Mars Attack: The Curiosity Rover’s Laser-Zapping Rock Analyzer
In a timely new memoir, a geologist chronicles his journey from shooting model rockets to becoming one of Curiosity’s lead scientists
Steven Cherry: Hi, this is Steven Cherry for IEEE Spectrum’s “Techwise Conversations.”
Manned space exploration captured the public’s attention and interest—and funding—ever since the 1960s. But robotic exploration is vastly more efficient when it comes to science and engineering, and the risks surrounding fragile human cargo.
From Genesis in 2001, which was the first robotic mission to go beyond the moon and return, to the Curiosity rover, a 1-ton behemoth with its own nuclear thermal generator, currently scurrying across the Martian surface, we’ve probably learned more about the solar system in the past 12 years than in the previous 42.
My guest today is Roger Wiens. He’s a physicist at the Los Alamos National Laboratory who has made key contributions to the scientific missions of both Genesis and Curiosity, and he’s written a book, Red Rover, published last month by Basic Books. Part autobiography—Kirkus Reviews called it “a winning memoir of great achievement”—and part journalism, it’s a fascinating look behind the scenes of some of NASA’s top projects of the past decade. He joins us by phone.
Roger, welcome to the podcast.
Roger Wiens: Thanks. It’s a pleasure to join you, Steve.
Steven Cherry: There’s a bit of background that we need first in order to understand your Genesis and Curiosity experiments. Beginning in the 1990s, NASA missions are now smaller, though still not exactly small, and scientist-led. How did that come about, and how did it change things for researchers like yourself?
Roger Wiens: Yeah, so what was going on was that following Apollo, I think the robotic space exploration was still thinking in a very big-mission sense, and the politics were still in favor of that, and so on, until there were a couple of very significant failures in the late ’80s and early ’90s. And along with that came a new NASA administrator, Dan Goldin, and he instituted this policy of faster, better, cheaper, which many people I’m sure have heard about. And it was widely maligned, but on the other hand, it did some very good things. And I think we’ve now achieved a much better balance as a result of that.
So what he did was he put scientists more in charge of the overall missions, and in many cases, an individual scientist in charge of a whole mission, but with severe cost caps and the threat of cancellation if the cost grew over that. So that kind of paradigm has really reigned for much of the time since the early 1990s and has really led to the revolution in robotic space exploration that we’ve had.
Steven Cherry: You wrote in the book that “Genesis failed, and yet it succeeded beyond our wildest expectations.” The failure was it crashed on reentry. Tell us about the wild success.
Roger Wiens: Yeah, it’s been interesting, because nobody really reported the success, although the news media was all over the crash back in 2004. So this spacecraft was collecting solar wind; these are rarefied particles that stream outward from the sun. It’s a great chance to understand the composition of the sun. And there are spacecraft out in space that are making measurements, but some of the things that we want to do in terms of measuring the composition cannot be done out there with instruments. We have to bring samples back. And so this Genesis spacecraft was just that. It was going to go out beyond the earth’s magnetosphere, collect solar samples for about two years, and then bring them back to Earth.
So it came back in 2004. I think many people might still be aware of the crash that occurred in Utah, when it was supposed to reenter and the parachute did not deploy. And so this capsule was seen lying there on the desert floor all smashed up, but it did have samples in it. And as opposed to instruments that could, of course, really be broken, the samples were broken, but we were able to analyze them anyway because of the fact that we had them in hand. And so, as a result of those analyses, we learned some really critical things about the composition of the sun and, by inference, about some of the processes that went on in the early solar system as the planets were forming.
And in particular, the oxygen isotope ratio of the sun looks to be significantly different from that of Earth and the other terrestrial planets. And the same is true of nitrogen as well. And so that speaks of a photochemical effect that was almost certainly happening in the time of the formation of the planet, and it just really gives us a key insight into what was going on as these planets were being formed.
Steven Cherry: Your current project is called ChemCam. It zaps rocks with lasers on Mars. Personally, I’d say that’s cool enough to merit the US $15 million it cost, but it has a scientific purpose as well, though. What is it?
Roger Wiens: Oh, absolutely, Steve. So we pitched this instrument, because if you’re going on a robotic mission, you have to have some way of seeing what is around the rover and understanding the compositions around the rover without having to go and actually tag every single sample that might be interesting. And so that’s called “remote sensing,” and you want to do it not just with pictures but with compositions. And you cannot actually really sample compositions well passively in certain senses. One is that you have dust on most of the rocks on Mars, and many of the passive remote-sensing techniques are sensitive to the dust and sometimes cannot see beyond the dust to the rock that’s underneath. In addition, there may be weathering coatings and so on.
So what we proposed was to use this laser system that basically can fire a high-energy but very brief pulse to these rocks, up to about 25 feet from the rover, and form a plasma with the ablated material. And then we look at that plasma, which is actually a bright flash, and we can determine the composition from the atomic emission spectrum from that. And we can fire multiple laser pulses, enough so that we could actually shoot down about to a millimeter into the sample if we need to, to really verify that there’s no real coatings on the rocks. Or if it’s dust, we can actually clear away more than a millimeter of dust, quite a bit more. And so this provides a window into what is around the rover compositionally. We can do this rapidly, so we get a large number of analyses compared with most of the other instruments that are on the arm or actually are inside the rover.
Steven Cherry: Tell us a little bit more about how ChemCam actually works.
Roger Wiens: So ChemCam uses this high-power laser, and I think a lot of people wonder how a high-power laser can actually operate on a spacecraft, which is generally low power. And so what happens is we have this laser beam that actually produces what I like to say is the energy of a million lightbulbs, and it projects it onto the size of a pinhead on a surface on Mars.
But the reason it works is because it does this for only a couple of billionths of a second. So if you take all those zeros in a billionth of a second and multiply them by the zeros in these megawatts, it comes out that it’s only using a few watts, and so we can do it because of that very short time duration of this laser pulse. But it does make a nice little flash on the surface of Mars. Not as big as some of the media try to make it, but it’s a very interesting little technique.
Steven Cherry: And then you’re just analyzing the light that it throws off?
Roger Wiens: Yes. And then we analyze this little flash that it puts out, and so we take and look at the color spectrum of that light. And if we break those colors down, visibly we can actually see different colors for different rocks, but with our instrument we can see different, what we call “emission lines” from different elements. And so that tells us whether there’s more silicon, more magnesium, more aluminum, and so on, in these rocks. And that’s what we’re after—to really understand the composition of the rocks.
Steven Cherry: So in all you’ve shot your laser at about 1000 different locations so far, an average of 40 shots per location. What else have we learned so far?
Roger Wiens: So the initial part of the rover traverse, we were seeing compositions on these rocks that were just strewn across the area, also on pebbles and some conglomerate outcrops that suggest that there was ancient riverbeds there. And all of these had a rather unusual composition relative to previous igneous rocks on Mars in that they tend to have higher silicon compositions and more alkali, that is, more sodium and potassium. And we’re even seeing things like rubidium, which is a heavy alkali element.
This suggests that we have much more feldspars on Mars. And along with that, we saw images that showed large mineral grains, like centimeters or almost inches in size. And that’s the first time we’ve ever seen these large mineral grains on Mars, and it’s the first time we saw that type of feldspar-rich composition. So that is clearly different, and it might suggest that we have greater diversity in the volcanism on Mars than we previously thought. So it’s really been very interesting for those who study kind of the magmas and the planetary compositions from those standpoints. This was supposed to be a mostly sedimentary geology mission, to study sedimentary geology in this crater, and it’s gotten the igneous geologists very interested, so that’s been exciting.
Then beyond ChemCam, we’ve also seen that the first rocks that were sampled by CheMin, a mineralogy instrument, show that these rocks do indeed have clay minerals in them. And so we know that the rocks where the rover is at now were laid down in a water environment. And the thing about that is that the water environment they were laid down in had a normal pH; it wasn’t too acidic or otherwise. And so that’s really conducive, potentially, to life. And so this has been hailed as a real discovery of a habitable environment here.
Steven Cherry: Curiosity is running on its backup computer right now. That’s actually something that came up in one of the rehearsal exercises. Is there a feeling of déjà vu when a rehearsed glitch happens in real life?
Roger Wiens: Oh, I would have to say our minds tell us that a rehearsal is just that—it’s a rehearsal. So the real thing is much more real to us, I’d have to say, Steve. And so the rover went into a safe-mode entry about a month ago from now, which was in early March of 2013. And it’s been, I think, a little bit of a useful exercise for the engineers to understand some new things and pull out of it and get the rover back to its normal thinking self, I guess you could say. So we think everything is good, and we’re all excited for the next few months.
Steven Cherry: Looking at the big picture, I’m not sure our listeners know of the stiff competition between all the various proposed project themes and schemes just to get on a mission. I certainly didn’t know about it before your book. Maybe you can just give a sense of how stiff the competition is.
Roger Wiens: Oh, this is basically almost a thing to die for, I guess you could say. And so I just never thought in my wildest dreams that I would get here. And as things were proceeding with our development of this laser instrument, first of all, if one is fortunate enough and has a good organization behind you, you can get accepted to get some development money from NASA to look into a new instrument concept.
And so we had had that for about five, six, maybe, I guess, running onto seven years, when we were actually selected by NASA for going onto the Curiosity rover. But we had been running along on fumes. We had been without funding several of those years. And then this opportunity came along to write the proposal for Curiosity. We had already been in several unsuccessful proposal attempts. And so there were many ups and downs along the way, but I think when we finally submitted our proposal, we were one of 49 proposals. And I think about seven or eight of those were actually selected; there were a couple of instruments that were preselected from other countries by NASA. So the success rate out of those 49 proposals was very low.
Steven Cherry: And then, even after acceptance, there’s always the threat of de-scoping, which momentarily happened to your project as well.
Roger Wiens: Yeah, that’s right. And so as the rover project got into a little bit of financial challenging times, we were picked on at that point. And we actually made it through, but it was a very harrowing time.
Steven Cherry: Roger, one thing that struck me about the book is the seamless transitions from science to engineering and back again. Your own interest in space started with building model rockets with your older brother. Your Ph.D. makes you a scientist, but it seems your engineering streak goes back all the way to your childhood.
Roger Wiens: Yeah, Steve. I would say that for many people, the ability to do both engineering and science is really key. And so I started on a mission called “Genesis,” in terms of my NASA involvement in missions. And so I was working with someone who was, you might describe as, more of a pure scientist. He was really involved in the science but really had not dealt with engineering drawings as much, and so on.
And so working with him, I was able to bridge the gap and really talk about now, when an engineer sends this drawing, it’s going to really look like this, and that looks really big or this is small, and so on. And so those kinds of things are really helpful. I would absolutely encourage any scientist to work with some engineering skills if they can, and likewise engineers with science skills. I just think it’s very fertile to be able to see both sides of the coin.
Steven Cherry: Speaking of your childhood as well, it seems there was something special about Mars for you even as a boy. What was it?
Roger Wiens: So when I was young, around 10 and so on, it was the time of the Apollo missions, and so, of course, we were extremely interested in those. But also in 1971, this will date me a little bit, but NASA was sending the first mission to orbit Mars, and it was Mariner 9. And, of course, the only times that we really send a mission to Mars is when the earth passes Mars. That happens about every 2⅓ years, and so this time was a good opportunity. What it means, though, is that Mars is coming close to the earth, and you’re going to be able to see it well with a telescope as well.
And so my brother and I figured this out. I should say my brother, Doug, who’s now a chair of the geology department at Washington University now, he was more knowledgeable and two years older than I. And so he suggested that we build a bigger telescope on our own. And we actually built, instead of a tube, we used a board of plywood, but we got a reflecting mirror that was a nice big, wide 6 inches, and got some eyepieces and put the whole thing together and were able to kind of carry it outside on our shoulders and put it on a fence post. And we got to see great views of Mars, and we could see the polar caps changing, we could see other features on Mars, and it was just really exciting. And it was just shortly before this Mariner 9 got into orbit around Mars. It was kind of an exciting time for us.
Steven Cherry: Roger, your book is part memoir, so maybe I can ask another personal question. You have an article online that was published by The American Scientific Affiliation called “Radiometric Dating: A Christian Perspective.” It gives the scientific basis for our current methods of dating rocks and, hence, the age of the earth too. People who, for religious reasons, have been skeptical of the great age of the earth. Astronomy and geology were the first battlegrounds of the historic conflict between science and Christianity. Is it a source of frustration to you that they still are?
Roger Wiens: Well, yeah. I think that there really needs to be more emphasis on understanding within the religious community. And if one takes a step back and thinks about what was happening in Galileo’s time, the Jesuits at that time would actually refuse, it’s recorded that they refused to look through the telescope because they thought it was a thing that was bewitching people that looked through them, and where Galileo was showing the moons of Jupiter and the phases of Venus. And so I think we have almost a similar thing going on today, where people are refusing to look into geology journals, which are published, you know, in which radiometric dates are published by the thousands each year. And so people just would prefer ignorance in some cases, and that’s unfortunate.
Steven Cherry: Do you picture humans ever landing on Mars, and given the expense and the risk, do you think it’s worth doing?
Roger Wiens: So the technical problem with getting humans to Mars is getting them back, of course. And so it’s been proposed to send them on a one-way trip. I don’t like that thought. I’m afraid it will happen one day. Now if you want to do a NASA-style mission, which would certainly bring humans back, you would have to have a fairly good-sized rocket on the planet to get people back. And who’s going to build that rocket or bring it there, and that’s the question. So there’s got to be quite a lot of work in order to really facilitate that at some point in the future.
And so what we’ve talked about in the interim is actually bringing back a small sample, something that’s less than 5 pounds of rocks, from Mars. That would be a pathfinder of sorts to eventually bringing humans back, but with a much, much smaller rocket to get things off the surface of Mars. Human exploration is, of course, fascinating, and it’s going to always capture imagination. I think that whether we are more excited about human exploration now or more excited about robotic exploration, that in the future I think we all do envision that humans will live somewhere else, and it will most likely be Mars. So the question is when, and would it be thousands of years from now? We don’t know, so that’s a big question. I think it’s great to imagine and to think about.
Steven Cherry: Very good. Well, thanks, Roger, for your work and for your terrific book, and thanks for joining us today.
Roger Wiens: My pleasure.
For IEEE Spectrum’s “Techwise Conversations,” I’m Steven Cherry.
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