Planetary Radio: Space Exploration, Astronomy and Science - Magnets Roving on Mars

Episode Date: April 19, 2004

This week we hear about the strategically located magnets on the Mars Exploration Rovers and how are telling us more about the red planet.Learn more about your ad choices. Visit megaphone.fm/adchoicesSee omnystudio.com/listener for privacy information.See omnystudio.com/listener for privacy information.

The show is positively magnetic. That's this week's Planetary Radio. Hi everyone, I'm Matt Kaplan. They may be the smallest and least complex instruments on the Mars Exploration Rovers, but a handful of magnets are returning real science in concert with the other players on Spirit and Opportunity. We'll learn more about them in a minute. We'll also hear from Bruce Betts with What's Up and our newest trivia contest.

From What's Up to a heads-up about next week, Ray Bradbury returns to our little program. We'll bring you the legendary writers' inspiring and sometimes hilarious remarks at last week's celebration of Yuri's Night in Los Angeles. Be sure to join us, because you won't hear this anywhere but here. And here's another Planetary Radio exclusive. Take it away, Emily.

Hi, I'm Emily Lakdawalla with questions and answers. A listener asked, I've heard that Mercury is both the hottest and the coldest place in the solar system. How is this possible given Mercury's proximity to the sun? Although Mercury is neither the hottest nor the coldest place, it's quite true that it's a planet of extremes. It's easy to understand why Mercury is hot, since it's the closest planet to the Sun. Occasionally, the Sun as viewed from Mercury is three times as big as it looks from Earth, meaning that the Sun is ten times as powerful. Daytime temperatures on Mercury can reach 430 degrees Celsius or 800 Fahrenheit.

Only Venus is hotter because of its runaway greenhouse effect. So how can Mercury also be one of the coldest places? Stay tuned to Planetary Radio to find out. Walter Goetz is the magnet dude. Well, that's what the student astronauts called him. And it's an appropriate nickname. His team is responsible for the collection of carefully prepared and monitored magnets that occupy some prime real estate on the two Mars Exploration rovers, Spirit and Opportunity. Born in Germany and with a Ph earned in Denmark, Walter has been a happy

member of the MER team at the Jet Propulsion Lab near Pasadena, California. He appeared to be even happier at the party the Planetary Society recently threw for the triumphant scientists and engineers. As you'll hear, the festivities continued all around us as he described his magnets and their role on the red planet. We have been making magnets for Mars Polar Lander, then for Mars Lander 2000, no, it was the 2001 Lander, sorry, and then Mars Exploration Rovers.

This is one of the few projects, instruments, on the Mars Exploration Rovers that we have not managed to cover yet, which is surprising because this is a project that the Planetary Society is actually involved with. What makes these magnets special? We could also ask what is special with the magnets on Pathfinder. The special thing with the magnets on Pathfinder is that they were different from the earlier Viking magnets. They were very different in strength,

and this is really a greatly refined version of the Viking experiment, the Pathfinder experiment. What is special with the magnets on the Mars Exploration Rovers is the main goal is not observation of the accumulation of dust with the cameras. The main goal is actually IDD work on the magnets. This means different kinds of spectroscopy of dust, exploration or investigation of the dust by the means of different kinds of spectroscopy. And you said IDD. Yes, this means instrument deployment device.

So you obviously know the characteristics of these magnets extremely well. Yes, definitely. I have been very much involved in manufacturing these magnets. This is a precision device also. It is, for instance, the surface is flat within a few microns, and it has been glass bit blasted in a very controlled way so that the magnets have controlled optical properties. Of course, we still observe the accumulation of dust on the magnets by the means of cameras,

but the main idea is really to get the chemical analysis of the dust, of the magnetic part of the dust, which accumulates on the magnets. And so I assume then that the dust is examined by the spectrometers on the rover. Yes, it is examined by the alpha proton x-ray spectrometer, which does measure the chemical composition of the dust. And then we also want to investigate the dust by the means of Muesbauer spectroscopy. Muesbauer spectroscopy tells us something about the ion mineralogy of the dust. But we have to wait more to get decent spectra from Muesbauer spectroscopy. The mission has to survive.

We need to wait until enough dust has accumulated on the magnets. And then we can also study it by muspore spectroscopy. This will be very important. Even though it's not the core of this particular experiment, that is to basically measure the amount of dust, magnetic particles that collect on the magnet, what are you seeing, what kind of data are you gathering about the amount and for that matter maybe the quality of that dust? We are mainly working with airborne dust because these magnets are exposed to the air into the dust-filled atmosphere.

We can compare MöA airborne dust, spirit airborne dust to opportunity airborne dust. That's one thing. And we do that. The differences are very small, as you can imagine. And we also compare it to Mars Pathfinder airborne dust. It looks that the airborne dust is rather uniform. Around the planet? Yes, around the planet.

But we also compare the accumulation rate, how fast it accumulates. And this is a measure of how much dust is near the surface. This quantity can then be compared to the so-called opacity of the atmosphere, where atmospheric scientists look all the way through an atmospheric column and determine how much light is absorbed or scattered out of the pathway. This is also a measurement of the amount of dust in the atmosphere, but it refers to the whole atmosphere, to the entire atmospheric column, whereas we are gathering dust from the...

Very near the surface. Yes, exactly. This would seem to be of enormous interest to many atmospheric scientists on Mars, and for that matter, those who are doing remote sensing of Mars from orbit, I would think they'd have to take it into account in evaluating their data.

Yes, it has to be put together, yes. But it is just like atmospheric studies. You do not, when you measure the tau for one day, it's not interesting, it's just one point. The interesting thing is to get frequent observations and study it over a long period of time. You said tau. Yes, sorry, tau is the dust opacity. The larger tau is the more light, think about a beam of light emitted by the sun propagating through the Martian atmosphere until it hits the surface of Mars. Part of this incident light is scattered out of the way due to

scattering of light on particles. part of the light is absorbed. Which is certainly something anyone who has sat inside a slightly dusty house on Earth and watched a shaft of sunlight, watched the dust pass through that shaft of sunlight. Or if there is a smoker in the family, you can see a scattering of light, the small particles, micron-sized particles from the smoke, cigarette smoke. Which leads me to another question. What do we know now about the amount of dust in the Martian atmosphere as compared to a typical site on Earth?

I don't know what a typical site on Earth would be. Oh, yeah, it's a very interesting question. First, it certainly depends on the region where you are on Earth. First, it certainly depends on the region where you are on Earth. Mars is extremely interesting, but the Earth is a planet which is much more heterogeneous. It's very diverse. It's much more diverse, exactly. In the Sahara, you certainly would have a larger amount of airborne dust than, let's say, on an island somewhere in the Pacific Ocean. By the way, dust particles from the Sahara, they are transported,

and also small sand-sized particles are transported over thousands of kilometers, and you can prove that. So they are also distributed over a large region of the Earth. But still, you have the kind of dust which you would find suspended in the atmosphere. It will be very different, for instance, in a desert-like region or near an ocean. So actually difficult to compare because Mars is as fascinating as it is. It's much more uniform than the Earth. Exactly. It's much more uniform.

But it's an unknown world, so therefore it's extremely interesting. Tremendously exciting, yes. And it is the planet which is closest to the Earth. If you average over all any kinds of properties, except the biosphere maybe, then Mars still remains the planet which is closest to the Earth. When we return, Walter Goetz will tell us more about his Martian magnets, including what they're made of.

Please stay with us. This is Buzz Aldrin. When I walked on the moon, I knew it was just the beginning of humankind's great adventure in the solar system. That's why I'm a member of the Planetary Society, the world's largest space interest group. The Planetary Society is helping to explore Mars. We're tracking near-Earth asteroids and comets. We sponsor the search for life on other worlds. And we're building the first-ever solar sail. You can learn about these adventures and exciting new discoveries from space exploration in the Planetary Report.

The Planetary Report is the Society's full-color magazine. It's just one of many member benefits. You can learn more by calling 1-877-PLANETS. That's toll-free, 1-877-752-6387. And you can catch up on space exploration news and developments at our exciting and informative website, planetarysociety.org. The Planetary Society, exploring new worlds. Planetary Radio continues.

Let's rejoin scientist Walter Goetz at the recent Planetary Society party honoring the Mars Exploration Rover team. I just realized I hadn't asked him a fairly obvious question about his attractive little devices. What is the magnet actually made of? Is it an alloy? Is it rare earths? Yeah, good question. It's different. We have, in total, we have seven magnets on each rover.

And then we have two astrobots. One astrobot, of course, well, this is your astrobot. We know them well, yes. But we call them our astrobots, but these are actually your astrobots. No, please share them with us. But these magnets are differently made. For instance, we have a magnet near the calibration target on the rear side of the rover. And this is a very strong ring magnet. About one-fourth of a millimeter below the top surface

is placed the permanent magnet which is made of samarium cobalt. This is a ring magnet, an extremely strong ring magnet at, as I said before, 0.4 millimeters below the aluminum surface. So this means you cannot see the magnet from outside but it creates a magnetic

field. These field lines, they can traverse aluminum without problems, and therefore, dust is accumulated on the surface. I think of anybody who's played with iron filings through a piece of paper with a magnet underneath. Yes. And then we have other magnets which are supposed to be investigated by the instrument deployment device, by the robotic arm which carries the Mössbauer spectrometer and also the... The microscopic imager and so many of the other instruments. Yes. And the Mössbauer spectrometer has to look for the iron mineralogy in the dust. So we wouldn't like to put iron in the magnets in any way

because we only want to see the iron which is in the Martian dust, not the iron which we bring along. So therefore, the magnets in front of the camera mast, designed to be studied by the robotic arm, the camera mast, designed to be studied by the robotic arm, is made of ultra-pure aluminum, 99.999% aluminum. This is at least the top layer of the aluminum housing, is ultra-pure aluminum.

Because any aluminum you use in today's world contains about 1% of iron and you could very easily see it with MÜSBAUR spectrometer. I can tell you we were very... When we started to develop these magnets we of course we used ordinary aluminum. We were very astonished that we saw a beautiful iron peak

after a few hours of integration. So we had to buy extremely expensive aluminum, which is, by the way, very soft. It's not pleasant for technicians to work with pure aluminum. Not typically what you'd want to make a Mars rover out of, I imagine. Exactly, yeah, exactly. But here it was very important so that we get only signal from the iron in the Martian dust. Really, as we've been talking, the party has kind of almost come to an end around us, and I haven't let you drink, I haven't let you finish your beer.

Yeah, but I... Oh, you already did finish. I enjoyed to talk to you. No, I did too. And as I said, this is the first chance we've ever had to talk about the magnet experiment on the Mars Exploration Rovers. When do you expect that you might be getting back more of the spectroscopic data that you said that you have to be patient about? We have already got data back from the magnets. They look much like the airborne dust we have, we knew from

Mars Pathfinder. So far we already got that there is this dust has the properties which we expect, but in order to study fine very fine difference between for instance spirit and opportunity

this takes long time, but very roughly speaking it has the properties which we know, which we did expect. By the way, we have also four other magnets. I just want to mention them briefly. They are on the bottom of the rock abrasion tool. And while we grind a hole into the rock, a dust plume made of rock powder,

not of airborne dust, made of rock powder, not of airborne dust, but of rock powder, is produced, and the magnetic part is attracted to these magnets. And we have also very interesting results from these magnets, actually. And it's a huge difference between spirit and opportunity.

Really? Now that's fascinating. Yes, it is. We did accumulate a huge amount of magnetic material on both rovers. But the material on the rock abrasion tool magnets on Spirit, they are just black. Black like magnetite, which is a common magnetic material on Earth. But the other one is a bright red, very intensely red. From Meridiani.

Yes. So it reflects them. Of course, it reflects the mineralogy of the rock. But it also tells us something about the amount of strongly magnetic material in the rock. And this is, of course, a support for Muesbauer, for the interpretation of the other spectra we have on board. For instance, we believe there is mechemite, another magnetic material, in the dust, in the rock powder.

We suggest to the other spectroscopists to take that into consideration if they can better fit their spectra and so on. So clearly these little magnets are very much playing their part in sort of a symphony of instrumentation on the Mars Exploration Rovers. That's right. It is quite unique in that sense that the magnets are involved or play together with most of the other instruments. Play together, I like that.

We play also together, the scientists. And we will let you finish playing here tonight at this party. Thank you very much for talking to us, and we'll look forward to hearing about more data from those magnets on the rovers. With pleasure. Thanks. Walter Goetz continues to monitor the Mars Exploration Rover magnets. Check our website at planetary.org slash radio for the link to a brief overview of the work underway.

I'll be back with Bruce Betts right after this return visit from Emily. I'm Emily Lakdawalla, back with Q&A. It's easy to see that Mercury can be hot, but how can it also be cold when it's the closest planet to the sun? The answer is that Mercury spins very slowly. It spins so slowly, in fact, that it takes two of Mercury's years, or 176 Earth days, for one solar day to pass on Mercury. So any place on the surface receives daylight for 88 Earth days, followed by a night lasting another 88 days. Without an insulating atmosphere, once the sun sets,

Mercury can't hang on to its incredible heat. Nighttime lows on Mercury can reach minus 180 degrees Celsius or minus 300 Fahrenheit. It's not the coldest place in the solar system, but Mercury's daily temperature variation of over 600 degrees Celsius or over 1,000 degrees Fahrenheit is truly extraordinary. Got a question about the universe?

Send it to us at planetaryradio at planetary.org. And now here's Matt with more Planetary Radio. Almost the end of this week's Planetary Radio, so it must be time for What's Up? And sure enough, Bruce Betts, the director of projects, joins us in the Planetary Society headquarters. What do you call this area, anyway, that we're sitting in today? This would be the guest's lounge.

The guest's lounge. No, it's not. It's the living room of the original house. The former residence, right? It's quite a place. We'll have to, you know, give people a radio tour of the headquarters sometime. What is it, a 1902? 1903. 1903 Craftsman?

Yeah, Craftsman House, designed by Green and Green. Yeah. Well, folks, drop into Pasadena, and we'll show you around. What do you got for us this week? But in the meantime, look up in the night sky and see Venus in the evening, right after sunset, still really, really bright over there in the east. You'll see the moon, the crescent moon, right near Venus on April 22nd. And then the following evening, the moon will climb up and be right next to Mars.

Mars is to the upper left of Venus these days, but really getting very close to it, only six degrees apart, only six degrees of separation right there between those two. So look up and look for Mars to the upper left of Venus. You really ought to say something. It's a universal constant, six degrees. It is indeed. If you look to the upper left of Mars, you'll see Kevin Bacon. Kevin Bacon?

No, not him. He'll explain later. I'll explain later. I'm sorry. We have my son Daniel here. He's a little perplexed. Continue to look. To the upper left, you will see Saturn, nearly overhead at sunset.

A little bit farther over, bending towards the west, you will see Jupiter, extremely bright. So four great naked-eye planets. Kevin Bacon did play an Apollo astronaut. And Apollo astronauts went to the moon. And the moon will be in the night sky. Wow, that's only like three. Anyway, moving on to this week in space history.

On April 19th of 1971, Salyut 1 was launched, the world's first space station. Moving on to random space fact. We're going to get solar once again. On the sun, sunspots appear dark, but it's actually because they are cooler than their surroundings. And so even though they are still bright, still hot, they appear darker because of their lower temperature. That's why you can see sunspots. I was always amazed by that as a kid because

I had heard this. We've known this for a long time. But I thought, boy, they must be like cold compared to the rest of the sun. Not really, right? They're still pretty hot. They're still pretty hot. You could still toast some serious marshmallows from several million miles away over those puppies. Uh-huh.

Daniel's here right because of the trivia contest. He is indeed. Okay, but we should go through last week's contest. All right, last week's contest, we asked you, what was the success criterion for each of the Mars Exploration Rovers in terms of distance traveled? They had to last 90 days to be considered a success in that aspect. What about 90 Martian days? What about what distance they had to travel? What do people say? This is the equivalent to 12-month, 12,000-mile, and this is the mile part of it.

We had a lot of entries. And, you know, I say that it's a cliche thing here because I say it every week, but it's true. We're getting our people who enter every week, and we get new people every week. And I want to let you new folks know, you know, hang in there. Hang in there. We're not that big a show yet that, you know, we've got 15,000 entries coming in. Everybody probably gets a chance to win eventually if you have the right answer. And the right answer this week came from Bjorn Isaacson.

It's another one of our international listeners on the web. Bjorn Isaacson. It's another one of our international listeners on the web. Bjorn Isaacson of Norway said that the MER rovers had a mission success requirement to go 600 meters per odometric count. And he adds, meaning they could turn a lot in place and meet that objective. I guess they can just kind of, you know, spin on a dime, which they can do, and that counts. So Bjorn. Subtlety I was not aware of. Thank you, Bjorn.

Yes, so success. Rovers, success. They're successful. Great. He will get a Planetary Radio t-shirt for this week. We'd love you to enter our contest. Go to planetary.org slash radio and answer the following question, which is having, once again, to do with the sun, the object of choice randomly chosen by my son, Daniel.

Who's holding his breath at the moment. Until I get the trivia question out, I've got to hurry. This is another tricky one to phrase, but every star in the sky, astronomers get bored and they've categorized them all using letters. What letter category is our sun in stellar classifications? What letter is it? Class what? So this is not Star Trek stuff.

This is what astronomers actually use to classify the different types of stars. I assume where they are on that thing called the main sequence, right? Indeed. I faintly remember that from astronomy class. On or off the main sequence, yes, yes, in terms of their temperature, color, things like that. You told people out, Andrew, they go to the website, and we will tell them, please let us know. Get it to us by Thursday noon Pacific time. It's noon here, and it should be where you are, too.

But noon on Thursday is the deadline. And do you have anything else to add? I just want to encourage everyone to go out there, look up at the night sky. Hey, Daniel, what should people think about when they look up at the night sky? What do you think? How the sun was made. All right, go out, look up in the night sky, think about how the sun was made. Thank you, and good night.

Bruce Bettson's son here at the Planetary Society, where we do What's Up whenever we can, and always at the end of this show, Planetary Radio, Bruce is the director of projects for the Planetary Society, and joins us each week. That's it for this week. Join us next time for

Ray Bradbury and more from the April 12 celebration of Yuri's Night. Take care, everyone.