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An awful lot has been written about the possibility that life on Earth started
somewhere other than on Earth itself. Somewhat less attention has been focused on the
inverse possibility, that is, the possibility that life on Earth has migrated to
other bodies in the Solar System.
Various studies have shown that under certain circumstances an asteroid impact on a
planet can eject surface material into space. This explains why, on Earth, fragments
of the Martian crust have been found in the form of meteorites.
Life has been present on our planet for over 3.5 billion years, and in this enormous
period of time there have been very many asteroid and comet impacts capable of
accelerating fragments of terrestrial crust to above the escape velocity of 11.2
km/s. Almost certainly, most of these fragments would have contained bacterial
colonies, that if they survived the trauma of the impact, are thought to be able to
survive in space for up to 30,000 years.
With this in mind, a group of Mexican researchers led by Mauricio Reyes-Ruiz have run
a series of simulations to verify, at least in theory, if meteorites with a
terrestrial origin could have deposited their biological contents on other planetary
bodies. The results are very interesting, and although they need further
verification, they enlarge the volume within which terrestrial life may have been
transported.
Reyes-Ruiz and colleagues followed the motion of 10,242 virtual fragments with at
least the escape velocity of the Earth but less than 16.4 km/s, a velocity sufficient
to take them completely out of the Solar System. A small fraction of particles with
velocities in this intermediate range end up impacting on Venus and the Moon if the
velocities are only slightly above 11.2 km/s, and preferentially if the terrestrial
material was ejected from the hemisphere that trails with respect to the orbital
motion.
Fragments ejected from the leading hemisphere with velocities of at least 11.62 km/s
can reach Mars, and with a probability 100 times greater than that found by previous
studies. For the first time the possibility of fragments reaching the Jupiter system
has also been considered, something which does appear to be plausible for particles
with velocities of over 14.28 km/s.
From this study there is a large leap to argue that terrestrial bacteria could have
colonised other bodies, especially because the impact on that body could easily be
fatal. Nonetheless, it does appear that the transfer of material, at least, is
possible. |
