NASA Probe Returns Stunning Views Of Mercury

The MESSENGER probe captured images of never-before-seen aspects of the closest planet to the Sun during a recent flyby. Researcher Sean Soloman discusses the MESSENGER mission, which aims to be the first man-made object to orbit Mercury.

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JOE PALCA, host:

From NPR News, this is Talk of the Nation: Science Friday, I'm Joe Palca. A brief program note, join Neal Conan on Monday Talk of the Nation for a final look at the polls. What they really tell us? Can you trust them? Plus, Mary Horowitz on the best movie presidents. That's next Talk of the Nation from NPR News. On this program, the next topic is Mercury.

The MESSENGER spacecraft made its second flyby of the planet earlier this month. Mercury, in case you need a refresher on your solar system, is the closest planet to the Sun. Before MESSENGER, the only pictures we had of Mercury were from Mariner 10 way back in the 1970s.

And it seems now that those images didn't do mercury justice. These new pictures show a dynamic planet with lots of volcanic activity and some mysterious blue matter. Joining me now to talk about that - what MESSENGER found and what scientists hope they will find is my guest, Sean Solomon, he's the principal investigator for the MESSENGER Science Team.

He's also director of the Department of Terrestrial Magnetism at the Carnegie Institute of Washington. Right here in Washington D.C., where they have the best sledding hill in the city. Welcome to the program, Doctor Solomon.

Dr. SEAN SOLOMON (Director, Department of Terrestrial Magnetism at the Carnegie Institute of Washington; Principal Investigator, MESSENGER Science Team): Thank you, Joe. I didn't know you knew about our sliding hill, it's a closely kept secret.

PALCA: Oh, yes. Oh, yes. No everybody - now I've really - I shouldn't have said anything.

Dr. SOLOMON: Yes. First snow storm, we'll see many more friends.

PALCA: I guess that's probably - that's a possibility. Anyway, thanks for coming on. So, what did the latest flyby reveal to us? What was the coolest bit?

Dr. SOLOMON: Well, we of course have our entire payload turned on. And in some ways duplicated the measurements that we took on our first flight by - which was in January of this year. But we flew by the opposite side of the planet, and so that enabled a variety of new measurements.

We imaged 30 percent of the planet for the first time by spacecraft, so we're seeing new terrain on area bigger than the land area of South America, that had never been seen by spacecraft before. We took some of the highest resolution - we took the highest resolution color images that have ever been taken of Mercury.

We carried out more very precise alt symmetry, this time over regions that we imaged either on this flyby or back in January, so that we had for the first time an ability to compare topographic profiles with high resolution images. So we're getting three-dimensional views of faults, and craters, and other geological structures.

We took new measurements of Mercury's atmosphere and its comet-like tail. New species, new combinations of measurement for the first time to unravel the question of how - what possibilities are contributing to that very tenuous atmosphere.

And we took measurements of the planet's magnetic field. And it's - the volume of space dominated by that field, the so-called planetary magnetosphere, which is much more dynamic this time than it was when we flew-by in January. So, it's a rich menu of topics, and I'd be happy to return to any of them.

PALCA: OK, well. And I'd like to invite our listeners to join this conversation. Our number to - the number to call is 800-989-8255, that's 800-989-TALK. Maybe I could just ask, because I'm curious?

When you talk about dynamic magnetosphere, what does that mean? Does it mean that the north is changing as you fly - because I looked at some of the pictures and it looks as if the direction of north is changing somehow?

Dr. SOLOMON: It's not that the direction of north is changing. We see - the earth of course has its own magnetosphere, and the earth's magnetic field is a thousand times stronger than the magnetic field of Mercury.

And what that means is that when the solar wind carries a changing magnetic field between the planets, we see some effects within the Earth's magnetosphere when there are magnetic storms, the Sun is particularly active. We hear about losses to satellites in orbit, particularly in the area of communication. So, our own magnetic sphere is dynamic, but Mercury's magnetosphere is as we have learned much more dynamic, because the magnetic field of Mercury is smaller, because the interplanetary magnetic field is stronger, closer to the Sun.

The difference we saw was almost a night and day difference between the direction of the interplanetary, magnetic field back in January, which was northward. And in October when it was southward, that direction changes all the time, but the response of Mercury's magnetosphere to that change in direction is really profound.

And we did not appreciate that until our flyby earlier this month on 6 October. Because with a southward-directed interplanetary magnetic field, the interplanetary magnetic field directly interacts with the planetary magnetic field at the north and south poles of the planet.

And because the ionized particles streaming out from the Sun all the time, the so-called solar wind that consists of ionized hydrogen, or protons, and ions of heavier elements coming from the Sun, these ionized particles travel along the lines of magnetic force in the solar wind, in the interplanetary magnetic field, and when those lines of force intersect the planet at the two poles, it means that Mercury's bombarded by energetic ions coming from the sun, and those ions are a major source of Mercury's atmosphere, it's neutral and ionized atmosphere, and also a major source of changing the color, that is to say, changing the chemistry on a very small scale of Mercury's surface material. So...

PALCA: Oh!

Dr. SOLOMON: The magnetosphere is a governor of a lot of activity on Mercury, ranging from the way we see the surface, to the atmosphere and the environment of the planet.

PALCA: That's amazing, and I've been - interesting you hear - talking about atmosphere, I mean, we don't really think of Mercury as having much of an atmosphere, and I've heard - referred to as an exosphere or an - something like that?

Dr. SOLOMON: An exosphere is the upper part of any planetary atmosphere, where the density of atoms is so low that they don't collide with each other.

PALCA: I got it.

Dr. SOLOMON: The top of the earth's atmosphere has an exosphere, the top of the atmosphere of Venus, a hundred times more massive than that of the earth, has an exosphere at the top. But Mercury is entirely exosphere. It's exosphere all the way down to the surface.

PALCA: So, no vacation spots. Maggie(ph) welcome to Science Friday.

MAGGIE (Caller): Hi. You mentioned that there are volcanoes and faults that you've seen on the surface of Mercury, and so I was wondering if there is a basic kind of framework that's going on there, or if there's some other sort of - you know, prompt season are going on that changed the surface?

PALCA: Huh.

Dr. SOLOMON: Good question, Maggie. The quick answer is no. We know of no other planetary body beyond the earth that has an organized system of tectonic plates, that as you probably know on the earth are in constant relative motion, and have boundaries that are the locus of most of the earthquake activity on our planet, as in much of the volcanic activity.

Mercury's volcanoes and Mercury's faults are mostly very ancient in terms of when they were active. But they're well preserved, because the only source of erosion on Mercury is the constant bombardment by meteoroids, and occasionally by larger asteroids and comets. And so we can see very ancient faults and very ancient volcanic landforms.

The existence of volcanoes on Mercury was something that had been debated from the images from Mariner 10, because there were no clearly-resolved volcanic centers. There were smooth plains that looked very much like what we know to be volcanic plains on the moon - the Lunar Maria - but they're a little different, because they're not as dark as the Lunar Maria, and they also looked like some of the highlands plains on the moon that are the same brightness as the surrounding, heavily-cratered terrain.

So, Mariner 10 left us with the debate as to how important volcaninism has been in the history of Mercury ranging in ideas from - as important or more important than on the moon to - of little to no importance, and MESSENGER resolved that back in January by showing us convincing evidence for ancient, volcanic centers, and giving us a lot of evidence that the - many of the plains on Mercury are products of ancient lava flows.

The deformational structures are quite profound. They - some of the faults have relief of as much as a mile, and almost everywhere we look on Mercury, there has been an expression of deformation recorded in those faults. Nothing like plate tectonics, but quite an interesting history of deformation.

PALCA: OK, Maggie. Thanks so much for the call.

MAGGIE: Thanks.

PALCA: All right. Let's take another call now, and go to Matt in Washington D.C. Oh, I know that. Matt, welcome to Science Friday.

MATT (Caller): Thank you for taking my call. I really enjoy this program.

PALCA: Good.

MATT: I try to listen every Friday. I don't have a lot of experience talking about planets, and the geology or what I'm actually looking at if I take a look at these new images eventually, but my interest is in the gear that you're using and how - and when I look at images that are produced by these spacecraft, are we looking at images that are like images that we look at on earth, whereas (unintelligible) type of equipment are we seeing like a different spectrum? I know that some of the images are really vivid, and you see things that you could only dream up.

I mean, some of the colors and the type of expressed, like spectrum that you're seeing. Could you give an explanation of what kind of type of equipment are taking these pictures, and what challenges you have to see these planets being so close to the sun, and their atmosphere being so different from our planet and just the overall conditions. Any general - just general bits of information about the technology you're using.

Dr. SOLOMON: Sure. Sure.

PALCA: OK. Yeah.

Dr. SOLOMON: Glad to - that's quite the longest of questions and I'll do my best, Matt. First of all, we are carrying two imaging systems. One uses a narrow angle camera at a single wavelength. We also have a wide angle camera that has 11 different color filters. Those filters span the wavelength range from - throughout the visible and into the near infrared.

The actual detector is a charge-coupled device. You might find something analogous in a digital camera, and we've taken great pains to show in the images that we've released - and I hope Joe will allow me to give the website address before the show is over - of images both at what might be the kind of color that you or I would see with our own eyes, although you and I might see things a little differently.

PALCA: Sean Solomon, I'll make a deal with you. I'll make a deal with you. I'll let you give the website if you let me pause for one moment, and tell people that I'm Joe Palca and this is Talk of the Nation from NPR News.

Dr. SOLOMON: I think I'll let you do that.

PALCA: OK. Good. We did it.

Dr. SOLOMON: OK. And our website so I don't forget...

PALCA: Yeah.

Dr. SOLOMON: Is messenger.jhuapl.edu.

PALCA: OK, and if you forget that, you can go to the sciencefriday.com website and find it there.

Dr. SOLOMON: But just to finish the answer that Matt asked about the unusual colors that he sees in some of the images that we have released. Even though the color variations on Mercury are very subtle, and if you looked with your own eyes, it would look like a pretty gray planet.

There are color differences, and there are areas that are redder and areas that are bluer. It's a very faint difference in color, but one that a sharp-eyed person might discern and certainly a digital imaging system can discern, and the more garish renditions, with apologies to my colleagues who produced these images...

PALCA: Mm-hmm.

Dr. SOLOMON: That have accentuated these blue and these red differences, are ones where we are taking advantage - much like Photoshop - of the digital imaging system to portray in a way that is clear to mappers and to those interpreting the geology, where those difference are and how they are related to the landforms, and to other aspects of what's going on in the surface of Mercury.

PALCA: OK. Well, Sean Solomon. I - thank you for that very interesting and colorful explanation, but we've run out of time. So, I'll thank you for joining us today.

Dr. SOLOMON: My pleasure, Joe. Thank you.

PALCA: Sean Solomon is principle investigator for the MESSENGER Science Team, and director of the Department of Terrestrial Magnetism at the Carnegie Institute of Washington.

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New Images Show Filled-In Craters On Mercury

An image of Mercury taken by NASA's Messenger i i

An image of Mercury taken by NASA's Messenger probe in early October. NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington hide caption

itoggle caption NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
An image of Mercury taken by NASA's Messenger

An image of Mercury taken by NASA's Messenger probe in early October.

NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Craters on Mercury i i

Some of Mercury's craters as shown in images taken by Messenger. NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington hide caption

itoggle caption NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Craters on Mercury

Some of Mercury's craters as shown in images taken by Messenger.

NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

New images of filled-in craters and large, smooth plains on the planet Mercury are helping scientists understand how volcanic eruptions helped shape this alien world.

A NASA spacecraft called Messenger zoomed just 125 miles above Mercury's surface earlier this month, and scientists are now analyzing hundreds of photos that show previously unseen regions of the planet, which is just a little larger than Earth's moon.

Some of the photos add to evidence suggesting that volcanoes have been very active on the planet.

"The bottom line is vulcanism was very important in the history of Mercury," says Mark Robinson, co-investigator and professor at Arizona State University School of Earth and Space Exploration.

Before this year, Mercury had only been visited by one spacecraft, a probe called Mariner 10 that flew past the planet three times back in the mid-1970s. But it glimpsed less than half of Mercury's surface.

When scientists looked at those Mariner 10 images, "there was actually a fair amount of ambiguity about whether or not vulcanism was even an important process on the planet," says Maria Zuber, co-investigator and head of the Department of Earth, Atmospheric and Planetary Sciences at the Massachusetts Institute of Technology. "We had a lot of materials on the surface, and we didn't know their origin."

That's changing as new images come in from the Messenger probe. The latest images were taken early on Oct. 6, in the second of three planned flybys of the planet.

Messenger launched back in August 2004 and is currently on a 4.9 billion mile trip that will send it around the sun more than a dozen times before it finally gets in position to start orbiting the planet in March 2011.

At a press conference, Zuber showed off one new image of two adjacent craters. Both are about 60 miles in diameter. But one of them is four times deeper, because the other crater is filled in with solidified lava — a huge amount of lava.

To get an idea of how much, Zuber explains, you could imagine the entire Baltimore-Washington region covered with a layer of solidified lava about 12 times the height of the Washington monument. "So it's a great, great deal of vulcanism," she says. "That's an awful lot of volcanic material in one place for such a little planet."

Other instruments on board Messenger took advantage of the latest flyby to measure calcium, sodium, and magnesium in the planet's tenuous atmosphere.

And Zuber says the spacecraft's laser altimeter saw hints that one hemisphere of Mercury appears to be about 30 percent "smoother" than the other. "The Western Hemisphere is smoother than the Eastern Hemisphere," says Zuber. "So there's some process that acted to smooth one hemisphere more than the other hemisphere."

Mercury is one of the more mysterious planets in the solar system, despite the fact that it was known to ancient astronomers and is one of Earth's rocky neighbors.

Messenger's final quick flyby will come next September. After that, when it finally begins to orbit Mercury, it will circle the planet for a year.

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