Earth may have 'infected' Titan with life

Panspermia postulations

The various meteoric slappings sustained by Earth over the millenia may have seeded other parts of the solar system with life, if calculations by Canadian scientists are to be believed.

Planetary scientist Brett Gladman and colleagues at the University of British Columbia in Vancouver worked out that for material to be thrown up with enough force to exit Earth's atmosphere, it would take an impact from a meteor 10 to 50km across. They reckon such impacts, which include the famous 'dinosaur-killer' that formed the Chicxulub crater, send about 600m potenitally life-bearing rock fragments into solar orbit.

The team looked at whether the fragments' microbial passengers might find a home on one of the solar system's potentially sustaining worlds. Speaking at the Lunar and Planetary Science Conference in League City, Texas, Gladman said in the course of five million years Jupiter's moon Europa would get 100 hits and Saturn's Titan be seeded 30 times.

Despite its lower hit rate, the researchers think Titan more likely to have been fertilised. They calculated that Jupiter's gravity would pile the fragments into frozen Europa too fast. Titan's thick atmosphere whould split the fragments and slow the descent meanwhile.

Gladman was asked if he thought Earthly microbes would be able to endure Titan's freezing temperatures. He said: "That's for you people to decide, I'm just the pizza delivery boy."

The finding tips the panspermia theory on its head, and makes it a more interesting proposition. This once-fashionable idea of how life got started on Earth postulates that it was brought here by rocks from other worlds. While an undeniably diverting speculation, a cosmic common ancestry seems unprovable. Advocates cling to the apparently short time it took from Earth's formation to the emergence of life - around half a billion years. However, with a sample size of precisely one we cannot know the likelihood of life.

More crucially, panspermia contributes nothing to the quest for a complete theory of how life can emerge spontaneously - an important missing piece in the evolutionary jigsaw. The idea simply shifts the problem to another world. ®

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