Podcast: Probing Asteroids in Space with Harold C. Connolly Jr.
by AMNH on
Asteroids can teach us a lot about the origin of our solar system—but they can also pose a potential threat if they come too close to Earth. Join Harold C. Connolly Jr. for an overview of the OSIRIS-REx and Hyabusa2 spacecraft missions that are currently probing the asteroids Bennu and Ryugu—two “potentially dangerous asteroids” whose orbits around the Sun are predicted to come within 5 million miles Earth.
This Frontiers Lecture took place at the Museum on December 4, 2018.
MODERATOR: I'd now like to introduce our presenters for the evening. Harold C Connolly jr. is the mission sample scientists and Co-I [co-investigator] on NASA’s New Frontiers Three asteroid sample return mission OSIRIS-REx, and Co-I on JAXA’s Hayabusa2 asteroid sample return mission. He's also the founding chair and professor in the Department of Geology, School for Earth and Environment at Rowan University. Dr. Connolly's research is focused on understanding the origin of rocky bodies in the solar system through the study of asteroids and meteorites. Please welcome Harold Connolly.
I do want to—before you start, Harold—I just want to mention our other presenters. Carter Emmart, the Museum's director of Astro Visualization, and Denton Ebel, the chair and curator of the Department of Earth and Planetary Sciences. Take it away.
HAROLD C. CONNOLLY JR. (DEPARTMENT OF GEOLOGY, SCHOOL FOR EARTH AND ENVIRONMENT, ROWAN UNIVERSITY): Thank you so much thank you for that lovely introduction. Good evening everyone, and thank you Carter and Denton for joining me this evening. We've worked together for many, many years and Denton and I have been colleagues here at this museum for 17 years–long time.
DENTON EBEL (DIVISION CHAIR, DEPARTMENT OF EARTH AND PLANETARY SCIENCES): Yikes.
CONNOLLY: As you heard, I am the mission sample scientist for OSIRIS-REx. I'm the first mission sample scientist for any mission. And a co-investigator, which basically is a fancy title from somebody who started with the program and is intimately involved in it. And that was 2008 that I got involved in this mission and ten years of my life devoted to the mission culminated beautifully yesterday as you know we'll go through that.
We'll go through the timeline but just to hit the punchline, the mission is over in the year 2025, and samples come back in September of 2023. So mission sample science is a branch of science within the OSIRIS-REx mission that covers all aspects of the origin, evolution, and collection of regolith and returned sample. In other words, this includes a dynamical history of Bennu–meaning how did it get to the orbit it is today from the main belt where most asteroids are? How did the regolith–or the fine grain particles on the surface–form? What's the science behind collecting of the material that we're going to bring back? And the sample analysis–in the end, my team will analyze the samples that comes home and we've been following it all along with a branch of science known as contamination knowledge.
This is a thin section which means this is a glass slide like you'd have in biology where a meteorite has been glued to it and made very, very thin–approximately 30 microns thick–and light pass through. In this case it's cross polar lights and this is a carbonaceous chondrite, which we expect the samples to look like. In fact, this is one of the very first rocks to form in the solar system–it's what gives us the date of the solar system–at 4.567 billion years. It's known amongst those that love it, called “cracked egg.” And within it was found the third mineral predicted to exist in the solar system, condensed in the earliest stages before planets were made, by our very own Denton Ebel who predicted it. And we had a student in 2008 as part of the REU program who discovered it in this slide, so that's really exciting.
EBEL: This is called exploration.
CONNOLLY: This is exploration. And the key point here to bring home is, down to the microscopic level that we'll be looking at when the sample comes home. We're going to go to the grand level next and discuss the big picture of asteroids so reference frame the Sun the earth right here and there's Bennu and of course OSIRIS-REx. Distance to the rendezvous: zero. We came there yesterday so if you didn't see the many news reports it was really, really exciting. But instead of being in Tucson, I'm here so I can talk to you about this wonderful event. with my team in Tucson right now working away I was up at 3:00 this morning working on some science because I was so excited I couldn't sleep properly.
[RECORDING OF OSIRIS-REx LAUNCH]
CONNOLLY: I took this video with my cell phone, and about now is when I started to cry with tears of joy and couldn’t see very well. This is an extremely impressive launch.
So you know, a launch can be a wonderful event–science culminating, your years of work and hard effort by a huge team of engineers, scientists, people who support you in clerical positions. It's a huge endeavor that gives jobs to many, many people which is really important. And it's also an incredibly wonderful social time period to share with friends and loved ones. So it's a tremendous emotional event as well as being one of science, exploration, and engineering.
So to recap, NASA's sample return mission OSIRIS-REx is going to, or has, arrived at a type b asteroid which is a spectral type, meaning carbonaceous-like. It launched at 7:05 p.m. on the 8th of September in 2016 from Kennedy Space Center. It launched 180 milliseconds after T equals 0 was called, the second-fastest launch in NASA's history. It has arrived and will bring back sample in 2023, with a mission being finished in September 30 of 2025. A timeline: we were selected in May of 2011, we're confirmed in 2013, which means you did everything you were supposed to, NASA says yes we have confidence in you, you can go. You build your spacecraft. And then we're at Bennu now. The sample collection is currently scheduled for July 4 2020. We depart Bennu in March of 2021, sample coming back in 2023. And then for a first in the history of sample return, we have two years of funding to analyze the sample after it comes back to test various hypotheses and understand the whole history of asteroid Bennu.
Here is the spacecraft in the Lockheed Martin facility where it was built–it's a sizeable size spacecraft. Solar panels. That is the sample return capsule right there with some scientific payload instruments. And this is our collector all bottled up in there. It has five major science instruments. Camera suite, which is three cameras which gets us down to a resolution of sub-centimeter, millimeter resolution on the surface from orbit. We have two spectrometers looking at the visible and thermal infrared. One laser altimeter to tell us distance and relief on the surface of the asteroid. And one x-ray spectrometer. This is the touch-and-go sample acquisition mechanism, otherwise known as TAGSAM, and it's three meters long with the collection head. How it works is we fire nitrogen gas onto the surface of the asteroid, it fluidizes the loose material and collects it into the interior of this head right here.
So we will collect a minimum of 60 grams, but up to two kilograms of sample being collected to bring back. I should point out that 75% of the sample is archived at NASA Johnson Space Center, where we will curate the sample for future generations to work on. And that's a policy to goes all the way back to the Apollo missions.
Here's a little animation produced by the mission that shows roughly what's going to happen. The spacecraft’s solar panels go backwards so it is like a bird going down to the surface, or Bennu. And that's how the asteroid got its name, by a young person–nine years old–who won the contest. Before that it was called 1999 RQ36. Doesn't roll off the tongue very well, does it? This is really, really cool. so on the 14 of November, we extended the TAGSAM arm fully, all three meters. And slightly after that, we imaged it with SamCam. And these are images of the collector head in space. And you can see very clearly the surface, and the interior where the sample will be collected. These tiny little paths here are actually another collector that will collect the fine particles on the very surface of the asteroid, which many scientists are only interested in those little tiny fine particles. Because they contain what we call space weathering, they've been barded with high-energy particles or other particles, solid particles, that make little pits. And this is one of the ways we are going to be able to tell that we have collected sample, is by looking at it and photographing the sample after we go through the collection process. It's pretty cool, huh Denton?
EBEL: Very cool.
CONNOLLY: So, before we even launched, we had three time periods that asteroid Bennu was imaged by radar. Two of which were at Arecibo in Puerto Rico, where at the time Mike Nolan was the director. Mike Nolan is the chief scientist on OSIRIS-REx. And from these images, he created this shape model of the asteroid–kind of diamond-shaped–and even predicted that this is a large boulder on the surface.
EBEL: So radar is radio waves, and because you know when you sent the radio waves out you know when they come back exactly how long it took the radio waves to get to each part of the asteroid. And then you can build a model, a shape model that is consistent with all the radio waves from each part of the asteroid. The accuracy of these models is amazing, because we here we have this big dish–that this hasn't done so well with the hurricanes lately–but it's an amazing tool.
CONNOLLY: It allows you to penetrate approximately a meter or so on the surface of an object. So you really get a feel for what it really looks like. In the case of Hayabusa2, as we'll see in a moment, we didn't have radar for asteroid Ryugu, we only had what they call light curves. It's by studying the way light moves around an object that you can create a model of its shape. And that can be right, and sometimes it cannot be. The asteroid itself is very dark, it reflects only four percent of the sunlight that hits it. And this earth-crossing asteroid has a one in 2700 chance for a keyhole impact in 2135.
A keyhole is a statistical probability at a certain spot in the solar system that an object may go through that will potentially put it on a hazardous trajectory towards any planetary body. The problem with that calculation is it requires that you know the composition of the body you're working with accurately.
EBEL: Because sunlight pushes it.
CONNOLLY: The sunlight moves it over time a very small amount, but in space a small amount of anything will accumulate. And we don't know the composition the asteroid, either asteroid: Ryugu or Bennu to any accuracy. Which is also another reason why we're going to them. From 3,000 kilometers away we all were confident that asteroid Bennu was spot on to Mike Nolan's shake model, he got it right. So it's not very big, in fact it's going to be the smallest object that we've orbited as a human race consecutively for a long time–year and a half.
EBEL: And the gravity on this thing is really low.
CONNOLLY: It's really tiny. So gravity on this asteroid is 0.0000978 meters per second squared, as opposed to earth which is 9.8 meters per second squared.
EBEL: So one ten-thousandth of Earth's gravity on the surface.
CONNOLLY: So tiny if you hit a golf ball, it goes off and goes bye, gone, see you. So the first asteroid samples returned came from our good colleagues in Japan that had Hayabusa. And they brought back tiny particles, 30 microns to 150 microns, so really, really tiny They were analyzed so that we could understand the history of this asteroid.
EMMART (DIRECTOR OF ASTROVISUALIZATION): And Hayabusa means falcon, right?
CONNOLLY: That's right. Total achievement in sample return missions. Which actually, in my opinion, culturally pushed many other nations to explore smaller bodies like Ryugu and Bennu. So, the JAXA asteroid sample return mission Hayabusa2 went to and is at a c-type asteroid which is again another kind of carbonaceous type asteroid. It was launched at 1:22:04p.m. on December 3rd 2014 from Tanegashima Space Center in southern main island of Japan, and arrived in June of 2018, and will return to earth in December of 2020. So it's a shorter mission than OSIRIS-REx, and they can move pretty fast because they have these ion engines that propel them.
This is an image of asteroid Ryugu taken from 20 kilometers a month and a half ago. So it's twice the size of Bennu–eight times the volume. Big impact crater, lots of huge boulders. This boulder here for scale is bigger than a bus, it's enormous. The Hayabusa2 space mission has three landers, two of which have been launched and landed successfully on the surface of asteroid Ryugu and moved around. Minerva, right here and MASCOT, Mobile Asteroid Surface Scout.
Here's a comparison done by The Planetary Society, which is to scale, of asteroid Ryugu and Bennu.
EBEL: This particular shape seems common to the two. They're different sizes, but very similar shape. This is what you'd expect for a rubble pile, a pile of material that's sort of collected by its own gravity. And you can't support like a long narrow thing because it'll collapse to a sphere, something like a sphere.
CONNOLLY: That's a great point, Denton. and so the many of these smaller asteroids are this sort of diamond shape. And they are that way in part because they are rubble piles, or accumulation, as you can see of lots of material. When they were in their original home in the asteroid belt between Mars and Jupiter, minding their own business, another one came along and smacked it and impacted it, possibly multiple times, and eventually it left the asteroid belt, was knocked out, re-accreted, came back together and this is what we're looking at now as the sibling of the original parent body of this asteroid. And even Bennu as you saw is also a rubble pile. The density of Bennu and Ryugu is very similar density, is a little bit more than one gram per CC. So basically that means it's a huge amount of pore space inside of it.
EBEL: Just a little more dense than a bucket of water.
CONNOLLY: I'm glad you said that, thank you.
EBEL: But these are also in near-earth orbit, which means they are potential impactors with the earth. So they're representative of the kinds of bodies that could impact the earth. They are small. So we've identified now about ninety-nine-something percent of all objects that are potential impactors greater than a kilometer in diameter, but these are smaller than that. So these are potential impactors, but very representative. So that's another reason to go and study them and bring some home because understanding them makes us able to defend against them if we have to.
EMMART: There was another issue that came up in a recent set of talks we had here, Denton. It was about when one of these rubble piles comes through an atmosphere, you might think it's just going to dissolve out like a skeet shoot and come out in all directions, but in fact the shock wave contains it, is that correct?
EBEL: It can, yes.
EMMART: So that's a worry, the mass is all sort of there and doesn't get distributed out into small pieces.
CONNOLLY: Not all asteroids in this smaller range–meaning less than a kilometer–are rubble piles. There are some that we would call monolith, which is one solid rock basically. And there was a landing of a small asteroid in 2008, TC3 about a decade ago in Africa, became a meteorite Almahata sitta, which is made up of multiple different kinds of meteorites, so it was a rubble pile. But Chelyabinsk, which came to earth in 2013 and impacted over Russia, it was a solid piece of–more or less, we think–meteor that exploded in an air burst of 440 kilotons of TNT.
EBEL: And it wasn't until the spring after the thaw that they found the 440 kilogram main mass, which was intact.
CONNOLLY: Right, in the lake. So, one more thing to point out to you: this is the first time in history since the Apollo and Luna days–the Apollo program obviously the U.S. program to the to the moon, the Luna programme was a USSR program to the moon–that two nations operated sample return missions at the same time. And of course in those days the USSR and the United States weren’t very good friends, there wasn’t a lot of cooperation. But here the U.S. and Japan, and the science teams themselves, have been working together in real collaboration to understand the science of asteroids. And I'm very proud to be part of that effort. I even spent time at the Hokkaido University in Sapporo, Japan in 2015 to work on our relationships.
Before we end, I’d just like to say thank you very much. Having any kind of life endeavors–in this case this space mission OSIRIS-REx and HYABUSA2–requires the wonderful generosity and kindness of so many people that you work with. And we really appreciate it, and I very much appreciate that you come to hear about these missions, so thank you thanks for coming.
MODERATOR: I have the mic so if you have any questions please feel free to raise your hand and I'll try to get to you. Yep.
AUDIENCE QUESTION: So is the mass of the actual spacecraft comparable to the mass of Bennu?
CONNOLLY: No, no, no, it's very small compared to them.
AUDIENCE QUESTION: So it won't affect the orbit?
CONNOLLY: No, no, no, we can't do anything to it. We can't move it or anything like that. No, it's not it's not like that, we don't have enough thrust to be able to do it, we don't have the mass to do it. It's often in the Hollywood movie you go and and move the asteroid. Not so easy. Or you're going you blow it up, and instead of having one piece at the earth, 15 pieces hit in 15 different places.
AUDIENCE QUESTION: Hi. How did Ryugu and Bennu get selected for study?
CONNOLLY: Yeah, that's a great question. Actually, we announced that we were going to Bennu first before the Hayabusa2 mission was officially established, and Ryugu was our backup option. And both of the selections were picked based on a matrix of how many earth-crossing asteroids there are. Of that how many– roughly 5,000–some roughly 139 were known to be carbonaceous. We wanted to go to a carbonaceous asteroid because we wanted to collect pristine carbonaceous material. Of that, only five of them came to the top as being dynamically economical to get to. And for us, really we picked Bennu. And Hayabusa2 picked Ryugu. We just sort of decided we would go to Bennu. In part the main decision was we had the radar passes of the object, so we had some idea of the shape before we would launch. Do that was a big important investment in it.
MODERATOR: Dr. Connolly, we have another question here.
AUDIENCE QUESTION: So what's going to happen with the rest of the hardware besides the sample return part? Will we get any more science from other pieces?
CONNOLLY: You mean after we're finished with the sample coming back to earth? So, both spacecrafts, after they released their sample return capsules, they didn't go into solar orbit. And they may be reprogrammed for other mission goals of some new mission, depending on how much fuel is left in them, and the lifetime of the batteries.
AUDIENCE QUESTION: How did you guys come to determine the method for collecting the samples with the nitrogen gas? What other options do you consider, and is that something you’d use in the future, or are you exploring other opportunities?
CONNOLLY: Both missions used two different totally different kinds of collectors. In Hayabusa2’s case, they use a collected of files fires a tantalum bullet into the surface–the material basically gets pushed up into the collector, into the actual chamber. And it has little teeth that also bring particles up and basically move up with the velocity as it moves. And that was designed by JAXA engineers.
In the case of the OSIRIS-REx collector with the nitrogen fire, that was a design that came from Lockheed Martin who had the idea of collecting regolith and sample from a planetary body using that kind of collector. And they approached us at the University of Arizona–I'm also a professor there–a long time ago to see if art we were interested in it. And Mike Drake, who was the original PI on OSIRIS-REx, jumped at the opportunity. Unfortunately Mike passed away in September of 2011. There's many ways you get these kind of things developed, it depends. So in this case it was an engineering team that designed it first.
EMMART: Harold, I want to also point out that the use of the gas is something…people say oh, you know, there's no air on the moon and how come the flag was moving. When the ascent stage of Apollo was leaving, and you have a camera aimed out the window and you see the flag wave, you're going to see the flag wave because you have an expulsion of explosive gas coming out that's made the flag wave. So when people say there's no wind on the moon, well there was for the brief time that we were firing rocket thrusters there.
AUDIENCE QUESTION: Doctor, as a geologist–we have downstairs, we have numerous carboniferous meteorites have landed–what do you anticipate, I realize you don't have the samples yet, but what do you anticipate is going to be the difference between them and the regolith that you're going to collect and what's already landed on the earth?
CONNOLLY: I would like to think that there'll be some similarities between what we collect and what we have in our collection, and there will be some significant differences. Because we don't have in-situ samples other than one from asteroids. And in the case of carbonaceous they're much more diverse in their chemistry in the hydrated phases, or phases which have OH or water on them, and amino acids than ordinary chondrites do for example. So that's our goal. And hopefully I'll see a few chondrules come out of it as well, which are inclusions or construction components of carbonaceous chondrites which I've studied quite extensively.
CHILD AUDIENCE QUESTION: Do you think that there's anything valuable, like gold, on the asteroids?
CONNOLLY: Hmm, well there may be. There certainly is tiny amounts of it there. But whether or not if you mean there's enough that we could like go and mine it, I really don't know the answer to that question. We'll have to find out. Great question.
AUDIENCE QUESTION: How do you explain the fact that on those two asteroids that the creators were so subdued, what's the weathering process? You know, all the other images I've seen of the other rocky planets do have fairly well-defined craters.
CONNOLLY: It's a rubble pile that's…if we are correct–which we'll have to wait for 2020 and 2023 to actually ground truth in what we have understood from spectroscopy–the carbonation material is actually quite a bit different in its properties than, say, something from the moon which has been differentiated. So it's a rubble pile with lots of mixed fine grains of a little bit softer kind of rocky material, and coarser grains, and it looks very much like the impacts–some of them may be low velocity, some of them may be a little higher–and on this small G, low velocity is very low. You know, just throw it up comes back down again, makes a little dimple. So we're still working on it, it's a great question. We don't have the answers right now, but there are a bunch of hypotheses that both teams are exploring, and stay tuned just in a week or two we'll have some more information.
EBEL: I think that it's probably really hard to experiment to try to mimic this kind of cratering, because it's a very low, low gravity situation. The regolith it's like loose sand or with some rocks in it, and the impact velocities are probably low. We don't know, you know? There's also space weathering, do you want to speak to that really quickly?
CONNOLLY: Well, yes. Space weathering is important, it's a process where cosmic rays, sunlight, high energetic particles, and even small micro-meteorites or meteors will impact on the surface of these airless bodies, and it will process them, it will weather them. The thing that we can hypothesize very openly about is that we are quite sure that the material on the surface of the Ryugu and Bennu has been moving around and migrating to the equatorial regions as it rotates. So you're actually moving material around as well. So ideally, with the OSIRIS-REx collector and Hayabusa collector, if we get stuff from slightly subsurface, that would be the best of all bests.
MODERATOR: All right, I think that's all the time we have for tonight. Thank you so much, Dr. Connolly, for coming. Denton and Carter as well.
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