Wednesday, January 19, 2011

"Suicide" Comet Storm Hits Sun. Bigger Sun-Kisser Coming?

Since its launch in 1995, NASA's Solar and Heliospheric Observatory, or SOHO, orbiter has captured pictures of 2,000 comets as they've flown past the sun.

Most of these comets are so-called sungrazers, relatively tiny comets whose orbits bring them so near the sun that they are often vaporized within hours of discovery.

The sun-watching telescope usually picks up one sungrazer every few days. But between December 13 and 22, SOHO saw more than two dozen sungrazers appear and disintegrate.

Seeing "25 comets in just ten days, that's unprecedented," Karl Battams, of the United States Naval Research Laboratory in Washington, D.C., said in a statement. "It was crazy!"

According to Battams and colleagues, the comet swarm could be forerunner fragments from a much larger parent comet that may be headed along a similar path. And such a large icy body coming so near the sun would result in a spectacular sky show.

Sun-Kissing Comet "Granddaddy" on the Way?

Despite becoming a leading comet hunter, SOHO was initially designed to study the sun. For example, one camera on the probe uses a device called a coronagraph to block out the main body of the sun so that it can see fainter features in the star's upper atmosphere.

(Related: "Sun Erupts—Epic Blast Seen by NASA Solar Observatory." With video)

As it happens, this setup also allows SOHO to spot tiny, house-size comets taking their death plunges.

Over the years, the number of sungrazing comets detected by SOHO has increased, from 69 in 1997 to 200 in 2010.

Even after accounting for more participation from comet hunters and efforts to optimize images for comet-spotting, the numbers appear to show a significant increase in sungrazers, the astronomers say.

(Related: "Weird Asteroid Really a Crusty Old Comet?")

And the recent flurry of kamikaze comets may be pieces from a larger body similar to the Ikeya-Seki comet of 1965, Battams and colleagues say.

The granddaddy of all sungrazing comets, the three-mile-wide (five-kilometer-wide) core of Ikeya-Seki swept within 280,000 miles (450,000 kilometers) of the solar surface.

Rather than vaporizing, the large comet survived its close encounter and whipped around the sun, becoming so bright in Earth's sky that, for a time, it was visible during the day.

Since there were no space-based solar probes at the time, no one knows whether that event was preceded by a storm of smaller comets

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