Unlocking The Mysteries Of A Metal-Rich Asteroid

KATHLEEN DAVIS: This is Science Friday. I’m Kathleen Davis.

SWAPNA KRISHNA: And I’m Swapna Krishna. Kathleen and I are filling in for Ira this week. Last week, NASA’s Psyche spacecraft launched successfully from Kennedy Space Center. It’s headed to an asteroid, but it’s not the kind of asteroid we’ve studied before, made of mostly rock or ice. Its target, located in the asteroid belt between Mars and Jupiter, is made of mostly metal. It’s something like 60% iron and nickel. Scientists are hoping that the metal-rich asteroid might help teach them about how planets form.

Joining me now for an update on the mission and its goals is Dr. Lindy Elkins-Tanton. She’s the principal investigator for the Psyche mission and vice president for the Interplanetary Initiative at Arizona State University in Tempe, Arizona. Welcome back to Science Friday.

LINDY ELKINS-TANTON: Thank you so much. I’m really excited to talk with you about Psyche today.

SWAPNA KRISHNA: So we last spoke with you on this program around six years ago, when the whole mission was just a future plan. How does it feel to have it off the ground, literally?

LINDY ELKINS-TANTON: It’s utterly surreal. I wonder if you’ve had this experience where you’ve been imagining, not even really consciously, but what an event would feel like and what it will look like and what kind of room you’ll be sitting in and how it will be. And I’ve been imagining that casually now for six years. And suddenly now I find myself sitting in the operations room with the team having watched our spacecraft shoot off into space. And I feel like I’m vibrating continuously between amazement and reality.

SWAPNA KRISHNA: So give us the quick update on the launch and the progress so far. Is everything going according to plan?

LINDY ELKINS-TANTON: Oh, my gosh. It surely is, I’m so happy to be able to say. As you said, it’s been a roller coaster getting to this point. So many challenges overcome. But we couldn’t have asked for a more perfect launch from SpaceX.

And then the spacecraft did all of its autonomous behaviors, all the things it has to do by itself without any commands, right after separating from the rocket perfectly. And now we are zooming away from the Earth at about six kilometers per second as we gradually and methodically turn on all the subsystems and make sure everything works. And so far, it’s just beautiful.

SWAPNA KRISHNA: Well, now let’s move on to the target, 16 Psyche. Where is it? How big is it? Can you tell us a little bit about it?

LINDY ELKINS-TANTON: 16 Psyche, an unusual asteroid. Really pretty unique in our solar system. One of just a few that we think are made mostly of metal, as you said, and also have at least a partially metal surface. By far the biggest of these and the most likely to be structurally intact from its formation. So the only one like that in our whole solar system, out of about, I don’t know, a million and a half asteroids in the main asteroid belt. This is the one we’ve picked. And it orbits in the outer main belt, so it’s often closer to Jupiter than it is to the Earth. It’s very far away.

SWAPNA KRISHNA: Sometimes space probe travel involves a lot of roundabout routes, swinging by different planets for gravity boots. How is the spacecraft Psyche getting where it needs to go?

LINDY ELKINS-TANTON: Yes, unfortunately, it’s not like in cartoons where you just retain the rocket and use that propellant to get all the way to where you’re going. We get released from the rocket, and then we’re shooting off in a certain direction, orbiting the sun just like everything else. So our spacecraft is going to swing around the sun and get a gravity assist from Mars and then continue out toward Psyche. And a majority of the time, we’ll be using our solar electric propulsion system, which is a very low thrust, but continuously run adds up to a lot of speed. It will take us 5.8 years to get out to Psyche, with one extra circuit around the sun to get that Mars gravity assist.

SWAPNA KRISHNA: So will the spacecraft be doing anything else during that time? For example, during the Mars flyby, are we going to be taking any readings of Mars or anything like that? Or is it just travel time?

LINDY ELKINS-TANTON: For the science team, it’s calibration time. That’s what we’ll be doing. We just turned on the magnetometer Tuesday, October 17. That was the first science instrument to be turned on. And it’s working beautifully. And so we’ll be calibrating and testing.

But the real thing the spacecraft’s going to be doing during its first couple of years is testing this technology demonstration, the Deep Space Optical Communications package. This is completely separate from our science mission. We are not using it for science, and it will not be on while we’re at the asteroid. But during these first two years, that team will be testing its ability to communicate back and forth between the spacecraft and the Earth using lasers instead of radio waves. You can put a lot more data into a laser than you can a radio wave. And so we joke that this is how eventually we’ll stream Netflix to Mars.

SWAPNA KRISHNA: Wow. So the spacecraft will get to 16 Psyche in 2029. So what happens next? What’s the first thing we do when we get there, and what’s the goal once we get there?

LINDY ELKINS-TANTON: Well, first of all, we’ll be taking approach pictures. And Psyche will be getting bigger and bigger. And I always try to remember to remind everyone that we’ve already written the software pipeline so that all the images that we get from the spacecraft via the Deep Space Network are going to go onto the internet for everyone in the world to look at for free within a half hour of our receiving them, because seeing the thing is a huge thrill. And we want to share that with everyone in the world because that’s what space exploration is for.

So we’ll be going into a high-up orbit, an orbit far from Psyche, as we learn about its gravity field. And then, gradually, we’ll step down closer and closer. And all the time that we’ll be orbiting, we’ll be using the imagers. We’ll be taking pictures. We’ll be measuring the magnetic field. We’ll be measuring neutrons off the surface of the body. And we’ll be measuring the gravity field. All those things will happen continuously.

And then when we get to the closest in orbit, we’ll also turn on the gamma ray spectrometer, this amazing instrument that allows us to measure the atomic composition of the surface of Psyche while in orbit above it. It uses the effects of intergalactic cosmic rays striking the surface of Psyche and sending up gamma rays that are then measured by our beautiful crystal in this instrument. It’s an amazing instrument.

So we’ll be doing all those things in an effort to gather all the data together and understand what this object is. How was it formed? Is it in fact a part of the metal core of a tiny little planet called a planetesimal that formed just in the first one million years of our solar system, and it was that melting and formation of its metal core that gave Psyche its big bulk of metal? Or is it in fact some other kind of object, some sort of material that we haven’t sampled yet on Earth from the early solar system? In either case, it’ll be an ingredient for our rocky planets as we try to understand what made our rocky, habitable Earth.

SWAPNA KRISHNA: And so once we get to Psyche, we’re going to study it, but we’re not going to land on it, correct?

LINDY ELKINS-TANTON: That’s right. We’ve been spoiled with landers and sample returns. You’re thinking about OSIRIS-REx and Hayabusa and these amazing feats. Those spacecrafts visited close by. Asteroid Psyche is much too far away to make that a practical activity. We’ll just be orbiting.

And I would add that having never had a close-up photo of a metal surface, we have no idea what it’s going to be like. It’s very hard to plan a lander if you have no concept what the surface is like. So this is a very important first step to understanding those few but very important metal objects in our solar system.

SWAPNA KRISHNA: Right. And so since we don’t know what the surface is like, it’s hard to say if we could even get a sample easily. But would there be any value in getting a sample of this metal for a future mission, let’s say?

LINDY ELKINS-TANTON: Well, there are a couple of different values. One is understanding really what the very first generation of metal cores was made of. The core of our Earth is the result of generations of merging of metal cores of smaller bodies as they collided and joined our Earth, culminating with the giant impact that formed our moon about 100 million years after the beginning of the solar system. So if Psyche formed in the first one million years, which we think it did, it’s that very first generation. So that would be wonderful.

But there’s also the thought that in the future, humans should get our resources from space if we can and protect our Earth. And so knowing more about what the metals are that are available would also be nice. But NASA is not doing asteroid mining, and that is not the primary purpose of the mission. But it sure would be nice to have a sample for all those reasons. But we’re going to have to end up sampling closer-by asteroids, not this one that’s, even at its closest, three times farther away than Mars ever is to the Earth.

SWAPNA KRISHNA: How many of these metal asteroids are there out there?

LINDY ELKINS-TANTON: We don’t know for sure how many metal asteroids there are out there. But there are about nine that we think are likely made mostly of metal. And they all belong to a class of asteroids called the M class. But I think it’s becoming fairly evident that not all the M class asteroids are made of metal. They could be dense or have a kind of a featureless reflected spectra without necessarily being made of metal.

But there are a lot of question marks there. So the answer is we don’t really know. This is just the biggest one.

SWAPNA KRISHNA: And so when people hear about these big chunks of metal, one of the questions that comes to mind is, how much must that be worth? What do you think?

LINDY ELKINS-TANTON: [LAUGHS] Yes. Back in 2017 when I got the call from NASA that we were selected, that completely life-changing moment, and then spent what felt like the next 48 hours on the phone being interviewed by members of the press, and PBS NewsHour asked me, well, if you could bring Psyche back and sell it on the metals market today, in January of 2017, what would it be worth? And I thought, well, that’s a fun calculation. And just looking at the iron– I can’t even remember right now if I included the copper or any of the other elements, maybe just the iron– $10 quintillion. So multiples of the gross domestic product of the economy of the entire Earth.

Of course, that was a very, very fun thing to calculate, but it’s false in every possible way. First of all, we have zero technology to bring Psyche back. We can’t bring it back to the Earth. If we could bring it back to the Earth, it would probably be a really bad day for the Earth because we have no technology to put it into a stable orbit.

This is an object the size of Massachusetts without the Cape. Its surface area is similar to the surface area of California. And it’s very dense. But then, even if we could somehow bring the metal to Earth, it would swamp the market, and basically be worth nothing.

And so that dollar value, I think the value of it is, first of all, to interest some people in space who had not previously been interested in space, which I love. I think everyone should look out and above and understand our place in the world. But then, also, again, I hope that in the future, people will be getting resources from near-Earth asteroids. And there are a bunch of companies working on this now. And so I know it helped attract attention to them as well.

SWAPNA KRISHNA: We talked earlier about some of the possibilities for what Psyche is– maybe a planetesimal core. Could it have become a planet eventually but failed somehow?

LINDY ELKINS-TANTON: It should have joined the process that made the other rocky planets. We think that Mercury and Venus and the Earth and Mars were all the result of many, many additive collisions, sticking-togetherness of these planetesimals. Some of them inevitably would have fallen into the sun if their orbits were perturbed by all this wild action and impacts. And some of them were thrown out into the outer solar system. And just a few were stranded in the asteroid belt like Psyche, so kind of the shrapnel, the leftover, of planet formation. And yeah, it could well have ended up differently in that it, like its brethren, would have become part of these big, rocky planets.

SWAPNA KRISHNA: You’re listening to Science Friday from WNYC Studios. If there’s stuff coalescing into larger bodies, how do you end up with this metal chunk? Why isn’t it more uniform or round?

LINDY ELKINS-TANTON: Well, first of all, I’ll tell you what sort of the scientific consensus is about this stuff. But I’ll just add that I think there’s an awful lot we don’t yet understand about how planets form. So lots of question marks.

It seems that the very first material in our solar system that came out of the gas cloud, really, that formed our sun and our planets, the first solids were just little grains almost like the size of sand or little pebbles. And they got crushed together by special kinds of gravitational waves or turbulence in the disk into these bodies called planetesimals the size of cities or continents. And some of them, if they formed early enough, like in that first million years, would have been heated up by the short-lived radioisotope aluminum-26. This is a very fascinating sleuth story that was figured out around 1950, 1960, that there was this short-lived radioisotope that was quite hot, hot enough to melt the planetesimals.

So those tiny grains and pebbles, some of them were rock and some of them were metal. And they would be intimately mixed, millimeter or centimeter scale. But once they melted, the metal would sink to the middle and make that metal core because it’s so much more dense than the rock. And so that’s the process called differentiation. And it’s the same structure as our Earth and the other rocky planets, with the metal core in the middle.

But the metal core is in the middle surrounded by rock. So why does Psyche have a metal surface and seemingly so much less rock than one would expect? And we think it’s because it’s been battered by impacts that ended up having some of its rock broken off or stripped from it in big collisions rather than being allowed to stay in its whole, original state.

And another clue to this is that Psyche’s spin axis is laying over into its orbit. And with the Earth and our other rocky planets, the spin axis is more or less vertical, spinning like a top, if you compare it to its orbit. And with Psyche, it’s laying over on its side like a rotisserie chicken. So something hit it really hard and knocked it over.

Those are all ideas. They’re models and hypotheses and then one observation, that it’s knocked over, which does not mean that our suggestion of how it was formed is necessarily the answer. It’s one possibility that’s non-unique among many.

And one of the things that makes this so interesting scientifically is that we’re not looking at a whole population. We can’t look at a bell curve, like what’s the average thing that happened to these bodies? There’s just one of it. And so with only one to hypothesize about, it’s also possible that it was made in a very unusual way. That’s part of the excitement of going. I think we’re going to be quite surprised.

SWAPNA KRISHNA: And is there any specific outreach with this mission that you’re doing?

LINDY ELKINS-TANTON: So much fun. NASA gives us a budget that lets us work with students at two and four-year colleges in the United States. We have a bunch of projects, capstone projects. We have some K-through-12 outreach done by college students. And we have free online courses that anyone in the world can take on our psyche.asu.edu website.

But the thing I want to highlight is this art program. Every year, we pick 16 students out of a pool of applicants, and we fund them to make four original works of art. And we have this amazing gallery on that same website, everything from cooking and jewelry to painting and concertos and dance. And it’s been a tremendous tool for outreach. And in the end, we’ve even ended up with– done by a professional musician who just really loves the mission– a heavy metal tribute song for the mission. Those things I love because they reach so many more people.

SWAPNA KRISHNA: We first spoke to you six years ago. Back then, it was around six years from the initial idea for the mission. But now it won’t get to the asteroid for another six years. What is it like to be on a mission with a timeline of decades?

LINDY ELKINS-TANTON: I find it surprising every day that I’m on this journey, because I hadn’t really– I hadn’t really set out to have a giant, lifelong project. I’ve been working on this for 12 years now, and we’re about halfway. And last year, when we did get delayed for a year, and that meant that– there just isn’t an opportunity to launch to Psyche at any given month of any given year. It’s much harder to get to than, for example, if you’re just launching into Earth orbit, you can do it any time. But Psyche is much harder to get to.

And so the trajectory we found for this month is a couple of years longer than the other one. And that made me sad for a while, and I kind of felt sorry for myself. And it was very stressful. And then I realized, probably the biggest first-world problem that there’s ever been is, my spacecraft is launching late.

And so I really got over myself and remembered what a huge privilege it is to work on these things and that my priority was the happiness and health of the team and sharing this as widely as I could. And so the longevity does not bother me anymore. I see it as an opportunity.

SWAPNA KRISHNA: So we are out of time. Dr. Lindy Elkins-Tanton is the principal investigator for the Psyche mission. She’s also the vice president for the Interplanetary Initiative at Arizona State University in Tempe, Arizona. Thank you so much for talking with us today.

LINDY ELKINS-TANTON: Thank you so much for your time. I appreciate it.

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