Gravity Assist Podcast: Mars, with Bruce Jakosky and Michael Meyer
The Gravity Assist Podcast is hosted by NASA’s Director of Planetary Science, Jim Green, who each week talks to some of the greatest planetary scientists on the planet, giving a guided tour through the Solar System and beyond in the process. This week, he is joined by the “man about Mars,” Bruce Jakosky from the University of Colorado, who is the principal investigator of NASA’s MAVEN mission, and Michael Meyer, NASA’s lead Mars scientist.
Here’s a short teaser of part 1 for this podcast:
You can listen to the full podcast here, or read the transcript below.
Jim Green: MAVEN was launched in 2013 to study the atmosphere of the Red Planet and how it interacts with the solar wind. So, what have you found out?
Bruce Jakosky: We’ve been looking at the way that sunlight and the solar wind hits Mars’ upper atmosphere, driving gases from the atmosphere into space and stripping them from the planet. We’ve discovered that, over the long term, the solar wind has the ability to change Mars’ climate by removing a large fraction of the gas from the atmosphere. This stripping of the atmosphere appears to be responsible for changing the planet from a warm, wet environment early in its history to the cold, dry environment we see today. That’s a major change.
Jim Green: Can you describe how this atmospheric loss is taking place, from a global perspective?
Bruce Jakosky: We’re seeing a lot of different processes taking place and all adding up. Hydrogen, for example, comes from water in the atmosphere, and hydrogen, [because it’s] light enough, can just escape into space directly. Things like oxygen, which comes from water or from carbon dioxide in the atmosphere, are not light enough to just escape on their own. They need the solar wind to grab them and knock them out. So, we’re seeing a lot of different processes, trying to understand how they play together. To me, what makes this exciting is that we’re looking at the thin, tenuous part of the upper atmosphere – so thin that we would call that a vacuum if we were doing experiments here on Earth. Yet, that’s where all the action is in affecting the climate at the surface of Mars and the ability of water to flow over the surface, controlling the degree to which Mars could have been habitable to microbes.
Jim Green: Some of the processes at Mars are unique in the sense that we don’t experience them in and around Earth because of our strong magnetic field. What are you finding out about magnetic fields at Mars?
Bruce Jakosky: We have a magnetometer in order to measure the properties of the solar wind [at Mars], and also what I call the morphology of how the solar wind interacts with the planet. It turns out that there are regions of the crust that have a magnetic field. Mars doesn’t have a global magnetic field, but it has localized crustal magnetism, and those create little pockets of [magnetic] protection over the atmosphere where the solar wind can’t hit them [because the magnetic field deflects the solar wind particles]. But they cover a very small fraction of the surface and, overall, we’re seeing interactions between the solar wind and the ionosphere and the planet that have a significant effect.
Jim Green: Those bits of magnetic field are a remnant of Mars’ ancient global magnetic field, and what really intrigues me about that remnant magnetic field trapped in Mars’ crust is that what we are actually measuring is a hint of the past. What do you think happened to the magnetic field?
Bruce Jakosky: Well, you’ve got it exactly right. Mars appears to have had a strong global magnetic field early in its history and that magnetic field is recorded in the ancient crust. The younger crustal regions don’t have it, so we think the magnetic field disappeared. The magnetic field on Earth is formed by motions within the molten iron core. You have an electrically-conducting material like metal, and it’s moving, and it creates a magnetic field. Mars would have done the same thing early in its history, but when the magnetic field stopped, that must have indicated that the core froze and became solid. The Earth’s core is still molten and still generating a magnetic field that we [experience] today, but Mars has stopped.
Jim Green: Here on Earth, one of the things that everyone knows is that our magnetic field helps organize particles, and we occasionally see aurorae when the Sun gets really active and hammers our magnetosphere. So, there’s remnant magnetic fields on Mars, but does Mars have aurorae?
Bruce Jakosky: It does and, in many ways, it’s more interesting than what we see on Earth. Of course I’m going to say that, because on Mars we don’t have a magnetic field to stop the solar wind. The particles from the solar wind come in and can hit the atmosphere directly and we see aurorae generated by electrons that are hitting the atmosphere, and they’re spread out over the whole planet rather than concentrated in northern and southern latitudes as on the Earth. In addition, we see aurorae generated by hydrogen hitting the atmosphere, and occasionally we see aurorae created as these particles from the Sun hit the crustal remnant magnetic fields and are focused into small regions, and that’s the most analogous to aurorae on Earth because it’s connected to the magnetic field. But most of the aurorae on Mars aren’t connected to the magnetic field.
Jim Green: You know, one of the recent spectacular moments in planetary science was the passage of an Oort Cloud comet, C/2013 A1 (Siding Spring), by Mars in 2014. How did the comet affect Mars?
Bruce Jakosky: Well, let me start by telling you what we thought when we heard about Comet Siding Spring for the first time. It was discovered about a year and a half before MAVEN launched, and when it was initially discovered, they didn’t know the orbit well enough. There was a chance it could hit Mars. My first reaction was, “Oh, my God, if it hits Mars and we’re in orbit around it, the debris sent up by that impact would destroy our spacecraft.”
Fortunately, as they learned more about the orbit, they knew it would pass close but not hit it [Mars]. The orbital dynamics were such that MAVEN would get there a month before the comet and there was nothing we could do about it.
We were worried about surviving the comet passage because of all this dust that comes off the comet, and we debated whether we should put extra shielding on the spacecraft. In the end, we did the thing that the engineers were most comfortable with, which was nothing. We took no precautions on the spacecraft, but operationally, we did. When we were in orbit around Mars, we timed where we were in our orbit so that we were shielded by the planet for about 20 minutes during the time of the peak dust flux to protect the spacecraft. For several hours we turned edge on to the flow of dust in order to minimize our cross-section so that less dust would hit us, and we survived. We couldn’t even tell that there was a comet there from the [data from] spacecraft itself.
Jim Green: That must have been a spectacular event if you were standing on Mars, looking up at night, seeing the cometary material coming in like shooting stars.
Bruce Jakosky: We see on Earth meteor showers that are pretty spectacular, and they’re left over from comets. To have a comet pass so close to Mars, only 140,000 kilometers away, and to have the coma of dust and gas hit the planet directly, it would have been a spectacular event to see.
Jim Green: I was delighted that all our spacecraft [in orbit around Mars] survived. But there are other objects in orbit around Mars that, I understand, MAVEN had to avoid. Can you tell us a little bit about your encounter with one of the moons?
Bruce Jakosky: Well, let me start with the difficulty we have in orbit because there are a lot of spacecraft, and their orbits evolve with time. Every now and then, the orbit of MAVEN will cross the orbit of one of the other spacecraft. We call those “COLA” seasons, (short for Collision Avoidance).
Occasionally, maybe once or twice a year, we have to do a maneuver to make sure we don’t come too close to another spacecraft. But recently we had a collision opportunity –maybe that’s the wrong way to put it – but a possibility that we would collide with the moon Phobos, and in that case the orbit predictions were such that we were definitely going to hit it if we didn’t take action. We did a maneuver about five days in advance of that (predicted) collision in order to avoid it and we missed Phobos by about 200 kilometers. We have to constantly watch every day to make sure we’re not going to hit something.
Jim Green: That’s unbelievable. It’s getting crowded at Mars, so to speak, but in a nice way. This is the way I like it.
Bruce Jakosky: Well, today there are five or six spacecraft in orbit: MAVEN, the Mars Reconnaissance Orbiter, Mars Odyssey, the Indian MOM (Mars Orbiter Mission), the European Space Agency’s Mars Express and their recent addition, the Trace Gas Orbiter. These are the ones that are operating today. In addition, there are “dead” spacecraft – Mariner IX, Viking I, Viking II, the Russian Phobos Mission. All of these are in orbit and it’s getting pretty crowded there.
Jim Green: I’m always interested in how we get into this business. For everybody I talk to, there’s typically something that happens that gave them that “gravity assist” that propelled them into the science that they’re doing. What was that like for you?
Bruce Jakosky: I was always interested in space, and I remember being a six-year-old sitting in front of the TV watching the countdown of the first Mercury astronauts in the very early 1960s. But, for me, what really sent me on this path was when I was an undergraduate at UCLA. I was a physics major, and I got bored with the classes because all they were doing was teaching us tools and techniques. So, I started looking around for something else and I took a planetary science class from Hugh Kieffer, who was one of the professors there. By the end of the semester, I had changed my major. I was working for him on the Viking mission, and that really sent me on this path. So, it happened to be one class that happened to be offered when I was looking around for something else to take.
You can read the second part of the transcript here [link available tomorrow].