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_Are We All Aliens? The New Case for Panspermia (cont.)_

___Support for parts of panspermia_

Other researchers agree that both space rocks and comet dust might in
fact harbor organic matter. But how these ingredients for life might
travel from one star to another is hotly disputed.

Even as doubters are beginning to give panspermia advocates a little
respect, most say the likeliest transfers of life would occur between
planets.

This sample salt crystal from New Mexico shows a supposed 250
million-year-old Earth bacteria, inside the yellow circle.

"That bacteria, or at least their spores, can survive for such
staggering amounts of time makes their transport from planet to planet
on meteorites possible," said Matthew Genge, a meteoritic researcher
at the London Natural History Museum. "Bacterial spores in their very
own kind of suspended animation could perhaps survive the millions of
years it takes for rocks to travel from planet to planet."

More Stories

[14]Life On Earth Could Have Come From A Mars Rock

[15]Panspermia Q and A: Leading Proponent Chandra Wickramasinghe

[16]Life's Travels: A Panspermia Q and A With Jay Melosh

[17]To Seed the Heavens with Life: Panspermia In Reverse

Related Links

[18]Cosmic Ancestry

But Genge, along with other scientists, cautioned that the
250-million-year-old bacteria found in New Mexican salt crystals are
not conclusive. There is a chance the samples were contaminated with
more modern bacteria, and follow-up studies need to be done.

Still, previous studies have found viable bacterial spores in 30
million-year-old amber. And [19]last year's discovery of living
microbes deep in the Antarctic extends the range of extreme conditions
under which life is known to survive.

Few researchers question that life is hardy, and that it can hang on
for a very, very long time. And some space rocks are known to make the
trip from Mars to Earth in less than a year.
__
Death rays and cosmic cannon balls

The trick for a much lengthier interstellar journey would be surviving
deadly cosmic rays.

Even the nearest stars known to have planets are many light-years
away. And none has been shown to have habitable planets. Some nearby
stars are becoming more interesting, however. The star [20]Iota
Horologii, just 56 light-years away, is the first to have a planet in
an Earth-like orbit and to show other signs of solar system formation
like our own.

But even 56 light-years is a bit longer than your average commute.

"Herein lies the problem," Genge said. "In Earth rocks, bacterial
spores may survive for millions of years cocooned beneath the Earth's
surface because they are protected from radiation. On a meteorite in
space, fast moving atomic and sub-atomic particles will plow through
the meteorite like cosmic cannon balls. If they encounter an organism,
DNA molecules will be shattered. If hit enough times, the organism
will not survive."

[inset]

Several scientists suggest that to survive, a spore, seed, bacteria or
other organism would need to be imbedded deep inside a good-sized
space rock, perhaps 3 meters (10 feet) or larger, shielded from
radiation. Even then, there is the problem of launching a
star-orbiting rock or comet into interstellar space.

The only way to do this is through repeated, and tricky, gravitational
interactions with planets, says Genge, explaining a process like the
one NASA used to sling the Voyager spacecraft out of the solar system.

"The thing is, it's taken a lot of very clever people, powerful
computers and cutting-edge technology to do this," Genge says.
"Terrestrial meteorites are just rocks and even with microbial
passengers they are pretty stupid and thus have to rely on chance."
__
Earth as an exporter of life

Somewhat lost in the current panspermia revival is the intriguing
flip-side of the "ubiquitous life" idea: If life could have come here
from somewhere, why couldn't an Earth rock have been dislodged long
ago, sending life to another planet or star system?

"It is possible that there are small fragments of the Earth out there
in space today, some with microorganisms, that were blasted off the
Earth's surface many millions of years ago," Genge says. "These could
reach the Jovian moons and through extreme good fortune seed the water
oceans with microorganisms."

Okay. How likely?

"The chances of this happening in reality are probably similar to
someone finding their way home after being blindfolded and airlifted
to another continent."

Genge and others say the more plausible scenario for the transfer of
life -- if it has ever occurred and given the scant solid evidence
currently available -- is that it started on Mars and came to Earth.
The recent discovery of water beneath the surface of Mars [21]has
researchers in many fields excited, suggesting that any life that was
once there might still exist.

"I consider it almost inevitable that microorganisms have been
transferred between Mars and Earth by hitching a ride deep inside
rocks blasted off the surface by asteroid impacts," says physicist
Paul Davies, author of _The Fifth Miracle: The Search for the Origin
and Meaning of Life_.

While Davies says life could have moved in either direction, the
Mars-to-Earth scenario is his favorite, based on presumed state of
things a few billion years back.

"Mars was a more favorable environment for life to get started,"
Davies told _SPACE.com_. "Being a smaller planet than Earth, it cooled
quicker, so the comfort zone for deep-living organisms (the ones safe
from impacts) was deeper sooner. It is easier for rocks to go from
Mars to Earth than vice versa, because Mars has a lower gravity."

Davies is rock-solid in his belief that it takes rocks, serving as
protective vessels, to move life from one planet to another. He
rejects the idea that "individual microbes waft naked through outer
space" -- one of the original tenets of the panspermia theory.

"I still believe it exceedingly unlikely that life could hop from one
star system to another that way, largely because of the radiation
hazard," Davies says. "It is possible for such transfer to happen
inside rocks, but the chance of a rock blasted off Earth ever hitting
another Earth-like planet beyond our solar system is infinitesimal."

So does this kill the idea that life on Earth arrived from another
star system, that we might have distant ancestors -- or maybe even
cousins -- waving to us from an orbit around Iota Horologii?

"Clearly it's possible," Davies says, "but the odds are exceedingly
low."

Wickramasinghe, the primary panspermia proponent, responded with a
different view:

"Not all microbes in interstellar space would survive of course,"
Wickramasinghe said. "But the survival of even a minute fraction of
microbes leaving one solar system and reaching the next site of planet
formation would be enough for panspermia to be overwhelmingly more
probable than starting life from scratch in a new location."

So despite all the new and important discoveries, we still don't know
how or where life began. But the search for it _has_ gotten a little
more interesting, now that we know we might all be aliens.
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