(from http://www.space.com/15192-sun-siblings-asteroids-earth-life.html)
Some scientists are searching not just for any life out there in the
universe, but for our distant relatives.
Earth may have seeded life on other planets if an asteroid smacking into
Earth sprayed DNA into space, researchers suggest. Now a team of
researchers is searching for siblings of the sun — stars born from the same
parent star cluster — whose planets could have been impregnated with Earth
life this way.
*The sun's birth cluster*
The sun is thought to have formed around 4.5 billion years ago within a
cluster of thousands of baby stars. After around 1 billion years, this
cluster broke up and the sibling stars went their separate ways. But before
that point, researchers say, some of these stars may have shared life in
the form of bacteria or DNA molecules.
"The idea is if a planet has life, like Earth, and if you hit it with an
asteroid, it will create debris, some of which will escape into space,"
said astronomer Mauri Valtonen of the University of Turku in Finland. "And
if the debris is big enough, like 1 meter across, it can shield life inside
from radiation, and that life can survive inside for millions of years
until that debris lands somewhere. If it happens to land on a planet with
suitable conditions, life can start there." [Gallery: The Smallest Alien
Planets]
That means that somewhere out there in the galaxy might be your long-lost
cousin.
If such a process ever happened, it was probably while the sun was still in
its birth cluster, near enough to other stars that the chances were not
negligible that debris bearing samples of Earth microorganisms might smash
into another planet.
During the time of the birth cluster, objects in the solar system were
under heavy bombardment by comets and asteroids, so researchers say
material could have been fairly easily transferred between planets.
Research suggests it's equally possible that Earth itself was seeded with
life in such a manner, though neither scenario is considered likely.
*Searching for siblings*
To pursue the idea, Valtonen is searching for these sibling stars of the
sun.
In a recent study, he analyzed a catalog called HIPPARCOS that recorded the
positions and motions of more than 100,000 stars. Picking out those stars
with radial velocities known to be similar to the sun's, Valtonen and his
colleagues identified two promising stars, called HIP 87382 and HIP 47399,
that also had the same metal content and were at the same evolutionary
stage as the sun. According to the researchers' analysis, there are a few
percentage points of probability that these two were born in the same
cluster as our sun. Both are about 100 light-years from Earth now.
Valtonen said the next step would be to search for planets around these
candidate stars.
"If we find an Earth-type planet, then it'd be a nice target for this new
generation of detectors to point at the atmosphere of the planet," Valtonen
told SPACE.com. "If there's a planet and it has signs of life, then we
could say perhaps they are relatives in some sense."
