Comet Vanishing Act Puzzles Scientist
'These objects are simply not where we expect them to be'

June 22, 2002

WASHINGTON (Reuters) -- When comets born at the edge of our solar system disappear from view, they don't just lose their tails and go dormant; 99 percent of them go "poof" and crumble to bits, United States researchers have reported.

"These objects are simply not where we expect them to be," Harold Levison of the Southwest Research Institute said in a statement. "The only explanation that I can think of is that they go 'poof.'"

The mystery of the missing comets has been debated for decades.

Some astronomers theorized that most of those that issued from a cloud of comets, known as the Oort cloud, at the edge of the solar system eventually stopped producing their highly visible tails and went dormant, making them harder to detect.

But Levison and his colleagues, writing in the journal Science, said their studies showed the vast majority of these comets broke apart after a few passes through the inner solar system.

Levison, based in Boulder, Colorado, and his team compared computer models with observations of comets to figure out where the missing ones went.

The team created thousands of fictitious new comets, tracked the comets as they entered the solar system from the Oort cloud, and calculated their evolution based on the gravitational influences of the sun, planets, and Milky Way.

By following comet trajectories until they were ejected from the solar system, hit a planet or struck the sun, team members estimated the number of dormant comets should have been 100 times larger than the number actually seen. From this, they deduced that 99 percent of comets simply vanished.

They noted that Oort cloud comets disintegrate far more often than those originating in the Kuiper Belt, a comet source just beyond Neptune.

Both kinds of comets are made of the same mixture of ice and rock, but differences in the chemical or physical characteristics of their formation areas might account for the variation in behavior, the researchers said.

http://www.cnn.com/2002/TECH/space/06/22/vanishing.comets.reut/index.html