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IRA FLATOW, host:

And continuing to talk about beautiful pictures, maybe some of these pictures will show up from NASA in Braille edition or in "Invisible Sky" or some other way for people to see in all different forms.

These are pictures coming up - from a probe that swung by the planet Mercury, snapping photos of its surface. And these are the first close up photos of the planet since the visits by Mariner missions in the mid-1970s. We're talking 30 years between visits to Mercury, and scientists are able to get the images of parts of the planet, you know, that they never really have seen before because when the last visits occurred, these parts of the planet were in shadow, and so, we could not take pictures of them.

So this Messenger spacecraft will be making several more passes by the planet before it settles into orbit about three years from now. It goes out and around back and forth around the Solar System until it settles into an orbit around Mercury in about three years.

And joining me now to talk more about the mission is a scientist who is studying those photos coming back. He is professor in the Department of Geological Sciences at Brown University in Providence. But this week, he's camped out at Johns Hopkins Applied Physics Laboratory watching the first images coming in.

Welcome to SCIENCE FRIDAY.

Professor JAMES HEAD (Geological Sciences, Brown University): Thanks very much. We're really excited that we're seeing some really amazing things. It's been a long time in coming, but we're totally excited and everybody is looking at the monitor, looking at the images.

FLATOW: Mm-hmm.

Prof. HEAD: And it's - seeing a lot of really exciting things.

FLATOW: Mm-hmm. James Head is a professor sitting out there. Are you seeing things that you did not expect?

Prof. HEAD: Absolutely. You know, Mercury being the closest planet to the sun is very unusual in many ways. It has a magnetic field. It's extremely dense, almost as dense as the Earth, which means since it's so much smaller it's made up of a lot of iron in the interior. It probably has, potentially, a liquid core. There are lots of really unusual things about it that we don't understand at all. And the surface, in some ways, looks like the moon, but many other ways, it's very, very different. It's some combination of things we see on the Earth, things we see on the moon.

And because Mariner 10 was unable to image more than, actually, less than half of the surface, we didn't know what was going to be on the rest of the planetary body. And we've seen a significant part of that from this flyby, and it's very exciting.

FLATOW: Mm-hmm. Talking with James Head about the Messenger mission to Mercury this hour on TALK OF THE NATION: SCIENCE FRIDAY from NPR News. I'm Ira Flatow.

Our number is 1-800-989-8255, 1-800-989-TALK if you'd like to talk about Mercury.

Why do we care so much about Mercury? You know, a lot of us think it's a hot, rocky planet that's getting burnt up by the sun.

Prof. HEAD: Well, it's interesting. Understanding Mercury is really fundamental to understanding the rest of the planets, the Earth-like planets, and even the Earth itself. We really don't have a good record on the Earth of the earliest part of Solar System history. Because it's such a dynamic planet, it's been completely destroyed and resurfaced.

And yet, places like Mercury provide us with detail clues about what was going on in that time period. Like these huge impact basins that we see on the surface of Mercury that now we've seen the other half of. We saw the first half in the Mariner 10, and we were able to see the complete basin, gives us an idea that huge impacts were forming in the early history of the Earth.

So it really does, not only fill us in on all the rest of the family members, but really gives us insight, more or less into our childhood, if you will.

FLATOW: Mm-hmm. And what is unusual about Mercury from - comparing it to the rest of the planets in the Solar System?

Prof. HEAD: Well, you know, in some ways, it looks like the moon. It has a lot of impact craters and the surfaces often heavily cratered, but it has these huge tectonic mountain ranges that are called scarps. They - they're up to a couple of miles high, they're very unusual, they go all the way across the planet. And we've not seen anything quite like this on the Earth, on the moon, on Mars, or even Venus.

And what we're looking at here is something that's very ancient that represents the crushing together of the crust. And it may be in fact, that this is the kind of thing that represents how plate tectonics started on the Earth. We have a very dynamic system on the Earth, but we don't know how it started.

So looking at these ancient, huge scarp features may provide real clues as to how the pushing together of the crustal material can ultimately result in the kind of tectonic regime we see today, which is something we just don't know the origin of on the Earth.

FLATOW: Do we think that Mercury may have formed like our moon did from breaking off some other part of some planet, some rocky surface, or did it just aggregate space debris leftover from the formation of the Solar System?

Prof. HEAD: Well, there's a lot of debate about that. And that's one of the key things that we're going to be able to try to address here. One of the ideas is that it might be more like the Earth in the sense that, to explain its very high density, one possibility is that something hit it and then the ejector from that essentially ended up going into the sun because the sun is so close by.

So maybe a similar kind of event to the impact process that hit the Earth and then ejected material to form the moon may have occurred on Mercury making it so dense. So, the idea is maybe similar kinds of things are going on there, and that's one of the jobs of the Messenger mission is, to try to look at the geology, this internal structure, and to decide, and as we go into orbit later on, as to which of those possibilities is correct.

FLATOW: Mm-hmm. Oh, we're going to take a short break. Stay with us, Dr. Head.

Prof. HEAD: Absolutely.

FLATOW: James Head, professor in the Department of Geological Sciences at Brown University and camped out there at the Johns Hopkins Applied Physics Laboratory.

If you'd like to talk about Mercury and the mission, our number, 1-800-989-8255. Also, if you're in Second - join us our - in Second Life, you can ask questions with your avatar, or you can go to Second Life and search for SCIENCE FRIDAY, or go to our Web site at sciencefriday.com and click on the Second Life SLurl there, that will take you right to a site in Second Life where the avatars are having T-shirts and getting free coffee mugs today. So, get one for your avatar. We'll be right back after this break.

I'm Ira Flatow. This is TALK OF THE NATION: SCIENCE FRIDAY from NPR News.

(Soundbite of music)

FLATOW: You're listening to TALK OF THE NATION: SCIENCE FRIDAY. I'm Ira Flatow.

We're talking this hour about the Messenger spacecraft mission to Mercury and the nice, cute pictures that are sent back. If you want to see some of them you can go to our Web site at sciencefriday.com and we'll send you to the NASA site where you can see more of the pictures.

Talking with James Head, tell us how, you know, this is a mission that's going take six years for the actual insertion into orbit around Mercury of the spacecraft. Why so long to get there?

Prof. HEAD: That's really a good point. We end up having a great difficulty getting to Mercury because the sun tends to pull the spacecraft very fast towards itself. So, it accelerates the spacecraft, if you will. And the trouble is, if you want it to stop just short of the sun at Mercury, you have to take a huge amount of fuel with you, which is literally impossible.

So, what you have to do is to find a way to wind your way through the Solar System so that you end up very close to the velocity of Mercury and then you can take the fuel you have on board and do a space grav(ph) burn that puts you into orbit. This is very, very hard to do that's why it takes so long to get there.

But I have to say that the engineers, the men and women here at APL, at the Applied Physics Lab, are just fantastic. We - they came within a couple of kilometers of the aim point on Mercury. And you know, we were thinking last night as we were wandering around trying to find a place to eat, we were like, we missed it by about four kilometers where we were supposed to go eat.

And I mean, we're thinking, these people actually got to a point on Mercury, above Mercury, better than we can do here wandering around in Laurel, Maryland, so it's really phenomenal. These people are so dedicated and just amazing in their ability to help us scientists to accomplish our goals and objectives from a scientific standpoint. So, this is one of the exciting parts about it, the scientific and engineering synergism that takes place in these kinds of missions.

FLATOW: That's why they call it rocket science…

(Soundbite of laughter)

FLATOW: …when it's really tough to do. That is amazing. You get to four kilometers. And how many billions of miles of travel?

Prof. HEAD: You know, we're hundreds of millions of miles away.

FLATOW: Yeah.

Prof. HEAD: And you can actually go to the counter on the Web site and you can just see them clicking off like crazy. And of course, by the time we get to Mercury ultimately, we have two more flybys, in October of this year and September of 2009. And then, we undergo what they call orbit insertion into orbit in March 2011 for at least a year of detail investigation of the surface.

So, you know, as far as frequent flyer miles go, I wish I had a credit card that counted these.

FLATOW: Yeah. That's what I meant. Eventually, you get to go way out into the Solar System and then back again. And you flew by Venus once already, correct?

Prof. HEAD: That's correct. Actually, we've been by Venus twice. We went by Earth first. We went out and then back by Earth. And all the things are designed to not use fuel, to do sort of gravity assist, they're called, to reorient the spacecraft to speed it up or slow it down so that ultimately, it can go into orbit around Mercury.

And one of the exciting things we had happen, of course, was that we had a great successful encounter on Monday, a flyby, we got all the data, we could see from the sensors that it was all on the spacecraft ready to be played back. And then, all of a sudden, a spacecraft that was studying the sun declared an emergency, which meant that it had priority for all the antennas that bring the data back, and we had to sit there and sweat bullets while we're waiting for that emergency to be cleared up so the data we knew had been obtained could actually come back down to Earth and so that we could see it.

So, that happened pretty quickly. But again, the engineers that work for NASA and the Johns Hopkins University Applied Physics Lab, you know, we have great confidence in them. And sure enough, they all came through. And we have all the data, over a thousand pictures.

FLATOW: That's great. They also serve those who stand and wait.

Prof. HEAD: Exactly.

FLATOW: Let's go to the phones to Chip(ph) in Little Rock, Arizona. Hi, Chip.

CHIP (Caller): Arkansas.

FLATOW: It's Arkansas.

CHIP: James, I'm so proud of you guys. Man, this is an outrageous accomplishment. And again, to further what you said, kudos to the engineers involved there. The calculations on this were so intricate. And to come within two kilometers is just an amazing feat.

Very quickly, I'd like to know something more on what we know about the temperature of Mercury, and does it not revolve as the moon does and keeps one face toward the sun?

And also, there was a blurb on the pictures that I saw yesterday that said that there may be a chance of ice caps on Mercury. I found that outrageous. Is that accurate?

Prof. HEAD: It's absolutely - first of all, thank you very much for your support because it's your tax dollars at work and we're hoping…

CHIP: You bet. I'm proud of you.

Prof. HEAD: …we spend them well. Mercury is extremely hot because it's so close to the sun. It does not have one face completely towards the sun all the time. It has a very intricate relationship that brings all the surface into contact with the sun eventually.

But the key is that the polar regions at the top and the bottom of the planet, if you will, if you have a hole, a crater there, those don't get illuminated by the sun, and that's why we see these unusual features that have been interpreted potentially to be ice. If you can imagine, a comet hitting the surface, and ice from that comet going to a cold trap, like going to the local refrigerator…

CHIP: Right.

Prof. HEAD: …and staying there. So, we hope to be able to sense that when we get into orbit and test to see, in fact, whether there's ice. But theoretically, it could be there and it will be incredibly exciting to have polar deposits of ice on a planet that is so close to the sun.

FLATOW: What are the…

CHIP: (Unintelligible)

FLATOW: Yeah. Are the poles tilted so that you have it like sometimes they're in the shadows, sometimes they're in the sun?

Prof. HEAD: No, they are - at least for the period of time, we understand the orbit, they have been permanently shattered, if you will. So it's pretty clear that if they get tilted towards the sun and the sun gets in there, that the ice wouldn't stand a chance given how close it is to the sun.

FLATOW: Yeah. Yeah, that's what I was asking. So, what kind of temperature extremes are we talking about right there? I imagine where the shadow just starts, you know, between the sun and the shadow, there must be an incredible temperature.

Prof. HEAD: Oh, there's - it's many, many hundreds of degrees and it's not the place you'd want to be standing any time of the day, believe me. It's basically hot enough to melt a lot of things like lead and other things like that in some cases. And, you know, the temperature extremes - I remember I worked in the Apollo program and the astronauts told me that when they were walking in front of the spacecraft and behind in the shadow, they could actually feel the temperature difference between their spacesuits. I hate to say what kind of things they would feel if they were walking with the Terminator(ph) on Mercury because it wouldn't be very comfortable at all.

FLATOW: Hmm. Corrine(ph) in Fargo(ph), welcome to SCIENCE FRIDAY.

CORRINE (Caller): Hi, Ira. Thank you so much for taking my call.

FLATOW: You're welcome.

CORRINE: I was actually wondering. Earlier, you guys were talking about the impact craters that were on Mercury and the moon. I was wondering if there was a theory behind this at all, if you guys know where it came from exactly or how they came about.

Prof. HEAD: Sure. There's lots of things that cause craters. So, largely, like comets and, you know, things like meteorites, that are in orbit around the sun. And what we understand is that in the early days of the history of the Solar System, there was a lot of that material as the solar - as the sun was forming and the material was forming around it, so all that collected together to form essentially the planets. But there's a lot of material left over, and so the bombardment of the planets continued for quite some time.

So, we know, from looking at Mercury and the moon, we couldn't tell this from the Earth, but looking at Mercury and the moon, for example, that the rate of bombardment was very high early on, you can almost think of it as the planets vacuuming up all the rest of the debris. And then there's places like the asteroid belt, where there's still a lot of debris out there. And some of that comes in and out of the inner Solar System continuing to hit the planetary surfaces. So this is where the material comes from. And we were able to actually use this information to try to date some of the surfaces on these planets.

CORRINE: Perfect. Thank you.

FLATOW: Thanks for calling. 1-800-989-8255. Let's talk about Mercury's magnetic field. And you're studying, you're looking for that, characterizing it. What is so important about knowing about that?

Prof. HEAD: Well, the magnetic field tells you a lot about the internal structure. It also tells you a lot about the way in which the planet interacts with the sun and the material essentially coming from the sun. So, for us, as geoscientists, we're really interested in whether the interior, like the core, is actually convecting or not. If it's liquid, if it's convecting, if it's moving around, circulating or whether it's frozen solid, if you will, because that tells us a lot about how the planet is losing its heat. It tells us a lot about heat gets transferred, how heat gets transferred from the interior to the surface and how all the geology should work. So, we'd look at the geology to try to interpret the interior. And measurements of the magnetic field can tell us whether things like, on the Earth, whether things are actually moving in the inside. It can also tell us a lot about, you know, how particles are interacting with the surface. If you have a strong magnetic field, for example, it affects the particles in the surrounding region from the sun. All of these things go together to really getting an understanding of the personality of the planet and its environment.

FLATOW: Let's go to Ed(ph) in Grand Rapids. Hi, Ed.

ED (Caller): Yeah, hey. Good afternoon. And I echo that first caller, a job very well done, tax dollars are well-spent. If it's true that the sun is expanding, is it possible that at one time that that actually could have had an atmosphere and then as it expanded, then - or Venus did then Earth and then maybe Mars next?

Prof. HEAD: Well, I'm not an expert on the evolution of the sun. I think, for the most part, the sun has been relatively stable since the formation of the planets, in that sense. But, you know, if you take a look at the long-term sort of billions of year evolution, the sun will obviously go through some phases when, in fact, the sun will expand out to the position of the planets. And if you think Mercury was hot now then you don't want to be around then either there or Venus or the Earth. But that's billions of years in the future, so don't sell any real estate yet.

ED: Okay. Thank you for the call(ph).

FLATOW: Thanks for calling. 1-800-989-8255 is our number. It's quite interesting that, you know, there is so much of this interest in our Solar System. We really don't know that much, I guess, right? Just trying to figure out. We have sort of two different kinds of planets. We have the inner planets, they're kind of rocky all the way out to Mars, then we have the gassy planets outside.

Prof. HEAD: It's really amazing I think, too, because, you know, we just celebrated the 50th anniversary of Sputnik. And, you know, I remember Sputnik, I was in high school at the time. And it's just stunning to me to think about what we've learned about the Solar System. And again, you know, we know so little about the early history of the Earth. It's really our formative years and it's sort of like if you wanted to understand another person, you would want to know their childhood, what that was like, what the traumatic experiences were, what their, you know, parents were like, et cetera.

And this is exactly why studying the planets is so informative about our own home planet. Because, in fact, we can see the geological records. We can see these traumas, these huge basins that surely formed on the Earth but we have no record of them. We can infer why we are today, where we are today and more about where we're going in the future.

FLATOW: Mike(ph) in Cleveland, welcome to SCIENCE FRIDAY.

MIKE (Caller): Thank you. Thank you. This is maybe an elementary question I don't understand but if the - since Mercury is still close to the sun, since the temperatures there are so extreme, did you have to - how did you account for that when you designed the actual spacecraft to keep the thing from cooking when it got there? You know, I'm just going to listen to the answer off the air. Thank you very much.

FLATOW: Okay. Thanks, Mike.

Prof. HEAD: You're absolutely right, Mike. It's an incredibly difficult mission. That's the second major reason why it's so hard to study Mercury is because of the, basically, the heat from the sun. And the, again, the brilliant engineers who worked on the spacecraft designed a sunshade. If you can imagine having an umbrella, you know, that would withstand the solar energy and heat, so we actually point the sunshade - actually, they point the sunshade at the sun and then they worked the spacecraft around so that we can get all our data without being cooked.

So it's like a huge umbrella - it's not actually huge, it's like an umbrella that would protect you from the sun, the intense solar radiation and heat. And again, if that thing fails or we rotate the spacecraft in a manner, you know, it's basically over in a very short period of time. But again, that's just testimony to the really great engineers that are in charge of this program.

FLATOW: Now when the - let me just remind everybody that this is TALK OF THE NATION: SCIENCE FRIDAY from NPR News. I'm Ira Flatow, talking about the Mercury, the Messenger Mercury mission with James Head.

When you go into orbit, eventually, when the Messenger goes into orbit, will it map the whole planet?

Prof. HEAD: Yes, it'll essentially map the whole planet. It will re-map things that we've seen before. But that's great because we'll get to see them from a different perspective. You know, each time you look at a different lighting angle, et cetera, you discover huge new things. And so we'll be able to map the whole planet and we'll be using a whole bunch of different images - different instruments.

We have an imaging system, a gamma rays spectrometer, a neutron spectrometer, X-rays, magnetometers, a laser altimeter that will get topography for us. It was very - a distinct instrument that will get surface mineralogy. And so we have a whole host of instruments that will be brought to bear on the planet to get global coverage, which will then really unravel all the rest of the secrets of Mercury.

FLATOW: You know, I'm thinking of the orbiting around the planet. I'm thinking you going from day to night, to day to night, the temperature extremes for the spacecraft and it must be unbelievable.

Prof. HEAD: It is. It is. But it's high enough so that actually, you're not in the shadow very much for the most part. But again, the whole thermal balance, the temperature balance that has to be maintained is a real challenge for the engineers. And I should say that the people - I'm very pleased that there's so much excitement about this mission because there's certainly is - here and among the students at Brown University and so on. But, you know, this was something NASA started a number of years ago called the Discovery Program.

And Wes Huntress started this as the associate administrator. And it's basically ask people from outside to propose missions to NASA and help lead them. And Sean Solomon, the director of the Department of Terrestrial Magnetism at the Carnegie Institution of Washington, proposed a team with APL and a number of scientists. And this is an amazing low-cost mission that's getting all of this done. And it's really a great way of doing business. And Sean and the team here have just been super.

FLATOW: But we keep hearing scientists talking about the robotic missions, such as yours, now facing possible cutbacks because of the idea of going - the man space missions might eat up so much money to go to the moon and Mars.

Prof. HEAD: Well, that's always a question, you know. As I mentioned, my first job was working on the Apollo program and astronaut training and site selection, mission operations and so on. And it's very clear, humans are excellent observers and they can do a significant amount on planetary exploration by just being there and really seeing things and collecting samples and so on. And certainly, if we go back to the moon and we will very soon, with humans, you know, we want to optimize their capabilities.

But at the same time, of course, you need to have balance. And I always look upon it as the partnership between human and robotic exploration. Obviously, humans aren't going to Mercury for quite a while. Does that mean we don't want to visit it? Absolutely not. So, we have to have a partnership and a balance between those. And I think that's - it's a constant struggle.

FLATOW: Yeah.

Prof. HEAD: But that's something that's really, really important. And again, even when humans go, they need robotic partnerships. They need to have rovers like they did on the Apollo missions. They need to have, you know, automated rovers and other spacecraft that can go out and do things that they can't, scouting and so on. So…

FLATOW: Let me see if I can get one more audio question in from Second Life.

Prof. HEAD: Absolutely.

ROB(ph): This is Rob Not Prospero Linden(ph) in Second Life. A few billion years from now, the sun's going to become much brighter, swell into a red giant and scorch the surface of the Earth. What we're looking at on Mercury right now, will that tell us anything about what it will be like on the Earth this time a few billion years from now?

Prof. HEAD: Wow. That's a really good question.

(Soundbite of laughter)

FLATOW: Good way, we only have 30 seconds to answer so you can…

Prof. HEAD: Oh, okay.

FLATOW: …cop out on this one.

Prof. HEAD: Somebody asked me - I don't know the answer to that. Somebody asked me will the Messenger spacecraft ever come back to the Earth, and the answer is when the sun goes through that phase and pushes it back to the Earth, but I don't think we're going to be here at that point.

FLATOW: You mean it can orbit back on its own for that many billions of years?

Prof. HEAD: Well, probably not.

(Soundbite of laughter)

Prof. HEAD: But anyway, it's - and again, that's an example…

FLATOW: Yeah.

Prof. HEAD: …of the kind of thing that we really want to look at to see if we can understand the future as well as the past. So, it's a great question.

FLATOW: Thank you, Dr. Head, for taking time to be with us.

Prof. HEAD: My pleasure.

FLATOW: James Head is professor of the Department - in the Department of Geological Sciences at Brown University in Providence. And, oh, we had a lot of fun talking with him about Mercury.

Surf over to our Web site, it's sciencefriday.com, if you missed any of the links we talked about, how to see the Mercury mission or anything else. There are links there. Also, we're blogging and podcasting. And if you go over to Second Life, there's some - avatars still hanging out, might want to talk to you, and you can now send us audio messages, audio questions from Second Life - first one today, hopefully more in the future.

I'm Ira Flatow in New York.

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