[meteorite-list] Earth Rocks Could Have Taken Life to Titan

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Mar 20 09:34:44 2006
Message-ID: <200603200229.k2K2SgB00667_at_zagami.jpl.nasa.gov>

http://www.newscientistspace.com/article/dn8867-earth-rocks-could-have-taken-life-to-titan.html

Earth rocks could have taken life to Titan
Maggie McKee
New Scientist
17 March 2006

Boulders blasted away from the Earth's surface after a major impact
could have travelled all the way to the outer solar system, new
calculations reveal. The work suggests that terrestrial microbes on the
rocks could in theory have landed on Saturn's giant moon, Titan. But
whether they could have survived once there remains unclear.

The fact that meteorites from the Moon and Mars have landed on Earth
confirms that impacts on solar system bodies can launch rocky debris to
other planets. And previous studies have suggested that any life on the
rocks could have survived the launch blast and the radiation and chill
of the journey through space, assuming it lasted less than a few million
years.

Such hardiness raises the possibility that life on Earth itself was
seeded from space - a concept called panspermia. But now,
researchers led by Brett Gladman of the University of British Columbia
in Vancouver, Canada, have analysed the reverse situation - that life on
Earth seeded other bodies in the solar system. Gladman presented the
results on Thursday at the Lunar and Planetary Science Conference in
Houston, Texas, US.

He says only boulders at least 3 metres across could punch out through
the Earth's atmosphere and escape the planet's gravity, and that only
extremely powerful impacts could achieve this. The cause of such impacts
would be comets or asteroids between 10 and 50 kilometres wide, Gladman
told New Scientist: "The kind of thing that killed the dinosaurs."
          
Brick wall

The team ran computer models of such giant impacts, estimating that each
would send about 600 million boulders into space to orbit the Sun. Some
of those launched at relatively high speeds - faster than 6 kilometres
per second - got as far as Jupiter and Saturn in about a million years.

In the simulations, about 100 of the boulders from each impact reached
Jupiter's moon Europa. But along the way, Jupiter's gravity boosted
their speed to an average of 25 km/s, with some moving as fast as 40
km/s. Impacting Europa's icy crust at such speeds would be like "hitting
a brick wall," says Gladman. "This must be rather frustrating if you're
a bacterium that survived launch from Earth."

But he found a different situation on Saturn's moon Titan, which boasts
a thick atmosphere. About 30 boulders from each Earth impact reached
Titan, and they slammed into the atmosphere at just 11 km/s - slower
than most meteors hit Earth's atmosphere. "Those reaching Titan can
aerobrake and drop their fragments onto the surface," says Gladman.

Home from home?

"That kind of entry should be no problem" for life to survive, says
Allan Treiman of the Lunar and Planetary Institute in Houston, who notes
that researchers recently found bacteria that appear to have survived
the break up of the shuttle Columbia when it re-entered Earth's atmosphere
in 2003. And Earthly lichen has also survived when exposed to the harsh
environment of space.

"I thought the Titan result was really surprising - how many would get
there and how slowly they'd land," Treiman told New Scientist. "The
thing I don't know about is if there are any bugs on Earth that would be
happy living on Titan." Titan's surface temperature is a very cold
-179?C and its chemistry is very different from Earth's.

Gladman agrees that life may be unlikely to survive once on Titan. But
he says major impacts may have happened "tens of times" throughout
Earth's history and that these could have sent Earth rocks to other
solar system bodies. "I just set out to answer this question: is it
possible to get something there?" he says. "The answer is yes."
Received on Sun 19 Mar 2006 09:28:42 PM PST