Planets That Harbour Life May Be Roaming Interstellar Space
BBC News Online: Sci/Tech
Thursday, July 1, 1999 Published at 05:02 GMT 06:02 UK
Life lost in space
Planets that could harbour life may be roaming the voids of
interstellar space, according to a report in Nature magazine.
Planetary scientist David Stevenson thinks it is possible that rocky
masses the size of the Earth are ejected from solar systems as they
form - kicked out by the gravitational effects of much larger planets.
However, even without the energy supplied by sunlight, he believes
these nomadic worlds could still maintain the conditions necessary for
Mr Stevenson, of the California Institute of Technology, says the
ejected planets would possibly carry with them an atmosphere of
hydrogen. This could act to trap any internal heat. It may even exert
enough pressure to maintain oceans of liquid water on the planet's
With ammonia and methane gases in the atmosphere, and volcanoes
bubbling heat and molten rock to the surface, these lonely planets
would look remarkably similar to the Earth when life began here some
four billion years ago.
All these planets would lack is the energy supplied by a sun.
Writing in Nature, Mr Stevenson says: "If life can develop and be
sustained without sunlight (but with other energy sources, plausibly
volcanism or lightning in this instance), these bodies may provide a
long-lived, stable environment for life (albeit one where the
temperatures slowly decline on a billion-year timescale).
"The complexity and biomass may be low because the energy source will
be small, but it is conceivable that these are the most common sites
of life in the universe."
Oceans on the nomadic planets would have surface pressures and
temperatures similar to those found at the bottom of the Earth's
oceans, places where we know life can exist, thriving on the heat and
nutrients supplied from hot water vents.
Mr Stevenson's ideas are controversial but it will be virtually
impossible to test them. Despite emitting some degree of radiated
heat, and possibly radio waves, the planets would be almost invisible.
Artist's impression of a developing solar system taken from the BBC
Science TV series The Planets.
*Out of this world discovery (15 Apr 99�|�Sci/Tech)
*Ocean vents were "factories of life" (09 Feb 99�|�Sci/Tech)
*New planets discovered (10 Jan 99�|�Sci/Tech)
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