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Are there "friendly" habitats in exoplanetary systems, where
Life may have developed and may persist over a significant period of
time? And not just on Earth-like planets? The existence of life on the known giant exoplanets is as possible
as is the existence of life on our own giant planet Jupiter, and this
seems to be rather improbable by our current standards. However, could
some of the moons of those giant exoplanets perhaps harbour life? An obvious place to look for life-friendly environments is in the
"habitable" zone that
is at a distance from the central star where water may exist in its
liquid form.
Until now, no Earth-sized planets have been discovered, but some of
the giant exoplanets do move in orbits which are located in the
habitable zone around their central star. One example is the planet
in orbit around the sun-like star HD 28185 It moves in a very
nearly circular orbit with a period of 385 days (close to 1 Earth
year), and its distance from the star, 150.6 million km, is almost
equal to the distance between the Sun and the Earth (149.6 million
km). Planets like the companion of HD 28185 may possess solid moons on
which the surface conditions are such that liquid water could be
present. It is therefore reasonable to speculate that life could have
developed on such moons. However, this is of course just a hypothesis
since we have at present no observational possibilities of verifying
that such moons around giant exoplanets really exist. Another possibility is that those giant exoplanets may have
satellites (moons) that are like those of Jupiter or Saturn. In other
words, exo-"Titans" may perhaps exist in other places in the
Universe. Some of the newly discovered bodies, e.g., those around the star
70 Virginis are at distances from the central star similar to
those of our giant planets from the Sun. The laws of physics and
chemistry being the same throughout the Universe, we may assume that
if those exoplanets possess systems of satellites, there is a strong
possibility for one of those satellites to have an atmosphere similar
to that of Titan. The example of Titan is indeed a hopeful message for the
existence of other worlds outside the Earth, with the possibility of
different formation and evolution processes, but which can
nevertheless evolve into life habitats. Perhaps like those whose
existence we are lucky to have witnessed in our lifetimes. Of course, it is easier to observe the giant planets than their
satellites. As giant bodies, however, they are usually gas balls, with
a higher possibility of having atmospheres of helium and hydrogen than
those gases, like nitrogen and oxygen, , that are of most interest
to us. The smaller planets of an extrasolar system could be observed
with more modern techniques. But who knows what will happen in the
future? The next step, which would not surprise most astronomers,
would be the discovery of an Earth-size planet. Sending their light
from distances of 35 to 50 light-years, these distant worlds bring
hopeful messages to those of us who dream that our great-great-great
grand children may be able to visit these worlds with super modern
spacecraft. They may be somewhere in those "billions and billions"
(as Carl Sagan would 'never say') of stars of solar type, similar to
our world - or not. For some people this may be a matter of faith. In the
meantime, with new techniques and with bigger telescopes we are
trying both from the ground and from space to discover new planetary
systems in more distant stars that will bring us new answers but also
new questions about our beloved Solar System.
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Last updated July 3, 2001