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Asteroids: Star-Hopping Travelers Could Sow Seeds of Life
By Leonard David
Senior Space Writer
posted: 07:00 am ET
09 April 2001
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Intellectually interesting
But the planetary scientist hastens to add that a central question remains.
Could any of those life-bearing rocks make it to the right kind of star, then become tossed and turned by the gravity grips of Jovian-style planets, followed eventually by a fall onto a terrestrial planet – and all that on a time scale such that microbes could survive?
Computer calculations suggest no more than a maybe. Nevertheless, it is "intellectually interesting," Melosh said.
"Although interstellar panspermia seems much less probable, my results, along with the recent evidence that microbial spores may have survived for periods of 250 million years on Earth, make it just barely possible that viable organisms might have been able to make an interstellar journey," Melosh reported at the Houston meeting.
"Much more work on the various survival factors must be done before this hypothesis can be granted even a degree of plausibility," Melosh said.
Tough sell
Saluting the work of Melosh is astrobiologist, Bruce Jakosky of the University of Colorado in Boulder, who said, however, that even by pushing all the parameters to try and make the idea favorable, it appears that interstellar exchange remains a tough sell.
Jay Melosh, professor of planetary science, University of Arizona in Tucson
Jakosky said that many scientists contend that terrestrial life originated in our solar system, with the "chemical" origin of life still the most plausible mechanism.
"This really should come as no surprise, given that the early Earth appears to have had a tremendous overabundance of all of the conditions that we think were required for an origin; in particular, that the tremendous stores of available energy really could drive the origin of life," Jakosky said.
Yet there is an open question.
"Which of the three terrestrial planets – Earth, Venus or Mars – really was the location of the origin? Given the interplanetary exchange of material, it really could have been on any one of them, or on all three! Going to Mars really gives us the best chance of answering this question," Jakosky said.
Wipe out
The exchange of materials from planet to planet within our solar system is no problem, said Michael Meyer, an astrobiologist at NASA Headquarters. "It just ends up being statistics," he said.
"We should be able to infect the solar system and have life in any habitable place," Meyer said.
Moving rocks from Earth to, say Jupiter’s Europa, is much harder, Meyer said. "You still have exchange, but now you’re talking a very small number of meteorites that land there over time," he said.
But "it’s a whole different ball game" when you start talking about life crossing interstellar distances, Meyer said. "It’s still a stretch."
"You can move things between stellar systems. But to have something survive the cosmic ray environment, that is the daunting problem. You have extremely long transit times, and even if you shield things from ultraviolet rays, which is a major problem, you still have cosmic rays. And just one hit is enough to wipe out an organism," Meyer said. | | | |
