Planetary Radio: Space Exploration, Astronomy and Science - Astonishing Mercury, With MESSENGER Principal Investigator Sean Solomon

Episode Date: July 21, 2008

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Water on Mercury? That's the message from Messenger, this week on Planetary Radio. Hi everyone, welcome to Public Radio's travel show that takes you to the final frontier. I'm Matt Kaplan. To the Final Frontier, I'm Matt Kaplan. Messenger Principal Investigator Sean Solomon returns to our show on the heels, the winged heels, of some amazing announcements about our solar system's innermost planet. What in the world is water doing there? That's the question, all right. Out at the other end of the system is frozen Pluto,

and Bill Nye is thrilled about its new name or classification. We've got Emily Lakawala, too. Her Q&A will tell us about the importance and the future of the Mars Odyssey spacecraft. And way down the line, we'll be joined by Bruce Betts. He's up at NASA's Ames Research Center this week. But we still have a WALL-E video game to give away in the What's Up Space Trivia Contest. Wow, here's reason to celebrate. The door to one of those little ovens on the Mars Phoenix lander has opened up just like it should, which is to say, all the way. Emily has the story and a picture

in her blog at planetary.org, where you'll find other news from beyond our pale blue dot. I'll be right back with Sean Solomon. Here's Bill. Hey, hey, Bill Nye, the planetary guy here, vice president of Planetary Society. You know, I am so very excited. Pluto, as you know, for the last couple of years, has been considered not to be a planet. Instead, the International Astronomical Union, the IAU, refers to it as a dwarf planet. Now, my friends, I won't say this is crazy or silly or thoughtless, but you can't say something's not a planet and then use the word planet to describe it. Dwarf planet is a dwarf human, not a human. What? What?

Well, get this. They picked a name, Pluto, the icy body beyond the orbit of Neptune that has enough gravity to be a sphere, to have hydrostatic equilibrium. That body is now called a plutoid. It is the first of the plutoids. And these would be Kuiper belt objects, KBOs, way out there that are icy and spherical, that we feel aren't really worthy of being a planet because they don't have enough gravity to sweep out the matter in their orbits. And so instead of being, oh, just another object, instead of being a diminutive planet, no, Pluto is now the first, the archetypical, the iconic Plutoid. You know, if you've been scoring along with us, I have done many, many lectures where I propose that these things be called

Plutonian planets. Plutonian, having the characteristics of or pertaining to Pluto. We say, what's in a name? And you'd be right to say, really not much. If there's anybody on Pluto or any Plutoidians, they probably aren't the slightest bit concerned what the earthlings call them. But you remember the uproar, the hubbub, the hullabaloo when people thought Pluto wasn't going to be a planet anymore. And it's many. If you're a kid, it's your favorite one. Well, heck, we're back and we're better. We are Plutoids. I say we, I mean, it's them. Well, way to go, Pluto. You are a Plutoid. Well, this is Bill Nye, the Planetary Guy. Keep listening to Planetary Radio. MESSENGER PRINCIPAL INVESTIGATOR SEAN SOLOMON MESSENGER PRINCIPAL INVESTIGATOR SEAN SOLOMON

has very good reason to be happy with his mission to Mercury. Last January, the spacecraft made the first of its three flybys of the planet that is nearest our sun. It passed just 200 kilometers above the surface. The data and findings from that brief visit have astonished planetary scientists, opened up at least one new mystery, and solved others. The Mercury's surface, space environment, geochemistry, and ranging probe will go into orbit in March of 2011.

I caught Sean not at his Carnegie Institution office or the Johns Hopkins Applied Physics lab, but in the middle of a family vacation. That's why the telephone audio quality could be better. Sean, I will bet you it's been a very long time since the journal Science had 11 papers about Mercury in a single issue. Indeed it has, Matt. The last time that the journal Science had a large set of papers, and I can't remember the number, was after each of the Mariner 10 flybys of Mercury. And those were in 1974 twice and in 1975 once. So nearly 33 years later,

a second spacecraft, Messenger, has finally revisited Mercury with three decades of rather, of advanced technology that's gone into a completely different instrument suite. And so just with another flyby en route to ultimately orbiting the planet, we were able to learn a lot of new things about Mercury. And you've already revealed a good piece of this planet that human eyes had never seen up close before. That's right.

Mariner 10 saw less than half the planet because the same face of the planet was in sunlight at each flyby. And we saw 20% of the area of Mercury during our flyby in January that had never been seen by spacecraft. And when we fly by the second time, less than three months from now, on 6 October, we'll be seeing another 30% of the planet for the first time by spacecraft. Well, let's get into at least some of these results before we run out of time, because there's a lot to talk about. And as you might expect, we got to start with the water.

Happy to do that. We carried a sensor provided by the University of Michigan called the Fast Imaging Plasma Spectrometer that made the first measurements as we flew near the University of Michigan called the Fast Imaging Plasma Spectrometer that made the first measurements as we flew near the planet of the ions that are surrounding Mercury that are generated either at the surface or in Mercury's neutral atmosphere by ultraviolet radiation and by charge transfer from the solar wind. But these species come, except for the very lightest elements that are derived from the solar wind, like hydrogen and helium, they come from the planet. They come from the planet's surface.

So we saw species that we expected on the basis of what we knew to be in the atmosphere, like sodium and calcium, probably potassium. All of those have been detected from Earth-based telescopes in the neutral atmosphere. We saw species that were not surprising because we know they're on the surface like silicon. We saw ionized silicon in the magnetosphere of Mercury. But the biggest surprise, and you alluded to it, is that we saw ionized bits of pieces of water molecules, what are called water group molecules, that must have been derived from water at the surface of Mercury. And the mystery is, how did that water get there?

And there are several ideas right now that are going to take more observations to sort out. One is that the water is continually delivered to the surface by small comets and meteoroids from far beyond the orbit of Mercury in the solar system, the main belt asteroids and beyond. Another is that there may be reactions going on between the energized particles from the solar wind and the material at Mercury's surface. And, of course, the third and most intriguing idea goes back to the discovery in 1991 from Earth-based radar that at the poles of Mercury are radar bright deposits trapped in the floors of very high-latitude impact craters,

the floors that are so deep that they must be in permanent shadow and therefore are cold enough to retain as ices, water other volatile species for millions or maybe even billions of years. And so did we see water from those polar deposits? That's an open question right now, but it's one that has us very intrigued. Do these results, and especially that possibility of water or ice in these shaded parts of these craters. Does that affect your plans for the next flybys and especially for when MESSENGER goes into orbit? Well, one of the objectives of the MESSENGER mission all along has been to turn a lot of the instruments that we're carrying toward those polar craters. We're in a nearly polar orbit. It's an 80-degree, not 90-degree inclination,

and so we'll be able to look with geochemical remote sensing, with altimetry at the floors of these craters. We won't be able to image the floors because they're permanently dark, but we'll also be able to look at the polar atmosphere to see if there are inhibitions of molecules and atoms that might be signature of what those volatiles are. But just the first flyby results have led us to improve the observing capability of the plasma spectrometer that made these observations. So we're going to have better resolution in angular position, better sensitivity to all of the species that have been detected by this spectrometer on the first flyby.

So we're very much utilizing the first flyby results to expand the operational plans using this instrument for the next flyby. Much more in a minute from Messenger PI Sean Solomon about the probe's first Mercury flyby. This is Planetary Radio. I'm Sally Ride. After becoming the first American woman in space, I dedicated myself to supporting space exploration and the education and inspiration of our youth. That's why I formed Sally Ride Science,

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Welcome back to Planetary Radio. I'm Matt Kaplan. Messenger Principal Investigator Sean Solomon just told us about the surprising discovery of water in the very thin atmosphere, or exosphere, of hot little Mercury. That story has gotten most of the press since it was published in the journal Science a couple of weeks ago. But there were 11 papers in that issue, and the other data gathered in a January flyby has revealed much more about a planet

we had not seen up close and personal in 33 years. Well, we better move on, and I will say, though, anybody who wants to read more about this in detail can certainly go to the Messenger website, which we will put up a link to, of course. But we also have a terrific article from July 3rd by my colleague Emily Lakdawalla that summarizes all of this and does her typically terrific job doing it. She talks also about this question of volcanoes versus meteors, having had a big hand in shaping the surface of Mercury. I remember from when I was a kid, this was a big question about our moon. But I guess the answer has worked out a little bit differently on Mercury. We sent spacecraft to the lunar surface with humans, in the case of NASA,

and robotically, in the case of the Soviet Union, and returned samples from the moon, proving definitively that the seas, the maria of the moon, are volcanic, and those rocks are volcanic. But the Apollo program also taught us that some of the smooth areas in the highlands of the moon are not volcanic. Apollo 16 went to one of these plains, the Cayley Plains. Before that mission, those plains had been thought by many to be volcanic, but in fact they were the products of large impacts that laid down ejecta that were so hot

that the material froze in place, much like a lava flow, and produced the planes that look much like frozen lava flows, except on the moon these are lighter rocks, as light as the rest of the highlands, and unlike the dark maria. When Mariner 10 flew by Mercury and saw planes, the dark maria. When Mariner 10 flew by Mercury and saw planes, the planes of Mercury are not darker than the cratered terrain that surrounds them. And so remembering what Apollo 16 found from the moon, the planetary geology community started a debate that went on for more than 30 years. Are the planes of Mercury the product of volcanism, or are they, like the Cayley planes in the Lunar Highlands, the product of large impacts? And that debate was one of the issues we hoped to resolve with MESSENGER's images, and that has been settled. high-resolution imaging system with sufficient color information compared to that of Mariner 10

that we were able to image features that are dead ringers for volcanic centers on the moon, areas that have deposits that have built up over preexisting terrain that appear to emanate from a center of a modest domical dome-shaped area, the center of which is a very irregular depression that looks like the center of a volcanic eruptive vent. These have been well-documented on the moon. They produce the lunar glasses, some of which have been returned from the Apollo program, the best evidence we have on Mercury, that there are volcanic centers, and therefore there has been volcanic activity,

and this is a huge piece of evidence in favor of the fact that many, if not most, of the planes on Mercury, despite the fact that they're not as dark as the planes on the Moon, have a similar volcanic origin. And anybody who has not seen some of the beautiful images returned during this messenger flyby ought to take a look. They are really stunners, both the false color and the realistic ones, but just beautiful stuff. We only have a little bit of time left, but we've got to get through at least one more topic, and that is this tantalizing evidence about the interior of Mercury, the still very hot core of that planet. Right. We knew before our flyby from some Earth-based radar results

that Mercury's core, which is a huge fraction of the planet, much larger than any of the other inner planets, including the Earth, the outer part of Mercury's core is molten. We know that from some Earth-based radar measurements. And the question that has, again, been with us since Mariner 10 is, how does Mercury have a magnetic field when Venus and Mars no longer have magnetic fields? It is produced, like on the Earth, by turning motions in this fluid outer core? On the Earth, the power source for our magnetic field is cooling of the core.

And one of the biggest manifestations of that cooling is the slow solidification of that molten iron and the growth of our solid inner core. Mariner 10, even though it imaged less than half the surface, saw that the surface of the parts of the planet that they were able to view appeared to have contracted. All of the major tectonic features of the surface, with a few exceptions, are great thrust faults, places where the horizontal distances across these fault features have shortened.

And these faults go in almost every which direction, cut all kinds of terrain. And so the hypothesis, rather boldly put forward by the Mariner 10 geological team, is that when we returned to Mercury and looked at the rest of the surface, we would see more and more of these thrust faults, because they predicted 33 years ago that the planet contracted, that it shrank. And the dominant contributor to that shrinkage is, in fact, cooling of Mercury's core because Mercury's core is most of the planet. And the dominant element of that contraction is, in fact, as it is on the Earth,

the growth of the solid inner core, because as iron solidifies, it gets denser. And that means that the volume of the core, as the inner core grows, gets smaller and smaller, and that acts to contract the planet. Anyway, the prediction of Mariner 10 was indeed borne out. We were able to take images of new terrain. We saw these same thrust faults that Mariner 10 had seen. Where we looked, where Mariner 10 had image, we saw more thrust faults than Mariner 10 image because we recognized that the ability to detect these faults is a function of the sun angle, the lighting conditions, and where these faults cast shadows, they're easier to see. So not only was that prediction

borne out, but the amount of contraction is at least a third greater, probably more, than anything we appreciated before this flyby in January. So we have the geological record of the cooling of the insides of this planet, including the slow cooling of this molten, churning outer core that powered Mercury's magnetic field probably over its entire geological history. And that's a unique situation for any planet. that powered Mercury's magnetic field probably over its entire geological history. And that's a unique situation for any planet. Sean, what should we look forward to on October 6th of this year? Well, again, we're going to see about 30% of the planet close up. That has never been seen by spacecraft. Expect some surprises there.

We're probably going to be flying by the time when the sun is a bit more active than it was in January. It's extraordinarily quiet. And so the magnetosphere will be different and dynamically interacting with the sun. The atmosphere will be different. The charged species, the ions in the magnetosphere will be different. And we'll be taking even more observations of those. So it'll be another view of this incredibly dynamic planet in which the sun and the core and the surface and the magnetosphere and the atmosphere all are strongly interlinked. Hard to believe it could beat this first flyby in terms of science, but perhaps you will surprise me.

Congratulations to you on this stupendous achievement. I take it the spacecraft is in good health. The spacecraft is indeed in good health. We expect to be surprised in October, but we will never again have the situation where 33 years goes by without new observations. So we won't be able to match quite the historic element of the flyby in January. But with that exception, we expect to have outstanding data returned. Thank you, Sean. We'll look forward to talking to you again, hopefully sometime after that, that October 6 flyby. Be delighted to chat with you anytime, Matt. Sean Solomon is the director of the Department of Terrestrial Magnetism at the Carnegie Institution of Washington.

the director of the Department of Terrestrial Magnetism at the Carnegie Institution of Washington. He's been involved in a lot of missions, but as you can tell, he's the principal investigator for Messenger, the ship that is flying by Mercury and soon, before too long, will be in orbit around that innermost planet. He is a member of the National Academy of Sciences, past president of the American Geophysical Union. We're going to move on now to Emily for this week's edition of Q&A. And after that, we'll take a look at the night sky with Bruce Betts. Hi, I'm Emily Lakdawalla with questions and answers. A listener asked,

Assuming that the Mars Odyssey spacecraft stays healthy, how much longer can it remain operational with the amount of fuel it has on board? The ongoing health of Mars Odyssey is important to fans of the images it produces using its Themis camera, but Odyssey's importance goes far beyond its own science mission. Odyssey is the main conduit through which data comes to Earth from the Spirit and Opportunity rovers and the Phoenix lander. Odyssey was the first spacecraft to go to Mars carrying software that conformed to a new protocol for interplanetary communication, allowing the rovers to send more data back to Earth while using much less energy than past landers.

But Odyssey's primary mission was over a long time ago, in August 2004. How long can it possibly continue? Barring any unforeseen problems like the ones that killed Mars Global Surveyor, Odyssey could carry on for many more years. In fact, running out of fuel is not among its concerns. Odyssey consumes less than a kilo of hydrazine propellant each year and has almost 40 kilos left on board. And Mars Reconnaissance Orbiter is equipped with the same communications protocols and can also serve as a telecom satellite for future landed missions like MSL, which is scheduled for launch in 2009.

for future landed missions like MSL, which is scheduled for launch in 2009. A bigger question is what future mission will need a telecom satellite for. There isn't currently another Mars lander under development after MSL, and it's not clear how plans for a possible Mars sample return mission will unfold. Who knows, Odyssey could outlast the presence of missions from Earth on the surface of Mars. Got a question about the universe? Send it to us at planetaryradio at planetary.org. And now here's Matt with more Planetary Radio. Bruce Batts is on the telephone. He is the Director of Projects for the Planetary Society,

and he joins us for What's Up, like right now. The reason he's on the phone is that he's somewhere up in the wilds of northern California. Where are you? Yes, deep in the wilds of Silicon Valley. Very close to the front gate of NASA Ames Research Center, where I was earlier today and will be the next couple days. They're hosting a lunar science conference for the NASA Lunar Science Institute, and I'll be talking about the international lunar decade that we're in the midst of with all these missions from all over the place going to the moon. Yeah, and we're going to get the director of that institute on fairly soon when they end their little competition that they have going.

Did they mention that? Yes, their little competition. Yeah, the one for millions. It's small. It's all relative. Yes, he mentioned that during the public talks today, just how excited he was that he'd be able to come on time for be able to talk to Matt Kaplan. Yeah, well, he better. It was the highlight.

Now tell us about the night sky. Night sky, it occasionally has the moon in it, and the moon is doing things relative to the sun, and that leads us to a total solar eclipse on August 1st. Even if you aren't in total land, you can catch a partial solar eclipse throughout much of Europe and Asia. Doing a partial lunar eclipse on August 16th. And that's visible from pretty much every continent but North America. And so for those, you can go

to the NASA eclipse site, which we'll try to provide a link to from planetary.org slash radio, find out exactly the visibility from your area and the times. You can also, wherever you are, though, you can check out beautiful Jupiter, brightest star-like object out there right now in the night sky, it is rising around sunset over on the opposite side in the east and setting an hour or two before sunrise over in the west. It's really bright, being that big giant king of the planets like it is. Also, if you look shortly after sunset over in the west, although it's getting tougher and tougher, you can still catch Saturn and Mars snuggling up with Mars being reddish to the upper left of Saturn being kind of yellowish, both looking like kind of brightish star-like objects.

And let us not forget the Perseid meteor shower peaking in mid-August, and you can check it out for many days surrounding its main peak, which is August 12th. Go out, stare up at the night sky, usually better after midnight. Just go out, look up, and watch those little streaks of light up to 60 per hour happening during the peak of one of the year's best meteor showers traditionally. And that's our night sky. A whole lot going on. There is, there is.

Got some more. I've got a random space fact. I hope they heard that in the hotel room next door. I'm sure they did. Both sides probably heard it. Let's talk moon. It's Apollo 11, 39th anniversary of humans landing on the surface of the moon. You know, they weren't there very long. They were there for only a little less than 22

hours on the surface of the moon, grabbing rocks like crazy, brought back about 22 kilograms rocks, about 45 to 50 pounds, so kind of the weight of one of my children in rocks. And as years went along and the missions went along, they stayed longer, they collected more rocks, and we got more science as time went along. And now we go on to the trivia question from the past. In the trivia question from the past, we asked you, what were the shortest and longest

duration space shuttle missions? That's duration time in space for single space shuttle missions. How'd we do, Matt? Oh, this is our big giveaway. A wee! Wally! That's right. I have it in my hand right here.

Disney Pixar's WALL-E. This is the version of the game WALL-E from THQ provided to us courtesy of Disney Pixar. And it's going to go to Michael Pollard. Mike Pollard from Cambridgeshire in the U.K. I don't believe he's ever won before, but he's entered many times. So, Michael, you hit the jackpot. He said, STS-80, November 1996, good Lord, almost 12 years ago, was the longest at 17 days, 15 hours, and 53 minutes, whilst, whilst, you can tell where he's from, STS-2, even farther back,

much farther back, November 1981, the shortest that made it into space, two days, 16 hours, 13 minutes, 12 seconds. And the shuttle, both times, Columbia. Congratulations, and let's give people another chance and come back to the moon. I told you how long the first mission to the surface of the moon was on the surface. how long the first mission to the surface of the moon was on the surface. You tell me how long was the last human mission to the surface of the moon on the surface. Apollo 17, how much time did the astronauts spend on the surface of the moon? This is not the EVA time, not just the time outside the lunar module,

but the entire time from when they sat down on the moon to when they launched off the moon. Go to planetary.org slash radio. Find out how to enter. You've got till Monday, July 28 at 2 p.m. Pacific time. That's it. We're done. All right, everybody. Go out there, look up in the night sky, and think about the moon, and especially think about it when it's gibbous, just because it's fun.

He's Bruce Betts, the director of projects for the Planetary Society, and I get positively gibbous when I get to talk to him every week for What's Up. Planetary Radio is produced by the Planetary Society in Pasadena, California. Have a great week. Thank you.