Ep. 492: Comets, Asteroids and KBO's

Another topic with plenty of updates. Since we started Astronomy Cast we’ve visited many smaller objects in the Solar System up close, from Ceres and Vesta to Pluto, not to mention a comet. What have we learned?
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Show Notes

Kuiper Belt Objects
Asteroids could be reason for water on Earth
Asteroids might be dead comets or KBO’s – the distinction may be fuzzier than we think
Dawn Mission
Asteroids with moons and rings
Non-metallic asteroids are more like rubble piles
Psyche Mission
OSIRIS-REx and Bennu mission
Halley Armada
Comet 81P/Wild
Philae lander from Rosetta Mission
Philae found – images
Interstellar asteroid Oumuamua
Kuiper Belt Objects are way more diverse than we thought
Pluto’s subsurface ocean


Podcast Transcription provided by GMR Transcription
Fraser: Astronomy Cast, Episode 492: Comets, Asteroids, and Kuiper Belt Object Update.
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, publisher of Universe Today. With me, as always, Dr. Pamela Gay, the director of Technology and Citizen Science at the Astronomical Society of the Pacific and the director of CosmoQuest.
Hey, Pamela, how you doing?
Pamela: I’m doing well. How are you doing?
Fraser: Doing really well. We just got the new cover art for the book that we are going to be publishing. Turns out, it’s gonna be coming out on December the 6th.
Pamela: Oh, cool.
Fraser: And it’s written by Dave Dickenson, and the title is The Universe Today: Ultimate Guide to Viewing the Cosmos, Everything You Need to Know to Become an Amateur Astronomer. And we’ve got probably close to a hundred different amateur astronomers, including some pictures from you. You’re writing the foreword in the book. Dave Dickenson wrote it. I am sort of helping out behind the scenes to actually bring the book together and coordinate with all of the astrophotographers. So, this is, I hope, gonna be a really great book.
And, anyway, so we now see the cover, we know the publishing date, the publisher is laying out all the pages. So, I’m sure you’ll hear more and more about this book as we get closer to actually publishing it, which is awesome. And, you know, another reminder, get writing.
Pamela: I know.
Fraser: You’ve got a foreword to write.
Pamela: I do.
Fraser: All right. Well, let’s get on with it. So, another topic with plenty of updates. Since we started Astronomy Cast, we’ve visited many smaller objects in the solar system up close, from Ceres and Vesta to Pluto, not to mention a comet. What have we learned?
Pamela: All the things.
Fraser: All the – Yeah. So, so much for all of those topics when we didn’t have a lot of updates. Now, there’s probably no way we’re gonna be able to get everything compressed into this show, but let’s just go quickly.
Pamela: Okay.
Fraser: So, let’s start with asteroids. What have we learned about asteroids since, I guess, you know, whatever episode we did asteroids, probably in the low teens.
Pamela: So, I think the most important thing that we realized, which makes out what I said in the comets episode to be a complete lie, is in our early solar system, things were really hot, the planet Earth got completely baked dry, and our water on our planet had to come from space. And what I said before was all of the Earth’s water came from comets bombarding our planet, and I was wrong. I was completely wrong. We now believe that the water on our planet Earth probably came from early asteroids impacting our planet, giving off their water, and thus from the delivery of many potatoes became many oceans.
Fraser: So, we got our water from asteroids, not comets?
Pamela: Yeah. So, this is one of those things that you hear it and you’re making the face.
Fraser: I know, I know, I know. This is actually kinda new to me, and so I’m just sort of trying to process this.
Pamela: So, we’ve now had spacecraft go out and sample the regular water to heavy water, the H2O to, well, with normal hydrogen, to the deuterium 2O water, so heavy water that has extra neutrons. We’ve gone out and for comet Halley, for one of the comet Hartley’s, and for [inaudible] [00:03:33] last year. We’ve measured their ratios, and well, Halley was like totally off, fine, move on. So, we looked at comet Hartley, and it was like, okay, this one matches, we’re good, it came from the Kuiper Belt, therefore we shall blame the Kuiper Belt comets for all of our water. But then, here we are looking with Rosetta at 67P CG, and its deuterium ratio is off.
And what was realized, just like one F in college can totally wreck your entire GPA even if everything else is all A’s and B’s, one super high deuterium ratio can wreck your entire ocean’s ratios. So, even if we run models where Earth was mostly hit by Kuiper Belt comets, and we assume most of them are like the Hartley that was studied and not like CG 67P, we can’t get to what’s actually observed on Earth with comets if any of them have this super high deuterium amount.
Now, while a lot of comets are dry, the Dawn Mission, which has gone out and given us up close observations of both Vesta and Ceres, found at Ceres that we have a world with ice geysers, with potential ice vulcanism that – well, Ceres is not wet with liquid water, but it’s wet with ice. And this existence of water frozen into rocks, in the past when asteroids hadn’t been baked by the sun for as long, they probably had significantly more water than they have today, and these wetter asteroids, when they get sent in on a collision course with the planet Earth due to all the gravitational interactions that were going on in the early solar system, they would have brought that not-yet-burnt-off water to our world to make our oceans.
Fraser: And I love that idea that, I guess, ten years ago when we sort of first brought up this topic – and I think we’ve done a whole episode just on where the water came from –
Pamela: Yes.
Fraser: – and it was still a bit of an unknown, right? And there was this idea that the water was just kinda there in the solar nebula and the Earth just sort of picked it up, there was the idea that it could have come from the comets, could have come from asteroids, could have come from Kuiper Belt objects, but now we’ve checked. We’ve gone and analyzed asteroids up close. We’ve gone and analyzed comets up close. A spacecraft has been to Pluto and checked it as well. And now, we’ve found the recipe that matches, the fingerprint of water.
Pamela: Well –
Fraser: Close.
Pamela: We’ve found the recipe that doesn’t match. We know comets don’t match, but since asteroids today are generally dry, we can’t measure what their hydrogen to deuterium, heavy water to regular water, ratio was in the early solar system. And in fact, we haven’t been able to sample the water on Ceres yet.
So, what we actually know is it doesn’t come from Kuiper Belt comets, and it doesn’t come from Oort Cloud comets, and all models suggest the Earth would have been baked, and that leaves asteroids. Now, we could still be wrong on the baking part. There are a few theories out there that the water has risen up from the internal mantle of the planet, but there are also all of these awesome papers pointing instead to asteroids being the origins of our oceans.
Fraser: That’s awesome. What’s next?
Pamela: Well, we are continuing to learn that the distinction between comets and asteroids is fuzzy.
Fraser: Right.
Pamela: We’ve found dead comets in the inner solar system that we mistook for asteroids and realized, no, no, no, no, no, they are actually just mostly melted comets that have this nasty layer of what looks like roadway sludge on the surface of the comet. And so, dead comets masquerading as asteroids, all good, we get that. We’ve now found asteroids – or at least an asteroid – out in the Kuiper Belt, which is not where asteroids are expected to be.
So, we have the mixing of locations where you occasionally get comets in the inner solar system, you occasionally get asteroids in the outer solar system, and as we look at more and more of both of these kinds of minor planets, what we find is there appears to be a continuum from the “I am a rock, I have no volatiles,” these completely dry rocky things. Cool. And these “I will melt if you put me in the sunshine,” icy objects.
And this continuum shows us that at a certain level, it’s useful for us to distinguish comets, which grow comas and have tails in the inner solar system, from asteroids, which are mostly just hanging out waiting to impact us and kill dinosaurs again. This time the dinosaurs might be called humans. So, it’s a useful distinction, but what we need to recognize is these are just the extremes of a continuum where there are objects in the middle. It’s just most tend to be at one end or the other.
Fraser: And it’s really just if you get to close to the sun, you’re gonna have your volatiles blown away by the intense solar radiation, and that’s why we have that ice line. That was why Dawn was such a fascinating mission, it was going to one object on one side of the frost line – snow line? I forget which term it is – in the solar system and then another that was on the other side of it, to see what is one that was too close to the sun to be able hang on to its volatiles, and what was one that was too far to lose them and was able to sort of stay fairly frozen.
One, sort of minor, update is that we’ve found asteroids with moons –
Pamela: Yes.
Fraser: – and rings.
Pamela: Yes.
Fraser: So, like that was unexpected.
Pamela: So, we had one asteroid with a moon before, but now we have several, and we’re also finding increasing numbers of Kuiper Belt objects with moons. And so, it turns out that gravity just likes to hold everything together, and even little tiny rocks will sometimes – by which I mean things smaller than a house, but not a lot smaller than a house – can find themselves gravitationally bound to bigger objects.
Fraser: Yeah, so many of the Kuiper Belt objects, which we’ll talk about in a second, have been found with moons of varying sizes, which is sort of an astonishing piece of science to even be able to find these, you know? Eris has a moon, right? And it’s really far away.
So, let’s talk a bit about then some of the – Did you have any more amazing updates in the asteroid territory? Do you want to move to comets next, and then to Kuiper Belt objects? You know, we can range.
Pamela: Yeah. So, when it comes to asteroids, we’re just finding them more and more places, we’re realizing that the ones that aren’t metallic, which is most of them, are rubble piles, it appears, covered in boulders and that the biggest of them are actually big enough to have fancy pants geology, such that you actually have differentiation of the substances and geological processes taking place at the surface.
Fraser: Let me just stop you for one second then. I mean, you talk about sort of this idea of these rubble piles, so like the traditional artwork of an asteroid is this ball of rock with maybe some craters on it, but it is clearly, you know, a space potato. But is that the case now, or is it more that it is just like a bunch of loose rock and material that’s happened to come together under its shared gravity?
Pamela: It’s looking more and more like it may not always be a rubble pile, but that it is often multiple objects that once were one big object, got split apart by something horrible happening, and then just kinda re-congealed and gravity’s now holding these multiple objects loosely together. And this is kinda cool, and perhaps we need to change our analogy from potatoes to – I don’t know about you, but I periodically plant bulbs in my yard, and few years later, these bulbs are like a cluster of ten bulbs because I’ve neglected them, and so you pull out one tulip and you find it would rather be ten tulips.
Just as those flower bulbs are all held together with roots and dirt, but you can shake them apart and then end up with ten different flowers, these asteroids are a variety of different objects held together through structural binding the same way any rock is held together, and you end up with multiple of these rocks tied together through dirt between them and the gravitational pull of these different parts towards one another.
Fraser: And, fortunately, there’s going to be room for us to have another episode exactly like this in about ten more years, I hope.
Pamela: Yeah.
Fraser: NASA’s working on a mission to send a spacecraft to a metal asteroid, asteroid Psyche, which they think might be the remnant core of a planetesimal and all that’s left is this nickel-iron chunk of metal out in space that the spacecraft is gonna visit, which is gonna be completely fascinating and completely different from places like Ceres and Vesta. You know, out of all the missions out there that are in the works right now, that’s one of the ones that I’m most excited about.
Pamela: And we can’t forget OSIRIS-Rex which, because it’s in space, is no longer dead to me.
Fraser: We should do an update on that spacecraft at some point. Let’s wait for it to get its sample and then –
Pamela: Yeah. So, it’s gonna get to Bennu in way less than 10 years, so we’re hopefully gonna have updates in the next year or two or multiple.
Fraser: And we saw it launch.
Pamela: We saw it launch, you and I got to be there face-to-face. So, yeah, lots of new science, and then once LSST is up and running, it’s going to be – one of its primary missions is to find all the things that might try and kill us, which is a good thing for a telescope to do.
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Fraser: Well, let’s talk about some comets.
Pamela: Okay.
Fraser: And of course, I mean, again, you know, before we had done – you know, ten years of Astronomy Cast episodes, again, I’m sure comets was like episode number six or whatever. I’m not looking through the history right now, but – because of course we went after the little hanging fruit, there has been the Rosetta mission to 67P, a lander attempting to land on a comet. There’s been a tremendous amount of scientific understanding of a comet up close. Stardust mission, flying through the tail of a comet, lots of great science.
Pamela: And there had been missions that went to planets before. One of the things that greatly amused me is it turns out they have nicknamed the small flock of spacecraft that all went to visit comet Halley back in 1984, The Halley Armada. That was a new one to me while I was prepping for this show. In addition to that, we also had a spacecraft that went to the – I don’t know if it’s actually pronounced Wild or if there’s like some different – like Wild?
Fraser: I think it’s Comet Wild, yeah, I think so, but who knows.
Pamela: Yeah, so, there’s whole group of comets that have now been visited, sometimes touched. With Comet 81P/Wild it was another close encounter, and as we visit these different objects, it gives us new information every single time. We’ve also started visiting asteroids, there was, I believe, a Japanese mission.
Fraser: Yeah, Hayabusa, and now Hayabusa2.
Pamela: And we have amazing data of Itokawa that shows us that it is, as near as I can describe, boulders all the way down. You look at it and it’s just – it looks like a load of rocks that you’d get to load your garden, just imaged really up close. So, we’re getting concrete results, and I think the most awesome thing and the saddest thing was the Philae lander.
Fraser: Mm-hmm.
Pamela: We’ve gotten a little bit of extra data we didn’t know about in the moment that show us that it touched down and it was able to get these amazing images that could be strung together into video of all of the debris flying around once it got to the surface, but since it’s harpoons didn’t deploy correctly, and as far as it was concerned, it only weighed as much as a piece of paper on Earth, well, it was as easy to move around as a piece of paper. And in that dynamic environment, it bounced and moved, and we didn’t get the data we hoped for.
Fraser: Yeah. The Rosetta mission alone and the kinds of images that we got from the spacecraft were amazing. And to be able to see these features, these cliffs and these boulders and these – they look like sand dunes – and just all kinds of things on the surface of this world of this comet, this chunk of ice and this dirty snowball. But that would have been the greatest, right, to have that lander get down, get down to the surface, harpoon in, and take some pictures Q comet. And we didn’t get that. And, unfortunately, two separate systems failed to get it down there, and so we’ll try again I guess.
Pamela: Yeah. It kinda reminds me of the Huygens Probe. We got this taste of what a completely alien environment is like, we got this tantalizing taste that we looked at and we could recognize because with Titan, it was like they were landing in the Mississippi Delta, with the Philae data, it looked like a bad day in Antarctica. We’re getting these tastes of how geology works the same on every world, it’s just the details that differ because you have a different gravitational value, you have a different atmosphere, but physics really is the same, and geophysics really is the same no matter where you look.
Fraser: We need to land on all the things.
Pamela: All the things.
Fraser: All the things, yeah. Like, you’re exactly right. We get just this glimpse to see what it was like on Titan or to see what it was like with the Rosetta mission. We’ve got the close up look of asteroid Bennu when OSIRIS-Rex tries to grab its sample and bring it home. That’s gonna be awesome, so that we want to see. But now – I had a chance to interview Alan Stern and David Grinspoon for their new book, and we talked about landers. Wouldn’t that be amazing to have a lander on the surface of Pluto?
Pamela: As long as it’s delivered by something that does the like Lunar Reconnaissance Orbiter or Mars Reconnaissance Orbiter, high resolution imaging of the entire surface. So, I believe strongly in partnering rovers with orbiting spacecraft.
Fraser: Yes, of course. That’s the way you go. You go fly by orbiter, lander, rover.
Pamela: Yeah, exactly.
Fraser: But like with the Viking mission, you can go orbiter, lander.
Pamela: And what I don’t think a lot of people realize is these orbiters are often the communications relays for the rovers, and so it’s a perfect partnership. It saves you electricity on your rover and let’s you get all that cool, contextual imagery of where you’re exploring.
Fraser: I have one thing to just go back to asteroids for a second, which was within the last year, astronomers discovered an asteroid from another star system.
Pamela: Yes, Oumuamua.
Fraser: Yeah.
Pamela: It’s the most fun name as well, who doesn’t like to say Oumuamua, Oumuamua. It just feels fun. Yeah, there was essential a cigar-shaped asteroid.
Fraser: It was a Rendezvous with Rama-shaped.
Pamela: Yeah, and every time I look at it, that’s exactly where my brain goes. But its orbit is consistent with it coming from somewhere else, and it had a shape like nothing we’ve ever seen before. And trying to explain it, and we’ll never see it again unless like we build advanced technologies and run it down later, in our lifetimes, we’ll never see it again. And it’s amazing to see something that you never knew could exist, and it’s so, so frustrating that we didn’t catch it before it’s closest approach to Earth because there could have been more data, and all we want is more data.
Fraser: And now that people has discovered this one, people have been running these calculations, and it’s thought that there could be, at any time, about 30,000 of these interstellar asteroids passing through the solar system right now.
Pamela: There’s so much sky.
Fraser: Space is so big, yeah. It’s so big. But the chances are, we’re going to dig up another one, and another one, and another one, and there’s even some plans like you could take a Falcon Heavy, put a tiny little spacecraft on it, and catch up with one of these interstellar asteroids, and then study it up close, which, again, would just be a stunning accomplishment in science.
Pamela: We need to run down Oumuamua.
Fraser: Yeah, exactly. Well, you still can, if you really want to right now, with ion engines and a really powerful launcher, and every day that goes by it gets harder and harder, and it’s gonna take longer and longer to catch up with it. You know, if you just like launched within the next year or two, you could catch up with it in, I don’t know, 30 or 40 years.
Pamela: And it’s not going to happen.
Fraser: Of course, it’s not gonna happen, but maybe we can be ready for the next time this happens.
Pamela: Yes.
Fraser: All right. Well, let’s talk about Kuiper Belt objects. I mean, we’ve talked about what happened with New Horizons and Pluto in the past, but so what do we know now about Kuiper Belt objects?
Pamela: That they are more diverse than we had ever imagined. We are finding them in all different colors; we are finding them in a variety of elliptical orbits that all point in one direction. So, there’s hints of another world that is a couple of times bigger than our own Earth if the maths are right, and potentially even bigger. And so, now, by studying the orbits of the largest of the Kuiper Belt objects that are in the weirdest of the orbits, we’re getting indications that maybe we captured a world, maybe we just flung it out during the early days of our solar system into this impossibly elliptical orbit that apparently was possible.
And I just love that we’ve gotten to the point that we can now say Kuiper Belt objects come in all colors, from fresh shiny, shiny surface to completely covered in the universe’s equivalent of road dirt on snow in the winter, from saying that some of them are in pretty circular orbits, there’s a lot of them surrounding Neptune and different kinds of resonances to, wow, there’s a bunch of them that go from hundreds of AU’s out to thousands of AU’s that are all aligned kind of in one way, and how do we explain this? And the way we do it is by adding another planet to our solar system.
Fraser: Yeah. And, in fact, I don’t know if you’d seen, someone had done some research into whether you could detect – get more data about where this could be by looking at like paintings.
Pamela: Tapestries.
Fraser: Yeah, in tapestries, and to see when comets had made close approaches to the Earth, and then you could use that to sort of extrapolate back to see if you could use that as a way to find out where Planet Nine could be. But it looks like – and we’re actually working on an article on this right now with Universe Today – that the LSST, the Large Synoptic Survey Telescope, which of course, you know, I want to marry that telescope, is gonna be the tool that’s going to be able to find it. It’s going to be searching the entire night’s sky, night after night after night, it’s gonna be the one that’s gonna turn up all of these new objects. So, we’re just a couple of years away now.
Pamela: Unless Gaia gets there first.
Fraser: Unless Gaia gets there first, right, of course, which I also want to marry that spacecraft too. So, anyway, I’m sure that’s legal. So, I cannot wait for all of the data that’s gonna come from the LSST and Gaia, and, you know, merge that together, and we’re gonna find so much about the night sky.
What are some other new things that we’ve learned about Kuiper Belt objects?
Pamela: Well, Pluto taught us they can have geology, and Charon reinforced that. And so, we’re still trying to figure out all the possible ways that Pluto ended up with a subsurface ocean because while it, and Charon, do interact, it doesn’t seem like it should be quite enough energy to do the things that we’re seeing, but whichever theorist’s theory you choose to believe, what we know is the best way to explain what we see on Pluto, is that there’s a subsurface ocean.
Fraser: And this, I mean, like we’ve gone from the best place to look for life in the solar system is Mars, to the best place to look for life in the solar system is gonna be these icy moons around Jupiter and Saturn, you know, Europa and Enceladus, and maybe Callisto, maybe. And now, we’ve gone to, oh, turns out there are these icy worlds and there’s probably subsurface oceans across maybe all of them, all the dwarf planets, all of the icy moons of the outer solar system, that there could be life on a thousand worlds under the oceans of all of these places.
There was this great research by Avi Loeb, and he calculated there’s about a thousand times more ice worlds and water worlds than there are terrestrial rocky planets like the Earth. Those are the places that life could have had all the different chances to grow. And, unfortunately, they’re gonna be really hard to explore.
Pamela: Yeah. No, it’s true, and this is really – we now, I think, can say there’s the Goldilocks zone, which is that area around a star that the temperature’s just right that a regular everyday world that doesn’t have a greenhouse effect and has enough magnetic field to hold on to its atmosphere, is capable of being at the triple point of water and sustaining life. But it’s no longer okay to call that the habitable zone because habitable has been expanded to be wherever the geology has said, let there be a solvent, let there be a energy-gradient, and let there be nutrients.
Fraser: Yeah, and so many more places.
Pamela: Yes. It’s a great universe out there.
Fraser: It really is.
All right, well, and I can’t wait for us to have this update in another, you know, ten years or so again because there will be the – potentially, you know, we’re gonna find about asteroid Bennu, there’s potentially the Psyche mission, New Horizons will have flown past its second Kuiper Belt object even closer, and that’s gonna be happening in just about six months.
Pamela: It’s flown past many Kuiper Belt objects.
Fraser: It’s going to fly closely.
Pamela: It’s going close.
Fraser: Yeah, way closer than Pluto.
Pamela: That’s the amazing part. And I don’t think enough people know that, and we need to have like a watch party when this happens.
Fraser: Yeah, that’ll be great.
All right. Well, what have we got keyed up for next week, Pamela?
Pamela: Why don’t we do an update on Mars, and then wind our way through the solar system?
Fraser: That sounds great. All right. We’ll see you next week.
Pamela: Bye-bye.
Male Speaker: Thank you for listening to Astronomy Cast, a nonprofit resource provided by Astrosphere New Media Association, Fraser Cain, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at astronomycast.com. You can email us at info@astronomycast.com, tweet us @AstronomyCast, like us on Facebook, or circle us on Google+. We record our show live on YouTube every Friday at 1:30 p.m. Pacific, 4:30 p.m. Eastern, or 20:30 GMT. If you miss the live event, you can always catch up over at cosmoquest.org or on our YouTube page.
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Duration: 30 minutes

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