[00:00:00] Host: Welcome Lockheed Martin Space Makers, the podcast that takes you out of this world for an inside look at some of our most challenging and innovative missions. My name is Ben, and I'll be your host. This season we'll explore the future of Space with past and present missions that are shaping our path forward and chat with experts about what they think the space industry will look like 30, 40, even 50 years from now. Now, let's go for launch.

[00:00:35] Space is a fascinating and mysterious place that often defies science as we know it, and this couldn't be truer than with the asteroid Bennu. As the spacecraft OSIRIS-REx got closer to this ancient interstellar object, they started noticing something strange happening with the asteroid. OSIRIS-REx's navigation cameras started witnessing Bennu shoot out rocks from its surface. Today's bonus episode takes a closer look at why scientists think this strange event is happening. Let's bring back our guests to help us better understand this mystery. You may remember Sandy.

[00:01:11] Sandy Freund: I am the Lockheed Martin OSIRIS-REx mission ops manager.

[00:01:15] Host: Then there is Beau.

[00:01:16] Beau Bierhaus: I'm a senior research scientist at Lockheed Martin.

[00:01:19] Host: And Dante, who is the scientist in charge of the OSIRIS-REx program.

[00:01:23] Dante Lauretta: I'm a professor of planetary science at the University of Arizona.

[00:01:28] Host: Sandy starts us off with what they were witnessing as they approached Bennu.

[00:01:34] Sandy Freund: That was about a month-and-a-half after we'd arrived at the asteroid and seen this rocky surface. It was essentially spitting rocks at us.

[00:01:41] Dante Lauretta: We were surprised by Bennu ejecting particles into outer Space, and those were only detectable in the navigation camera system. So all of a sudden, the nav cams became science instruments for particle tracking, and we got a whole bunch of bonus science that we didn't even anticipate before we got there.

[00:01:56] Beau Bierhaus: This is the great thing about space exploration. It's any time you send the spacecraft somewhere new, you get to answer the questions you knew to ask, but you also realize that there are these amazing questions that you didn't even think to ask that you get to answer. We had no idea that was happening before we got there, and it was totally unexpected. [laughs] And it caused a scramble for the mission. We had to figure out whether or not these were gonna be a risk to the spacecraft if it was still gonna be safe to orbit Bennu.

[00:02:24] Sandy Freund: So that was another really amazing finding from the science team, but also a little bit scary on the engineering side in that Bennu was now classified as an active asteroid where on occasion, particles come off the surface and some stay in orbit for a short period of time. Others fall right back.

[00:02:39] Host: Most of these rocky ejections were the size of marbles, and a few of these were as large as bowling balls. After being kicked out into Space, they would float around the asteroid for a few days before Bennu's weak gravitational force would pull them back to the surface. Sometimes these rocks would even ricochet back into Space after colliding with the surface. And in some instances, these rocks were ejected with enough force to fly away from Bennu into the depths of Space entirely.

[00:03:09] Beau Bierhaus: It's a major discovery that Bennu was actively ejecting material, and we now have a couple of different theories for why this is happening, and it could be a combination of them as opposed to any one particular process. Two of the potentially leading theories are micrometeorite impact. So you've got dust particles in Space, and they can have very fast relative velocities compared with Bennu, so they can be hitting the surface of Bennu at 15 or 20 kilometers per second. Even a small particle moving that fast can deposit a lot of energy into the surface. And so one of the things that may be causing these ejection events is that they're just mini impacts that are ejecting material from the surface.

[00:03:56] Host: These particle ejections are traveling somewhere between 30,000 and 45,000 miles per hour. At those speeds, you could fly from L.A. to New York in less than five minutes or fly around the Earth and arrive back in L.A. in the time that it takes most people to finish their lunch break. So it makes sense that these particles traveling at those speeds would have a tremendous impact when they hit Bennu, and it could explain the reason for these particle ejections.

[00:04:25] Dante Lauretta: Another possibility is thermal fracturing. Bennu's rotation rate is about 4.3 hours. On Earth, a rotation rate is 24 hours, one day is 24 hours long. On Bennu, one day is 4.3 hours, so several times faster than Earth. And there's also no atmosphere on Bennu, which means that when the surface is exposed to the sun, it gets really hot, and then when the surface is pointed away from the sun, it gets really cold. So you have this thermal cycling from very hot to very cold, and you're doing it a lot faster than the rotation rate of the surface of the Earth. You know, when things get hot, they expand, and when things get cold, they shrink, and now you're doing that to an extreme repeated several times over the course of a day.

[00:05:11] And this thermal cycling can cause cracking of material, and depending upon the nature of the material and some of the cracking, it might actually be able to eject some material. And because the escape speed of Bennu is so low, it's between 10 and 20 centimeters per second, and for reference, walking speed is about 10 times faster than that, so you have to slow down your walk by a factor of 10 so you don't escape from the surface of Bennu. But the point is that material moving very slowly can still escape. So this thermal fracturing, even if it's not ejecting material very quickly, that material could still escape.

[00:05:51] Host: Granted, it doesn't take very much to break free from Bennu's gravitational pull. At the speed of someone on a leisure slow-motion walk would be enough force to send you flying away from Bennu. But it's remarkable to think that this extreme change in temperature occurring every four hours could be causing the rocks on Bennu to crack with enough force to send them flying into Space. OSIRIS-REx gave scientists first of its kind imagery of these ejections. The spacecraft's navigation cameras observed that Bennu was spewing out streams of particles a couple of times each week. Because these particle ejections are so small, I'm not sure we would have discovered how active Bennu was without OSIRIS-REx's help.

[00:06:35] Beau Bierhaus: So, it's an amazing process that's happening on Bennu, and even more importantly, if we see it on Bennu, it's probably happening on asteroids all across the solar system. It's this whole new understanding of how the surface of Bennu evolves, but then it informs us about these millions of other objects that are flying around the solar system. So, it's a pretty amazing discovery.

[00:06:59] Host: And the third reason is aliens. Well, at least not that OSIRIS-REx has seen anyway. All kidding aside, this remarkable discovery is helping us better understand what might be taking place on other asteroids all over our galaxy. OSIRIS-REx's mission is to find the source of organic material that led to the origin of life on Earth. I, for one, am excited about all of the new things we will learn when the sample returns to Earth in September of 2023. You can check out some incredible imagery and animations of these particle ejections from the links provided in this episode's show notes.

[00:07:40] You've been listening to Dante Lauretta from the University of Arizona, Beau Bierhaus, and Sandy Freund from Lockheed Martin, and they are space makers. Whether you're a software engineer, systems engineer, finance, or H.R. professional, we need space makers like you to make these seemingly impossible missions a reality. Please visit this episode's show notes to learn more about the Osiris-REx sample return mission to Bennu or the careers available at Lockheed Martin. If you enjoyed this show, please like and subscribe so others can find us and follow along for more out-of-this-world stories from Lockheed Martin Space headquartered in Littleton, Colorado. Join us on the next episode, as we introduce you to more space makers.

[00:08:29] Space Makers is a production of Lockheed Martin Space.

It's executive produced by Pavan Desai.

Senior producer is Lauren Cole.

Senior producer, writer and host is Ben Dinsmore.

Associate producer and writer is Kaitlin Benz and Audrey Dods.

Sound design and audio mastered by Julian Giraldo.

Graphic design by Tim Roesch.

Marketing and recruiting by Joe Portnoy, Shannon Myers, and Stephanie Dixon.

These stories would not be possible without the support from our communication professionals, Tracy Weise, Natalya Oleksik, Gary Napier, Lauren Duda, and Dani Hauf. Thanks for joining us and see you next time.