and what did people used to think?

Dr. Pamela Gay:

Well, the, the older scientific way of looking at this was you, you have warm, gooey gunk getting struck by lightning and molecules forming. And somehow this combination of warm, gooey, carbonaceous goodness and electricity led to life in a very Frankenstein kind of way.

Fraser Cain:

And there were experiments that were able to prove that you could make things like amino acids. Yeah. The molecules in this kind of process.

Dr. Pamela Gay:

And they did a really good job of creating the molecules, but they couldn't get the molecules to suddenly become cells.

Fraser Cain:

No, of course not.

Dr. Pamela Gay:

Well, they tried. They did try.

Fraser Cain:

Yeah. Yeah. Like, come on.

Like, why isn't this turning into a bug or something? Yeah. Just keep zapping it.

Dr. Pamela Gay:

And what I love is, is they then turned around and they froze a bunch of the base atoms necessary to form these molecules and waited to see, would the molecules also form in ice? And this was a multi-generational experiment where everything went in decades and decades ago. Yeah.

Then got opened. And the answer was, yes, actually molecules will also form in ice. So then the answer started to broaden to, well, maybe in cold, safe places, the slow evolution of ammonia and carbon into more advanced molecules could lead to the formation of life.

And, and then astronomy hopped in and we're like, wait, wait, hold on. These molecules, we got them. We got them everywhere.

Fraser Cain:

But you, but you, but you did miss a step, which was that they also thought, well, maybe you're getting these molecules in the undersea environment.

Dr. Pamela Gay:

Yes.

Fraser Cain:

We talk about these, these volcanic vents at the bottoms of the ocean and that a lot of really interesting chemistry is happening around these things. You've got hot water. You've got a lot of, you know, those raw materials, they're being mixed and we've got completely separate ecosystems from what you have on the surface.

And so in fact, this became this entirely separate pathway to say, oh, maybe actually life on earth got started around these volcanic vents. You had enough of the raw material that, and enough chemistry going on, enough, clearly energy being dumped into this area that you just got this, this life. So, you know, there are plenty of, of weird ideas about how life could have gotten started.

And then I think you're exactly right that the, that the Senate, the astronomer said, wait a minute, we don't need any of that because it's all out there in space.

Dr. Pamela Gay:

Yeah. And then enter the astrobiologists and the astrobiologists have been diligently attempting to find places where there isn't life on the planet earth. They have looked under ice, they have looked in mines, they have looked in really nasty volcanic springs and pretty much anywhere you go, life literally does find a way.

There are currently microbes eating up radiation at Fukushima nuclear power plant. And it's, it's not like they were already hanging out there. They just decided I'm going to evolve to do the thing that needs done.

Fraser Cain:

Yeah. I wouldn't, I mean, are they consuming radiation? They are surviving despite radiation.

Dr. Pamela Gay:

They are consuming things that contain radiation and still surviving.

Fraser Cain:

Right. Yeah. Yeah.

Totally interesting side note. That's one of the most effective ways to clean industrial sites is with life, with bacteria, with plants that you can actually sort of reset. You can bring a contaminated environment, something that's been used, like has a lot of heavy metals and stuff in it back to normality just by, by growing plants, having life.

But that's a totally separate thing. So, so then, okay, so we've got like life finds a way, life can, life, wherever there's liquid water, you get life. That's cool.

And, and so let's talk about this discovery of, of just the raw materials of life and where astronomers have been finding it. All right. So let's talk about this.

Like, like I guess there's sort of like two main places and let's sort of build up the story of, and not just like say amino acids, like there's, I want to talk about all of the kinds of chemicals that play a role in life that have been found out there. Do you want to start with asteroids or just deep space?

Dr. Pamela Gay:

Um, let's, let's start with deep space cause I think that's where they found them first.

Fraser Cain:

Hmm. Okay.

Dr. Pamela Gay:

And, and this is where it comes down to, you, you have these molecules, um, but you don't know initially that they're there. What, what happens initially is you have all, all the astronomers out there with their spectrographs trying to figure out, we have these really pretty nebula, what are they made of? And when you take spectra of cool gas, you get this diversity of absorption lines that will make you want to cry if your job is to identify them.

Fraser Cain:

Yeah. Yeah. It's just a mess.

Dr. Pamela Gay:

And, and this is because molecules are capable of absorbing photons in two different ways. First of all, you have the molecules vibrating and then you also have spin going on. And, and all the different ways that, that they can absorb depends on how many connections there are, depends on the temperature, clearly that's just going to be the one I bring up over and over.

Um, and, and so when you start looking in the red part of the spectrum, the infrared part of the spectrum, you see this rich diversity of lines and then you curse at it. And part of the problem is we used to be able to just like reach for the, the spectral, uh, Atlas for everyday atoms. So hydrogen, helium, lithium, beryllium, boron, carbon, nitrogen, oxygen, yada, yada, yada.

And down in Los Alamos, they've done tremendous work, uh, defining all the different absorption lines of all the different, or emission lines of all the different ionization states for a lot of these atoms. But molecules aren't the kind of thing that places like Los Alamos are interested in. So initially there was a lot of, okay, so let's start, uh, going to the lab and hey, biologists help, um, hey, chemists help and heating up different molecules and looking to see what absorption lines occur in this, this kind of a thing.

And then you have to go through and use software to basically puzzle out, okay, this suite of absorption lines is because this cloud contains this amount of formaldehyde, this amount of tryptopane, and there's some polycyclic aromatic hydrocarbons in there for spice.

Fraser Cain:

Mm-hmm. Mm-hmm. Um, so I mean, what's, so I just did a quick check and it's formaldehyde was the first molecule that was detected in 1969.

So yeah, yeah. You know, water, formaldehyde, so, so, and that is, you know, a fairly complex molecule. Um, but it's kind of amazing that they're going and they're doing these practical experiments.

They are essentially burning these various molecules and then detecting the, you know, taking the spectra and then mapping that out onto the mess, the forest that they're seeing to be able to see the, I guess, the trees from the forest, right? But now this process, just like it's, again, it's kind of amazing how much of life's precursor molecules have been found now out there in space. Give us a sense of the, of the landscape of what's been discovered so far.

Dr. Pamela Gay:

Oh man. So, so it has gotten to the point that with some of these things, they're just like, uh, there's polycyclic aromatic hydrocarbons here because of the density of lines and they can't quite identify which one they need to blame.

Fraser Cain:

And the, and sorry, just to give people the, the translation of, of what you just said is soot.

Dr. Pamela Gay:

Yes.

Fraser Cain:

Like, like soot from a fire is, is a polycyclic aromatic hydrocarbon, a PAH.

Dr. Pamela Gay:

It's not just soot.

Fraser Cain:

Yes.

Dr. Pamela Gay:

A lot of high school chemistry classes will mix chemicals and heat them up so that you get various scents. So wintergreen, coconut, I'm violently allergic to that particular scent. All these artificial smells are actually polycyclic aromatic hydrocarbons.

PAHs, PAHs. Artificial scents are exactly what we're finding in space right now. I kind of love that.

Fraser Cain:

Yeah. There was a story like the universe smells like raspberries, but this, this, uh, nebula smells like raspberries. Yeah.

Cause it's like the same PAH that you would get in, in raspberries. I guess if you burn raspberries or whatever the smell, then you would, then you would get that.

Dr. Pamela Gay:

If you burn it, it actually like, this was one of the high school chemistry experiments I had to do and I was trying to make wintergreen and it was smelling like wintergreen. It was smelling like wintergreen. And then I got it too hot and it smelled like puke.

So keep your polycyclic aromatic hydrocarbons cool people or you will have regerts.

Fraser Cain:

Yup. Yup. But, and at this point like, uh, alcohol.

Dr. Pamela Gay:

Oh yeah. Alcohol is super common.

Fraser Cain:

Yeah. So I've got a, a kind of nerdy deep dive here, which was that you remember when we were the, the American astronomical society in Austin, like two years ago.

Dr. Pamela Gay:

Yeah.

Fraser Cain:

Okay. Yeah. Yeah.

Yeah. Yeah. Yeah.

And so we had to get into this bar and we had to provide a space fact.

Dr. Pamela Gay:

Yes.

Fraser Cain:

And I was in line behind Neil deGrasse Tyson. And, and so Tyson got hit with the question and he was like, they found alcohol in space.

Dr. Pamela Gay:

It's true.

Fraser Cain:

And then Bruce was like, come on in, sir. It was awesome.

Dr. Pamela Gay:

And we found multiple kinds of alcohol, both those that you should and those that you should not drink. Yup. We found solvents and, and here's, here's the thing.

Cold molecular clouds have all the raw atoms that have come off of stars. This is what we've been discussing the past few weeks. There's, there's the massive stars that are undergoing massive amounts of mass loss.

There's the small stars that are creating planetary nebulae. There's basically stars just can't hold on to their atmospheres. And the outer atmospheres of stars either already contain some of these heavier molecules in the case of smaller stars, like our sun, there's a certain amount of slow, uh, nuclear processes going on in atmospheres.

And then you have like the Wolf Ray stars that are just like convecting and throwing all sorts of stuff that forms dust outward.

Fraser Cain:

So you're talking about the sort of this process, how this stuff is coming together.

Dr. Pamela Gay:

Yeah. So, so all of this stuff is now in space, running rogue, gathering up in interstellar clouds. And in these cold, slow moving environments, atoms can, in the fullness of time, because again, it's cold, everything's moving super slow.

They can get close enough to bond, but everything is moving so slow that molecules aren't getting collisionally disrupted, which is what happens in warm clouds. So because they are cold, you have slower motion reactions. You have the ability for large molecules to form.

You have the ability for small molecules to come together and form bigger molecules. And it's just the slow motion clumping up of atoms into bigger and bigger things. And it's just a matter of time before you can get anything that is capable of bonding.

Fraser Cain:

Yeah. And I mean, you know, one of James Webb's, you know, we talk a lot about the red dots and the things that James Webb is doing out there at the edges of the universe. And we also talk about it's scanning the atmospheres of exoplanets, but it's not a lot of really interesting work in the solar system targeting this exact process that you're talking about.

Like one of the mysteries is that why are we finding these very complex organic chemicals in comets and things like that, places that have never been close to the sun. And now, as you said, it turns out there is this alternative way that these molecules are coming together. They're not coming together in heat, they're not coming together in water as a solvent.

They're coming together in places that are cold more slowly, but still are able to go through this process. And so there was this mystery, this paradox, like how do you get these chemicals when it was assumed that, okay, well, the comet had to be warm at some point and then it was out in the middle of nowhere and got cold and then things were kind of locked in place. But no, it turns out that you can get this process in this kind of grinding slow motion way that still gets you the same outcome, which is really good news for, because there's plenty of places that are cold out there, both in these molecular clouds in deep space as well as in the comets and asteroids.

And so now we, thanks to a couple of missions, right, we have samples of asteroids in our hands down here on earth.

Dr. Pamela Gay:

Not our hands. We would never put them in our hands. That is totally disrespectful.

Fraser Cain:

In our freezers and in our very careful calibrated lab equipment, but still in our hands, in our hot little hands. And so we've got samples of Ryugu from Hayabusa2 and we've got samples of Bennu from OSIRIS-REx. And so what have the scientists found?

Dr. Pamela Gay:

All the amino acids have now been discovered in space. And so the key thing, and this was like, I had already come up with the schedule for this show and last week they found the last of the amino acids.

Fraser Cain:

Yes. Yes. I mean, the ones used by life.

So just to be clear, there's 20 amino acids used by life. And then there's been about a hundred amino acids more that have been found in these various samples. But yeah, the last one that was used by life has been found.

Dr. Pamela Gay:

We have found all of them now. And it's really cool because amino acids, like once we know they're there, we know they can form, they can distribute themselves. They then create this really weird concept, but if you're into science fiction of the stuff of life on earth is common in the universe.

So does that set us up? And this is an astrobiology question, not an astrophysics question. So all I can do is pose the question.

This sets us up for life everywhere being built out of the same building blocks, or at least out of amino acids. And so the definition of amino acids is you have an amino group, which is N with two hydrogens attached to a carbon. Off the other side of the carbon, you have a carboxyl group, which is a carbon, a double bonded oxygen and an OH.

And then the other two bonds off of the carbon, because carbons are really bondy, is a hydrogen. And then whatever the heck wants to attach. And it's that whatever the heck wants to attach that leads to this diversity of amino acids.

So yeah, it's really cool.

Fraser Cain:

But not just amino acids. They've found peptides, which are the sort of the building blocks of proteins. So you've got all the building blocks of DNA.

You've got a bunch of the building blocks of RNA. You've got all of these additional molecules that are needed for various things by life. As you said, alcohols, poly...

Dr. Pamela Gay:

Polycyclic aromatic hydrocarbons.

Fraser Cain:

Polycyclic aromatic hydrocarbons, yeah. PAHs. It just goes on and on and on at this point.

And so now we have this issue. We have this question, which is how... If this stuff is all out there, it's being delivered as asteroids or comets are raining down on Earth early on in the history.

Dr. Pamela Gay:

And we think they're also the source of water. So the thing that we think delivered water...

Fraser Cain:

Yeah, yeah. They're delivering water. They're delivering the raw material for life.

How did they survive the impact? Because now you've got this thing that's going several tens of kilometers per second that's crashing into planet Earth. So this...

I actually did an interview with a researcher who was looking into this exact question. And he found... They did a whole pile of simulations and found under certain conditions, if the angle of the asteroid is right, that it's moving with the Earth, then the actual difference in velocity between the asteroid and the Earth is very low.

It's maybe a single kilometer per second range. And that these things will explode when they hit the atmosphere. And so they were able to simulate and find mechanisms where if the geometry was right, you got these things not being annihilated in the explosion.

And so it may very well be that, obviously, most of them are... They're going to hit the Earth and they're going to go... And then everything is going to be vaporized.

But there would be enough of this. It really looks now like life can handle the journey from Mars to Earth, this idea of panspermia. And so same thing, that while the exterior of the asteroid may ablate, you could have some of these molecules deeper inside that can survive and handle the crash, or smaller particles of dust and so on.

So this is still a bit of an unknown, yet it appears that there are mechanisms for this to be able to make that journey.

Dr. Pamela Gay:

And it's just really cool to think about how the outer solar system was cool enough that it didn't even just have to be the amino acids that were in our original molecular cloud. The outer parts of the dust and protoplanetary disk of our own solar system could have continued to form these proteins and amino acids and complex organic molecules. And then as cometary bodies and rocky bodies from the outer solar system were sent careening inwards through either interactions with stars or three-body interactions or torquing from being just Jupiter and Saturn or a thing, all these different processes that sent these objects inward allowed the baked, dry part of our solar system to become the diversity that it is today.

Nothing was the way it is today, and everything will change over time. Everything is constantly changing. But somewhere in the mix, the molecules formed somewhere, got here, or formed here.

And all these different processes can all be true at once. And you and I can be made of amino acids that formed in deep space, formed in the outer solar system, formed on Earth, formed in a plant somewhere not too far away.

Fraser Cain:

Right. I mean, most likely formed on Earth out of our bodies. The turkeys do that to us.

Our bodies, yeah. Our bodies, the chemistry and the things that we eat, but still. Yeah.

So just to show people the level of how complicated this is. So we reported on Universe Today earlier this year that they found something called pyrene which has 26 atoms. And that was the largest pH ever detected in the cold molecular cloud.

So this cold chemistry was able to create a molecule that has 26 atoms in it. And then there was something called thiopene, which is a 13-atom ring-shaped sulfur-bearing molecule. And that was detected, again, in a cold molecular cloud.

And you just wonder, if we're finding these things hundreds, if not thousands of light years away with our telescopes, if you actually ran a spacecraft through there and scooped up all of the molecules that you could find, how far would this go? How complicated would these molecules go? And so I think the takeaway that I've really been getting as a journalist in the last 10 years of doing this job is that the emphasis is now moving away from what weird conditions down here on Earth set forth the process of life on Earth, and instead, what inevitable processes have been happening, grinding away out there in the cosmos for billions of years, and then this stuff was delivered to the surface of planets to some amount. These things would be brought into the protoplanetary system and potentially kept cool and delivered by meteorites. It just gets weird.

And then it just takes this idea of the Fermi Paradox and goes, well, man, life should really be everywhere. And so why isn't it?

Dr. Pamela Gay:

I mean, just to give you an example of how weird the chemistry can get, take a world like Europa. It has convection. It has ice that is recycling and moving.

We know these amino acids can form in ices. It has liquid beneath. There's debate over whether or not there are hydrothermal vents.

I was talking to someone who's like, no, Paul Byrne's paper is wrong. And so I'm waiting to see that takedown in the journals occur.

Fraser Cain:

Yeah. See it in a journal, not over a beer or in YouTube comments.

Dr. Pamela Gay:

It was at least a researcher I was talking to. And so there is the potential for both the hot and the cold all being in process in this one world that has oceans. And I just love thinking about that.

Things that make me want to live long enough for us to have probes that go tell us what's under the ice.

Fraser Cain:

Yes.

Dr. Pamela Gay:

I hate that we're at that point now.

Fraser Cain:

Right. Yeah. But I mean, we're going to have, eventually, some mission go to Enceladus.

It's going to fly through the plumes and try to detect the presence of whatever is down there. And there's some really interesting ideas. I know Sarah Walker is working on this idea of assembly theory that you may not be able to detect the raw material of life directly, but that life seems to create more complex molecules than non-life.

Dr. Pamela Gay:

Yes.

Fraser Cain:

And so if you take samples and you detect a lot of just more complicated molecules in there, then there's a high likelihood that life is what's generating it. And life, did you know what life is? You don't know, it doesn't matter.

Complex molecules, the more complex the molecules are, the more life is probably responsible in some way. Yeah. Yeah.

And then you think about the places where you could get samples. I mean, it was just like, turns out bringing samples of asteroids home was incredibly scientifically useful. Now we want comets.

Now we want samples of comets from deep space, like the long period comets. What about an interstellar object?

Dr. Pamela Gay:

Yes.

Fraser Cain:

Imagine doing a sample return mission from an interstellar object. That would be, oh man, that would be perfection.

Dr. Pamela Gay:

And we have the technology to do all these things. Totally do. We just don't have the funding.

Fraser Cain:

Yes. The will and the funding.

Dr. Pamela Gay:

Yeah. I'm going to just insert the political rant on how money gets spent around the globe and we'll move on from there.

Fraser Cain:

More money on space science and more sample return missions from interstellar objects, please. Yes.

Dr. Pamela Gay:

I said that so aggressively, my camera shook.

Fraser Cain:

Yikes. Bold. All right.

So there you go. Life finds a way and it turns out the precursors of life is everywhere out there in space. Thanks, Pamela.

Dr. Pamela Gay:

Thank you, Fraser. And thank you so much to everyone who funds us through Patreon and puts up with me destroying your names on a regular basis. You allow us to do what we do.

Astronomy Cast is here thanks to the amazing support of all of our patrons at patreon.com slash astronomycast. This week we would like to thank by name a bulky 60, Adrian Bradley, Alex Cohen, Andrea Segel, Andy Moore, Antonio Reese, Arthur Button Brook, Astro Zatz, Beat Fares, Benjamin Mueller, Bob Blanswitz, Brad W. Nelson, Brian Breed, Brock, Bryce 80, Carolyn, Charles Peck, Chris, Christopher Cup, Claudia Mastroianni, Conrad Hailing, Craig Fisher, Dan Skelton, Daniel Otte, Dave Gallagher, David Bogarty, David Harvey, David Schlatt, Dean Case, Derek Buckley, Doc Knappers, Doug Pearson, Dwayne Clare, Eron Zegev, Eric Lee, Eva Joata, Flower Guy, Frodo Tanenbaugh, George Henry Schneider, Ghoul Bucket, Glenn Howell, Greg Gee, Gregory Singleton, Heather Lane, Hu Shen, J.R. Conlin, Jaco Danar, James Michael Nichols, Jan Benisse, Jason Rutherford, Jeanette Wink, Jennifer Bills, Jeroen, Jim of Everett, Joe McTeon, John Chenenbaugh, John Jers, John Thays, Jonathan Poe, Joshua Queen, Justin Bernow, Carl Daldin, Christian Van Der Heiden, Kelly, Kevin Beamer, Kimberly Reck, Cooper Belt Transport dot space, Laura Kettleson, Leslie, Lonnie Spencer, Lynn Raymond, Margaret Fester, Mark Reynolds, mark stephen rasnack matt vallas madam 19 whw 1961 supersymmetrical michael perchelle michael regan mike dog morgan gordon morgan jordan natalie metzger nicholas merit noah albertson olgar patrick coleman paul lucas pete hall in y phyllis foster rajiv archery rian van lerop riii robert glenka robert swain ronan french russell qualls sergio sansevero john and sarah scott briggs scott wallace sherry hackett soaker 117 steven steven coffee stewart rider taz tally the brain thomas vertigo tim mckee tim mcmacken tom rustland tricor verne mere wess william graf and znar bartz thank you all so much and i'm so sorry about my pronunciation you are amazing my pronunciation is not if you too would like to hear me struggle with your name please join our patreon at the five dollar and up level it's patreon.com slash astronomy cast

Fraser Cain:

all right thanks everyone and we will see you next week

Dr. Pamela Gay:

bye everyone

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