Planetary Radio: Space Exploration, Astronomy and Science - The Sun - Thief of Comets

Episode Date: August 2, 2010

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Comets from the Stars, this week on Planetary Radio. Welcome to Public Radio's travel show that takes you to the final frontier. I'm Matt Kaplan of the Planetary Society. Were many of the comets circling our sun stolen from other stars? Hal Levison and his colleagues say it's very likely. He'll be here to explain the findings of an international team of researchers. Say it ain't so! Emily Lakdawalla questions the wisdom of a NASA press release

that seems to be preparing us for the possible loss of Mars exploration rover Spirit. Bill Nye, the science and planetary guy, considers the reality of gravity. While Bruce Betts and I realize a lifelong dream in this week's What's Up segment, yes, we finally worked Lindsay Lohan into the space trivia contest. Life is good. And so are conversations with Emily, the Planetary Society Science and Technology Coordinator, as well as Mistress of the Society blog. Emily, as always, you've covered a lot of interesting stuff, you and others, over the last week of entries in the blog. But I think

the story that is really going to stand out and maybe get people worked up is about spirit. Seems to have gotten you worked up. Yeah, mostly it's the headline that JPL and NASA released with this week's story about Spirit that got me worked up, which is, and I quote, NASA's hibernating Mars rover may not call home. Well, you know, it's a pretty, let's just say it's a downer. Because the fact of the matter is that, you know, they've already told us this. We already know that.

It's not news. And in fact, there's very little in the content of this matter is that they've already told us this. We already know that. It's not news. And in fact, there's very little in the content of this press release that is news. The one piece of news that there is is that JPL has now started actively hailing Spirit, sending up a command from the Deep Space Network asking for Spirit to respond. And the reason that they're doing that now is because we're just a little bit on the other side of the winter solstice from when Spirit went silent. Spirit went silent about 52 Earth days before the solstice, and it's now about 60 days after the solstice. So this is probably the earliest possible time that we could expect Spirit to start talking to us again. So it's the right

time for us to try to start healing her. But I suppose in announcing that they were going to try to start healing her, they wanted to manage our that they were going to try to start healing her, they wanted to manage our expectations and make sure that we didn't get our hopes too high up. And, well, I guess they succeeded. Yeah, several times over. Is it, therefore, entirely reasonable for us not yet to be hearing from Spirit? It is certainly reasonable. And, in fact, I've heard that even with sort of reasonable guesses for what's going on up at Mars,

it could be October or November before we hear from Spirit. Now, if it gets past November and we haven't heard from Spirit, then I think it really is time to start maybe not giving up. But, you know, it's going to be a much longer shot if it's gotten that long. But now is not the time to be giving up hope. We've kept hope alive all winter long. Now is the time that we should really be pushing for Spirit to respond to our commands. Do you wonder if this shows a shift in the thinking of the scientists and engineers on the team? Because after all, when this was just getting underway, when we knew we were going to lose Spirit, we heard a lot of

optimism about coming out of this long winter on Mars from leaders of the mission. I don't believe there's been any shift in the feeling of people on the team. I think what they're concerned about is their perception in the wider public who perhaps hasn't been paying attention. And that's why they worded the release in the way that they did. Yeah, so they're covering themselves. All right, well, let's hope that reports of the demise of Spirit have been grossly exaggerated. One other piece we just want to mention in passing here,

and that's an important anniversary out at Saturn. That's right. It's been exactly one year, well, not exactly, but just slightly more than a year since the first of the Voyagers passed by Saturn. Okay, now explain yourself. One Saturn year, that is, which of course is not quite 30 Earth years, and I suppose it's notable to point out that it's very close to 30 Earth years since Voyager passed by. But the reason that one Saturn year is relevant is because it means that the ring shadows and the season on Saturn look pretty much the same as they did back when Voyager passed by. So now Cassini's pictures of Saturn show Saturn looking very similar to what Voyager saw. So, very significant anniversary after all. Emily, as always, thanks very much.

Thanks for having me, Matt. Emily Lakdawalla is the Science and Technology Coordinator for the Planetary Society and a contributing editor to Sky and Telescope magazine. I'll be right back, but first, here's Bill. Hey, hey, Bill Nye the Planetary Guy here, soon to be Executive Director of the Planetary Society. And this week, I attended a conference at the Google Complex, and I saw a lecture by one Eric Verlinde. He's Dutch. And he

published this paper a few months ago that says, here's the idea. You can derive gravity from scratch. That gravity maybe isn't a real fundamental force. You know, we have the four fundamental forces of nature, the weak atomic force, the strong atomic force, electromagnetism, that's light and radio waves and heat, and then gravity. But he's saying, maybe gravity isn't fundamental at all. It comes from the other three forces, or it comes from something before the other three forces, and it's like entropy, the disorder, the spread-outedness of energy, the tendency of energy to spread out. He had this lecture, and these guys, in the way I describe it, they got sharp elbows. They're trying to tear him down.

They're trying to tell him he's wrong and all this stuff, and he was defending himself. And here's the thing. If his theory is right, I'm not saying it is, it predicts dark energy very accurately. And how would you go about verifying his theory? That's right, my friends, through space exploration, by exploring space, by knowing our place in space, we can figure out whether or not gravity is its own thing or this consequence of other stuff in the universe. Now, this may not affect you day to day, but it might change the world. Thanks for listening. Bill Nye, the Planetary Guy. The June 10 press release was titled, Many Famous Comets Originally Formed in Other Solar Systems.

Well, that was more than enough to make it one of those space stories I couldn't ignore. So late last week, I called Harold Hal Levison at the Southwest Research Institute's Boulder, Colorado facility. He led the American, Canadian, and French research team that used computer modeling to reach an amazing conclusion. They believe that more than 90% of the vast Oort cloud of comets that surrounds our solar system may have been captured by the sun from other stars billions of years ago. Hal, thanks so much for joining us on Planetary Radio today to talk about this very interesting research that you've done about the comets that we see and the many more that we don't see in our solar system. It's my pleasure.

What led you and your team to begin looking at this question? Was there a mystery involved? Yeah, there's an observational mystery concerning an area of the solar system that we call the scattered disk. This is a population of comet-like objects outside the orbit of the planets. So these objects tend to hang out just outside the orbit of Neptune. They're on very eccentric orbits that extend hundreds, thousands of astronomical units away from the sun. So this is sort of akin to the population that we call the Kuiper Belt, which is on more circular orbits beyond the orbit of Neptune. We believe that this population actually started off between the giant planets.

And as the giant planets' orbits evolved and as the planets grew, they got scattered outward gravitationally by the planets, leaving sort of this leftover population of small things on these very eccentric orbits. Okay, so the basic theory is that as the giant planets formed, they scattered things out into this so-called scattered disk. And the gravitational interaction between the planets and these comets caused the comets' orbits to sort of fuse and spread outward until they get to the point where the gravitational effects of the galaxy itself can change the orbits. And at that point, they enter the Oort cloud. So basically, the scattered disk is sort of a highway between the planetary

region and the Oort cloud itself. And because of that, we can predict what the ratio should be between the number of objects we see in the scattered disk and the number of objects in the Oort cloud. And that number should be roughly 10 Oort cloud objects for every scattered disk object. But when we look, there's roughly 700 Oort cloud comets for every scattered disk object. That's quite a discrepancy. That is a huge discrepancy. And my colleagues and I have been worried about this for five years. discrepancy. And my colleagues and I have been worried about this for five years. So we've done a lot of experiments on our computers trying to somehow decrease the number of things in the

scattered disk to solve the discrepancy, and we just couldn't do it. So we decided we needed to look for another source for the OAR cloud, and that's what led us to this new work. source for the Oort cloud. And that's what led us to this new work. And so you developed yet another model, which discovered that our sun, the star that we all revolve around, was quite a thief in its early days. Yes. What we discovered is that as the sun grew and evolved in the cluster, if we look out into the sky, most stars seem to form in big star clusters, containing tens to hundreds of stars. This is a very compact population where the stars are so close to the sun

that they would actually fit inside the modern oar cloud. Wow. And I heard this was referred to in the press releases as a birth cluster. Yes, that's what we called it, the sun's birth cluster. Wow. And I heard this was referred to in the press release as a birth cluster. Yes, that's what we called it, the sun's birth cluster. You know, this is cool because we have very little information about the type of cluster that the sun formed in. And this kind of experiment allows us to put constraints on where the sun formed. You came up with, I guess, some answers for your question about this imbalance.

Yeah, what we find is that the sun can capture a lot of comets from other stars as it moves around in this cluster. And the other stars get comets from the sun as well, right? But overall, the efficiency of building this Oort cloud structure is much higher than it would be just in the standard models where the comets that we see come from our disk. You had a colorful description metaphor for describing all this sharing of material. Yeah, well, the way I like to think about it is that the sun and its siblings or cousins are really kissing cousins, right? And so they've shared a lot of spit in their early childhood.

I love it. And that spit we see now is frozen out there in the cloud. That's right. So most of the, if this theory is right, then most of the comets that we have seen, the really bright, famous comets like Halley and Halbopp and McNaught last year, all are objects that formed in the protoplanetary disks of other stars and ended up in orbit around the sun during the early period of the sun's evolution. That's pretty cool. We'll continue our visit with the Southwest Research Institute's Hal Levison in a minute.

This is Planetary Radio. Hey, 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. Hal Levison and his

colleagues have built a computer model that says our sun stole most of its up to one trillion comets. Yes, I said one trillion, with most of them spending their icy lives circling in the Oort cloud that starts far beyond the orbit of Pluto. Hal spoke with me last week from his office at the Southwest Research Institute campus in Boulder, Colorado. The model fits what we know of the physical reality very well, but finding further confirmation presents challenges.

How will this be refined or duplicated to arrive at more confidence that, yes, indeed, a lot of these actually came from elsewhere? Well, that's the hard problem, okay? We're faced with this difficulty that while we can, in our computer models, just put down a bunch of comets in orbit around one star and watch it evolve in this cluster and watch them move from one star to another in order to show that this process actually works, the actual number that we expect in the cloud depends on things that we just don't know. actual number that we expect in the cloud depends on things that we just don't know. It depends on the masses of protoplanetary disks around other stars. We don't know what those are. It depends on where the planets are, particularly the giant planets are, around those stars. We don't have a

good answer for that either. So the next step, I think, will come as we learn more and more about other planetary systems. We'll be able to quantitatively estimate how much stuff should be in orbit around our sun. We currently can't do that. So at least the data is beginning to come in with all the great work that's being done on exoplanets. Yeah, the exoplanet data, there's this new telescope being developed called ALMA, which will be able to study the protoplanetary disks around young stars. We'll be able to develop a better understanding of how much stuff is there. So I think in another five or ten years, we should be able to do a much better job at quantitatively estimating how much of our Oar Cloud is from other stars. If this proves to be the case, it does seem to offer some extremely promising science opportunities.

Could you say that, well, we may not need to go to another star to sample it up close? We could just grab one of these comets that used to be circling it. Absolutely. That's true. Except for the fact that these are our cousins, right? The sun collapsed from a cloud of material, and these other stars collapsed from the same cloud. When we first came up with this idea, I contacted some of the people that I know that actually study the chemistry of comets and said, what would we expect? And the answer is, we don't know. Because if we look at star clusters, the chemistry of the stars seem to be very similar to one another. it's true that we can go out and let's say grab a piece of Halley's Comet and say, hmm, this may be from another star. What's it look like?

It is still related to us. It's not just some random piece of extrasolar material. This whole field and the interaction of bodies so dynamically in our and other solar systems, this really fascinated you for many years, hasn't it? Yeah, absolutely. I was interested in dynamics from the time I got into graduate school. I mean, even earlier than that, it's always fascinated me to think that, you know, what we see in the sky today, if we would come back in 100 million years, would look very different,

If we would come back in 100 million years, it would look very different, right? We tend to think the sky is being very stable and not changing very much. But it's changing a lot. It's just changing very slowly from our perspective. How things move around and how they interact and how that led to what we are has been something that I really have been fascinated with. has been something that I really have been fascinated with. How important and how powerful are now the sorts of models, the sophistication of the models that you use to do much of your work,

including the work behind this recent publication? Yeah, I mean, the development of modern computers and modern computer techniques have really revolutionized our field because we've just gotten to the point maybe 10 years or 15 years ago where we can actually follow the dynamical evolution of the solar system or the Oro Cloud or the galaxy for a long enough period of time to actually be able to say how it would change. So before 15 years ago, we could only guess on the long-term behavior of the solar system. And now we can actually do it on our computers. And that has really led to a revolution, I think, on our view of how stable the solar

system is and how much the orbits of the planets have changed over time. You know, there's been sort of a revolution in the last five years, I think, where, you know, we now think that the orbits of the giant planets have changed significantly over their history, that the solar system formed in a much more compact configuration, maybe a quarter of the size that it is today, and the orbits of the planets became unstable and reoriented themselves or reordered themselves to the system that we see today. Wow. We just have a few seconds left. I want to give you a chance to mention some work

you've done that is very much related to this as part of a team that created something called SWIFT. Yes, I'm a member of a team that developed the first package of subroutines that will allow us to do this long-term evolution of the planetary system. And to do planet formation simulations accurately for the first time. And this software is freely available? Yes, just look up at the Southwest Research Institute's website and do a search for SWIFT and you'll find it. Excellent. Hal, we're out of time. Thank you so much for spending a few minutes with us today

to help us get back out there into the Oort cloud. You're welcome. Harold, or Hal Levison, is an institute scientist at the Southwest Research Institute. He's based at their facility in Colorado and does lots of work in the area of dynamics of astronomical objects, including these icy dust balls that we know as comets, that have a far more interesting history than maybe many people thought until some of the work that Hal has been involved with.

interesting history than maybe many people thought until some of the work that Hal has been involved with. We'll take another look at the night sky as we do every week with Bruce Betts in just a few moments. Time for What's Up on Planetary Radio. And sitting across from me is the Director of Projects for the Planetary Society, Dr. Bruce Betts, who's going to tell us about the night sky. And a little bit later, hear about all the grief that he caused many of you out there who entered the trivia contest. Only one of you, sadly, will win the Celestron Deluxe Compact Weather Station, but more about that shortly. Hi, welcome back. But I'm sure all of them are better for the trying.

Many of them actually were very surprised and pleased to learn the correct answer to this tricky one, but we'll get back to it. I hardly wait later in the show, but right, it's an exciting night sky going on. We've got planets doing a little dance over in the west after sunset. Check out, can't miss, extremely bright Venus, extremely bright star-like object. Above it, and kind of moving around relative to each other over the next couple weeks, are Saturn and Mars. Mars being more reddish, not surprisingly, and less bright of the two, and Saturn brighter and yellowish.

So check that out, but also check out the Perseid meteor shower, peaking on August 12th, one of the best showers of the year, particularly for those of us in the northern hemisphere, with a peak from a dark site averaging around 60 meteors per night. And you can check it out a few days before and after August 12th, and still get an increase in meteors. Go out, stare at the night sky, and relax. But you'll do better after the moon sets in the early to mid-evening,

and always better in the middle of the night, approaching dawn, but harder to stay awake. I hear this may be a pretty good one. Yes, yes, we think so. You go through different parts of the trail of comet Swift-Tuttle, sometimes a little clumpier. But good news about the Perseids is they're pretty constant, unlike other meteor showers. So you're going to get a decent show as long as you can get to a somewhat dark site.

Yeah, okay. All right, we move on to this week in space history. Had Messenger launched in 2004 this week, now successfully bopping around the inner solar system and headed to orbit Mercury next year after some great flybys. And Phoenix launched this week in 2007 on its way to the successful mission in the Martian polar regions. We also have a birthday shout-out for Neil Armstrong. 80 years ago, Neil Armstrong. Happy birthday, Neil.

Neil Armstrong. 80 years ago, Neil Armstrong. Happy birthday, Neil. And, you know, by coincidence, same age as a close colleague of his, whose name will be arising in this segment shortly. You know stuff. I see the future. We move on to Random Space Fact. Don't sing too much or we'll have to pay royalties.

But I wanted to tell you more about meteor showers and the radiant. Meteor particles, when they're still meteoroids flying around in space, are traveling in basically parallel lines in an orbital stream around the sun. When they hit the Earth, they appear, therefore, to spread out from one point in the sky. If you connect all the little lines back that you see in a night, if they're from the meteor shower, they'll go back to one place. That place names the meteor shower. So, like, Perseids are named after the constellation Perseus.

And you are looking radiant today. Oh, why, thank you. As are you. Thank you. A little less so since lunch, though. Too many fries. Yeah, maybe. Thank you. A little less so since lunch, though.

Too many fries. Yeah, maybe. We move on to the trivia contest that apparently caused such consternation. That's the word. Lots of terms. Many, many adjectives. I can't possibly remember all of the adjectives used by listeners to describe you. Crafty, sneaky, tricky.

Brilliant, clever. Well, like I said, some of them were quite pleased by the somewhat surprising answer to this. There is a surprising answer. Now, many, many people, unfortunately, did not quite catch on. And they came up with, well, have you even mentioned the question yet? No, I haven't. Is that important? Why don't you do that? We're going to play Planetary Radio Jeopardy today. I asked you, who was the first person born in Italy to fly in space? Yes. Well,

many people did say Franco Malerba, first citizen of Italy to travel in space. That was on STS-46, the shuttle back in 1992. Ah, but not the first person born in Italy. Who was? Michael Collins. Wow. Michael Collins, Apollo 11 astronaut, Gemini astronaut. And his parents lived in Rome at the time. Go figure.

1930, Mussolini's in charge. Parents were American. I don't know what they were doing there. Many listeners wondered. Maybe someone will write in and tell us. Well, actually, I have an answer. Yeah? His parents moved there just so I could have this trivia contest.

Oh, that time machine comes in so handy. It really does. The same age this year, 80 years old, turning 80, as Neil Armstrong. So happy birthday to both of you guys. We move on to another question that at least I— Oh, wait. I didn't give the winner. Is that important?

I suppose it's important to the winner. We're considering all our priorities here today. You know what? It was Peter Carr. Peter Carr of Dingley Village, Victoria, Australia. Now you know why it was especially important because I got to say Dingley Village. Congratulations. And, Peter, we're going to send you the Celestron Deluxe Compact Weather Station.

There it is. It is very cool. It's really nice. It's got the remote temperature readout thing. Our friends at Celestron provided this, known as makers of fine telescopes, but also all kinds of other cool stuff like weather stations. So congratulations, Peter. We move on to another trivia contest, this time for the all-encompassing fabulous Planetary Radio t-shirt. Be the envy of all your friends

by being the one who gets this right and is randomly selected as our winner. Here's the question, less devious, harder to phrase. What is the name of the star? Which is really a three-star system we now know. In Perseus, which I mentioned earlier due to the trivia contest, and no, this is the trivia contest, due to the meteor shower, gosh, I'm going to make this complicated. Hopefully you'll clean it up later on for the question online. I don't think I will.

All right. No, just put all of this online. Known for its variable brightness. This is the real key. This is if one can say there is a most famous variable star. This is certainly it. What about Lindsay Lohan? Well, okay. You got me there.

But she doesn't come in threes. If you can say there's a famous star who's a hot ball of gas, well, you know what I mean. Yeah. Yeah. Then it would be this one. Every three days, it becomes only 30% as bright as itself because it's an eclipsing binary. It's actually one of the stars going in front of the other, making things less bright. So in Perseus, variable star.

Remember, in Perseus, that's why it's not Lindsay Lohan. Go to planetary.org slash radio. Find out how to enter. Perhaps the Greek gods will someday elevate Lindsay to the zodiac. Be that as it may. You really tickled yourself with that one. It's a nice concept. You have until Monday at 2pm Pacific Time, Monday, August 9, 2pm Pacific Time,

to get us this answer. After completing 12 noble tasks. She's got three down for sure. All right, everybody, go out there and look up at the night sky.

I know what you will be thinking about, but instead try to think about dodecahedronal mystic orbs. Ooh. You cut your deal with Wham-O for those yet? I'm trying. We're still negotiating a contract. He's Bruce Betts, the director of projects for the Planetary Society, and he joins us here every week for What's Up.

The giant Magellan telescope is moving closer to becoming a reality. We'll learn more about it next week here on Planetary Radio, which is produced by the Planetary Society in Pasadena, California, and made possible in part by a grant from the Kenneth T. and Eileen L. Norris Foundation. Keep looking up! Thank you.