Life beyond our Solar System|
The chance of finding life beyond our Solar System took a leap in 1995 when Michel Mayor and
Didier Queloz at the Geneva Observatory
discovered the first planet orbiting another star.
Since then, ground-based telescopes have detected no fewer than 74 planets orbiting 60 stars - and
the number is rising almost monthly.
Most of these planets, however, are large (at least the size of Jupiter) and orbit too close
to their stars for life's comfort. Earth-like planets, capable of supporting life as we know
it, will be much smaller and orbit their stars within 'habitable zones', that is at such a
distance and in such a way that liquid water can exist on their surfaces most of the time.
"About 1000 stars are being searched for planets at the moment and it seems that about 5 per cent of
them have closely orbiting Jupiters. The reason we haven't detected small planets is because
our methods are not sensitive enough," says
Alan Penny, a member of the Darwin study team from
the Rutherford Appleton Laboratory, United Kingdom.
"If you think of the extra-solar planets as the
occupants of a zoo, we've only looked inside one cage so far - the one containing large
planets near to their star," he adds.
Increases in the sensitivity of ground-based telescopes are expected to take the size of
detectable extra-solar planets down to one sixth of a Jupiter, or 50 Earths in the next
ten years. But "space is best", says Penny and plans are afoot at ESA to launch three
spacecraft to look for Earth-like planets and the signs of life on them.
First will be Eddington
with a possible launch date of 2008, which will search 500 000
stars for orbiting Earth-like planets. Next will be
Gaia which will watch for stars
wobbling along their orbits because they are being tugged by planets. Finally,
will employ a sophisticated technique called nulling interferometry to detect Earth-like
planets directly and determine the composition of their atmospheres through spectral analysis.
"If we see oxygen or ozone, we'll know that something is pumping it out continuously,
as oxygen is very reactive and doesn't stay around long. People have wracked their
brains to think of methods of getting a lot of oxygen into the atmosphere that have
nothing to do with life - and they can't think of any. So in all probability, if
we see oxygen or ozone, it will mean life," says Penny.
Darwin, however, is a complex and challenging mission technologically. "Recent studies
by industry have shown Darwin to be feasible within the next decade," says Malcolm Fridlund,
Darwin study scientist at ESA. "Nevertheless, a very large amount of technological
preparatory work is needed which will be carried out in pre-cursor missions over the
next few years."
Whether it's looking for life close by in our Solar System or far away in
distant galaxies, ESA is forging forward with exciting and ambitious
exploration plans to enable European scientists and engineers come closer to
answering the question: "Is there life out there?"
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