Ep. 656: Smashing Asteroids for Science!

This week we saw the incredible image of DART smashing into asteroid Dimorphos. Beyond avenging the dinosaurs, what can we learn scientifically from this and other asteroid/comet impact missions?

Download MP3 | Show Notes | Transcript

Show Notes

Jupiter at opposition (In-The-Sky)

Jupiter to Reach Opposition, Closest Approach to Earth in 59 Years! (NASA Blogs)


DART’s Final Images Prior to Impact (NASA)

Light Italian Cubesat for Imaging of Asteroids (LICIACube) (ASI)

Hera Mission (ESA)

Deep Impact (NASA JPL)

Deep Impact (EPOXI) (NASA)

9P/Tempel 1 (NASA)

Evidence Of Liquid Water In Comets Reveals Possible Origin Of Life (Science Daily)

LCROSS: Mission Overview (NASA)

NEAR Information (NSSDCA)

Beagle 2 Mars Lander: How It Was Lost and Found on Red Planet (Space.com)

NASA finds likely crash site for ESA’s ExoMars probe (Engadget)

Lunar Reconnaissance Orbiter (NASA)

The Moon’s Permanently Shadowed Regions (NASA)

LCROSS Impact Data Indicates Water on Moon (NASA)

The Rosetta lander (ESA)

Rosetta (ESA)



The small exploration rovers, MINERVA-II1 (JAXA)

JAXA Hayabusa2 Project (JAXA)

OSIRIS-REx Mission

Planetary Defense (NASA)

Moment of Inertia (Hyperphysics)

OSIRIS-Apophis Explorer (LPL)

The First Mission to Jupiter’s Trojan Asteroids – Lucy Mission (SwRI)

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Transcriptions provided by GMR Transcription Services

Fraser:                         Astronomy Cast Episode 656: Smashing Asteroids for Science. 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 Cain, the publisher of Universe Today.

                                    I’ve been a space and astronomy journalist for over 20 years. With me is Dr. Pamela Gay, a senior scientist for the planetary science institute and the director of CosmoQuest. Hey, Pamela. How you doing?

Dr. Gay:                      I am doing well. We have hit the month of October, and all my Halloween decorations are going out. And Jupiter is at opposition. And these things have nothing to do with each other, but both bring me joy.

Fraser:                         Yeah.

Dr. Gay:                      Have you seen Jupiter?

Fraser:                         Oh, of course. Yeah, hard to miss. We got out the binoculars, half the telescope – the seeing part but not the holding part – which made the whole process worthless. So, I need to go and find the tripod and get it all set up. But, yeah, it looks amazing, at least just in the binoculars. Like, there’s the moons.

Dr. Gay:                      Yeah.

Fraser:                         Bands across the planet. You can see it in just my astronomical binoculars. It’s such a good time. And this is the closest Jupiter has been in 60-ish years and the closest it’s gonna be for decades more.

Dr. Gay:                      Yeah.

Fraser:                         If you haven’t already, now is the time. And it’s gonna be – this closest event has already happened. But still, it’s a slow-moving, closest opposition. So, if you can, beg, borrow, steal some way to be able to see Jupiter with your own eyeballs. And while you’re at it, Saturn is also up in the sky, so you can see both of them.

Dr. Gay:                      Yes.

Fraser:                         It’s a good time to do some amateur astronomy.

Dr. Gay:                      Couldn’t agree more. And a good 300-millimeter camera lens was actually my friend on this endeavor.

Fraser:                         Yeah.

Dr. Gay:                      So, yeah, I went out with one of our community members, and we got to see Galileo moons. What more could a girl ask for?

Fraser:                         I’m going to follow my own advice very soon and buy a 8-inch Dobsonian telescope.

Dr. Gay:                      Oh, yeah.

Fraser:                         Yeah.

Dr. Gay:                      Yeah.

Fraser:                         Our skies are so much darker here. They’ve been clear. But then, we’ve got the weirdest, clearest October I think I’ve ever experienced. We’re breaking temperature records. And it’s just been clear every day all night and perfect for astronomy. And so, I think I will bring it to a close by buying a new telescope.

                                    All right, this week we saw the incredible image of DART smashing into asteroid Dimorphos. Now, beyond avenging the dinosaurs, what can we learn scientifically from this and other asteroid and compact, impact missions? All right. Take that asteroids! Dinosaurs, we got your back. We have avenged you.

                                    So, did you watch the DART mission live in real-time this last week?

Dr. Gay:                      So, I have the greatest irony. The Planetary Science Institute where I work, we were producing a video with some of our scientists who are part of the DART mission. And instead of getting to watch the impact coverage live, I was frantically video editing the release about how we successfully smacked an asteroid.

Fraser:                         Right.

Dr. Gay:                      And there’s irony in this. But I watched it after the fact, and it was absolutely amazing.

Fraser:                         Similar to you going and reporting on a solar eclipse and not being able to see a solar eclipse, but anyway. No, it was amazing. The footage from NASA started up about an hour before the actual impact and was just this little, gray dot in the middle of the screen.

Dr. Gay:                      Yeah.

Fraser:                         And for the first 45 minutes, it never went beyond a little, gray dot. And then suddenly it was a couple of pixels across. And then a few more pixels across. And then in the last five minutes or so, the asteroid got a lot bigger. And then in maybe like the last minute, the smaller asteroid separated from the bigger one. You realize you were going right towards the small one.

                                    And then the big one drifted passed the field of view, and then Dimorphos just got bigger and bigger and bigger. And then it filled the screen. And then you got one last frame that was like a little ribbon of asteroid at the top and then a red stripe down below, and you knew that was [inaudible] [00:05:13]. You could see exactly where it was no longer able to transmit.

Dr. Gay:                      Yeah.

Fraser:                         And I think what made this mission different from other missions that we’ve seen in the past was it really felt like we were experiencing this one in real-time. I mean, it was a 45-second delay, which is not long. But you saw the images stream at what felt like video rate, which I don’t think we’ve ever seen this before. NASA, this is all everybody has ever wanted, and you delivered it.

Dr. Gay:                      Yes, yes.

Fraser:                         So, this…but more, again. Keep doing this. And I get it; it’s hard to transmit from far away. And it takes a big receiver. And there’s science to be done, and so on. But still, you nailed it, literally and figuratively.

Dr. Gay:                      What I really enjoyed was they carried a CubeSat with them, and they like dropped the CubeSat, which popped out and unfurled. And then the CubeSat was there to photograph everything that was happening. But because the CubeSat is so tiny, it’s like the worst 1980s dial-up ever experienced. And so, all those images that that wonderful little CubeSat took are going to take days, weeks, and months to get back to us.

Fraser:                         Yeah.

Dr. Gay:                      And then we have Hera getting there in 2024, which I think all of us are excited about.

Fraser:                         But the purpose of this episode is the value in smashing asteroids for science.

Dr. Gay:                      And it’s not just asteroids.

Fraser:                         And comets, yeah.

Dr. Gay:                      Yes.

Fraser:                         And moon, and the moon, and all kinds of things. So, do you want to start most recently? Or should we start back at the beginning? When has humanity intentionally first tried to smash a solar system object for science?

Dr. Gay:                      The first time it was done on purpose – and the “on purpose” is very important – that was with Deep Impact. And Deep Impact had a number of different goals. It was set out to help us understand the structure of comets, the composition of comets, and to smack the bejesus out of one particular comet so that we could differentiate between what are the surface materials and what are the things that may be buried down deeper that we can only see if we dredge with our spacecraft.

Fraser:                         Right, yeah. And so, how did the mission work?

Dr. Gay:                      So, Deep Impact carried with it basically a refrigerator-sized impactor that it placed in front of the comet, and the comet smacked into it. So, NASA folks, a few of them really like to correct people and say, “We did not attack the asteroid. We simply stood in its path, and it attacked us.”

Fraser:                         Right.

Dr. Gay:                      And I love that little fact. And so, with the refrigerator-sized impact set loose, the main body of Deep Impact, which has now gone on to be called EPOXI, it collided with Comet P/Temple-1 on July 1st, 2005. Sorry, it rendezvoused on July 1st. I have to get this right because it got your Independence Day with the day that it rendezvoused, and it got my Independence Day, July 4th, with the actual impact.

Fraser:                         Right.

Dr. Gay:                      Thus, maximizing the number of holidays destroyed.

Fraser:                         Yeah, impacting the Astronomy Cast team. Yeah, yeah.

Dr. Gay:                      Yes.

Fraser:                         My holiday. Then you holiday. Now, what did they learn?

Dr. Gay:                      Well, they’re primarily looking to see what is the composition of a comet nucleus. And what they found is there’s clays. There are carbonates. There are silicates, the stuff of sand. But it was more the consistency of talcum powder. And there were crystalline silicates found as well.

                                    And all of this added up to say comets carried earth, not just water. And that one gets trickstery because the kinds of water atomic ratios they found don’t match our planet particularly well, but they found all these other atoms that helped enrich the environment of our world back during the age of, well, a whole lot more comet bombardments than we’re experiencing today.

Fraser:                         So, what came after Deep Impact?

Dr. Gay:                      As near as I can tell, the next big thing was LCROSS in 2009. And the reason I phrase it that was is there were so many things that either didn’t mean to reach out and touch an object with violence –

Fraser:                         Right.

Dr. Gay:                      – or touch something very gently. The NEAR-Shoemaker mission back in 2001 even before Deep Impact demonstrated that we have the capacity to control the spacecraft so that it will touch down lightly on an object within a 1-meter region of what it’s hoping to. In this case, it’s the asteroid Eros. And they just settled down and sat there for a while. They landed on February 12th, 2001. And we remained in contact with the space craft until February 28th.

Fraser:                         Yeah. It had no landing system. It was never intended to land.

Dr. Gay:                      No.

Fraser:                         They just were able to slowly decelerate it until it just gently sat on the surface and, I don’t know, rolled over or something.

Dr. Gay:                      It’s anticipated that it rolled over a bit.

Fraser:                         Yeah, they were able to communicate with it. And, of course, there were all of the spent upper-stage boosters for the Apollo mission.

Dr. Gay:                      Yes.

Fraser:                         There were al of the times that the Soviets attempted to land on Mars, other moon missions. There are craters across the Solar System that are left by unintentional spacecraft failures.

Dr. Gay:                      And it’s not just the moon. Mars. The Beagle crash site has actually been useful in, okay, this is what a fresh crater looks like.

Fraser:                         Yeah, Schiaperelli as well.

Dr. Gay:                      Yes.

Fraser:                         The [inaudible] [00:11:55] mission. There’s a bunch of these.

Dr. Gay:                      Landing on Mars is hard.

Fraser:                         Yeah.

Dr. Gay:                      It’s really, really hard. But crashing fuel stages into the moon is something we have sort of, kind of continued to do on purpose. The Lunar Reconnaissance Orbiter mission did not fly alone. It was part of a two-mission launch. And on October 9th, 2009, it’s companion, LCROSS, followed their second-stage empty fuel tank to the moon. Where the tank hit first, and LCROSS sent back information, sent back information, sent back, died, information. And this was when we for the first time got to see just how much water is out there underneath the surface of the moon.

                                    The surface of the moon can only have water in the eternally shadowed regions. And places that are completely shadowed, we can’t exactly see. So, with LCROSS, it hit, and it splashed out a plume of material that wasn’t what we had hoped for. It turned out our models over the moon weren’t quite what was – they weren’t as accurate as one would hope, but there was nonetheless enough of a plume that we were able to measure water ice that was liberated from the surface of the moon during this impact event.

Fraser:                         That’s really cool. All right, we’ve talked about Deep Impact. We’ve talked about LCROSS. Are there any others beyond DART?

Dr. Gay:                      So, there have been a whole series of things that were sent down onto small bodies, minor planets with the purpose of just bouncing around. Some of them bounced in ways they did intend.

                                    My favorite of these is the poor little Philae Lander that traveled with Rosetta, and it was in storage for so long. It traveled so far. And then it just didn’t quite do its job because it was meant to harpoon the asteroid and attach itself to the surface that way. And its harpoon just didn’t quite fire correctly. So, there was an accidental impact.

Fraser:                         Yeah, the thinking is that it landed, bounced a couple of times –

Dr. Gay:                      Yeah.

Fraser:                         – came to rest, fell over, but was operational.

Dr. Gay:                      Yes.

Fraser:                         And then its batteries ran out, and then that was that.

Dr. Gay:                      Now, in addition to the international mission that was Rosetta and Philae, JAXA with their Hayabusa mission has been doing some of my absolute favorite let’s fling everything we possibly can, including anti-tank weapons that have been repurposed at the surface of an object. And it all started with Hayabusa 1 at Itokawa, an asteroid that led us to believe that not the entire solar system is made of rubble piles.

                                    And when Hayabusa 1 got to Itokawa, it was carrying with it the first of the Minerva series of missions. And these are little flywheel having robots. They’re cylinders. And the idea is that they bounce around looking in high detail at different places on the surface. And they tested all of this out with Hayabusa 1. Hayabusa 1 went and stole a piece of Itokaya. It tried twice. It didn’t as much as it wanted. But it demonstrated that all of this is possible and set things up for the more ominous Hayabusa 2 mission.

Fraser:                         Right. Anti-tank weapon armed Hayabusa 2.

Dr. Gay:                      Yeah. Yeah, yeah. They referred to it as a “small carry-on impactor.” We all know that the reality is it was basically an anti-tank weapon flung at an asteroid instead of at a tank, which I approve of, by the way.

Fraser:                         Yeah.

Dr. Gay:                      And on April 5th, 2019, it attacked. And the idea was the exact same thing that we did with LCROSS, that we did with the original part of Deep Impact. It released materials so that we could see what is beneath the surface. And Hayabusa 2 was at the rubble pile asteroid Ryugu. And it got to allow us to see how craters form within the rubble pile structure. In addition to that, they had a whole series of little flitting, flying –

Fraser:                         Hopping, jumping.

Dr. Gay:                      Yeah.

Fraser:                         Yeah, yeah.

Dr. Gay:                      There’s a whole series of different things they did, including, again, reaching down, touching down to the surface of the asteroid, grabbing a sample – which has made it back successfully to Earth. This mission was remarkably successful in everything it did.

                                    And from there, we also had our own little favorite OSIRIS-REX mission that on October 20th, 2020, during a pandemic, managed to pull off a beautifully successful smash-and-grab of asteroid samples.

Fraser:                         That was a very gentle impact –

Dr. Gay:                      No.

Fraser:                         – in terms of – compared to DART and others.

Dr. Gay:                      This is true.

Fraser:                         Yeah.

Dr. Gay:                      But they still shoved the spacecraft like 30 centimeters into the asteroid.

Fraser:                         Yeah. Apparently, if it hadn’t fired its retrorockets, it would have sunk into the rubble pile, which is kind of amazing.

Dr. Gay:                      Yeah, yeah.

Fraser:                         So, let’s talk about DART.

Dr. Gay:                      Okay.

Fraser:                         What was the purpose of the DART mission?

Dr. Gay:                      To see if we can move an asteroid sufficiently that we can see a change in its orbit around its parent body. In this case, the parent body isn’t the sun. In this case, we have Didymos with Dimorphos going around and around. And depending on how the impact took place, different amount of momentum would get transferred.

                                    The pretty much worst case would be if Dimorphos was hanging out and the spacecraft plowed in and had a fully inelastic collision and became one with Dimorphos. The best possible situation is one where the spacecraft hits the surface of Dimorphos and flings out a vast amount of debris, carving out a crater, and also itself elastically bouncing off. In the case of a fully-elastic with shrapnel joining it, in that case you get the greatest transfer of momentum to the main object.

                                    And we’re still waiting for NASA to release the details on exactly what happened. We know that there was that plume. We don’t know if the spacecraft stuck, bounced, or anything else.

Fraser:                         So, at this point, no matter what happened, the change in the orbit for Dimorphos is gonna be so tiny –

Dr. Gay:                      Yeah.

Fraser:                         – that it won’t be visible until several weeks or even months of constant observation to detect the slightest difference in the orbital trajectory of Dimorphos. And we’re not there yet.

Dr. Gay:                      Yeah.

Fraser:                         So, right now, we don’t know how much of a change that it made. But what does that tell us? I mean, if we see a big change, if we see a small change, if we see no change, what does that tell us about this goal of potentially being able to protect Earth from asteroids in the future?

Dr. Gay:                      If we see no change, it means that momentum transfer failed and physics is broken. So, I’m pretty sure we’re gonna see some sort of a change.

Fraser:                         Well, we talked about this, that it could punch right through, right –

Dr. Gay:                      Yeah.

Fraser:                         – and not change the physics, and maybe it’s still out there.

Dr. Gay:                      But the plume that came off, the amazing thing about it is, if you have a body and part of it flies away, there’s going to be – for all of the momentum that goes away in one direction, it’s going to have the same amount of momentum transferred to the parent body that’s moving forward. So, because we saw a plume, we have to see a change in orbit, within error bars.

Fraser:                         Right.

Dr. Gay:                      And so, we can fully expect to see something. We just don’t know did its orbit around Didymos change enough that it’s super easy to see. Or is it something that’s really hard to see?

                                    Ideally, we want to see the change over three different orbits. But because of where the asteroid is positioned, there’s large sections of ocean that make it challenging to get 24-hour coverage. This is a target that is good to see from the Southern Hemisphere, okay to see from the Northern Hemisphere but pretty low down right now. Yeah.

Fraser:                         So, we really might have to wait for the Hera mission – to the following Hera mission.

Dr. Gay:                      We should not before then.

Fraser:                         Right.

Dr. Gay:                      We should know before then.

Fraser:                         But it’ll do the really precise analysis of the orbit –

Dr. Gay:                      Yes.

Fraser:                         – and the consistency and look at the impact crater and all of that. But, I guess, can we learn about this asteroid, asteroids in general? Like, are they balls of rubble the way OSIRIS – the way Bennu and Ryugu –

Dr. Gay:                      Yeah, yeah.

Fraser:                         – or are they a chunk of rock surrounded by a think veil of rubble?

Dr. Gay:                      Yeah.

Fraser:                         Will the different outcomes of the orbit tell us which of those models is more correct?

Dr. Gay:                      It should help. The only way to get at what is the structure all they way through is to measure the moment of inertia for that moon. And this is where Hera’s going to be able to probably do better observations than we’re currently doing with the LICIACube, CubeSat, and definitely what we’re doing here from the surface of the planet Earth.

                                    That moment of inertia will tell us is it the same density all the way through, is it different densities going through, and what is that difference. It’s the difference between spinning a raw egg, a hard-boiled egg, and a soft-boiled egg. All three of them will spin differently because of their moment inertia.

Fraser:                         I like that analogy. Totally.

Dr. Gay:                      Yeah.

Fraser:                         Yeah, when you spin those three.

Dr. Gay:                      I mean, how do you check if you actually hard-boiled your egg? You spin it.

Fraser:                         You spine it. Yeah. Yeah, I like that a lot. I’m gonna use that. I’m gonna steal that. Thank you.

Dr. Gay:                      You are welcome to it.

Fraser:                         Right on. So, are there any more comet-impacting missions planned for the future? Or asteroid impacts.

Dr. Gay:                      There are always people with plans. There are not currently any we-are-going-to-go-out-and-smack-something missions that are in the near future, fully-funded, and we can count on to actually do their job.

                                    But right now, it’s really cool to get to see the Deep Impact mission has been repurposed to become the EPOXI mission, which is out there visiting other objects. We’re all waiting to see just what does OSIRIS-REx in its new phase do when it gets to Anubis. That is an amazing object. And, yeah, it sure looks like DART discovered another rubble pile out there.

Fraser:                         Yeah.

Dr. Gay:                      So, the Lucy mission is hopefully going to show us other examples of asteroids that hopefully aren’t rubble piles. I look forward to seeing more Itokawas, like rubbly cashews. We need more of those in our lives.

Fraser:                         Yeah, yeah. We need to go to all the asteroids –

Dr. Gay:                      Yeah.

Fraser:                         – and smash a bunch of them and find out what they’re made of. All right, thank you, Pamela.

Dr. Gay:                      Thank you, Fraser. And thank you so much to all of our patrons who are out there who are supporting us through patreon.com. If you would like to join that community, go to patreon.com/astronomycast.

                                    Each week, I read out some of our patrons. And this week, I would like to specifically thank: Astrosetz, Stephen Veit, Burry Gowen, Jordan Young, Kevin Lyle, Jeanette Wink, nanoFlipps, Børre Andre Lysvoll, J.F. Rajotte, Andrew Poelstra, Brian Cagle, Venkatesh Chary, David Truog, TheGiantNothing, Aurora Lipper, David, Gerhard Schwarzer – I’m gonna go with that – Will Hamilton, Buzz Parsec, cacoseraph, Laura Kittleson, Robert Palsma, Les Howard, Jack Mudge, Gordon Dewis, Jow Hollstein, Adam Annis-Brown, Frank Tippin, and Richard Drumm. Thank you all so much for everything you do.

Fraser:                         Thanks, everyone. And we will see you all next week.

Dr. Gay:                      Bye-bye

Female Speaker:          Astronomy Cast is a joint product of Universe Today and the Planetary Science Institute. Astronomy Cast is released under a Creative Commons attribution license. So, love it. Share it. And remix it. But please, credit it to our hosts Fraser Cain and Dr. Pamela Gay. You can get more information on today’s show topic on our website, astronomycast.com.

                                    This episode was brought to you thanks to our generous patrons on Patreon. If you want to help keep this show going, please consider joining our community at patreon.com/astronomycast. Not only do you help us pay our producers a fair wage, you will also get special access to content right in your inbox and invites to online events. We are so grateful to all of you who have joined out Patreon community already. Anyways, keep looking up. This has been Astronomy Cast.

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