What is a potentially hazardous asteroid like? Up close and personal? Very few space missions have visited asteroids and fewer still have touched an asteroid and brought some of it back to Earth. Dean chats with NASA's OSIRIS-REx mission's image processing lead scientist, Dr. Daniella Mendoza DellaGiustina, to learn more. Let’s go to the asteroid Bennu!
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Episode Transcript: Looking Up is transcribed using a combination of AI speech recognition and human editors. It may contain errors. Please check the corresponding audio before quoting in print.
Dean Regas: How do you save the Earth from an incoming asteroid? Well, move it out of the way. Sure, but how?
[Behind the Spacecraft: NASA’s DART, the Double Asteroid Redirection Test]: NASA is crashing a spacecraft into an asteroid.
Dean Regas: What? In 2021, NASA launched the DART mission, DART standing for Double Asteroid Redirection Test, to purposefully and forcefully crash into an asteroid. The unlucky asteroid to receive this DART was Dimorphos, a tiny 525-foot-wide moon of a larger asteroid called Didymos. So after 10 months in space, impact day came, and DART hit the target.
[Behind the Spacecraft: NASA’s DART, the Double Asteroid Redirection Test]: I don't think I've ever cheered for losing a signal with a spacecraft before, but definitely did that time.
Dean Regas: It not only moved the little asteroid moon but changed its whole orbit around Didymos. Near-Earth asteroids better watch out. Don't even think about coming for us. From the studios of Cincinnati Public Radio, I'm your host, Dean Regas, and this is Looking Up, the show that takes you deep into the cosmos, or just to the telescope in your backyard to learn more about what makes this amazing universe of ours so great.
My guest today is Dani Mendoza DellaGiustina, an associate professor at the University of Arizona's Lunar and Planetary Laboratory, and works on another asteroid mission called OSIRIS-REx. Now, if you want my opinion on the DART mission, okay, I, hmm, I guess that's one way to handle an asteroid: brute force. But I don't know. What I'm really surprised at is that the scientists acted surprised by the results.
[Altering Orbit: The Impact of NASA's DART Mission]: People were trying to measure how much we actually changed the orbit of the asteroid. We were hoping for something like three to 10 minutes. We actually made a period change that was more like a half-hour, and we made a lot of ejecta.
Dean Regas: I mean, we knew the mass of the asteroid Dimorphos, the mass of the DART spacecraft, and the velocity that we'd dart into it. So yeah, it worked. It better, or we don't know physics.
I'm not exactly sure I like the idea though of going around the solar system and moving things around, especially things that aren't heading towards Earth. But some scientists do admit, "Yeah, we just wanted to do this and see if it would work." As in see if they could actually hit the tiny asteroid millions of miles away, and they did it.
So let's add this to our arsenal of planetary defense. And yes, there is a department of planetary defense with scientists doing planetary defense strategies against asteroids. I mean, really massive impacts are linked to extinction events on Earth where whole species were wiped out by the changes caused by an asteroid or cometary collision.
So yeah, we should probably do it. While most of the 1.4 million known asteroids live in the asteroid belt, a huge region between the orbits of Mars and Jupiter, and thus tens of millions of miles away from us, there is another population of asteroids that gets closer to Earth. Some are called near-Earth asteroids that come close to our orbit around the sun, and the more dangerous designation of potentially hazardous asteroids.
Those have a possibility of someday hitting our planet. What kind of odds are we talking about? 1 in 10? 1 in 1 million? Oh, I don't know. I'll just leave you hanging on that for now for dramatic effect. But what is a potentially hazardous asteroid like up close and personal? Very few space missions have visited asteroids, but only one has touched an asteroid and brought some of it back to Earth.
Let's go to the asteroid Bennu.
Daniella Mendoza DellaGiustina: Hi, my name is Dani Mendoza DellaGiustina. I am an associate professor at the University of Arizona's Lunar and Planetary Laboratory.
Dean Regas: Well, Dani, thanks so much for joining me today.
Daniella Mendoza DellaGiustina: Thanks, Dean.
Dean Regas: Well, first, tell us all about the asteroid Bennu.
Daniella Mendoza DellaGiustina: Well, I could spend a lot of time telling you about the asteroid Bennu, so I'll stick with the highlights. It is a near-Earth asteroid, which means that its orbit crosses that of Earth's. And it's relatively small as far as asteroids go, but there is a big scale here. So it's 500 meters in its longest dimension, which is about the height of the Empire State Building, and it is very dark. We predicted it might be carbon-rich.
Because it is so dark, it reflects only about 4% of the sunlight that is incident on its surface. And carbon is a great darkening agent, so that was a good clue when we were proposing the OSIRIS-REx mission that it might be full of organic material, things that are carbon-bearing, maybe water and other volatiles that look really similar to the things that we would need on planet Earth to kickstart life.
Dean Regas: Well, and so out of all the asteroids out there, why was Bennu selected for a mission like this?
Daniella Mendoza DellaGiustina: Yeah, that's a really great question. So Bennu was selected for the OSIRIS-REx mission, which is or was a sample return mission, for a number of different reasons. But one of the most compelling reasons is, like I mentioned earlier, it's a near-Earth asteroid, which means it's accessible in a way that makes it easy to send a spacecraft not just there, but also back with sampleable material.
But it's an object. There's a number of different types of asteroids, and it's one of these objects that we thought might be a good place to look for clues in terms of the origin of life on Earth and the materials that were needed to seed life on Earth. We know really early on in our planet's history, things got very hot.
We had a magma ocean Earth, which just meant that our planet was a ball of lava that extended a few kilometers deep. And when Earth was in that stage, it would have been really difficult for things like water to stay stable on the surface. And so we know that some type of objects, perhaps things that look like Bennu, had to resupply those materials back to Earth, and we were really hopeful that Bennu would fit the bill.
Dean Regas: And I remember when OSIRIS-REx launched, and I was surprised that it's been so long. It was 2016. But the craft had quite a round-trip journey through space. Where has it gone, and how did it get back home?
Daniella Mendoza DellaGiustina: Yeah, so the OSIRIS-REx spacecraft, like you mentioned, it launched in 2016, but then it took us about two years to catch up to asteroid Bennu. In order to do that, we had to complete an Earth gravity assist. So Bennu sits a little higher above the sun than the same plane that most of the planets orbit the sun around. So we had to get a little extra energy from our own planet in order to boost up and rendezvous with Bennu, which we did in 2018.
We spent about two and a half years at Bennu and sampled it, so got all the way down to the surface, touched the surface, ingested some material into our sampling mechanism, and then after confirming that we had collected material and making sure it was safely stowed, in the spring of 2021, we took one last look at Bennu's surface, just to get a feel for what sampling and having a spacecraft close by had done to the asteroid.
And the answer is, we really kind of moved around a lot of material. The surface was really, really weak, a lot weaker than we had predicted beforehand. And so after that final look, which we called our farewell tour, we headed back to planet Earth, and we dropped off the sample of Bennu in September 2023. So we have been studying it now for a little more than two and a half years, and it's been really incredible. And in the meanwhile, our spacecraft is orbiting the sun, and it'll rendezvous with an asteroid called Apophis in 2029.
Dean Regas: So the main craft is still going to be out there and reused for another mission.
Daniella Mendoza DellaGiustina: That's right. Our spacecraft was really healthy, and it had a lot of life left when we returned the sample of Bennu in 2023, and we had predicted that would be the case. As we were winding down the primary mission at Bennu, we were keeping an eye on all of our subsystems—how much fuel do we have left in the tank—and we thought, "We can probably use this spacecraft for another mission."
And so we proposed to do that to NASA. They gave us the green light in 2022, which enabled us to start doing some planning ahead of the end of the primary mission and sample return. And now we are on our way to eventually rendezvous with Apophis. As part of that journey, we're just circling the sun.
We're getting a little closer to the sun than we had ever intended to get, which has been interesting. We got everything a little warmer than it was supposed to, but everything has survived and is operating in great shape. So we're really excited and really confident for our next mission, which will be dubbed OSIRIS-APEX, or OSIRIS the Apophis Explorer.
Dean Regas: Well, getting back to Bennu and the pictures, the close-up pictures just seem like such an alien world. It looks like a pile of rubble that's barely held together. What was most surprising about the images that you studied?
Daniella Mendoza DellaGiustina: Yeah, so you're exactly right. Bennu is a rubble pile. It is barely held together. The gravity on Bennu is microgravity, so it's a small fraction of what we experience on Earth. And we thought when we had planned the entire OSIRIS-REx mission that we would be getting to an asteroid that had sort of a fine-grain, sandy area that would make it really easy for us to sample material, and we designed our entire sampling device around that hypothesis.
So we could only ingest centimeter-scale, about two centimeters and smaller particles. Unfortunately, when we arrived at the asteroid, that is not what we found. We found it strewn with large boulders. There were not large areas of the surface that were sandy or full of fine grains. And in fact, even the small areas that we honed in on that appeared to be fine-grained, they had really big boulders surrounding them, which posed a hazard to the spacecraft.
You can imagine if you're descending your spacecraft—it's about the size of an SUV—right next to a 30-story boulder, you might have an issue if you don't do things just perfect as far as your touchdown. And so we had to rethink a lot of how we were looking for sampleable material on the asteroid, but we were able to do all of that.
Dean Regas: Well, you get everything back to the lab, and how much material is collected, and what are you finding inside the asteroid samples?
Daniella Mendoza DellaGiustina: So we got everything back to our curation facility, and the sample is kept in a very pristine chamber that was specifically designed to house the Bennu sample. It's under a nitrogen purge, so it can't react with our atmosphere.
And what we have found has been just amazing. Bennu's material is full of a lot of things that we had anticipated, like clay minerals. They indicate that we visited a world that is the remnants of an older, larger object where rocky material was interacting with fluids, and water in particular.
But we've also seen a lot of other things. We found organic molecules, many, many amino acids that are used by life. We've also identified nucleobases, the sugars ribose, and phosphate as well, and that demonstrates that Bennu's materials contain all of the ingredients that were used by RNA, which is an incredible finding, especially since many people consider RNA might look really similar to the first form of life on Earth.
So what this tells us is that although there is no life on Bennu, it contained a lot of the precursors for life that we would have needed to have on Earth in order to jumpstart that process very early on in our history.
Dean Regas: Well, I am curious about this idea of prospecting and mining asteroids that comes up from time to time, and I wanted to see what your take was on that, especially the plans that involve moving asteroids closer to Earth. Is this something that we should do or leave well alone?
Daniella Mendoza DellaGiustina: I am a fan of leaving asteroids alone so long as they're not on a collision course with our own planet. But there are lots of ideas that involve prospecting asteroids that wouldn't necessarily involve moving them closer to our own planet. We have quite a zoo of asteroids in near-Earth space, and so I think there's plenty of objects we can take advantage of if we decide to go that route.
Dean Regas: Well, this has been so much fun talking about this asteroid. I can't wait to see more of the science coming out of the sample returns. Dani, thanks so much for chatting with us today.
Daniella Mendoza DellaGiustina: Yeah, thanks for having me, Dean.
Dean Regas: Let's talk about Apophis just a bit. This is the asteroid that the spacecraft renamed OSIRIS-APEX will visit next in its long journey through space. Apophis. For some reason, that little 1,000-foot-wide rock scared the heck out of us.
[This Asteroid Could’ve Caused an Apocalypse—Now It’s Barely Missing Earth]: At the time when Apophis was discovered in 2004, it had this chance of impact of 4%, and that is kind of the highest probability that we ever know for any other asteroid. A kilometer-size object, which is kind of really global devastation.
Dean Regas: When it was first discovered in 2004, astronomers then tried to compute its orbit and found, uh-oh, Apophis regularly swings very close to Earth, and in 2029, April 13, 2029 to be precise, this asteroid could hit Earth. Or if it doesn't hit the Earth on that date, it could pass close enough to redirect it ever so slightly in a way that seven years later, April 13, 2036, it would hit Earth.
All right. That's pretty scary. And initially, there was a lot of uncertainty about where Apophis was going to go and how the flybys of Earth would affect it. But I think the real impact on the public, or me at least, was the certainty of those dates. I mean, Apophis could hit Earth April 13, 2029, or April 13, 2036.
Knowing those dates, like, you know, it made me think, like, whoa, I got a lot of stuff to do before then. But good news: More observations led to more certainty, and now astronomers have pinned down the orbit of Apophis so accurately that there is virtually no chance of it hitting Earth in 2029 or 2036. But just to be safe, we better keep an eye on it, or a spacecraft around it. Because if we have to, we can dart that thing right out of the way.
Looking up with Dean Regas is a production of Cincinnati Public Radio. Kevin Reynolds and I created the podcast in 2017. Ella Rowen and Carlos Lopez Cornu produce and edit our show and are never surprised when they beat me at a game of darts.
Jenell Walton is our Vice President of Content, and Ronny Salerno is our digital platforms manager. Our theme song is, “Possible Light” by Ziv Moran. Our social media coordinator is Hannah McFarland, and our cover art is by Nicole Tiffany. I'm Dean Regas, keep looking up!
