Planetary Radio: Space Exploration, Astronomy and Science - A MESSENGER Mercury Mission Update From Sean Solomon

Episode Date: December 7, 2009

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Back to Mercury with Sean Solomon, 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 of the Planetary Society. The Messenger spacecraft is on course to orbit our solar system's innermost planet. We'll spend time once again with the leader of that mission. We've also got the entire cast of regulars this week except that one of the players begins a new role. Emily Lakdawalla, the Planetary Society Science and Technology Coordinator

will join me in a few seconds for the first of our weekly conversations about what's new in planetary science. Bill Nye has news of plans for a human mission to an asteroid, and Bruce Betts will be along with a look at the night sky. First, let's get Emily on the Skype connection. Welcome, and I'm looking forward to these conversations. Yeah, me too. The people have spoken, and they want me to just have a conversation with you.

They certainly did, and it was pretty much unanimous as well. So let's start with something that you featured on the website, and I only just watched it a few minutes ago. It is one of the prettiest little fanciful animations I've ever seen. Yeah, you know, I get suggestions quite frequently to go check out this animation. I don't usually have very high expectations, but this animation showing what the sky would look like from the surface of Earth if Earth had Saturn's rings was just spectacular. He really did a terrific job, and it was smart picking Ave Maria behind it as well.

Yeah, the music's nice too. So you get to see from different spots on Earth, and apparently very accurately, what Saturn's rings would look like if we had them. That's right. And, you know, one of the things that you don't realize is because Earth's places don't move around and the rings stay aligned with the equator, the shape of the rings in your sky would be constant all the time. You would see them always occupying the same arc across the sky. It's just their illumination that would change a bit. I noticed in Kuala Lumpur, because it's almost on the equator, you'd basically see the rings edge on. You would always see the rings as an arc that would cross right over your head,

whereas in other spots on Earth, especially if you're closer to the pole, you would see the rings as being very broad and they would be close to the horizon. pull, you would see the rings as being very broad and they would be close to the horizon. Was there more actually that you were thinking, not to get nitpicky, that you wish that you'd gotten out of this? Well, yeah. I mean, he did explore a little bit about how things would change from day to night. Quite a lot of the rings would be lit at night. And when you consider the fact that they reflect sunlight just like the moon does, it would

be like having full moons all over the sky wherever there were rings. And that's an awful lot of light that you would get on the night side of Earth. But one of the things that he didn't go into that I kind of wish he had would be what would change with the changing seasons. One of these things is that the rings cast an enormous shadow. And so in winter, when it's already kind of dark and cold, you would also have the rings shadowing you quite frequently as the sun was going behind the rings during the course of the day. So you'd spend a lot of time in the dark during the winter.

Think of the myths that would have grown up in a thousand Earth cultures if we'd had our own ring system. Ah, well. Yeah, talk about a rainbow bridge. That would be a rainbow covering the whole sky all year round. By the way, we will, of course, put up the link to Emily's blog entry where you can go directly to that beautiful YouTube video. What else you got? Yes. Well, this week, it's going to be exciting. We have another spacecraft launching called WISE, the Wide Field Infrared Survey Explorer. It's mostly an astronomy mission, but I'm

interested in it because it can actually discover brown dwarfs and even very large planet-sized objects that are relatively close to the solar system. So it's quite likely we will find a brown dwarf that is closer to us than the nearest star, which I think is very exciting. And it could even discover Neptunes or Jupiters that are lurking way out as far out as the Oort cloud. So that would be very cool. Still opening doors on your advent calendar? Absolutely. I decided that every single day this month, I would post an image of a different planet, moon, or asteroid in the solar system, and just do a little description. It's kind of like,

it's just an advent calendar. I'm going to keep it going, though, past Christmas, so as to be non-denominational, and I'll end it with the new year. Happy holidays, Emily. Talk to you next week. Thanks. See you next week, Matt. There's no need to wait. You can enjoy more of Emily through her blog at planetary.org. Check out her Twitter feed, too. I'll be back with Sean Solomon of the Messenger Mission to Mercury, right after Bill. Hey, hey, Bill Nye, the planetary guy here, vice president of the Planetary Society. And this week, I am very excited to report that a major U.S. aerospace corporation is planning a mission they're calling Plymouth Rock. This would be a mission to an asteroid with humans on board. These would be astronauts going to an asteroid. Instead of going

to the moon, which was cool and exciting and fun, they'd be going to someplace new, a new adventure using new orbital mechanics to operate a new spacecraft, the Orion, to go to a destination that will give us clues about the origin of the solar system. It'll be cool. It'll actually be extremely cold. But that's part of it. That's why these rocks have been spinning around our sun since things began around here. The deal is they're planning this seriously. So the U.S. would be using its resources to go to a new place. And this is fantastic. This is great news.

Meanwhile, not so good news. The Obama administration has decided to lift an injunction. has decided to lift an injunction. And the injunction was injunting against an ordinance that made people get background checks who were not a security risk, just to work on, let's say, robots on Mars. It's not a matter of national security. It's just sort of a tradition of not trusting anybody. It's very costly. I hope the administration gets over this and goes back to doing things in a smooth way so that we share information around the world using space exploration, if I may, to promote international understanding and planetary peace. Meanwhile, to Plymouth Rock. It's an exciting week in space. I've got to fly. Bill Nye the Planetary Guy.

Sean Solomon has joined us several times. The principal investigator of the MESSENGER mission is also the director of the Department of Terrestrial Magnetism at the Carnegie Institution in Washington, D.C. His spacecraft won't begin orbiting Mercury till March of 2011, but it has been very busy this fall. Here's just part of an update I got from Sean a few days ago. You can hear much more about MESSENGER, and especially what it has helped us learn about Mercury, in our complete conversation. It's available at planetary.org slash radio. Sean, welcome back to Planetary Radio. You made Time magazine. Indeed we did, Matt. We were listed as one of Time magazine's top 50 inventions of 2009, which pleased us and surprised us a little. Of course, our spacecraft was invented some years back. We launched in 2004 and have been flying for five and a half years.

But what I think time was recognizing was that we had to make a number of innovations to fabricate a spacecraft that would fly as close to the sun as we must do to reach Mercury in terms of materials, in terms of thermal design, in terms of protection, autonomy. And it's only in the last two years that all of that design work was shown to be just what we needed. So I view Time's mention of MESSENGER as a nice validation of our engineering team and all the work they did to make a spacecraft that could survive as close to the sun

as 70% of the distance from the Earth to the sun. You know, this is something that has only just occurred to me, and I won't even remember the name of the other mission, but I just read this week about plans for a new mission that is going to get pretty close to our home star. And I wonder if maybe they've learned some things from you and your folks. Indeed. I think you're probably thinking of the solar probe, which is a mission concept that NASA is now working on and will soon be calling for instruments. And that spacecraft is going to fly much closer to the sun than even MESSENGER does and try to understand all of the physics that goes on as the solar wind is accelerated near the sun and begins its long journey out past all of the planets to the outer reaches of the heliosphere.

long journey out past all of the planets to the outer reaches of the heliosphere. And indeed, a lot of the technology that went into MESSENGER and that was tested for MESSENGER is the starting point for the design of a mission that's targeting the sun and will have a very challenging environment even compared to what we're experiencing. I'm not a bit surprised. Indeed, you are closing in on 2,000 days in space and 4 billion miles, or 6.5 billion kilometers. And yet the best is yet to come. Tell us what happened just a few days ago that kept you on course for orbit around Mercury. Right, Matt.

Between almost all of the planetary encounters, and we've now had six of them since we launched, there is a major propulsive event, what we call a deep space maneuver. That's been planned from the outset as a way to retarget the trajectory of the spacecraft from the path it's taking after the most recent flyby toward the next flyby. There have been five in all. And last week, we completed the fifth and final deep space maneuver. So we are now on target to encounter Mercury for orbit insertion in March 2011. But let me tell you how good a job our mission design and navigation team did at threading the needle for that deep space maneuver. We are now on track to encounter Mercury to within about 170 kilometers of our aim point. And that aim point is 16 months away. We've got

to go around the sun many times. And yet we already can project that we're going to come in very close to where we want to be. And furthermore, the team has become very experienced at making small changes to the trajectory of the spacecraft by a technique known as solar sailing, in which they tilt the spacecraft or they reorient the solar panels and use the radiation pressure from the sun, bombardment of the spacecraft or they reorient the solar panels and use the radiation pressure from the sun, bombardment of the spacecraft by photons, to make small but continuous changes in the trajectory of the spacecraft. And so this distance that we are now estimating we are from our endpoint is easily correctable over the rest of the trajectory by solar sailing. So this is the last event.

It's behind us. We're right on track, and we're exactly where we want to be for orbit insertion in March of 2011. Well, thanks for the proof of concept for solar sailing since the Planetary Society, and we should say the Japanese Space Agency, hope to emulate your solar sailing next year. Tell us about the third and final flyby that was just last September 29th. Some scary moments, but you did pick up some science and some beautiful new images. Indeed, Matt. Your notes are very complete. All from your website.

The scary moment was a safehold. Your notes are very complete. All from your website. The scary moment was a safe hold. As we were approaching the planet, just about four minutes before closest approach, we lost contact with the spacecraft. The signal disappeared. And we were in eclipse, so we were on battery power. We were about to be occulted by the spacecraft, meaning that the line of sight between the spacecraft and the Earth was about to disappear as Mercury passed in between the two.

But we were still in contact, and we lost communication. And it was only after the eclipse and after the Earth occultation that we learned what had happened. that we learned what had happened. There was a configuration in one of the autonomy rules that tracks battery discharge during a solar eclipse that led a spacecraft to decide that it needed to switch power distribution units. We have a redundant power system. It made the switchover, but that switchover, by our autonomy rules, puts us in a safe hold mode.

And what that does is it keeps all of the science data we've acquired, but it stops the command sequence, the set of commands that govern the acquisition of new science data. So from that safe hold until we recovered more than a day later, we stopped taking science data. And so a lot of the observations that we had hoped to take during the flyby were not, in fact, made. That said, we took all of the data we planned up until four minutes before Claus's approach, and those Claus's approach data gave us a view of new parts of the planet.

They gave us a variety of observations of the planet's atmosphere and some new observations of how Mercury's magnetosphere behaves in response to variable solar wind conditions. I'm beginning to think that these SAFEN experiences are a rite of passage for most deep space spacecraft, but I'm sure it was still a very tense moment there in your control room. Well, take the following view. The messenger spacecraft, which is near Mercury, is sometimes on the opposite side of the sun from the Earth. Mercury can be as far as one and a half times the Earth-sun distance away from us, and that means that the one-way radio time from the spacecraft to the Earth can be as large as 12 minutes. Because we're so close to the Sun, if something unexpected happened and it went into a tumble,

we believe that under an arbitrary tumble, an arbitrary axis of rotation and speed, that our spacecraft could survive 30 minutes, but under the worst conditions, no more. And so if the two-way radio time between the spacecraft and the Earth is 24 minutes, which it would be on the opposite side of the sun, there's not enough time for us to detect that kind of anomaly and command the spacecraft to correct itself. And so a spacecraft-like messenger must be autonomous. It must have a set of rules that protect the spacecraft under foreseeable anomalies. And those autonomy rules have to be conservative. They have to act to preserve the spacecraft.

And sometimes that means, you call it a rite of passage, but sometimes it means we have to sacrifice a few of our scientific observations to ensure, in a conservative manner, that we are protecting the spacecraft. Sean Solomon of the Messenger Mission to Mercury. Just ahead is a small part of our conversation about the latest science data. Planetary Radio continues in a minute. I'm Robert Picardo. I traveled across the galaxy as the doctor in Star Trek Voyager.

Then I joined the Planetary Society to become part of the real adventure of space exploration. The Society fights for missions that unveil the secrets of the solar system. It searches for other intelligences in the universe and it built the first solar sail. It also shares the wonder through this radio show, its website, and other exciting projects that reach around the globe. I'm proud to be part of this greatest of all voyages and I hope you'll consider joining us. You can learn more about the Planetary Society at our website,

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Welcome back to Planetary Radio. I'm Matt Kaplan. The Mercury Surface, Space Environment, Geochemistry, and Ranging Mission is better known as MESSENGER. Principal investigator Sean Solomon says its instruments are revealing surprising details about a starkly beautiful little world. I know everybody loves to start with the images. We've talked about this in the past. But your spacecraft is doing much more than that. That includes your field of magnetism. It does include magnetism.

What we saw during the third flyby was a different interaction between Mercury's magnetosphere and the solar wind. Just to give some context, the first time we flew by Mercury in January of 2008, the magnetic field carried by the solar wind, the so-called interplanetary magnetic field, was steady and in a direction that let it flow smoothly around Mercury. And so the interaction between the solar wind field and Mercury's magnetic field was very, very modest, and there wasn't much energy transport between the two systems. The magnetosphere was very steady. And then in October of 2008, we flew by, and the solar wind field, which fluctuates in direction of 2008 we flew by and the solar wind field which which fluctuates in direction uh on a variety of time scales was in the opposite direction and instead of flowing smoothly around the neck news there was a very strong interaction between the solar wind field and mercury's field and a

phenomenon known as magnetic reconnection where energy is transported and field lines break and reconnect as they move around the planet was extraordinarily high, 10 times higher than typical at the Earth. And we could see a pulsating magnetosphere as we flew through it, and we could see evidence of magnetic reconnection events in the tail that we flew through before we encountered the planet. events in the tail that we flew through before we encountered the planet. Well, when we flew by in September of this year, we saw a third type of state of the magnetosphere.

The solar wind field was not steady. It flipped back and forth in the important direction north or south for these interactions. And what we saw was an extreme condition that we've experienced at Earth known as magnetic tail loading, where magnetic energy from the solar wind builds up in the magnetic tail of a planet to a point where it is released suddenly in a magnetic substorm. And this phenomenon is much more extreme at Mercury than at the Earth. First of all, it happens much more quickly. On the Earth, the timescales for these magnetic loading and unloading of energy in the tail

are in the range one to three hours. But at Mercury, the timescale is one to three minutes. Wow. Much, much faster, nearly, well, a factor of 60. But equally importantly, the amount of energy stored in the magnetic tail is so high that most of the energy in the system for a time is in the tail. And what that means is that on the opposite side of the planet, the day side of the planet, the magnetosphere loses most of its ability to stand off the solar wind.

loses most of its ability to stand off the solar wind. So during these kinds of transitions, the surface of the planet tends to be exposed to direct bombardment by the solar wind. This has great implications for the generation of the atmosphere and for the space weathering of the surface. So we've been really fortunate. The magnetosphere of Mercury is extraordinarily dynamic. It's the most responsive of all the planets to changes in solar wind conditions. And we've seen three different snapshots that are all very different. And what they promise is that we're going to have a great show when we get in orbit around the planet. What an incredible environment this poor little planet has to exist in. But what a great place to study all of this.

Sean, we will want to check in with you again, perhaps just before orbital insertion, as we build up to that many times amplified examination of this fascinating little world. Happy to join you at any time, Matt. And we will also put up the link, as we always do, to the official Messenger website, where you can find much more about everything that Sean has been talking about, including some very beautiful images and some pretty stunning animations

as well of the kinds of dynamism that this planet experiences in its environment, which may be invisible to the human eye, except through the help of our computers. Sean, once again, thank you so much. And I'll just say once again

that anybody who's hearing this as part of the radio show or the regular podcast will make sure that the entire interview is available as well, and you'll want to check that out. Sean Solomon is the director of the Department of Terrestrial Magnetism at the Carnegie Institution of Washington, but he has, as you've heard, been the principal investigator for this mission,

the MESSENGER mission to Mercury, which will be entering orbit around that planet, the first spacecraft ever to do so, after already having shown us much more of the planet than we have ever seen before up close. That'll be happening in 2011. And we'll be right back with this week's edition of What's Up, featuring my friend Bruce Betts. That's just a Planetary Radio. Bruce Betts is the Director of Projects for the Planetary Society, and he's going to talk about the night sky.

I don't know what else may come up. We'll just see. Happy December, Bruce. Happy December. Okay, we've got Jupiter up in the evening sky. We've got Mars rising in the mid to late evening over in the east, looking reddish and looking like a pretty darn bright star these days. It'll keep getting brighter until the end of January.

Pre-dawn Saturn high up in the south. We also have the Geminids meteor shower peaking on December 14th, the traditionally best of the year from a dark site, perhaps 60 meteors per hour. And it's a bit of a broad peak, so if you go out a day before, day after, even a couple days before or after, you should see an increased number of streaks of light going across the sky as dust and sand burn up. So check that out out it also occurs very nicely around new moon so there won't be a moonlight interference from that very nice i've

been looking forward to that uh since i haven't had much luck with the uh the last couple that you've mentioned now this one's really this one's more solid and consistent so if you if you don't have the bad weather then uh you're in pretty good shape. Yeah, the bad weather like we're headed into right now here in Southern California. Doubt many places will feel sorry for us, but okay. I also have this week in space history. Let's go there. And Apollo 17, the final human mission to the moon, was launched and landed this week in 1972. Can't believe it was this long ago because I'm just that old now.

1995, the Galileo probe enters the Jupiter atmosphere, the atmospheric probe part of the Galileo spacecraft 14 years ago. Wow. Yeah, time flies. On to random space fact.

Random space fact. Random space fact. Random space fact. Random space fact. The surveillance I have on you does pay off. That satellite, finally getting some value out of it. So Mercury, the diameter of Mercury basically would stretch from one side of the United States to the other side. Oh, okay. Well, it's a good-sized piece of rock there. I'm glad you brought that up since it didn't come up, talking to Sean. All right, we go on to the trivia contest.

And we asked you, what is the densest natural satellite in our solar system? Densest moon in our solar system. How do we do, Matt? Some very interesting answers. Almost everyone, even people who propose something else, like someone said Pluto's Hydra, hard to believe that we could figure the density of something that small that far away. But really, the error bars are so huge there that there isn't much point. Even that person said Io. That that's old pizza face, actually.

As it's known by its friends. who got the nod from random.org, got this in with a density of 3.530 rounded grams per cubic centimeter. So, Timo, we are going to send you a hug-a-planet. Actually, to be specific, a hug-a-Mars. Don't have a hug-a-io, and you wouldn't want to anyway. It would make a mess of your face. The most disturbing gift of the holiday season. Hug a I.O. Hug a I.O.

Hug a I.O. Hug a I.O. That's hard to say, too. Now with real lava. And it smells nice thanks to all the sulfur. Yeah, right. That'll clear out the science fair.

Whole new Make a Volcano project. We got this entry from Evan Demski, who did say Io, but Evan didn't get the nod. But he did say it's a well-known fact that Io is the most popular moon amongst dwarf stars. In fact, they wrote a song about it. Do you know the song? I apparently do not. Io, Io, it's off to work we go.

That's all he provided anyway. I'm done interrupting now. That's good, because I get grumpy when you do. And if you believe that, I have a pockmarked moon to sell you. Really? I will talk later. So anywho, on to the next trivia contest. Right now, as we speak, there are only two people on board the International Space Station.

After just being crazy busy for a while, there are only two up there. When's the last time there were only two people on board the International Space Station? Go to planetary.org slash radio to find out how to enter. By the way, they won't be that lonely for long. They'll be joined a little bit later this month by another three people. So this one you may have to work for a little bit, but it's worth it, isn't it? I don't know what we're giving away this time. Should we do another Hug a Planet, Hug a Mars?

Oh, I think you should decide. It's the king of prizes. I didn't even check to see that we have any left, but I'll tell you what, we will do that. In which case, you win absolutely nothing. Yeah, right. We'll go out on a limb and say you're going to win a hug of Mars and leave it at that. You'll need to get us your answer by December 14th at 2 p.m. That would be Monday, December 14th at 2 p.m. Pacific time. By the way, a hug of Mars, it's a squishy, ball-shaped geologic map of Mars that's fun to hug or to throw around the house. Our cat doesn't seem to be terribly interested in it,

but your child will be. It's quite lovely. Or even other people. I hope so. Anyway, everybody, go out there, look up at the night sky, and think about heaters when it's cold. Thank you, and good night.

He's Bruce Betts, the director of Projects for the Planetary Society. It's getting warm, getting warmer. He joins us every week here for What's Up. Planetary Radio is produced by the Planetary Society in Pasadena, California. Keep looking up. Music Thank you.