LIFE may thrive on small planets that have been captured and enslaved as
moons by giant planets such as Jupiter, a new computer simulation suggests.
Gas giants similar to Jupiter have been found orbiting close to other stars.
But even if they orbit their stars at similar distances to the Earth鈥檚 orbit,
they would not have the right conditions, such as a rocky surface, to support
life as we know it. Astronomers have suggested that their moons might support
life, but that raises another problem. Moons that form in orbit around giant
planets are unlikely to grow large enough to have enough gravity to hold onto an
atmosphere.
Bertil Olsson, a postgraduate student at Pennsylvania State University in
University Park, wondered whether there was another possibility鈥攖hat a
giant planet could capture a nearby Earth-sized planet. Astronomers believe
giant planets that orbit close to a star must have formed in the outer reaches
of the solar system, then migrated inwards. They might capture small inner
planets as they migrate.
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When Olsson ran computer simulations of the inward migration of a giant
planet toward a Sun-sized star, he found it could easily capture a terrestrial
planet into a stable orbit. 鈥淚 was surprised by how easily it happens,鈥� he told
New Scientist.
The simulations showed that giants up to ten times as massive as Jupiter
could capture planets up to ten times the Earth鈥檚 mass. Ten times Earth鈥檚 mass
is thought to be the heaviest a planet can be for life to develop. Olsson
described his results last week at a meeting of the American Astronomical
Society in Atlanta, Georgia.
However, he has yet to calculate the probabilities of Earth-sized planets
being captured into orbit. Although it seems to happen easily, the gravity of
large planets can also eject small planets from their systems.