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Kamikaze Comets Don't Stand A Snowball's Chance In Hell
By Robert Roy Britt
Senior Science Writer
posted: 06:18 pm ET
09 February 2000
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soho_comet_000209 If you are a comet, then you live a precarious life, alternately being boiled by the sun and then zooming out for a deep freeze in the outer reaches of the solar system. At points in between, you must slog through the denser regions of the solar system, where planets and asteroids lurk, and where a collision could at any time bring an instantaneous end to a life you've been living for 4 billion years or so. But it's that trip around the massive central furnace that you fear most. One slip, gravitationally speaking, and your travels are over. You'll be vaporized before you even get close enough to know what you hit.You are a kamikaze comet, and more than 100 of your comrades have already been imaged by the SOHO spacecraft, just prior to their death plunge -- the typical end for most, at least. 
The 100th comet spotted by SOHO, found February 3, is a rare breed expected to survive its trip around the sun. SOHO orbits in a constant relative perch between Earth and the sun, 932,050 miles (1.5 million kilometers) away. Its instruments block out the sun's bright disk and view the surrounding space out to 12.5 million miles (20.2 million kilometers). The primary comet-imager is called LASCO, for Large Angle and Spectrometric Coronagraph. During SOHO's more than four years of imaging, it has spotted 102 comets challenging the sun. Only 10 have survived, including the last three. NASA's Douglas Biesecker, who has bagged 45 of the streaking balls of ice and vapor, found the most recent comet. To hell and probably not back again Comets, thought to be pristine leftovers from the formation of our solar system, are often likened to dirty snowballs, and the hell they go through hath multiple methods of fury. If not vaporized, a comet's nucleus is often broken apart by the sun's immense gravity. Only the largest comets survive the risky inner voyage. Researchers theorize that many of the daring comets now being imaged have a common ancestry -- some large grandparent that broke up long ago. 
Two comets in are shown plunging sunward on June 2, 1998. "The rate at which we've discovered comets with LASCO is beyond anything we ever expected," Biesecker said, adding that there could be as many as 20,000 fragments on a loopy trajectory through space, with our sun as their anchor. "SOHO is seeing fragments from the gradual breakup of a great comet, perhaps the one that the Greek astronomer Ephorus saw in 372 BC," said Brian Marsden of the Center for Astrophysics in Cambridge, Massachusetts. "Ephorus reported that the comet split in two" 
SOHO's sixth sun-grazing comet was spotted on December 23, 1996 and named the Xmas comet. Marsden says this fits with his calculation that two comets on similar orbits re-visited the Sun around 1100 AD: "They split again and again, producing the sun-grazer family, all still coming from the same direction." (All Images: NASA/GSFC/ESA/SOHO)
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