Earth-like planets may be more rare than thought
Philip Ball
In cosmic terms, our solar system could be special after all.

We could be alone in the Universe after all. The discovery during the past
decade of over a hundred planets around other stars has encouraged many
scientists to think that habitable planets like ours might be common. But a
recent study tells them to think again.

Martin Beer of the University of Leicester, UK, and co-workers argue that
our Solar System may be highly unusual, compared with the planetary systems
of other stars. In a preprint published on Arxiv, they point out that the
alien planets we have seen so far could have been formed by a completely
different process from the one that formed ours. If that is so, says Beer,
"there won't necessarily be lots of other Earths up there".

Most of the planets around other stars, known as extrasolar planets, are
detected from the wobble that they induce in their own sun's motion. This
wobble is caused by the gravitational tug of the planet on the star. Because
stars are much bigger than planets, the effect is tiny, and it is only in
the past decade that telescopes have been sensitive enough to detect it.

Even then, the wobble is detectable only for giant planets, which are those
about as big as Jupiter, the bloated ball of gas in our Solar System. It is
not possible at present to detect planets as small as the Earth.

Jupiter is not habitable: it is too cold, and is mostly composed of dense
gas. And it is unlikely that extrasolar giant planets would support life
either. But astronomers generally assume that if they detect such a planet
in a distant solar system, it is likely to be accompanied by other, smaller
planets. And maybe some of the smaller planets in these systems are just
like Earth.

This is what Beer and colleagues now dispute. They say that the properties
of almost all the known extrasolar planets are quite different from those of
Jupiter.

Read the rest at Nature
http://www.nature.com/news/2004/040726/full/040726-14.html

Comment:
This has implications for theories relying on an extra-terrestrial genesis
of life, especially theories considering complex life forms.

Posted by
Robert Karl Stonjek
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