This transcript was generated automatically and lightly edited for readability.

Oliver Strimpel: This is Geology Bites with Oliver Strimpel. We can learn a great deal about the bodies that populate our solar system by looking at them with Earth- or space-based telescopes. This gives us images and spectra, which can be very detailed, especially when captured by space probes traveling close to these objects. However, there are some things one just cannot learn without actually having one's hands on a sample of a celestial body and analyzing it here on Earth, using the battery of techniques that have been refined for the analysis of terrestrial rocks.

Harold C. Connolly Jr. is a professor in the Department of Geology at Rowan University. He investigates the origin of the very oldest planetary materials from which the Earth was made. Asteroids are a good place to look for such materials, and to that end, he is mission sample scientist on NASA's asteroid sample return mission called OSIRIS-REx, as well as a member of the sample analysis team of the Japanese asteroid sample return mission Hayabusa2. Harold C. Connolly Jr., welcome to Geology Bites.

Harold C. Connolly Jr.: Well, thank you very much, Oliver. It's a pleasure and an honor to be here.

Oliver Strimpel: You're currently involved with two asteroid sample return missions. Just to be clear, what is a sample return mission, and why is it important?

Harold C. Connolly Jr.: Sample return missions are missions which return extraterrestrial material from solar system objects back to Earth for analysis. We have solar system objects on Earth which land here completely by accident, an accident of the universe, if we can call it that, which are meteorites, and also small dust grains coming through the atmosphere. But those are actually delivered to us, and we don't necessarily know the context, the geologic context, of where those materials come from. We have a vague idea, such as, you know, that this rock came from a mountain range, but you don't know which formation in the range, for example, when you find a stone in a river. So sample return missions are really incredibly important for giving us the geologic context that we don't have, by having spacecraft, or in the case of Apollo, humans, bring back samples to Earth.

Oliver Strimpel: Could you give us a quick overview of the sample return missions that have happened so far?

Harold C. Connolly Jr.: Yeah. So the sample return missions started back in the Cold War days, in the late '60s, between the USSR and the United States. That was the Luna program and the Apollo program. And of course, as we all know, the USSR and the United States of America weren't very good friends back then. So those were the first samples to be returned, first by robot, which would be the Luna program robotics, and then, of course, by humans in the Apollo missions. And then we speed forward to the early 21st century, when we have material coming back from the coma of a comet, Stardust. We have solar wind that was collected by a mission called Genesis, which collected solar wind and brought it back. And we also have Hayabusa, which was the first mission to go to an asteroid and bring back samples from an asteroid. The Hayabusa mission was Japanese, and Genesis and Stardust were from the US. Other upper-atmosphere sorts of missions have taken place and brought back cosmic dust spherules as well, but they're not completely off-planet expeditions.

Oliver Strimpel: OSIRIS-REx has just captured a sample from asteroid Bennu, and Hayabusa2 is nearly back home now, after having grabbed a bit of the asteroid Ryugu. Why were these particular asteroids chosen?

Harold C. Connolly Jr.: So, to go backwards a little bit, with the Hayabusa mission: the first Hayabusa mission went to asteroid Itokawa, which spectrally is an S-type asteroid, and it was predicted to be the same composition as what we know as equilibrated ordinary chondrites. Chondrites are meteorites that are similar to sedimentary rocks, but they're cosmic sedimentary rocks, made up of multiple kinds of materials from different time periods and different locations in the earliest moments of the formation of our solar system, believed to be the precursors to the planets. And speeding forward, we wanted to get a better understanding of another kind of chondrite that we find here on Earth, which are called carbonaceous chondrites. We don't have the geologic context for them. We believe they come from, or hypothesize that they come from, asteroids such as carbonaceous ones that we know as, for instance, Bennu and Ryugu.

So it was deemed important, to understand basic questions of the origin of planets and the origin of prebiotic compounds, and at the same time to study how asteroids move, to go to a near-Earth object, an asteroid which crosses the Earth's orbit at some point during its revolution around the star we know as the Sun, and rendezvous with it, collect samples and bring those precious treasures back to Earth for study. So that was the large-scale picture of it. And they were both chosen in the end because they were relatively close to fly to, so the expense was more or less within the cost cap of what could be done.

Oliver Strimpel: Let's talk about OSIRIS-REx specifically. Now, what happened when it arrived at asteroid Bennu in December 2018, after a long, long two-year journey from us?

Harold C. Connolly Jr.: So we had designed our spacecraft and planned our operations and our science thinking for an object which contained large areas, or ponds, as we like to call them, of fine-grained material, 2 centimeters and smaller, sand-sized grains of material. And we got to the asteroid, and it was anything but full of sand-sized particles. Boulders the size of 10-story buildings sticking up; boulders the size of buses and cars and SUVs. So after a moment of panic, we regrouped and began to study this amazing object that never ceases to show me wonders that I never expected we'd find.

Oliver Strimpel: So when you got there, you found it was very different from what you expected. So what happened next, then?

Harold C. Connolly Jr.: So we chose Bennu because it was going to be carbonaceous, like something similar to what we have in our collections, and there are elements of that that are true. But the most important thing for us was collecting the sample, because we're a sample collection mission, just like Hayabusa2. So we had to then begin to really look in detail at the surface of the asteroid for materials that we would be able to collect: materials that we could collect in an area that was safe; materials that we could collect in an area we could fly the spacecraft to; and finally, materials that would have high scientific value. And of course, anything that comes back from the asteroid has high scientific value at this point. So we immediately changed some of our thinking about flying the spacecraft. Navigation was able to get us down to a very small bull's-eye, compared to what we originally were planning to be a larger bull's-eye, to touch the surface of the asteroid. We began to look in more detail, and added extra flybys of the asteroid, to home in with our camera system to find grains 2 centimeters and smaller, which is the size range we need to collect with the design of our collector, called TAGSAM, which is the Touch-And-Go Sample Acquisition Mechanism.

Oliver Strimpel: So you said 2 centimeters is a maximum. It's like a little pebble.

Harold C. Connolly Jr.: That's right. Yeah, 2 centimeters, at least in a direction that it can get into the orifice of the TAGSAM collector head, right? It might be a little longer in one dimension, but 2 centimeters is the maximum amount. And for Hayabusa2, it is 1 centimeter.

Oliver Strimpel: And can you collect finer-grained material as well?

Harold C. Connolly Jr.: Yeah, absolutely. That's the best kind of material to collect. It's just like a reverse vacuum cleaner, the TAGSAM collector. So we had tested it and tested it and tested it, and modeled it and modeled it, for the collection of material that was 2 centimeters or smaller in size, and we did.

Oliver Strimpel: OK. So you were talking about how the sampling site was chosen, and there are obviously some constraints about what was possible. You know, obviously you want to avoid these huge boulders and get to a place on the surface where it's feasible to maneuver, but you also mentioned science value. So how do you define the science value of a site?

Harold C. Connolly Jr.: One of the main priorities of the mission was to bring back a sample that is rich in volatiles and organic compounds, because we want to understand how materials such as water or prebiotic compounds get delivered to Earth. It's a huge scientific and, if you will, philosophical issue: why does Earth have as much water as it has? Where did that water come from? And also, of course, life. We want to be able to try to constrain that better by bringing back a sample of carbonaceous material, planetary material, with geologic context kept. So we would look for areas of the asteroid that would have more, what we thought would be more, of these volatiles than another region. This is how we planned, but as it turned out, the volatiles are everywhere. So we didn't have to really worry about that issue.

Oliver Strimpel: When you say volatiles, you're talking about material which melt at low temperatures, including water that's locked up inside clay minerals, and prebiotic material is naturally occurring, mainly organic material, which may have contributed to the origin of life on Earth. Naturally occurring amino acids are an example. So you actually spent two years circling the asteroid before descending to the surface to grab a sample, and during that time, then, were you taking spectra to try and locate these volatiles?

Harold C. Connolly Jr.: Yeah, we were using our scientific instruments for all kinds of exploring. So we looked at the spectra from about 0.5 microns to about 4.5 microns, and then from about 5 microns out to 25-plus, looking at the different chemical properties of the surface of the asteroid.

Oliver Strimpel: Just to explain, these wavelengths span the near-infrared to the far-infrared.

Harold C. Connolly Jr.: That's right. We also looked at the heat distribution on the surface of the asteroid, because, again, we want to collect volatiles, and you want to try to make sure you collect them from an area that's not too hot, for example the equator, perhaps. So we were constantly looking at the nature of Bennu. The big surprise was when we discovered, in January of '19, that asteroid Bennu is an active asteroid. In other words, it is actually spewing material off into space. Some of it pops up and circles; we can see it orbit around the asteroid for a day or two or three, and then it's not there anymore, so it probably fell back down to the surface of the asteroid. So that was a great and wonderful surprise. We had actually had a campaign to search for outgassing, plume-like outgassing, as you might expect in comets, because one hypothesis for these asteroids is that they're potentially dead comets. We didn't see that, even in the approach phase, where normally you would expect to see that kind of activity from a distance. Then we got into orbit, and then we saw these active outbursts happening, of just particles, basically, and sometimes it's just a few of them that pop off the surface.

Oliver Strimpel: Do we have any idea what's causing those plumes?

Harold C. Connolly Jr.: That can be things such as the pressures of the asteroid as it rotates around its own axis, which takes a little over four hours, so that the material is actually crunching itself, and the pressure is causing it. It could be that these are phyllosilicate minerals, meaning sort of sheet-like minerals, like serpentines, or, for those people who may be pretty good with plants and pick up vermiculite, for example, which is a sheet silicate and expands because it has pore space that holds water. So it may be something to do with the interaction between the solar energy and the surface of the asteroid that's popping material off. So it's a great riddle.

Oliver Strimpel: You mentioned that some parts of the surface might actually be too hot, in the sense that they might have driven off some of the volatiles. What kind of temperatures are we talking about? And were there some thermal surprises for you when you got there?

Harold C. Connolly Jr.: Not really, as far as the thermal surprises go. So we work in kelvin on the asteroid, so it's something up to 380, 400 kelvin, so subtract 273 from that. So it gets a little hot, and we have a requirement to maintain the temperature of the sample below 70. The greatest hope was that our collecting mechanism is designed actually to go into the surface of the asteroid and penetrate a little bit, and collect material from the subsurface, not just the surface. And of course, that's exactly what happened. We sunk in about 48 centimeters, so we probably collected material that's quite cool, and maybe hasn't seen anything on the surface for a very long time, if at all.

Oliver Strimpel: How much material was in fact collected?

Harold C. Connolly Jr.: So our collector can collect up to 2 kilograms of material. We basically stuffed it full, probably 2-plus. And I say 2-plus because the collector is also not just a bulk collector, like a reverse vacuum cleaner. There are little pads, contact pads, we call them, on the surface of the actual collector that are slightly indented into the head, and they're kind of a steel wool material that picks up particles. And one of the first things we did to confirm we had sample was to articulate the 3-meter arm at the elbow joint and bring it back to the camera, so that the collector head was exposed to the camera's view, with the sunlight hitting that sample. And much to our surprise, and at some level delight, and also a slight bit of panic, we were losing grains out of the collector head. It was so stuffed that some particles were actually keeping open what appears to be our Mylar flap, which keeps material in the actual inside collector unit from escaping. It was keeping it open because the particles were quite large.

So the PI, NASA headquarters, Lockheed Martin, all the interested parties got together, went over all the data, and made a decision. The next step would have been to confirm the mass by doing a simple physics experiment of extending the arm back out, or keeping the arm out, rather, and spinning the spacecraft to see how the inertia changed with the mass we collected, which would give us an estimate of the amount of material we collected. We decided not to do that, and to stow the sample as quickly as possible, so that we wouldn't lose any more particles, because our estimate was that we were losing quite a bit of material with every movement of the arm. So that went absolutely smoothly. The sample collector head was put right into the sample return capsule. The clamps did their job, holding it down. We then removed the bolt that holds the TAGSAM head to the actual arm of the unit, and also cut the tube that the nitrogen gas had fired through. And we were done one week ahead of time.

Oliver Strimpel: OK. So the spacecraft begins its journey home in March of next year, and all being well, when it arrives on September 24, 2023, it will release its capsule containing the Bennu samples, which will parachute down in the dry lake beds of Utah. What happens next?

Harold C. Connolly Jr.: Well, as we all watch it gently descend to the surface of the Utah desert, we clap very loudly, and then quickly get in our vehicles and go recover that capsule. We have a couple of priority issues we have to deal with. We have to get it into a nitrogen atmosphere in the field, so we have a small sort of field curation camp that will be set up. We put that sample return capsule into it. We then package it correctly, locally, with the curators and colleagues from Lockheed Martin and NASA, and we'll then ship it to Ellington Air Force Base in Houston, Texas, outside of Johnson Space Center. And then it gets brought to the Johnson Space Center, to the area once known as the Lunar Receiving Laboratory, the Astromaterials curation facility, where it will be opened up in a nitrogen environment in the curation facility. And then we take lots of pictures and smile.

Oliver Strimpel: So as far as I know, the curation at Johnson Space Flight Center is sterile. Is that to make sure the samples aren't contaminated by Earth materials, or are we also protecting ourselves from something potentially harmful on the asteroid?

Harold C. Connolly Jr.: No. The main purpose is to protect the sample from getting contaminated by any human input or any terrestrial input into that sample. Asteroids do not contain anything that's a threat to human life, and that we learned in part from the Apollo missions, which brought samples back. Lots of research was done on the Apollo samples, which showed that they'd been sitting on the surface of the Moon for four and a half billion years. They've been cooked, irradiated. So there is nothing there that is of any harm.

Oliver Strimpel: So what kinds of analysis will be performed on these samples?

Harold C. Connolly Jr.: That's something I've been waiting for, for 12 years of my life so far. So the sample analysis will be broken down into two major categories, the organic analysis and the inorganic analysis. In the case of organics, we'll go through the usual steps that one does when measuring organic materials. There'll be some dissolution of the returned material, some dissolving of it, and we'll be looking for soluble and insoluble organics, amino acids, sugars, et cetera. And then the inorganic: we will be looking at the petrology, the petrography of the rock. What is the rock? What does it look like? How do the minerals arrange themselves? And then what are the minerals' compositions? What is the structure of the overall mineralogy that is present, in either the structural components of this material or the rocks in general? We expect that there'll be several different types of rocks, what we call lithologies, and we'll be looking at the elemental composition, major, minor and trace elements; the isotopic composition, stable and radiogenic; the absolute age of materials, or the relative age of materials; whether or not it is a chondritic material we have in our collection, or whether it's something we've never seen before, or contains components we've never seen before. It's going to be really fun. And we have two years to do that.

And meanwhile, the curation facility, in the first six months, will be developing a catalog of the materials, coarse, medium and fine particles, that will be released, so that scientists around the world can request samples of OSIRIS-REx to study. And our sample analysis routine is actually set up in a way that is, for a mission, a first, in that we have a whole series of hypotheses that we will be testing by analyzing the sample, to uncover and constrain the entire history of asteroid Bennu: from material that was part of a molecular cloud before the solar system was formed, to material that formed in the disk as planets were being made, to, finally, material that would be sitting on the surface, and how long it's been sitting on the surface since the actual object Bennu was formed.

Oliver Strimpel: Are there any specific questions that you're particularly interested in answering as a result of all these analyses that you'll be performing?

Harold C. Connolly Jr.: I would love to see chondrules inside of this material, which are millimeter to submillimeter-sized igneous spheres that were melted in the early solar system. We don't really understand how they were melted. And I would also like to see the first rocks, the ones that actually give us the age of the solar system. I would like to see that material in this returned sample, new kinds of what we call calcium-aluminum-rich inclusions. Those are two classes of objects I have spent my career working on, and I can never get enough of them. They're beautiful.

Oliver Strimpel: So these are some of the very, very earliest materials of the solar system. Is that why you're particularly interested in them?

Harold C. Connolly Jr.: That's right. Some of my colleagues work on material that's actually older, which are presolar grains. I enjoy that as well, but I'm a petrologist, an igneous petrologist, so rocks that have been melted are my forte.

Oliver Strimpel: I know it's a seemingly weird environment to form sedimentary rocks, but do you think you'll see some sedimentary lithologies in the samples as well?

Harold C. Connolly Jr.: We seem to be able to see flat particles that are ejected off the surface, some kind of foliation or layering in some of the rocks on the surface, the boulders, and potentially even in some of the material that escaped the sample collection head when we moved it. We don't really understand how meteorites were lithified. We don't understand how they were turned into rocks, and we're hoping that we will get a better idea of that process from the returned samples.

Oliver Strimpel: So I guess this is a kind of oxymoron, but do you actually expect to see some surprises when you get your hands on those samples?

Harold C. Connolly Jr.: First of all, I would like to see a different population of chondrules, one that we don't have represented very well, or that's certainly represented at a very small level. That would be something that would really excite me. And I'd like to see, in the lithologies we return, that while the dominant one would be carbonaceous chondrite-like, there would be other material there that, before we got to the asteroid, we probably never would have predicted we would find as a mixture with carbonaceous material. And we know that there's most likely exotic material, what spectroscopists call pyroxene-rich material, on the surface of Bennu, which appears to be material that may have come from Vesta. So that indicates that in the collision stage, while Bennu's parent body was still in the asteroid belt, it got banged by something that wasn't carbonaceous. It collided, catastrophically perhaps, with something that was differentiated, or melted, and there may have been more cycles of collisions.

Oliver Strimpel: Just to explain, you mentioned there might be something that came from Vesta. That's the largest known asteroid, is that right?

Harold C. Connolly Jr.: Correct. Vesta and Ceres are two large asteroids. Vesta is the largest differentiated asteroid. The largest asteroid, period, is Ceres, and Ceres is a large carbonaceous-like asteroid, which is actually potentially similar to both Ryugu and Bennu.

Oliver Strimpel: And they might get there as a result of some kind of shuffling from collisions during the process of formation of Bennu. Is that the thought?

Harold C. Connolly Jr.: Right. During the formation of Bennu, during what we call the catastrophic disruption that broke the parent body apart and produced Bennu, and potentially cousins of Bennu or Ryugu that are out there in the solar system. How that happened is potentially random, but it also may be related to the migration of giant planets at some point in the early solar system, or much later on. It's difficult to constrain, but our hope, or our expectation, is that with the samples that we return, we can constrain some of that timeframe of catastrophic disruption.

Oliver Strimpel: For my last question, I'd like you to imagine that you are in charge of NASA's scientific space mission budget. What would you use it for?

Harold C. Connolly Jr.: The solar system is a big place. One of the areas that I think would be really important to explore is objects that are known as centaur objects, or Kuiper Belt objects. These are cold objects, hypothesized to be truly primordial, volatile-rich, with lots of ice and rock in them, that are out in the outer solar system. Even going so far as to go to some of the rocky moons of the Jovian planets and bring back samples to study would, I think, be really illuminating, for many scientific reasons.

Oliver Strimpel: Harold C. Connolly Jr., thank you very much.

Harold C. Connolly Jr.: Appreciate it very much. Thank you.

Oliver Strimpel: For more about Geology Bites, as well as pictures and diagrams that illustrate this podcast, you can go to geologybites.com.