The temperature associated with the light is much cooler. In the early history of the solar system comets picked up enough viable microbes from interstellar space to incubate them in their warm watery interiors. A million years later, the bacteria exhausted the comet's heat source, were freeze dried, and became dormant. Then, as the comet approached the Sun, some of its material was blown off into space. It is these ready-formed bacterial particles that entered the Earth for the first time 4 billion years ago and established the ancient Kingdom of Archaea, for which we have evidence in the geological record.
Caution reigns Other researchers are warming to the idea of panspermia, but remain cautious.
Weiss led a recent study of a Mars meteorite found in Antarctica, discovering that the space rock remained cool enough to have supported the transfer of microbial life. Jenniskens and his colleagues will not conduct such thorough research of this year's Leonids, but they hope to be back at it in 2001. Meanwhile, NASA will loft a weather balloon toward the stratosphere on Saturday to record the sights and sounds of the 2000 Leonid meteor shower. Click here for more headlines and information on comets and meteors.