December 21, 2007
Narrator: Is an asteroid heading toward Mars?
I'm Jane Platt with a podcast from NASA's Jet Propulsion Laboratory in Pasadena, Calif.
Joining me is Steve Chesley, an astronomer with NASA's Near Earth Object Program at JPL.
Steve, tell me a little bit about this asteroid, the name, how big it is, and where it is.
Chesley: Well, this asteroid is given the designation 2007 WD5. Right now it's about halfway between Earth and Mars. It just flew by Earth in early November and it's heading toward an encounter with Mars in the end of January. It's about 50 meters in diameter, maybe 164 feet, although there's a lot of uncertainty actually about how big that asteroid is.
Narrator: So you think it is heading, or you know it is heading toward Mars, but what are the odds it actually might hit Mars?
Chesley: We're very sure that it's going to come very close to Mars. There's right now about 1 in 75 odds of actually hitting the planet. So of course that's something like 99% likely to miss.
Narrator: OK, so a good chance it will miss, a very good chance it will miss. But nonetheless, 1 in 75 chance that it will hit Mars is pretty high, right?
Chesley: This is a very high impact probability for what we're used to dealing with, which is usually in the one in a million, even one in a billion odds. So 1 in 75 is certainly startling for us, and we've been paying close attention to this object since as soon as we realized that it was going to come so close to Mars.
Narrator: How did you discover it, and when?
Chesley: This object was discovered by the Catalina Sky Survey operating a telescope in Arizona. It was discovered November 20, and it was followed up the next night, and then again about 10 days later. And then at that point in early December, we realized that it was a very remarkable object indeed.
Narrator: So if it does hit Mars, that would be when?
Chesley: It's going to fly past Mars January 30. If it does hit it would be right around 3 in the morning, Pacific time. Of course it could fly by a good deal earlier or later, as much as eight hours' uncertainty on that arrival time. And so if it's early or late, of course Mars won't be in the way.
Narrator: So you'll be tracking this and refining the orbit over the coming days and weeks?
Chesley: Yes, we're working with the telescope operators and observers to get more tracking on 2007 WD5. And as we gain more knowledge through tracking, we're able to narrow the uncertainties and refine the odds of impact, and the expected turn of events is that these impact probabilities will go down as soon as we get enough information to refine the orbit.
Narrator: But right now the 1 in 75 chance that it will hit Mars. If it does hit Mars, what will that be like, what will happen on Mars, and how fast will the asteroid be traveling and what power will it carry?
Chesley: This asteroid will be traveling as much as 13-and-a-half kilometers per second, if it actually impacts the planet. That's going to make a tremendous explosion, as much as 3 megatons, and it will leave a crater on Mars. We don't exactly know how big, but a rough guess would put it in the order of a half mile across.
Narrator: And we've got, NASA's got multiple spacecraft at Mars, we've got the two rovers on Mars, and we've got Mars Odyssey and Mars Reconnaissance Orbiter. So at the least there'd be a chance for possibly some interesting images.
Chesley: In the event of an impact, it would be a very interesting and exciting scientific bonanza, especially for the mapping spacecraft like Mars Reconnaissance Orbiter that could map the crater in great detail. And we would also learn a lot about the atmospheric effects and the dust loading and a number of other aspects that would be tremendously scientifically interesting.
Narrator: And there are a lot of other craters on Mars, we have craters on Earth, all the planets have craters.
Chesley: Impacts are a recurring phenomenon in the solar system, and that's of course more of a concern for Earthlings. That's how we found this, by searching for Earth-threatening asteroids. This one, of course, has been checked for Earth hazard, and we don't see anything in the future for Earth.
Narrator: OK, that was my next question that you anticipated, so we don't need to worry about this one?
Chesley: 2007 WD5 is an Earth-crossing asteroid, it's a near-Earth asteroid, but we have checked and we find no possibility of Earth impact in the future.
Narrator: If this asteroid does hit Mars, what part of Mars?
Chesley: It looks like right now if it's going to hit, it would be in the southern hemisphere, It would be along a pretty narrow strip that cuts across the planet. The strip might be something like a couple of hundred kilometers across. Of course, it could also miss the planet altogether.
Narrator: It's going to be a busy few weeks for you coming up, I imagine.
Chesley: We are going to continue to track this thing, it's not really going to be observable between now and the New Year. We should be able to get more observations in January, but at that time it's going to be very faint. It's going to require some of the biggest telescopes on Earth to observe it.
Narrator: OK, well thank you very much, Steve, and we'll definitely check back with you and the team.
We have more information on this asteroid online at http://neo.jpl.nasa.gov . NEO as in Near Earth Object.
Thanks for joining us for this podcast from NASA's Jet Propulsion Laboratory.