Planetary Radio: Space Exploration, Astronomy and Science - Turning the Spotlight to Uranus and Neptune with Heidi Hammel

Episode Date: July 17, 2006

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Transcription by CastingWords the final frontier. I'm Matt Kaplan. They are beautiful, and they are much farther away than Jupiter and Saturn, and they've gotten a bad rap with some scientists saying they're not particularly interesting. Wrong, says Heidi Hamel, and she'll tell us why she loves them. The Space Science Institute's co-director of research makes a good case

for much more research on these true blue gas giants. Later today, we'll go to Bruce Fetz for the lowdown on what's high up in the night sky, along with a new space trivia contest and your chance to win a Planetary Radio T-shirt. Let's hope that by the time you hear this week's show, Discovery is safely back on the ground. At last word, NASA had given the go-ahead for a Monday morning July 17 landing. That was after astronauts took another look at the nose of the spacecraft and determination that the slow leak of either hydrazine fuel or nitrogen gas

from one of the shuttle's three auxiliary power units won't be a problem. German astronaut Thomas Reiter won't be along for the ride. He's the newest resident of the International Space Station, which now is back up to a crew of three. Robert Bigelow has proven he's not full of hot air, but his Genesis 1 spacecraft is. The big inflatable test module made it to orbit, atop a converted Russian missile,

and appears to be working well. Bigelow Aerospace's goal is creation of a huge inflatable space station, and they want to get there soon. Mars Exploration Rover Opportunity is currently detouring around a sand drift that is between it and Beagle Crater. You can read more from Emily Lochte-Wallace's blog at planetary.org, which is a nice segue to Emily's Q&A contribution for this week. It's in living color. I'll be right back with Heidi Hamel. Thank you. But how would they really look to the eye of an astronaut? Four spacecraft have produced most of our iconic images of the outer solar system's giant planets and moons,

Voyager 1, Voyager 2, Galileo, and Cassini. As each spacecraft whizzed by a target, mission scientists have produced stunning color image after image of these strange places. But the colors in these images are usually not quite what human eyes would see. If present, human eyes would still perceive plenty of color. But the colors would be more muted, pastel tints and shades of the yellows, reds, and browns that the space images show us. Jupiter's so-called red spot would look a light brownish-orange. The globe of Saturn would not be yellow, but instead pale peach.

Why don't the images that are released from space missions more accurately represent what the human eye would see? Stay tuned to Planetary Radio to find out. It's high time we had a conversation with Heidi Hamel. She's not a complete stranger to our show, since she has been heard briefly in a couple of previous episodes, but we've wanted to get a full report on Uranus and Neptune for ages. Heidi is co-director of research for the Space Science Institute in Boulder, Colorado. We caught her at her home in Connecticut, but she could almost as easily have been on top of Mauna Kea on the big island of Hawaii,

where the gigantic Keck telescopes have provided some of her best images of these distant blue gas giants. Heidi, welcome to Planetary Radio. It's great to be here. You've actually been on before, as we pointed out, but it's a good chance to catch up on what's going on in the outer solar system, particularly with, I don't know if they're your two favorite planets. I imagine Earth is up there someplace. But Uranus and Neptune, which, you know, I hate to say this, but seem to be at sometimes,

at least in terms of missions within our solar system, are sort of left out in the cold, almost literally. Well, yeah, literally, figuratively, metaphorically, they're always left out in the cold. And, you know, the reason for that is that they're hard to do. And not only are they hard because they're so far away, much, much further than Jupiter. Jupiter's practically our neighbor. But they were affected by some bad timing, at least in the case of Uranus. When Voyager flew by Uranus in 1986, it happened to fly by at a particular season, which we have

been learning over the past few years was probably the most boring season of Uranus that one could have chosen if one had a choice. We didn't have a choice, obviously. Voyager flew when it flew. But, boy, we wish we were flying by Uranus right now. And, you know, there is new horizons, and, of course, we are thrilled that it is on its way to Pluto. But it does seem like maybe Pluto gets more attention just because it's that little body that's a lot farther out. Well, yes, Pluto does get more attention just because it's that little body that's a lot farther out. Well, yes, Pluto does get more attention. It's not just because it's the little guy and everybody loves the underdog,

but it's also an interesting class of bodies, the Kuiper Belt objects. Sure. Yeah, I think it's fine that Pluto gets its day in the sun, so to speak. But I do wish that Uranus and Neptune got more respect. They deserve more respect. And they certainly are interesting places. They can hold their heads high. Let's start with Uranus, which is a pretty exciting place, we've learned,

and in fact has a major event, something we get two of every year here on Earth, but is coming up for the first time in, what, over 40 years. That's right. That's the equinox of Uranus. This is the point in the season of Uranus when the planet is sideways to us. You know, this planet spins tipped over on its side, kind of like rolling around the solar system, where its pole around which it spins lays in the plane of the solar system. And it takes a full 84 Earth years for Uranus to make a trip around the sun.

And what that means is that its seasons are each 21 years long. And it just so happened that when Voyager flew by in 1986, the pole of the planet, the south pole of the planet, was pointing directly at the sun. And that means no matter how much that planet spun, you only saw the southern half of it. Uranus, at least current theory says, got knocked for a loop, got knocked on its side, unlike the other planets. Well, actually, current theory, if current means within the last month, has a different explanation for that. You're kidding. Within the last month?

Yeah, within the last month. There's been a publication in the Journal of Nature saying that, well, you know what? You don't really need to have a collision that knocked this planet over on its side. It's possible that during the early years of the solar system, when Jupiter, Saturn, Uranus, and Neptune were forming, they weren't exactly in the locations they were now. They tended to migrate. You know, they changed their locations a little bit as they were forming and drifting around that early sun.

And at some point, they interacted with one another to the point that you could have, you know, pumped up the axial tilt of these planets just a little bit and a little bit more and a little bit more and eventually ended up with one turned on its side like Uranus. Wow. And so which of those is correct? You know, collision is easy to understand, but this new theory suggests maybe you don't need the collision. And so that's interesting. It kind of makes us all take a step back and think about that.

We don't really have any way of knowing which of those is the correct answer yet, but we'll probably be trying to think of some observational test, measurement of some chemical in the atmosphere or something like that, that might help us to distinguish between the cases. But isn't that interesting? Absolutely. Very, very recent change in our thinking. And regardless of how it happened, this explains why the south pole of a planet could be pointed at the sun.

That's right, yeah. But, you know, as the planet moves in its path around the sun, a quarter of a year later, you're at the point where they're looking at the planet sideways. And so the entire planet is getting sunlit now from the South Pole all the way to the North Pole. And if you think about that for a second, that's kind of neat because not only does that mean we can see the whole planet for the first time in 21 years. But it means that that North Pole that has been sitting in darkness for 20-odd years

is now getting sunlight. And getting warmer. And, well, I don't know if it's getting warmer or not. You know, when Voyager flew by, it had an instrument called the IRIS, the Infrared Spectrometer, that could look at the temperature of the planet and oddly found that the poles seemed to be equal temperatures, even the one that was in the sun and the one that was in the darkness. So that told people, hmm, well, there's some kind of an atmospheric circulation going on here. But even so, the planet itself, to the visible cameras that Voyager had, was really very,

well, there's no other word for it. It was boring. There was really no clouds to speak of. You did a lot of image processing. You could pull out the banded structure on the planet, which was banded like Jupiter, like Saturn, with, you know, the bands going around the planet and changing their brightnesses with latitude. But it was tipped over, you know, so it looked kind of like a bullseye because the pole was pointing at the sun. The famous bullseye, yeah. Yeah, that's right. But what's really fascinating about Uranus to us right now is that as we are approaching this equinox,

where the entire planet is starting to get sunlight, both hemispheres of the planet, we're seeing all kinds of cloud activity. You know, in a single set, a single image from the Keck telescope, the Keck 10-meter telescope, a single image of Uranus might have as many as 35 or 40 clouds in it. Now, the entire Voyager encounter with Uranus reported only, you know, less than a dozen clouds. So a single image from Keck has 10 times as many clouds. So that's telling us that it looks like the activity on this planet, the convective activity,

the clouds, thunder clouds that we see, are turning on. And it's not just, you know, a single image. We have series of images where we see bright clouds, and then a day or two later those clouds are gone, literally gone. They've subsided. So the planet is active, and we're seeing that activity now. Whether or not it's related to this changing sunlight is a question of major debate, because all our theories say this is a dormant planet.

But, of course, all our theory is based on the time period of the Voyager flyby. And so, hmm, maybe, maybe it's not as dormant as we thought. Maybe it was just, just a case of timing. We'll be back with Heidi Hamel when Planetary Radio returns in a minute. 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.

We didn't just build it. We attempted to put that first solar sail in orbit, and we're going to try again. You can read about all our exciting projects and get the latest space exploration news in depth at the Society's exciting and informative website, planetary.org. You can also preview our full-color magazine, The Planetary Report.

It's just one of our many member benefits. Want to learn more? Call us at 1-877-PLANETS. That's toll-free, 1-877-752-6387. The Planetary Society, exploring new worlds. Welcome back to Planetary Radio. I'm Matt Kaplan. We'll get to its even more distant neighbor, Neptune, soon. But the Space Science Institute's Heidi Hamel has more to tell us about Uranus and its approaching equinox. Is the equinox going to help us at Uranus in other ways, Maeve, to study the Uranian system? Absolutely. You know, already we have learned some really amazing things about the Uranus system as we are watching its appearance changing. One of the things we've been doing is we've been looking at the ring system of the planet. Imke de Potter at Berkeley has been

leading this effort with the Keck telescope, and Mark Showalter has been using the Hubble Space Telescope to look at the ring system of Uranus. And what we've been seeing, and you can imagine, when the planet was pointing at us, when the pole was pointing at us, its rings were sort of more of a bullseye pattern encircling the planet. But as we approach equinox, we're seeing the ring system from the side. So what we say is that the rings are closing up. So what we say is that the rings are closing up. They're going from a face-on configuration to more of the kind of ring system you're used to seeing around Saturn. So we'll see them on edge.

We're seeing them on edge, exactly. And what happens is as these rings close up or go into this edge-on configuration, it becomes easier to detect fainter rings because you can see them near their edges more clearly when they're sort of closed up like that or on edge. And what's happened is Mark has discovered two new rings, rings that we didn't even know about prior to four or five months ago. And he found them in Hubble images and went back and looked at the Voyager images, and sure enough, they were there, but they're outside the main ring system and so no one looked out there for them.

I want to mention that on the planetary.org website, if you look for the listing on Uranus, you can see a series of four images that actually shows this shift year by year as we head toward the equinox on Uranus. And the other thing it shows, Heidi, that's just fascinating, each image year by year gets better, I guess, because we're getting so much better at ground-based astronomy. Well, it's a combination of things. Yeah, those images were taken by Imke de Potter and I at the Keck 10-meter telescope using their adaptive optics system on the Keck.

And what happened was, you know, when the Keck started working with this adaptive optics, it was really designed to be used with a star, with a point source. And Uranus is not a star. It's not a point source. It's this big, well, big is a relative term, isn't it? It's bigger than a star appears to be in the sky.

But it's certainly what we'd call an extended object, not a point source. What you see in that progression of images on the website, you can see us learning how to adapt the adaptive optics system to do its tracking on an extended object. In other words, we optimize the way the telescope works to do a better job of taking out the Earth's atmospheric motion. It's a combination of us getting better in general and also really tweaking our system to do the best job it can for the object we're looking at. But you can definitely see improvement over the years. We think we're almost near the end of what we can do. I mean, we've gotten it tweaked up that we're working right at the limit of the telescope's performance,

and it's pretty darn good. Heidi, we've got to save at least a couple of minutes here, which is about all we have left for Uranus's big blue neighbor. But I do want to ask you, are you satisfied with this big event coming up in 2007? Are you satisfied that at least there will be enough ground-based observation to learn everything we can? Well, I'll tell you, we're working very hard to prepare for the equinox. everything we can. Well, I'll tell you, we're working very hard to prepare for the equinox. We had a workshop last May where we got observers from all over the country and even from some other countries to come and talk about the event. And we are doing everything we can to coordinate the

observations. It's tough, though. You know, we have to apply for time just like any other astrophysicist. It's a unique event, but it's a body that we've already sent a spacecraft to. And so there are some people who think that since we've sent a spacecraft there, we already know everything about it. And why should we use our valuable telescope time to look at it? So it's a challenging situation for us to change people's thinking and really make them understand that Uranus is not a static object, that it really is time variable.

And boy, if we miss this opportunity next year, we're going to have to wait another 42 years. I hate to do this to you, but let's take a minute to talk about that other planet, the one that you helped turn into a movie star. That would be the planet Neptune. Yeah, it's another favorite planet of mine. You know, the thing I love about Neptune is that I never know what I'm going to see when I go to the telescope to look at it. You know, when Voyager flew by, it had the great dark spot, which dominated all the beautiful pictures we got from Voyager. But when we looked a few years later

with Hubble, that was gone. The dark spot was gone, and there was a new dark spot. Now, what's it doing right now, you may ask? Well, we just got some images with Hubble just a few weeks ago, and we don't think we're seeing any big dark spots, but we think there may be a few little dark spots. We're really not sure yet. There's nothing really obvious there, but I can say that the planet is changing again. The banded structure in the southern hemisphere is spreading out and getting more

muted. So watching Neptune, it's like watching a work in progress. You never know exactly what it's going to do next. And it's so beautiful. It's a gorgeous planet. People should go to planetary.org and they can watch that movie that I mentioned. Give us a 20-second description of what you were up to there.

Really, we're trying to understand the overall cloud structure on the planet. And so the way you have to do that is you have to take a long sequence of images of the planet. You can't just take one snapshot because you don't know what's lurking on the other side. You know, are there dark spots? Are there bright spots? And it changes so dramatically from year to year that you really need to do a full-up imaging sequence to understand it. And then once you've got all those images, well, why not make a movie, huh? And it's beautiful. We're out of time. Heidi, you've got to come back as we get closer to this equinox on Uranus, and for other reasons, too, to talk about what's going on with these gas giants

that don't get the attention they deserve. And I think that's been made very obvious from this conversation. I look forward to talking to you again soon. Thanks. It's been a pleasure. Heidi Hamel is with the Space Science Institute in Boulder, Colorado, although she spends most of her time in Connecticut, and now and then some on top of Mauna Kea where the Keck telescopes are, those incredible 10-meter instruments.

And she is also a member of the board of the Planetary Society, we should mention. We'll have her back on sometime soon as we approach that great event that's being watched carefully from the ground and from the Hubble Space Telescope, the Equinox, approaching in 2007 at Uranus. Approaching us quite a bit sooner is a return visit by Emily with the rest of this week's edition of Q&A, followed by What's Up with Bruce Betts. Bruce Betts. I'm Emily Lakdawalla, back with Q&A.

Why don't they make space images a more accurate representation of what the human eye would see? Because spacecraft cameras aren't actually designed to have high fidelity to human color vision. Human color vision depends upon three different kinds of light-sensitive cells in our retinas that respond to three different broad bands of colored light. Spacecraft color vision usually depends upon color filters that block out all but some wavelengths of colored light. While it would be possible to fly a spacecraft camera with filters that see wavelengths similar to the ones our eyes see, such filters would not make good science data. Scientists like to choose filters in which commonly occurring

space materials, like hydrogen and methane, strongly absorb or reflect light. The way a target's appearance changes as you look through these different filters tells scientists what materials compose them. Such images may even be in ultraviolet or infrared wavelengths that the human eye can't perceive at all. You can combine any three filtered images to make a color view, which is how they make their pretty false color pictures. But to make pictures that really show what human eyes might see, it takes a lot more data and time-consuming processing.

Not a lot of scientists are doing this work, but there are increasing numbers of amateur image processors out there who are undertaking the task. Got a question about the universe? Send it to us at planetaryradio at planetary.org. And now here's Matt with more Planetary Radio. It's time for What's Up on Planetary Radio. Bruce Betts is not quite here, but within reach electronically. He has been vacationing a bit, and so, Bruce, we find you out there on the cell phone, I believe. Indeed, but always there in spirit.

Always with us, close to our hearts. Exactly, and speaking of other things close to our hearts. Exactly. And speaking of other things close to our hearts, let's talk about the night sky. So our planets, as I mentioned before, they're just disappearing on us in the sky these days. But still, in the pre-dawn sky, Venus, the brightest object there, but you have to look not too long before dawn, very low in the east. Jupiter, still very easy to see. Up high in the sky, brightest object in the evening sky.

And if you get really lucky and you look shortly after sunset, but after it gets dark, look in the west. You'll almost certainly still see reddish Mars in the west. And below it, you may or may not see Saturn. But they're dropping away. There's also a mediocre meteor shower that I mentioned for completeness. The Delta Aquarids, usually producing about 20 meteors per hour at their peak, that's from a really dark site. Good news about meteor showers is you can just go out and lie down

or sit down and stare up at the sky and see if you see any of those streaks going across. Anyway, it peaks on July 28th. That's our sky roundup this time around. Yeehaw! This week in space history, of course, has some gigantic anniversaries. 1969, humans first walked on the moon in this week. And then seven years later, in 1976, 30 years ago, Viking 1 successfully landed on the surface of Mars, giving us our first successful Mars robotic lander. And some great photos. Well, yeah, yeah.

It's red, it turns out. Kind of reddish. Uh-huh. On to Earth. Earth, our planet, has the highest density of any planet at 5.52 grams per cubic centimeters. Remember, water, of course, being one gram per cubic centimeter. Though people often throw out mercury, and if you adjust for all the gravitational squishing that happens on the inside of the Earth

due to it being bigger than mercury, it would have a higher density because it's having a higher percentage of iron. However, darn it, we win in the real world. I'm glad we're ahead in something. I think we're ahead in a few other areas, like, oh, presence of life. Well, as far as we know. Yeah. But, yes, I think in terms of, yeah, civilization, details like that.

We win. All signs indicate. Yeah. All right, let's go on to the trivia contest. We asked you, which planet has the smallest axial tilt? So tilt of its rotational axis relative to

the line perpendicular to its orbit. How'd we do, Matt? Everybody got it right. Everybody but one person. We won't go into detail, but one person did think it was Uranus, and I think that's because they got tilted about 90 degrees off of where they should have been by that question. I've been that way before.

I've seen that. You kind of list. But the seasons are good on one half of you or the other, which you can't say about Mercury, because Mercury has virtually no tilt. Now, Bruce, we actually, there was a range here. While almost everyone said mercury, there was a big range from zero degrees of axial tilt up to 2%. And our winner, Josh Cumby of Cincinnati, Ohio, he's one of the two percenters. And so, Josh.

Two degrees there, man. Sorry, two degrees? Not percent. Oh, did I say percent again? I did that before we started recording. I don't know why I insist on saying percent, but it is two degrees. There must be some Freudian explanation for that, but just the same. Josh, you're going to be getting our less than Freudian planetary radio T-shirt.

I'm just going to leave that one. Yeah, well, essentially Mercury has no axial tilt, so its spin axis is completely perpendicular to the plane of its orbit, so the planets do have some variability over time scales ranging from tens of thousands to many millions of years in their axial tilt, including Earth, which varies by a couple degrees, or Mars, which actually has a very extreme variation in its tilt, which changes the climate on Mars quite significantly over these time periods.

You know, you're a planetary scientist. Can I ask you a question? Sure. Can I look at my books? Yeah. One of our listeners said that there is some indication that Mercury may eventually be tidally locked to the sun and therefore would do what, you know, I guess astronomers thought it did for many years, which is only show one face to the sun. Interesting. That would surprise me, considering it's already in a resonance right now, 3 to 2. So its year and its day are related by the ratio 3 to 2,

which already gives it some benefit in the land of orbital mechanics in terms of the resonance. But I can't guarantee that it wouldn't happen, especially if, I don't know, Venus burps in the wrong direction. But still, yeah, right now it is in this weird resonance, and as you say, astronomers assumed it would be tidal. No, sorry. Oh, yeah, you're fading out.

Oh, now you're gone. Stupid cell phones. Bruce, Bruce, have we regained your signal? I think so. How do I sound, Matt? Oh, you sound 10-12-40-12-hike. I don't know what the 10-4. You sound good.

God, you know, we had an easier time talking to Ellesmere Island. Well, the miracle of cell phones. Yeah, you have any explanation for this sudden dropout? You didn't even move. I'm guessing it was one of those Venus burps. Oh, the infamous Venus burps. Just a thought. It doesn't even say excuse me. That's the really annoying part.

That's a rude planet. It is. It totally is. Alright, do we have anything else? No, I don't think so. Everybody go out there, look up the night sky and think about the miracle of air conditioning, because I know I will be today. Me too. He's Bruce Betts. He's the Director of Projects from the Planetary Society, and he joins us with some difficulty sometimes every week for What's Up. Planetary Radio is produced

by the Planetary Society in Pasadena, California. We'll take another lap or two around the universe next time. Have a great week, everyone. Thank you.