Washington DC
WHILE space agencies spend hundreds of millions of dollars developing a host
of space-based missions to discover distant terrestrial planets, researchers are
making ingenious use of existing technology back here on Earth. They鈥檙e
confident that expensive space missions will be pipped to the post before they
even get off the ground.
The ultimate prize would be the discovery of a rocky Earth-like planet
orbiting its star at a suitable distance for liquid water, and perhaps life, to
exist. So far, the best candidate system for harbouring such a planet is 47
Ursae Majoris
(快猫短视频, 12 January, p 32).
47UM is 51 light years away and
has a Sun-like star, along with two gas giants. The planets move in comfortable
circular orbits like Saturn and Jupiter do, unlike the bizarre eccentric orbits
of most of the 74 extrasolar planets found so far.
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Gregory Laughlin of the University of California at Berkeley is using
computer simulations to work out whether 47UM could contain an Earth-like
planet. Rocky planets form by the conglomeration of asteroid-sized rocks.
However, the gravity of gas giants creates a zone where small rocks are
constantly jostled from one orbit to another and can鈥檛 stick together. In our
Solar System this is the asteroid belt between Mars and Jupiter, but in 47UM,
the asteroid belt would be slap-bang in the habitable zone, Laughlin
calculated.
Although 47UM is not a possible home from home, Laughlin told 快猫短视频
that with gas giants being found every few months, he expects to find a system
that does have terrestrial planets before NASA鈥檚 planet-finding Kepler mission
is launched in 2006 (快猫短视频, 12 January, p 10).
Laughlin鈥檚 colleague Andrea Lommen announced her discovery of a system in
which a planet the size of Mars orbits a pulsar. She analysed radio waves
emitted by the pulsar and found disruptions in the signals caused by the gravity
of the orbiting planet. She鈥檚 using a similar technique to look for
gravitational waves (see opposite). Although a planet orbiting a pulsar couldn鈥檛
support life, Laughlin says the example 鈥渟hows terrestrial planet formation is
pretty easy鈥�.
Even if the major prize is scooped soon, there will still be plenty of work
for Kepler and similar missions. Once astronomers know we鈥檙e not alone in the
Universe, they鈥檒l want to know just how many friends we have.