A Trojan Asteroid Keeps Earth Company

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The moon isn't the only heavenly body hanging out near Earth. Astronomers say a Trojan asteroid is following Earth's same path around the sun. And it might not be alone out there. Professor Martin Connors of Athabasca University talks about Earth's newly discovered neighbor.

JOE PALCA, host: This is SCIENCE FRIDAY. I'm Joe Palca. This week, scientists are reporting they've found proof for something that's long been speculated about. Earth has at least one planetary hitchhiker, an asteroid that sits about 50 million miles away from Earth and is sort of riding our gravity as we make our way around the sun.

Astronomers have found these asteroids, called Trojan asteroids, around Jupiter, Neptune and Mars, so it seemed likely the Earth would have one, but no one had found one until now. Joining me now is the leader of the team that found Earth's Trojan. Martin Connors is a professor in the Department of Physics and Astronomy and the - sorry - and the Canada Research Chair at Athabasca University in Alberta, Canada. Thanks for talking with me today, Dr. Connors.

MARTIN CONNORS: Well, very happy to do so, Joe.

PALCA: Good. And if you have a question for Dr. Connors and you want to join the conversation, our number is 800-989-8255. That's 800-989-TALK. You can tweet us on Twitter, @ sign followed by scifri. And there's more information about this topic at the website: www.sciencefriday.com.

So, Dr. Connors, let's start. What is a Trojan asteroid?

CONNORS: Well, as you mentioned before, it's one that either follows or leads the planet in its orbit, kind of held in place by the combination of the planets and the sun's gravity. I kind of liked your music there, because this particular one also does a little dance. It's a rather complicated motion, but on average, it's 60 degrees ahead of the Earth and along Earth's orbit.

PALCA: So it's not just - I saw the simulations that you made. It's not just parked in one spot 60 degrees away. Why does it have this additional wobbly-ness in the orbit in a way that Earth or the Moon doesn't?

CONNORS: The eccentricity - that is to say the oval-ness of this orbit - is a little bit more pronounced than that of Earth's orbit, and that makes it slow down when it gets a little bit further away from the sun. And it is also tilted about 20 degrees with respect to our orbit, and that makes it go up and down. So all in all, it ends up doing a little bit of a dance instead of just staying in one place.

PALCA: And why Trojan? Do you know?

CONNORS: Why the name Trojan?

PALCA: Yeah. Why the name Trojan?

CONNORS: It would appear that - I mean, here's another great name. It's Max Wolf. There's a really good name for an astronomer. And in 1906, when he found the first one, they were sort of giving out names from classical history, and it just happened, as far as I can tell, that the first one was given the name Achilles - of course, the Greek warrior who went to the Trojan war.

Then when they found another couple of asteroids that were very similar, they gave them Trojan-themed names, Patroclus and Hector. And then that tradition picked up, so they're now about 5,000 known for Jupiter. So they've gone through all the names in the Iliad.

(SOUNDBITE OF LAUGHTER)

PALCA: There are quite a few names in the Iliad.

CONNORS: Yeah.

PALCA: So I'm curious, though. Why - what's special about this position, 60 degrees ahead? I mean, is that the sweet spot for finding these things?

CONNORS: Yeah. I think you could call it a sweet spot. You have to think of people thinking these are dire times, but Lagrange was basically working during the French Revolution, and he did some mathematical proofs that there could be these so-called Lagrange points, or sweet spots, where a small body could stably exist going around with the large body.

PALCA: And there are several of these Lagrange points, as I remember.

CONNORS: Yes. There are also others that are called the Collinear Lagrange points. For Trojan asteroids, they form a triangle and they're called the Triangular Lagrange points. But Lagrange points are used for spacecraft between the Earth and the sun and that's mainly for looking at the sun and then, on the other side, if they're looking out into deep space, it's a good place to park them is at that Lagrange point.

There is yet another Lagrange point on the other side of the sun and this asteroid spends a little bit of time there, but it's not a stable point, so it's a fairly little bit of time.

PALCA: We're talking with Martin Connors about an asteroid called a Trojan asteroid that he's reporting that's been discovered in Earth's orbit and we're taking your calls at 800-989-8255. And let's take a call now, and go to Darren in Chicago. Darren, welcome to SCIENCE FRIDAY. You're on the air.

DARREN: Thank you very much. Appreciate you taking the call.

PALCA: You bet.

DARREN: I'm fascinated by the fact that we've been looking at the solar system for so long in so many ways and yet, still, discoveries like this are being made. And I'm curious as to why this one has been so elusive and are you now expecting, by virtue of the way you discovered this, to find others? Or what's the significance of this as far as proximity and other ways to track it?

PALCA: Great question there.

CONNORS: Thanks, Darren. That's a good question. And the trouble is that this situation of 60 degrees from the planet as seen from the sun. It also means that the asteroid kind of sticks near 60 degrees from the sun as seen from the Earth because it's an equilateral triangle and that really isn't that far from the sun in the sky.

So as a result, if you wish to do a search with a telescope, which we have done in the past, you're restricted to a very short period of time, near sunrise or just after sunset and while the sky is still dark, however. So the opportunity to actually look for these with ground-based telescopes is very restricted in time and you have a lot of sky to cover. The sky is actually a pretty big place.

So the game changer here was a NASA satellite called WISE, which was looking a little bit closer to the sun than most asteroid searches occur and, therefore, it could find this asteroid.

PALCA: And was WISE designed to look for this or is this just an ancillary benefit from WISE?

CONNORS: WISE was a general survey of infrared bright objects, which does include asteroids and so there was also a part of WISE called NEO, for Near Earth Object WISE, which was specifically looking for near earth asteroids, including Trojans.

PALCA: Okay. Let's take another call now and go to John in Indiana. John, welcome to SCIENCE FRIDAY. You're on the air.

JOHN: Thank you. My question is primarily related to these objects that they found around the moon. The photos were released back in January or February, allegedly by NASA. Is there any link or ties to that and these Trojan asteroids? Are there any similarities or perhaps were these objects discovered out of the program that discovered the asteroid?

PALCA: Dr. Connors?

CONNORS: John, I'm afraid I'm drawing a blank on that one. I didn't hear about these objects associated with the moon.

JOHN: They're all around the sun. You can see them in the corona of the sun in near orbit to the sun, but then they've also found some that they've seen, or they've photographed around the moon towards the dark side. We're unable to really see them plainly from Earth, but they've - like I said, I don't know. I don't even know if there's any legitimacy to these photos. They were allegedly released by NASA and they're all over the Internet everywhere.

PALCA: Wow. John, I think you might have stumped us on this one, unless that rings a bell for you, Dr. Connors.

CONNORS: Definitely not. And I don't really know how you even tell if things are genuine NASA, so sorry. I really can't be of any help.

PALCA: Okay. Well, let's see if we can do better, not that you should feel bad. It's a little bit outside of your knowledge base, but let's go next to Scott in Wild Lake, Michigan. Scott, welcome to SCIENCE FRIDAY. You're on the air.

SCOTT: Hello. I love your show. I'm calling to inquire if the discovery of this Trojan could maybe make a better model for how we move to the solar system, much like the discovery of Uranus kind of changed the model a little bit of how we view things.

CONNORS: Yes. Well, thanks for that question. I think that the dynamics or the way that these bodies move has been known for quite a long time. And recently, there is a new model of the early solar system called the Nice model and it has implications as to why material piles up at these Trojan or Lagrange points.

But we do know it's there and we're now kind of trying to explain that it's there. It's, of course, interesting to know that it is also there for the Earth, as well as for Jupiter.

PALCA: Okay. Scott, thanks for that call. Let's go next to Wyatt in Michigan, also. Welcome to SCIENCE FRIDAY. You're on the air.

WYATT: Yes. Thank you for having me on the air. I love your show and just a question, Mr. Martin Connors. I'm a graduate student at Oakland University and I'm also President of Engineering Intelligent Solutions. And I wanted to know, what's the impact of these Trojan asteroids on the Earth? Like, watching them, what's the reason behind it? I know there's Lagrange points that maybe tell you the distance of these objects, but like for technology and space sake, what's the impact on the Earth?

CONNORS: Well, to me, one of the interesting aspects of these asteroids - and I hasten to add that, because of the tilt of the one we have found, it is not a suitable target for what I'm about to talk about. But if we could find other Trojan asteroids that actually just stayed in the plane of the Earth's orbit, then they and other related objects could be extremely easy to get to with a spacecraft. In fact, the previous discussion was about how to land on Mars and do it gently. One advantage of an asteroid is, as is happening with the current mission to Vesta by the Dawn spacecraft, you don't have much gravity to contend with that's going to suck you in and make you crash on the surface. So you can just kind of gently pull up to it.

So, in fact, asteroids could be very advantageous things for space missions. And, indeed, it's part of the U.S. space plan to send astronauts, rather, to asteroids.

PALCA: Really? So it's a little bit more like parallel parking than landing on another planet.

CONNORS: Exactly, yeah. In fact, your biggest problem is once you're there, you might drift off. So what do you? Lasso it or shoot a harpoon into it, or whatever? But you don't need to worry about crashing into it, because the gravity is so weak.

PALCA: Interesting set of problems. OK. Let's go next to Darren in Virginia. Darren, welcome to SCIENCE FRIDAY.

DARREN: Hi. Thanks for having me. I've got a question about the size of the asteroid, and also what kind of material it's made out of.

PALCA: Hmm. OK.

CONNORS: OK. Well, the basic answer to your second question is we don't actually know what it's made out of, so we just kind of guess that it's kind of the average color and darkness of other asteroids. And in that way, we can guesstimate that the size is a few hundred meters. So there would be - more detailed investigations can be done from the ground, particularly with spectroscopy or detailed study of the color that might be able to tell us what it's made of. But, for the moment, we just have a rough guess as to how dark it is. And that allows us to judge the size to be a few hundred meters.

PALCA: OK. Darren, thanks very much for that.

DARREN: Thank you.

PALCA: You're welcome. I'm just wondering: Why is it so hard to predict the motion of these guys?

CONNORS: Well, this particular one is very subject to the effects of chaos. The old views in the time of Lagrange and back in the time of the French Revolution was that if you could get all the rules down, then you could predict the universe forever. But we now know that, in fact, there are so many bodies out there - and some of them are in sort of precarious situations - that are subject to small influences from others that can actually change their behavior quite a bit.

This turns out to be one of those. So just small shoves from Jupiter and other planets can actually make it very difficult to predict the future of this asteroid with any precision, so it is actually a chaotic orbit.

PALCA: We're talking with Martin Connors. He's a professor in the department of physics and astronomy and the Canada research chair at Athabasca University. That's in Alberta, Canada. This is SCIENCE FRIDAY, from NPR. I'm Joe Palca. Let's take another call now, and let's go to Jerry, if I can push this button. Yes, Jerry in Rochester, New York. Welcome to SCIENCE FRIDAY. You're on the air.

JERRY: First time caller, big fan. I actually have my iPod set to go off, so I can to listen to the show. I'm very excited because back in the 1970s, there was the physics was applied to the idea of Lagrange points here on Earth, between the Earth's moon system, and they had actually talked about building 10,000 - at the time, they were all aglow with the Apollo program and all that, and they were thinking about building a colony that would exist in L5. Do you recall hearing anything of that? And I'll take my answer off the air.

PALCA: OK. Thanks, Jerry.

CONNORS: Yes. I believe that O'Neill was a big proponent of these space colonies. And, obviously, for those of us, for example, going further back who were big fans of "2001" and expected amazing things to happen in space, they haven't quite happened that way. So I believe that you're referring to O'Neill's work, and a very interesting work, but performing major engineering feats of the magnitude that he was talking about in space has eluded us. Obviously, we're proud of the accomplishments of the space station, but it's not quite on the scale that the futurists of the era that you're talking about were thinking of.

PALCA: Thanks for that question. Let's go now to Corey in - or is it Kerry(ph) in Menlo Park, California. Are you there?

TERRY: Hi. Yes. This is Terry in Menlo Park.

PALCA: Terry. Sorry. Go ahead.

TERRY: My question is: Do they know, or have they considered how these things end up there?

PALCA: In other words - I was interested - that's an interesting question, because I was wondering: How do these get captured and brought into these stable points in the orbit?

CONNORS: Yes. That is, of course, an extremely good question, and it has a rather unfortunate answer, which is that we don't know in great detail. So the answers range all the way from they were there at the beginning of the solar system - and that would be very interesting - to, well, things kind of move around, and if there's a place for junk to pile up, it'll be one of these Lagrange points. And that may be what's happening.

So that may be a little bit of an unsatisfactory answer. But with this particular object, we really have difficulty predicting the motion or back - going backwards with the motion for very long because of the chaotic nature. So this is an open research question. And it might be partly answered if we could go and get materials, et cetera. And then we would be able to say if it was made of sort of similar material to the Earth that might argue for it having been there a very long time.

PALCA: Is there - are you going to look for any more? Or do you think this is it, for now? I mean, around Earth that is.

CONNORS: Well, I am a big proponent of the idea that there are more of these, and that we have simply not been able to observe them very much because of the difficulty of observing them. So I hope that actually having an object will stimulate searches. I certainly will be trying to get telescope time to do so. Big telescopes are difficult to get time on, and you have to argue strongly, and hopefully this will strengthen the argument, and then we can find more.

PALCA: Any thoughts about looking at other planets, or are you going to stick with Earth?

CONNORS: Well, it does turn out - and sorry for not mentioning this earlier. Jupiter, of course, has a huge collection of them. What actually stimulated my interest in Earth was the discovery about 20 years ago that Mars has Trojans. So there are a handful of those known. And then much more recently, it was found that Neptune has Trojans, as well. So I have written papers about Mars Trojans and Jupiter Trojans, in fact. So I am interested in the whole general topic.

PALCA: OK.

CONNORS: But I think, for now, the hot thing is Earth Trojans.

PALCA: You got it. All right. Well, Dr. Connors. Thanks very much.

CONNORS: Thank you.

PALCA: Martin Connors is a professor in the Department of Physics and Astronomy at the Athabasca University in Alberta, Canada. When we come back, we'll be moving out to one of those outer planets, Juno - Jupiter, about - and we're going to talk about the new Juno mission that's heading there next week. We'll be right back after this short break.

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