IRA FLATOW, HOST:
Last Monday, an amateur astronomer in Wisconsin, Dan Peterson, was gazing through his telescope when he caught sight of a flash of white light in Jupiter's gassy atmosphere. Lucky for him, someone else also had a scope trained on Jupiter that night. George Hall, an amateur astronomer in Dallas caught that flash on video, hard evidence that an explosion had indeed happened on the giant planet.
But what caused it? An asteroid, a comet? Will we ever know? Joining me now to talk about it is Tony Phillips. He's an astronomer and the author of spaceweather.com. Welcome to SCIENCE FRIDAY, Dr. Phillips.
TONY PHILLIPS: Thank you, Ira.
FLATOW: So what was it?
PHILLIPS: Well, we'll probably never know for sure, but it was probably a small asteroid hitting Jupiter. In fact, this isn't the first time amateur astronomers have caught asteroids hitting Jupiter. We've seen it happen a few times in the last few years. And this appears to be just the latest example.
FLATOW: And what exactly was happening that they saw?
PHILLIPS: Well, you summarized it beautifully at the beginning. Dan Peterson is an amateur astronomer, and really he was just, sort of, bent over his telescope looking through the eyepiece when he saw this brilliant flash of light in the cloud top of Jupiter.
And he immediately went onto the Internet and told a forum of amateurs what he had seen. Now, you know, 10 or 20 years ago, if he had made that report, people would have told him oh, you're crazy, you're seeing things. But in this case, another amateur astronomer, George Hall in Texas, happened to be video recording Jupiter at the same time.
He wasn't actually watching the planet with his own eyes, but he was making a video recording. And when he went and looked back at his footage, he found sure enough, there was a flash of light just when Dan Peterson said that he saw it. And most likely what happened was that an asteroid hit Jupiter - and not a huge asteroid, probably an asteroid about 10 meters or 30 feet in diameter - and it would have exploded at about the - with an energy equal to about 10 times our early atomic bomb.
FLATOW: Wow, what is an asteroid doing near Jupiter?
PHILLIPS: Oh, well, there are a lot of asteroids near Jupiter. You know, Jupiter orbits pretty close to the asteroid belt, for one thing. So that's a part of the solar system that's very cluttered with space rocks. And Jupiter ends up being a target for a lot of them because - mainly because it's such a big planet. It has so much gravity. It actually pulls some of these space rocks toward it.
FLATOW: What makes you not believe it was - might have been a comet?
PHILLIPS: Oh, well, it might have been a comet. The only way to tell the difference between an asteroid and a comet impact is to look at what kind of debris it leaves behind in Jupiter's atmosphere. Now - but the problem is, in this case, astronomers have been watching the impact site - the place where the flash of light occurred - all week long, and they've been looking through debris, but there is none. Now, if you could look at the debris and see what it's made of, you could say, oh, yes. That's material that's characteristic of an asteroid, or in the case of a comet, you know, comets tend to be very watery. And the debris cloud has chemical byproducts of water in it if a comet has hit...
FLATOW: Yeah.
PHILLIPS: ...Jupiter. But there's no debris right now. It looks like whatever hit Jupiter, Jupiter just kind of swallowed it whole.
FLATOW: Yeah. You know, I'm reminded - when you say debris, I'm reminded of that famous Shoemaker-Levy 9 comet that broke up and smashed into the planet in 1994.
PHILLIPS: Well, you're right. And, you know, I said 10 or 20 years ago, people might have said that Dan Peterson, who saw the impact, was just, you know, seeing things. But back before comet Shoemaker - excuse me, SL9 hit Jupiter, astronomers were very skeptical that big impacts like that occurred in the modern day solar system. And then we saw that tremendous series of 21 impacts with our own eyes, when Shoemaker 9 hit Jupiter. And, of course, that was a comet.
FLATOW: Yeah.
PHILLIPS: And we got to see, at that time, what a comet impact on Jupiter looks like. And from the chemical signatures of that impact, we can compare that with modern or more recent impacts and say, oh, yes, this is an asteroid or, no, that was a comet.
FLATOW: Have amateur astronomers - and I say that that they must be amateurs in name only, because they're pretty sophisticated folks, aren't they?
PHILLIPS: Well, you hit the nail on the head. A lot of the amateur astronomers who are making these observations are just as skilled as many of the very best professional astronomers. And the only difference between the two is sort of the size of the telescopes that they use.
FLATOW: Yeah.
PHILLIPS: And a big advance in recent years that has allowed amateur astronomers to observe and record these impacts is digital photography and digital video recording. You know, we can make very sensitive digital video recordings of planets now, and we can capture these impacts when they occur.
FLATOW: Mm-hmm. I'm Ira Flatow, and this is SCIENCE FRIDAY, from NPR, talking with Tony Phillips, astronomer and author of Spaceweather.com. If you want to see the impact on our - go to our website at sciencefriday.com. We have the video up there of the impact. It seems - it's pretty big. I mean, we can see that, right? That flash, you said it was - how many megatons of...
PHILLIPS: Oh...
FLATOW: ...equivalent to a nuclear bomb?
PHILLIPS: Well, it's about - its equivalent - the energy in that explosion is about 10 times the energy in the first atomic bomb...
FLATOW: Uh-huh.
PHILLIPS: ...in World War II.
FLATOW: Wow.
PHILLIPS: So it is a very large explosion.
FLATOW: Now, if you were watching Earth from Jupiter, would you see the same type of flashes in our atmosphere, because don't(ph) we get bombarded?
PHILLIPS: Theoretically, you could. You know, these flashes are visible at distances of many hundreds of millions of miles away. And if you were on a spaceship orbiting Jupiter and you were looking back at Earth, you could see similar impacts. Now, here on our own planet, impacts of objects - let's say asteroids about 10 meters wide, like we think this one might have been - are pretty rare. They only occur every 10 or 20 years or so.
FLATOW: Yeah, yeah. What about astronomers now? Has their - have they been motivated to turn their telescopes, amateurs, now toward Jupiter and turn on their digital recording devices so they might catch one?
PHILLIPS: Oh, I think - yes, absolutely. You know, one reason that amateur astronomers are monitoring Jupiter with video recording equipment is to try to capture these explosions. I mean, you know, just imagine looking through the eyepiece and seeing something on an alien planet exploding like an atom bomb, that's very cool.
FLATOW: How big was the telescope that they used?
PHILLIPS: Oh, these were - there were two different telescopes involved, and they were 12 to 14-inch class telescopes. So, really, these are sort of off-the-shelf backyard telescopes.
FLATOW: Mm-hmm. Is there any chance they might point Hubble at it or see...
PHILLIPS: Well...
FLATOW: ...find a hole or something?
PHILLIPS: ...back in the - I think the big telescopes like Hubble and other ground-based telescopes will be used to observe the impact site if any debris appears. In fact, back in 2009, there was an impact of a much larger asteroid on Jupiter that caused a really - a debris cloud on Jupiter that was about as big as the Pacific Ocean.
FLATOW: Wow.
PHILLIPS: And the newly repaired Hubble was used to observe that impact, and a lot was learned about that impact from Hubble observation.
FLATOW: So folks are really tweaking it up now. I mean, and having a good weekend, you just need a nice clear sky, and you too might discover something.
PHILLIPS: Well, Jupiter is not the only place. You can look at the moon with your telescope and also see small asteroids hitting the moon.
FLATOW: No kidding.
PHILLIPS: Yeah. There's a group at the Marshall Space Flight Center, the NASA Marshall Space Flight Center, and since 2005, they've been using amateur-class telescopes to watch the dark terrain of the moon. And they actually see meteoroids hitting the moon, and it observes 260 explosions in the past seven years, right on the surface of the moon.
FLATOW: Wow. Wow. There's a project for the weekend. Thank you very much, Tony, for taking time to be with us today.
PHILLIPS: Oh, it's my pleasure.
FLATOW: Tony Phillips, an astronomer and author of Spaceweather.com. As I say, again, if you like to see that impact on Jupiter, we've got it up on our website at sciencefriday.com. And it's quite an event to see. And I can imagine how exciting it must have been to see that explosion in real time in the telescope, because just looking at the planets themselves is pretty exciting. That's certainly an added benefit.
We're going to take a break, and when we come back, we're going to look at whether the microbes from Earth may have hitched a ride on to Mars on NASA's Curiosity rover, and if they did, what that might mean for the science mission there. So stay with us. We'll be right back.
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FLATOW: I'm Ira Flatow. This is SCIENCE FRIDAY, from NPR. Transcript provided by NPR, Copyright NPR.