365daysDate: August 19, 2009

Title: What Slammed Into Jupiter?


Podcaster: SkyGuy, Tom Vilot

Organization: SkyGuy, LLC: http://SkyGuy.com/

NOTE: As of December, 2016, the website SkyGuy.com is no longer active.

Description: Something slammed into Jupiter on July 19, 2009. What was it? And does Jupiter protect Earth from being hit? SkyGuy talks with Dr. Hal Levison of the Southwest Research Institute in Boulder, Colorado.

Bio: Tom Vilot, SkyGuy, is the author of the video podcast series at SkyGuy.com where he answers kids’ questions about space. Mr. Vilot is an artist, software engineer and amateur astronomer with a passion for getting kids excited about astronomy and space exploration.

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by George Brickner in the memory of Basil the Cat, 1991-2009.


Welcome to 365 Days of Astronomy. I’m SkyGuy, your host for this installment….

Normally I tell kids cool stuff about space and astronomy in my video podcast at Skyguy.com, but I think everyone will get a kick out of this.

Since you’re listening to this podcast, I’ll assume you know that something slammed into Jupiter on July 19. It was discovered by the very lucky amateur astronomer, Anthony Wesley, in Australia.

So what hit Jupiter?

Scientists don’t know yet, but the obvious candidates are either a comet or an asteroid. Either that — or aliens who couldn’t manage to avoid the largest planet in our solar system!

But what interests me about this event is how soon it occurred after the last Hubble Space Telescope servicing mission. In May, astronauts aboard the shuttle Atlantis spent 11 days and completed five EVAs to repair and upgrade the famous telescope. If you go to SkyGuy.com, you can see my video describing what to me must have been the most nervous moment of the entire mission.

So why is this interesting?

I’m intrigued by the timing. It’s just a little teensy bit odd. Suspicious, maybe. Here’s the deal: We send astronauts up to Hubble to fix and upgrade this device JUST in time to see something nasty slam into Jupiter.

Does this sound familiar at all?

It’s almost exactly the same thing that happened the FIRST time we fixed Hubble. As I’m sure you know, when Hubble was first placed in orbit, we discovered its primary mirror was incorrectly shaped. That was a huge problem. So in December 1993, astronauts visited Hubble to install two packages: the Wide Field Planetary Camera II and COSTAR, the Corrective Optics Space Telescope Axial Replacement. These two packages fixed Hubble’s vision.

And what happened just seven months later?

Comet Shoemaker-Levy 9, which on its first pass around Jupiter had broken apart into 21 pieces, SLAMMED into Jupiter! Hubble, with its new optics, was ready and able to provide incredible imagery of this historic event.

Here’s what I can’t help wondering: We fix Hubble, a comet slams into Jupiter. We fix Hubble again, and something slams into Jupiter. It’s almost like someone is out there waiting for us to have a working space telescope so they can throw something at Jupiter! Or maybe their aim is bad, and they’re trying to throw stuff at US.

So I suggest that in order to save Jupiter — and maybe us — we STOP FIXING SPACE TELESCOPES! Seems like whenever we do, someone out there is waiting to put on a cataclysmic show.

OK… seriously …. we are VERY lucky to have Hubble to snap pictures of this. But we are even more fortunate because of all the amateur astronomers right here on Earth who make many of these discoveries. The professional astronomers are very busy with detailed work using the Hubble, other space telescopes, and ground-based telescopes. But the sky is pretty big, and the pros can’t be looking at everything.

So thanks to Anthony Wesley, someone was looking at Jupiter at just the right time last month.

The resulting blemish on Jupiter in July grew larger than the size of the Pacific ocean! Whatever it was that hit Jupiter — if it had hit Earth, it would have been absolutely catastrophic.

The last time something like that happened was June 30, 1908, when something hit eastern Siberia. It is known as “The Tunguska Impact.” Whatever that was, the explosion was more than 2,000 times the power of the nuclear bomb that destroyed Hiroshima. It leveled 830 square miles of the Siberian forest. Had it happened a few hours earlier, the city of St. Petersburg would have been completely destroyed. Consider how that would have altered the history of the 20th century! Even so, the Tunguska object was most certainly much smaller than whatever hit Jupiter in July.

There will probably always be disagreement as to what is responsible for “The Tunguska Impact.” Some say it was an asteroid, but no meteor remains have been found at the site. Others say it was a comet that exploded just before hitting the surface. More wild ideas claim it was a miniature black hole, an alien spacecraft, or a WWII bomber that traveled back in time. OK, I don’t take that seriously. People say a lot of weird stuff about the Tunguska impact

Anyway… whatever hit Jupiter, we can safely say: better it than us!

In fact, many astronomers believe that is exactly the role Jupiter plays in our solar system. Part of what makes the Earth such a nice place to live is that Jupiter’s massive gravity acts as a kind of shield, deflecting incoming comets away from the inner solar system where they could do for us what an asteroid did for the dinosaurs 65 million years ago. As a result, astronomers looking for planets in other solar systems that might harbor life look for similar configurations — a giant outer planet with room for smaller planets in closer to the home stars.

I talked with Dr. Hal Levison of the Southwest Research Institute about this recent impact on Jupiter.

SkyGuy: “Dr. Levison, I’m sure scientists don’t know for sure yet, but… what hit Jupiter?”

Dr. Levison: “Well, statistically, we can answer that question. It’s almost certainly a Kuiper Belt Object. There are three basic sources of impactors for both Jupiter and the Earth. There is the Asteroid Belt, there is the Kuiper Belt, and there is the Oort Cloud. And the Kuiper Belt is made up of cometary type things, the Oort Cloud is made up of cometary type things, and the Asteroid Belt is mainly rocky type things.”

SkyGuy: “So, we don’t know for certain. But… statistically, it’s highly likely that it is a Kuiper Belt Object.”

Dr. Levison: “That’s right. I should point out that statistically is like… I… I don’t remember the numbers. I would have to go look. I’ve worked out the impact rate on Jupiter from the Kuiper Belt, not the other objects. But my guess is it’s a thousand to one. Or maybe even higher. I mean, Jupiter is a big attractor of Kuiper Belt Objects. So it’s almost certainly a Kuiper Belt Object.”

SkyGuy: “Comet Shoemaker-Levy 9 hit Jupiter fifteen years ago. Does having two events like this in just fifteen years alter estimates for how often something like this occurs?”

Dr. Levison: “Yeah. I’ve been having a debate with one of my collaborators on this where I had a lower number for the impact rate than he did. And it turns out he’s right. But all that was based on theory. We see one event, and it tells us nothing, because you could just be seeing a statistical fluke. Once you get two, then you can start really doing statistics on it.”

SkyGuy: “And does this increase the odds of something like this happening to Earth?”

Dr. Levison: “No, it turns out, of those three populations, the Kuiper Belt is most important for Jupiter and least important for Earth. So it really doesn’t affect our understanding of the impact rate on the Earth at all.”

SkyGuy: “So does Jupiter actually protect us?”

Dr. Levison: “No, it drives everything. Most of the impactors that hit the Earth are asteroids that come from the Asteroid Belt. First of all, the Asteroid Belt probably wouldn’t be there if Jupiter hadn’t formed. So, in that regard, it’s important. But also, the way these things get out of the Asteroid Belt is by gravitationally interacting with Jupiter. So, Jupiter, for the main source of impactors on the Earth, Jupiter is the cause. It’s not protecting us. For the Kuiper Belt Objects, although the impact rate on the Earth is really low, if Jupiter was… if you just reached in and plucked Jupiter out of the solar system, you wouldn’t get any Kuiper Belt Objects down here. Jupiter needs to be there to divert them in. So from that perspective, it hurts. For the Oort Cloud it helps a lot. And so the Oort Cloud is probably the second most important source of impactors on the Earth, and Jupiter really does play an important role in protecting us from the Oort Cloud.”

Hmm. Not quite as simple as I had thought. I’m thankful Jupiter is keeping Oort Cloud objects away from us, but not so thrilled that it nudges asteroids in our direction.

Y’know… It’s easy to look up at the night sky, night after night, and think not much of anything changes out there. But in fact, there’s crazy stuff going on out there all the time! Asteroids and comets flying around and slamming into planets, gamma ray bursts, black holes gobbling up stars. The Universe is a very busy place.

So we need to have more eyes looking through more telescopes. And that’s one reason we need to get today’s kids excited about astronomy.

That’s why my passion is sharing the wonder of space and astronomy with kids, at Skyguy.com.

Are you a teacher or a parent? Or do you just know some kids who have questions about space? Go to SkyGuy.com and click on “ask a question.” If I don’t know the answer, I probably know a scientist who does…

That’s all for now. And remember: The sky is not the limit.

You — or the kids in your life — can go MUCH farther than that!

End of podcast:

365 Days of Astronomy
The 365 Days of Astronomy Podcast is produced by the New Media Working Group of the International Year of Astronomy 2009. Audio post-production by Preston Gibson. Bandwidth donated by libsyn.com and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org. Until tomorrow…goodbye.