Life could have come from outer space

Researchers suggest microorganisms that crashed to Earth embedded in the fragments of distant planets might have been the sprouts of life on this planet.

The researchers report that under certain conditions there is a high probability that life came to Earth-or spread from Earth to other planets-during the solar system's infancy when Earth and its planetary neighbors orbiting other stars would have been close enough to each other to exchange lots of solid material.The findings provide the strongest support yetfor lithopanspermia, the hypothesis that basic life forms are distributed throughout theuniverse via meteorite-like planetary fragmentscast forth by disruptions such as volcanic eruptions and collisions with objects such asasteroids.

Eventually, another planetarysystem's gravity traps these roaming rocks,which can result in a mingling that transfers anyliving cargo. Previous research on this possiblephenomenon suggested that the speed at which objects hurtle through space made the chance ofthem being captured by another planet verysmall. However, this new research, based oncomputer simulations of the star cluster our Sunwas born in, suggests that a process called weaktransfer, in which solid objects can gradually meander out of the orbit of one object and intoanother, greatly increase the odds that thisprocess could have happened.The research is based on principles of weaktransfer developed by mathematician EdwardBelbruno. Belbruno first demonstrated weak transfer in 1991 when guiding the Hiten probeto the Moon using minimal amounts of fuel."Our work says the opposite of most previous work. It says that lithopanspermia might have been very likely, and it may be the first paper todemonstrate that. If this mechanism is true, it has implications for life in the universe as awhole.

This could have happened anywhere,"said Belbruno. The team noted that low velocities offer very high probabilities for theexchange of solid material via weak transfer,and also found that the timing of such an exchange could be compatible with the actualdevelopment of the solar system, as well as withthe earliest known emergence of life on Earth.The researchers report that the solar system andits nearest planetary-system neighbor couldhave swapped rocks at least 100 trillion times
well before the Sun struck out from its nativestar cluster. Furthermore, existing rockevidence shows that basic life forms could indeed date from the Sun's birth cluster daysandhave been hardy enough to survive aninterstellar journey and eventual impact. Belbruno's collaborator Amaya Moro-Martin(Centro de Astrobiologia and PrincetonUniversity) said, "The conclusion from our work is that the weak transfer mechanismmakes lithopanspermia a viable hypothesisbecause it would have allowed large quantities of solid material to be exchanged betweenplanetary systems, and involves timescales thatcould potentially allow the survival of microorganisms embedded in large boulders."The study shows that exchange of materialbetween different planetary systems is likely, but it stops short when the solid matter iscaptured by the second planetary system. Forlithopanspermia to actually take place, the material needs to land on an Earth-like planetwhere life could flourish. "The study of theprobability of landing on a terrestrial planet is work that we now know is worth doing becauselarge quantities of solid material originatingfrom the first planetary system may be trapped by the second planetary system, waiting to landon a terrestrial planet," said Moro-Martin.

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