Planetary Radio: Space Exploration, Astronomy and Science - A Winged MESSENGER Reaches Mercury, and Bill Nye Premieres!

Episode Date: January 7, 2008

A Winged MESSENGER Reaches Mercury, and Bill Nye Premieres!Learn more about your ad choices. Visit megaphone.fm/adchoicesSee omnystudio.com/listener for privacy information.See omnystudio.com/listener for privacy information.

A winged messenger reaches Mercury, 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. We've had to wait more than three decades since the last visit to our solar system's first big rock from the sun. I'm Matt Kaplan. he hopes it will tell us about that still mysterious planet. Bruce Betts will make the night sky a bit less mysterious with another edition of What's Up, including a chance to win a year in space calendar. And this week we welcome the premiere of a new regular segment. Bill Nye the Science Guy will share his unique take on the passion, beauty and joy of space exploration, beginning on the sands of Mars.

Speaking of which, there's a new update on the sojourn of Spirit and Opportunity at Planetary.org. Science payload principal investigator Steve Squires says 2007 was a really good year for the Mars exploration rovers. That may be the understatement of the year. We think you'll agree after you read the report. Want to see what the star Antares looks like as it passes behind Saturn's rings? Look no further than Emily Lakdawalla's space blog, also at planetary.org. The very cool sequence of images is a nice bonus from the recent ring crossing completed by the Cassini spacecraft, which remains in excellent health out there a

billion miles from home in the silence of interplanetary space. Or is it so silent after all? Listen up as Emily arrives with a Q&A that says the answer is blowing in the wind. I'll be right back with Sean Solomon. Hi, I'm Emily Lakdawalla with questions and answers. A listener asked, what does it mean for the solar wind to go from supersonic to subsonic when there's no sound in space?

The solar wind blows through interplanetary space at hundreds of kilometers per second. As the solar wind collides with the interstellar medium, it has to slow down from these fantastic speeds. The two Voyager spacecraft have both crossed the boundary, called the termination shock, between the fast flow of the solar wind and the much slower flow in a region called the heliopause. Scientists on the Voyager mission do call the speed of the solar wind and the much slower flow in a region called the heliopause. Scientists on the Voyager mission do call the speed of the solar wind supersonic and the speed of the heliopause

subsonic, which confuses those of us who have learned the lesson that in space no one can hear you scream. Indeed, sound doesn't travel through a vacuum, but there's really no such thing as a perfect vacuum. In fact, the particles in the solar wind itself comprise a medium in which sound waves can travel. Just how fast does sound in the solar wind go? The speed of sound at sea level on Earth is a measly one-third of a kilometer per second. In the rarefied environment of the solar wind, the speed of sound is nearly 200 times faster. Throughout the Voyager missions, the solar wind has been blowing past them, four times

faster than the spacecraft were traveling out of the solar system. But once the Voyagers crossed the termination shock, the situation changed, so they are now going faster than the wind. Voyager principal investigator Ed Stone tells me that the solar wind isn't the only medium through which sound waves can travel. He said that magnetic fields can also propagate waves. Pluck a magnetic field and a wave will travel along it just as it does along a violin string.

Got a question about the universe? Send it to us at planetaryradio at planetary.org. And now here's Matt with more Planetary Radio. Mercury, surface, space environment, geochemistry, and ranging. That's the messenger probe, and it has already been traversing the inner solar system for almost four years. On January 14, it will finally take its first pass at Mercury, showing us portions of that planet that have never in history been seen up close. Sean Solomon has been looking forward to this achievement for much longer.

MESSENGER's principal investigator directs the Department of Terrestrial Magnetism at the Carnegie Institution of Washington. But on the 14th, you can bet he'll be at the Applied Physics Lab, where MESSENGER was built and is controlled. The veteran of many other space missions and former president of the American Geophysical Union joined us by phone just a few days ago. Sean Solomon, we are so pleased to have you on Planetary Radio as we are barely a week from humanity's first encounter with

Mercury in 33 years. You must be pretty excited. Matt, I'm delighted to be with you, and yes, I'm excited. The whole science team on the Messenger mission is excited. I was a very junior assistant professor at MIT back when Mariner 10 flew by Mercury three times in 1974 and 75, the only spacecraft ever to have visited Mercury. It made some important discoveries that raised questions that have been with us for three decades. So to be returning to Mercury, initially with this flyby, but ultimately to go into orbit with a modern suite of instruments

to answer those three-decade-old questions as all of us at the edge of our seats. You know, I'm so glad you mentioned Mariner 10, and I was going to ask you toward the end of the conversation, but I'll move it up. Have you had any contact with any of the folks who worked on that mission 33 years ago? I'm thinking of Bruce Murray,

who, of course, we're well familiar with here at the Planetary Society, who was the head of the imaging team. Well, of course, we've had guidance from participants on, the direct participants on Mariner 10 throughout the planning stages for Messenger. And interestingly, one of the members

of Messenger's science team, Bob Strom, of the University of Arizona, was on the imaging team for Mariner 10. So we have a direct link, an individual who has been pumping for returning spacecraft to Mercury ever since Mariner 10 and has the unique pleasure of sitting on the science teams for both missions. I should add that Bruce Murray has a special place in my education. He taught a course at Caltech when I was an undergraduate. It was on scientific speaking, giving presentations on scientific materials. One of the assignments was to talk about the scientific paper of the students choosing.

As it happens, I picked a paper on mercury. Gave a presentation in his class and got a pretty good grade. So it was a good beginning. We'll make sure he hears about that. It's so nice to hear about this kind of connection with that mission more than three decades ago. But let's talk about your mission, for which you're the principal investigator. Tell us about the current status. I know you had another trajectory correction just a few days ago,

December 19th. We did. MESSENGER came out of a long period when it was on the opposite side of the sun from the Earth, what's known as the solar conjunction. And for a little more than two weeks, we had no contact with the spacecraft. But we recovered the spacecraft as it came out of conjunction at the end of November. We've been tracking it carefully since. The first opportunity we had to make a small correction, a change in spacecraft speed of a little over a meter per second, was on December 19th, and we were able to do it at that earliest opportunity, which saves us a bit of propellant. It looks like we're on track to get very close to our target point, which, of course, not only is important for viewing Mercury, but is critical

to keep the spacecraft on the trajectory that will return it to Mercury for the subsequent encounters that we need for the later orbit insertion. Let's talk about that trajectory because, of course, you won't go into orbit around Mercury until 2011. And not only will you have several of these quick encounters with Mercury on the way to that orbital insertion, you've had to do the same at Venus, you've had to do the same at Earth. Why is it so difficult to head toward the sun rather than away from it, or am I imagining that? No, you're not imagining anything, Matt. It's a good question.

The main reason is that as a spacecraft heads toward the sun, it picks up speed. The sun, of course, is a very large source of gravitational attraction, and any spacecraft moving toward the inner solar system speeds up. To go into orbit around a planet, we must slow down, must slow down enough to be captured by the gravity field of the planet. And for Mercury, which is only a little more than 5% of an Earth mass, we have to be going quite slowly, less than a kilometer per second, for our propulsion system to do an orbit insertion burn. The first time we fly by Mercury, about a week from now,

we'll be going several kilometers a second far too fast to turn on our propulsion system and be captured into the orbit we want. The whole architecture of what's called the cruise phase of the mission, between launch and orbit insertion, makes use of gravity assists at Earth, at Venus, we had two of them, at Mercury we need three of them, to slow the spacecraft relative to that of the planet Mercury. But each encounter is spaced farther and farther apart in time because we're getting closer and closer to Mercury's speed around the sun, and it takes longer to catch up each time. The first encounter is the one coming up. The second encounter, also a flyby, is October

of this year. The third flyby is not until September of 2009, so 11 months after the second flyby. And then the fourth encounter, when we can go into orbit, is 18 months after the third flyby. We'll hear more from Sean Solomon, Principal Investigator for the Messenger Mission to Mercury, when Planetary Radio returns. Hey, Bill Nye the Science Guy here. I hope you're enjoying Planetary Radio. We put a lot of work into this show and all our other great Planetary Society projects. I've been a member since the disco era. Now I'm the Society's Vice President. And you may well ask, why do we go to all this trouble? Simple.

We believe in the PB&J, the passion, beauty, and joy of space exploration. You probably do, too, or you wouldn't be listening. Of course, you can do more than just listen. You can become part of the action, helping us fly solar sails, discover new planets, and search for extraterrestrial intelligence and life elsewhere in the universe. Here's how to find out more. You can learn more about the Planetary Society at our website, planetary.org slash radio, or by calling 1-800-9-WORLDS. Planetary Radio listeners who aren't yet members can join and receive a Planetary Radio t-shirt. Members receive the internationally acclaimed Planetary Report magazine. That's planetary.org slash radio.

The Planetary Society, exploring new worlds. Welcome back to Planetary Radio. I'm Matt Kaplan. Welcome back to Planetary Radio. I'm Matt Kaplan. Sean Solomon heads the Messenger mission to Mercury, now rushing toward the first encounter with that planet in 33 years. In spite of this being a fairly quick encounter, a fairly quick flyby, you're going to be conducting quite a bit of science with a very impressive suite of instruments. We hope to get quite a leg up on all of the activities that we have planned for Mercury, including the observations that we eventually want to make in orbit.

All of our instruments will be turned on. Of course, we're coming in from the night side. We're exiting on the day side. Let me give you just a quick rundown of some of the new things that we're going to be able to do on this flyby compared to what Mariner 10 did more than 30 years ago. Please do. First of all, Mariner 10 did some very important imaging of the surface, but because the three flybys of Mariner 10 were precisely one solar day apart on Mercury, two Mercury years apart, the same side of Mercury was lit by the

sun at each flyby. So Mariner 10 saw only about 45% of the surface in sunlight. So there's half of the surface that's never been seen close up by spacecraft. And of that half, approximately 50% will be sunlit a week from now when we fly by. So we'll be seeing much of the area of Mercury's surface that Mariner 10 missed. We don't know what to expect, but we'll be completing gradually the full global mapping of Mercury with this mission. Mariner 10 carried no experiments to address what the composition of mercury surface materials, either of chemistry or mineralogy. This is this miracle of remote sensing that we talk about frequently on this show. It is. And that field has advanced enormously in three decades. We use three

types of spectrometers to go after elemental composition, using different parts of the electromagnetic spectrum, different kinds of particles that interact with the surface in a way that is diagnostic of particular atoms. And this is to say nothing of a magnetometer, which must be pleasing to you as head of the Department of Terrestrial Magnetism, but also a very capable imaging system. And anybody who might doubt that should, well, we'll link to some of the images that you caught of our home planet Earth during one of those flybys that you mentioned earlier.

Yes, I hope you can give information on the Messenger website at some point in the show. But posted there are images of the Earth from our flyby in August of 2005, as well as images of the planet Venus from our flyby in June of last year. It's a dual imaging system with a wide-angle camera that has 11 color filters that span from across the visible spectrum into the very near infrared, and then a narrow-angle camera that's broad monochrome, but has higher resolution and a narrower field of view. So we'll be doing a mix of imaging with those two camera systems, building up global images in color, but also doing targeted higher resolution imaging using the narrow angle camera. So the color information will give us additional context for trying to

understand the sources of that color and distinguishing different rock types on the surface of the planet. The higher resolution images will, we hope, reveal some of the geological processes that have led to the landforms on the surface. The first question, why is Mercury so dense, stems from the fact that we know from its bulk density that the planet must have a huge metal core. We know that all the inner planets have metal cores surrounded by rocky silicate shells, but in Mercury's case, it's so small and yet has a density nearly that of the Earth. Because it's so small, the effects of self-compression, internal pressures, cannot be nearly as large. So there must be a core that's 60 or more percent by mass, 75 or more percent by radius,

that's dominantly iron, the only solar system element dense enough and common enough to account for that density. Let me just mention, if I might, one more of the six questions that might be of interest to some of your listeners. Please do. I was going to ask you about another one myself. I was going to leap to the polar deposits. Oh, wonderful. That's the one. Which were discovered by Earth-based radar in the early 90s. Those polar deposits sit in the floors of polar craters and behave in terms of radar backscatter and depolarization, much like water ice elsewhere in the solar system.

So standing in a polar crater in permanent shadow, you're looking out into open space with no ability to heat the surface materials, and the temperature there gets as cold as perhaps 90 Kelvin. Cold enough to freeze water and many other voluptuous as well. Yeah, I was going to say, and then some. And then some. The notion that water would find its way into what are called coal traps at the poles is a very reasonable one if there's a source of water.

And we don't know what that source is. It could be outgassing from the interior. But more likely, that water could come from impacts by a comet. But messengers, spectrometers will be able to tell us if that's water ice? If the water ice is exposed at the surface, if there's some exchange between the exosphere and the water ice deposits, we will be able to see those signatures. We'll certainly be able to test the notion that these areas where these deposits are are in permanent shadow, both by imaging and by direct altimetry.

So we'll learn a great deal more about the regions of these deposits, and we have a good shot at actually determining the composition of these deposits. How soon after this January 14th encounter will we start to see images and other data? Within days. The communication system is such that we can't transmit the observations we make at the flyby in real time. We can't point our instruments at the planet, point our sunshade at the sun, and transmit data back to Earth at high downlink rates all at the same time. We must protect the spacecraft, so keeping the sunshade pointed at the sun is always our top priority.

Wise move, yes. Sunshade pointed at the sun is always our top priority. A wise move, yes. As we fly by, insofar as we can meet that constraint, pointing our sensors at the planet is the next priority. We will, as we said earlier, put up a link to the JHU Applied Physics Lab website where you will, I assume, be putting up some of those early images that will be available from this first encounter in over three decades with the planet Mercury. Sean, once again, thank you very much for joining us on Planetary Radio.

My pleasure, Matt, and we appreciate the interest in MESSENGER and in Mercury among your listeners and look forward to talking to you again as our mission evolves. Wonderful. Sean Solomon has a lot on his plate that he balances. He's the director of the Department of Terrestrial Magnetism at the Carnegie Institute of Washington. He is also, though, involved in the sciences in many other ways, past president of the American Geophysical Union

and the principal investigator for the MESSENGER mission, now about to make the first human visit to the planet Mercury in 33 years. And you can hear an extended version of my conversation with Sean, including much more about the science Messenger will conduct at Mercury by visiting planetary.org slash radio. And now, something I've been looking forward to for many weeks. Bill Nye is vice president of the Planetary Society and a hero of mine. Few have done so much to bring the wonder and thrill of science to people around the world, and especially to children. And no one has made science so much fun or so funny. Here he is with the first of his contributions to our show.

Hey, hey, Bill Nye the Planetary Guy here, talking to you from the headquarters of the Planetary Society in Pasadena. I'd just like to give you an update on Mars. I mean, not on Mars, about Mars. Speaking of which, we just took our 200,000th picture from that other world. You know, it's been almost four years that the Spirit and Opportunity Rover has been operating on Mars, two Martian years. We have proven beyond a shadow of a Martian doubt that there was once liquid water in abundance on Mars, liquid water everywhere,

red ponds and lakes. And you can't help but wonder if there was once liquid water, perhaps once there were living things. And it is not beyond imagining, it is not beyond beyonding to conceive that life was conceived on Mars originally and made its way here after a huge planetesimal impact on Mars about three billion years ago. And these living things made their way all the way through space from the orbit of Mars to the orbit of the Earth, where they landed and you and I came to be. I'm not saying that's what happened, but it certainly might have. Just to give you an update, the Spirit rover, it's working its way across a big plane up there, trying to get onto a hillside for the very cold Martian winter so it can point its solar panels at the sun for the winter.

You know, it was in a big crater that was, actually it wasn't very big, it was just 10 centimeters deep. But the rover could hardly work its way out because it's got one bad wheel, but it did. And we're working our way across. Then opportunity to the other one, it's descending slowly, carefully into the Victoria crater. Because when you get into a crater, see, it's like a Whitman sampler, except you can see what's inside. You can see what's inside the candy. And that's why you go to a crater. You can look deep into Mars's past by looking into ancient layers of rock.

So who knows what's next on Mars? Stay tuned to Planetary Radio. We'll give you updates as we wheel along. And there's the premiere of Bill Nye the Science Guy on Planetary Radio. We hope he'll be coming back for a long, long time. We move now to somebody who's been here from the beginning. It's Bruce Betts, the Director of Projects for the Planetary Society, with this week's Look at the Night Sky, which I'm always excited about.

I always look forward to this. Good, so do I. And we've got good stuff for you to look forward to this week. Still got Mars not that far past opposition. Still the extremely bright incarnation of Mars shortly after opposition. As bright as the brightest star in the sky, Sirius, which is also up later in the evening. And you can compare the reddish-orangish of the very bright Mars with the bright bluish of Sirius over the right of Mars. So that's a good thing to check out. It will continue to dim as we go through the coming weeks.

So it looks sooner rather than later. dim as we go through the coming weeks. So it looks sooner rather than later. Saturn, Saturn coming up in the mid evening in the east and up very high before dawn, looking nice and bright, it'll move towards opposition and another couple months opposite side of the earth from the sun. And we've got Venus still the brightest star like object in the predawn sky over in the east can't miss it looking groovy for those of you who've become cometophiles or always have been comet holmes is still up there i wouldn't say really naked eye but with binoculars you can see it it's it's uh covering a a big chunk of sky still in perseus and there's another comet out there also similar brightness much smaller with kind of a

greenish tint and that is comet 8p Tuttle, but it's much closer, so moving much faster relevant to us. It's in Cetus right at the moment, but flying through the sky. So check out finder charts if you're interested in looking. Again, I think even from a dark site would be really tough to be naked eye, but with binoculars you can probably pick it up. So Holmes, if you look in Perseus, just look for a big fuzzball? Well, yeah, that's, that's what they are, big fuzzballs. But if you look for Comet 8P Tuttle, look for a little fuzzball and kind of a greenish fuzzball because of the, uh, the ions getting all excited and just the right way. So that's kind of our

night sky going on. Well, uh, Jupiter will start coming up pretty soon in the pre-dawn, but we're not quite there yet. If you want, do pull out the binoculars or a small telescope. You can still check out Uranus nicely placed in the evening sky. Uranus, Neptune getting a little tougher, getting lower, but you still might pick that up too. Let us move on to this week in space history. 1968. Forty years ago, Surveyor 7 becomes the last of the Surveyor series to soft land on the moon, the robotic precursors, some of them to Apollo.

10 years later, completely unrelated, the first triple docking in space, Soyuz 26, 27, and Salyut 6. I had forgotten about that. Random Space Fact! about that yeah random space fact that was lovely thank you i'm trying to make up for the the sick times yeah a little week that was very healthy oh thank you mariner 9 when it arrived at mars as the first martian orbiter in 1971 it arrived to a global dust storm. Big bunch of nothing. And then over time, over the months, the global dust storm started to fade away. And what's really interesting, I may have mentioned this part before, is that Mariners 4, 6, and 7, who had flown by Mars before, just saw the southern cratered highlands boring Mars. But it was Marineriner 9 when the dust cleared, started seeing the giant volcanoes and the giant canyons and all sorts of exotic Mars and all the,

started giving us hints of the mysteries that are Mars today. Suddenly Mars was an exciting place again. It was, it was. It looked like it was going to end up boring and it ended up quite interesting. Let's embark on our trivial pursuit. Okay, let's roll for who goes first. No, let's not. We asked you, what's the longest gap between exploration of a planet? In other words, what planet has it been the longest since it was last explored by a spacecraft?

And you've probably figured out, many of you, this was not a coincidental question, but one leading up to the end of that gap. And how'd we do? Aren't we clever? Oh, yeah. Clever, clever, clever. Because that answer is, of course, Mercury. As Sean Solomon pointed out in our interview just a few minutes ago.

He should know. Yeah, if anybody knows. You want to know who won? I do. It's been a year since he won. It's Reverend Brent Livingood, who we've sometimes said is the unofficial chaplain of Planetary Radio, out there in, I believe it's North Carolina. He didn't put it down this time,

but that's where his congregation is. Well, he can abuse you and correct you if you're wrong. I'm sure he will. And we want to say congratulations, and he has won himself a Planetary Radio t-shirt. I think it's the last t-shirt for a while. I think we're going to calendars beginning next week.

All right. We're on calendars, and we'll give a calendar away for the next prize winner. This is a year in space desk calendar, beautiful pictures, fabulous, fabulous calendar, the official source of this week in space history. You can win one by being the randomly selected winning entry, correct entry, for the following question. How many legs did the Surveyor spacecraft have? I remember I did something similar with Phoenix not that long ago. But now we're talking Surveyor to celebrate the 40th anniversary of the last Surveyor landing.

How many legs? Pretty straightforward question. Go to planetary.org slash radio. Find out how to get your entry to us and compete for the This Year in Space History calendar. More than one? This week in space history calendar. I was going to say more than one, less than 12 legs. That is correct.

So we've narrowed it down considerably. Stop giving hints. You've got until the 14th of January in this brand new year, 2008, Monday the 14th at 2 p.m. Pacific time to get us your entry. And you'll love that calendar if you're our big winner. All right. We're done? Yeah. Okay.

Everybody go out there, look up at the night sky, and think about bears in a river. Thank you. Good night. Oh, bears in the river. A bunch of major ursas there. Be careful because they can be really dangerous. Keep your distance. He's Bruce Betts, the Director of Projects for the

Planetary Society, and he joins us every week here for What's Up. Planetary Radio is produced by the Planetary Society in Pasadena, California. Have a great week. Thank you.