[meteorite-list] Microbes Flying Across The Galaxy Aboard Meteorites
From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:44:39 2004
EMBARGOED FOR RELEASE: 14 MARCH 2001 AT 14:00 ET US
Contact: Claire Bowles
Microbes flying across the Galaxy aboard meteorites
DON'T worry about contact with aliens from other solar
systems-they may be our distant cousins. According to an American
astronomer, there is a slim chance that microbes could be carried
from one solar system to another on rocks blasted from terrestrial
planets by asteroid impacts, spreading life across the Galaxy.
"About one meteorite ejected from a planet belonging to our Solar
System is captured by another stellar system every 100 million
years," Jay Melosh of the University of Arizona told the Lunar and
Planetary Science Conference in Houston this week.
Although radiation would threaten stowaway microbes, Russell
Vreeland of West Chester University of Pennsylvania says it would
be quite possible for meteorites to carry well-protected organisms
over interstellar distances.
In the 1970s, astronomers Fred Hoyle and Chandra Wickramasinghe
put forward the still controversial theory, dubbed "panspermia".
This says that comets bombarding the Earth brought the bacteria
and viruses from interstellar space that started life here 4
billion years ago, and continue to bring in new biological
material today. Melosh argues that alien organisms might also come
from a distant planet similar to our own.
He is part of a group that earlier showed microbes could hitch a
ride on meteorites travelling between planets in our Solar System
(New Scientist, 15 January 2000, p 19). At the time, he didn't
think any microbes could survive the millions of years a meteorite
would take to travel between stars. That view changed, however,
after Vreeland successfully cultured bacterial spores from a
250-million-year-old salt deposit in New Mexico (New Scientist, 21
October 2000, p 12). The longer survival time makes the transfer
of life conceivable, Melosh says.
Transfers between solar systems depend on gravitational
interactions between meteorites and other planets. As a starting
point, Melosh considered rocks blasted off the surface of Mars by
impacts. His simulations show that Jupiter can act as a slingshot,
flinging roughly 500 kilograms of Martian rocks each year right
out of our Solar System in all directions. Their velocity averages
5 kilometres per second, so in a million years they would travel
about 17 light years-far enough to reach nearby stars.
Most ejected meteorites would continue to drift in the
interstellar void, but a few would eventually pass near other
planetary systems. "The probability of direct capture by an
Earth-sized planet is very, very tiny," says Melosh. However, the
gravity of a Jupiter-sized giant planet can capture meteorites
passing within a hundred million kilometres of it, if the two are
moving at similar velocities in the same direction. The meteorite
would then fall into an eccentric orbit about the star.
It is still far from certain whether the meteorite would go on to
collide with a terrestrial planet, and Melosh's calculations
suggest that the likelihood of such an event is low for a solar
system like our own. The chances would be higher, he says, if
terrestrial planets orbited near to a Jupiter-sized planet.
"The probabilities are pretty low," acknowledges Melosh. But they
aren't impossibilities, he adds. Wickramasinghe believes that his
panspermia theory, in which bacteria can drift on their own
between solar systems, propelled by radiation pressure, is a more
likely scenario. "The only advantage that you might have [with]
huge chunks of rock [is that] the interior is shielded totally
from any damaging radiation," he says.
Author: Jeff Hecht
New Scientist issue: 17th March 2001
PLEASE MENTION NEW SCIENTIST AS THE SOURCE OF THIS STORY AND, IF
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Received on Wed 14 Mar 2001 08:33:06 PM PST