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There has been a long time quest to find evidence for life in other worlds, on planets surrounding other stars than the Sun. Now there is a new way to try to locate our distant relatives which may have migrated to other planetary systems. The research shows that microbes can survive for long periods of time inside meteoroids which have originated from the Earth. These meteoroids were flung out most frequently during the first billion years since the formation of the Earth when the solar system was not yet fully settled but was full of bodies crisscrossing the system. Many of them impacted the Earth, and the impacts raised meteoroids off the Earth's surface. Some of the meteoroids may have carried life forms inside them, most likely bacteria which are thought to have existed on Earth at the time. Many of the life-carrying meteoroids found their way out of the solar system, and some them landed on planets which circle other stars. There the life may have spread, and may have evolved into our "cousins" advanced life-forms based on the same DNA as our life on Earth. What is the probability that this process of spreading life has actually taken place? In this work a group of leading biologists, planetary scientists, radiation physicists and astronomers have put their expertise together to calculate the probability that a meteoroid loaded with bacteria has made a successful landing on another planet in another solar system with bacteria well and alive. Surprisingly, the number of events like this turns out be non-negligible; there may have been thousands of successful transfers of life. But there is a limitation: the systems that can exchange life have to be situated in the same cluster of stars. The birth cluster of the Sun has long since scattered about in the Galaxy, and we do not see our original stellar neighbours close to us any more. The present neighbors have come from some other star clusters, and they cannot be carriers of our DNA based life. But hope is not all lost: the satellite observatory GAIA will soon start to survey the motions of stars in our part of the galaxy, and it is quite likely that it will be able to identify our original neighbors. Then there are two new satellite observatories, SIM and DARWIN, under planning which may detect signs of life in the planets circling these stars. If everything goes well and the planned missions are launched and are successful, in about 10-15 years time we may be able to know if we have cousins in the The reverse side of the same story is that the life on Earth may not have originated here but may have come from one of our sister systems of the Sun's birth cluster of stars. We may never know the true origin, but it is exciting to see the results of the search of life around other stars in the decades to come. The researchers involved in this work from Tuorla are Mauri Valtonen, Pasi Nurmi and Jia-Qing Zheng. The project was originated by Curt Mileikowsky from Sweden, but he unfortunately died before its completion. Partly for this reason, the final publication of this work was long delayed. The original announcement of the results was made already in January 2000 in the Atlanta meeting of the American Astronomical Society in a press conference by Valtonen and Mileikowsky where the first phase of the work was emphasized, the transfer of life between Earth and Mars in our own solar system. More information is available in Swedish or in English The study is available as a Preprint. |
