24 July 2009

Jupiter deserves a medal for doing its job of sucking up dangerous rocks

The dark bruise that appeared suddenly near the south pole of Jupiter several days ago, likely as the result of an impact by a comet or asteroid, is as big as the Pacific Ocean, astronomers report.

The dark spot was first noticed by chance by amateur astronomer Anthony Wesley in Australia on Sunday, July 19.

The blemish is thought to be the result of an impact similar to that ofComet Shoemaker-Levy 9, which pummeled the gas giant 15 years ago.

After he was convinced the spot was not just another storm or the shadow of one of Jupiter's moons, Wesley alerted other astronomers around the world to the scar's appearance.

University of California, Berkeley, astronomer Paul Kalas took advantage of previously scheduled observing time on the Keck II telescope in Hawaii to image the blemish in the early morning hours of Monday, July 20. The near-infrared image showed a bright spot in the clouds of Jupiter's southern hemisphere, where the impact had propelled reflective particles high into the relatively clear stratosphere.

In visible light, the bruise appears dark against the bright surface of Jupiter.

These observations mark only the second time that astronomers have been able to see the results of an impact on the planet, the first being Comet Shoemaker-Levy 9's collision. Many theories were formed after that collision.

"Now we have a chance to test these ideas on a brand new impact event," Kalas, said.

Kalas and his colleagues hope their observations will shed light on the nature of the impact.

"The analysis of the shape and brightness of the feature will help in determining the energy and the origin of the impactor," said Marchis. "We don't see other bright features along the same latitude, so this was most likely the result of a single asteroid, not a chain of fragments like for SL9 [Comet Shoemaker-Levy 9]."


An Australian amateur astronomer detected the first indications that a comet had slammed into Jupiter only fifteen years after the Shoemaker-Levy impacts. It left an impact signature on the giant planet the size of earth. William Harwood writes:

We’re not sure how large this fragment could have been,” Leigh Fletcher, a researcher at the Jet Propulsion Laboratory in Pasadena, Calif., told CNET. …”We’ve compared it in size to the little red spot on Jupiter, you can see the two are roughly a similar order of magnitude in size,” he said. “It’s smaller than Earth-sized, but it’s certainly gargantuan by earthly proportions.”

Over the next few days and weeks, the Hubble Space Telescope, other space-based telescopes, and observatories around the world will focus on the impact site to learn as much as possible about what might have hit Jupiter and how the impact affected the planet’s atmosphere.

This is the second large hit on Jupiter we’ve observed in fifteen years. Does it tell us anything about the likelihood of an impact on earth? The answer is we don’t really know because we don’t have the detection systems in place to gather the data. Glenn Reynolds, writing in TCS notes that politicians have devoted a relative pittance to watching the skies. And even if an incoming object were detected, there are no established protocols to respond to the event, nor any realistic defenses against a massive incoming. This is probably a function of politics more than anything else, I think. Its deemed essential to spend trillions to prevent “climate change” in the name of the precautionary principle, but the ranging shots of the artillerist of the Solar System are left to amateur astronomers from Australia to observe.

But the most interesting issue that Glenn Reynolds raises in his TCS article is that, without a planetary defense and with an inadequate detection system, then humanity will at most have a short time between the detection of a life-ending incoming space projectile and impact. In that case, he asks, would we want to know? Should governments keep it secret from us?

Quite some time ago, I wrote about scientists’ questions on whether to deliver bad news. The news in question had to do with a potential life-ending asteroid strike. Perhaps, I suggested, it might be best not to deliver that news, if things were bad enough that nothing could be done. I also noted that this was an active question within the astronomical community.

Personally, I would want to know if the end were imminent. In the case Reynolds cites, the panic spawned by a sighting was premature. Further observations by astronomers showed the feared object was going to miss. Somebody should do a disaster movie like that one day, when everybody closes his eyes at the anticipated moment, only to look up to see, blazoned in flaming letters across the sky, “Nyah, nyah! Fooled you! Fooled you!”

Holst looked up at Jupiter and heard laughter. Here’s’s his Jupiter, Bringer of Jollity, from The Planets. On winter nights, after the last bus down Trapelo road had gone, I used to run the distance from Harvard Square to Belmont with a Walkman in my pocket. And the everything after 2:38 was my favorite on the track.

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