[meteorite-list] The Amazing Trajectories of Life-Bearing Meteorites from Earth

[Ron Baalke]

http://www.technologyreview.com/blog/arxiv/27720/      

The Amazing Trajectories of Life-Bearing Meteorites from Earth

The asteroid that killed the dinosaurs must have ejected billions of
tons of life-bearing rock into space. Now physicists have calculated
what must have happened to it.

About 65 million years ago, the Earth was struck by an asteroid some 10
km in diameter with a mass of well over a trillion tons. We now know the
immediate impact of this event - megatsunamis, global wildfires ignited by
giant clouds of superheated ash, and, of course, the mass extinction of
land-based life on Earth.

But in recent years, astrobiologists have begun to study a less well
known consequence: the ejection of billions of tons of life-bearing
rocks and water into space. By some estimates, the impact could have
ejected as much mass as the asteroid itself. 

The question that fascinates them is what happened to all this stuff.

Today, we get an answer from Tetsuya Hara and buddies at Kyoto Sangyo
University in Japan. These guys say a surprisingly large amount of Earth
could have ended up not just on the Moon and Mars, as might be expected,
but much further afield. 

In particular, they calculate how much would have ended up in other
places that seem compatible for life: the Jovian moon Europa, the
Saturnian moon Enceladus, and Earth-like exoplanets orbiting other stars.

Their results contain a number of surprises. First, they calculate that
almost as much ejecta would have ended up on Europa as on the Moon:
around 10^8 individual Earth rocks in some scenarios. That's because the
huge gravitational field around Jupiter acts as a sink for rocks, which
then get swept up by the Jovian moons as they orbit. 

But perhaps most surprising is the amount that makes its way across
interstellar space. Last year, we looked at calculations suggesting that
more Earth ejecta must end up in interstellar space than all the other
planets combined <http://www.technologyreview.com/blog/arxiv/27092/>.

Hara and co go further and estimate how much ought to have made its way
to Gliese 581, a red dwarf some 20 light years from here that is thought
to have a super-Earth orbiting at the edge of the habitable zone.

They say about a thousand Earth-rocks from this event would have made
the trip, taking about a million years to reach their destination.

Of course, nobody knows if microbes can survive that kind of journey or
even the shorter trips to Europa and Enceladus. But Hara and buddies say
that if microbes can survive that kind of journey, they ought to
flourish on a super-Earth in the habitable zone. 

That raises another interesting question: how quickly could life-bearing
ejecta from Earth (or anywhere else) seed the entire galaxy?

Hara and co calculate that it would take some 10^12 years for ejecta to
spread through a volume of space the size of the Milky Way. But since
our galaxy is only 10^10 years old, a single ejection event could not
have done the trick.

However, they say that if life evolved at 25 different sites in the
galaxy 10^10 years ago, then the combined ejecta from these places would
now fill the Milky Way.

There's an interesting corollary to this. If this scenario has indeed
taken place, Hara and co say: "then the probability is almost one that
our solar system is visited by the microorganisms that originated in
extra solar system."

Entertaining stuff!

Ref: arxiv.org/abs/1204.1719 <http://arxiv.org/abs/1204.1719>: Transfer
of Life-Bearing Meteorites from Earth to Other Planets