[meteorite-list] Microbes Flying Across The Galaxy Aboard Meteorites

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:44:39 2004
Message-ID: <200103150133.RAA22754_at_zagami.jpl.nasa.gov>

http://www.eurekalert.org/releases/ns-mfa031401.html

     EMBARGOED FOR RELEASE: 14 MARCH 2001 AT 14:00 ET US

     Contact: Claire Bowles
     claire.bowles_at_rbi.co.uk
     44-207-331-2751
     New Scientist

     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
     PUBLISHING ONLINE, PLEASE CARRY A HYPERLINK TO:
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Received on Wed 14 Mar 2001 08:33:06 PM PST