Look out for giant triangles in space
09 April 2005
Exclusive from New Scientist
THE search for extraterrestrial intelligence (SETI) could be taking the
wrong approach. Instead of listening for alien radio broadcasts, a better
strategy may be to look for giant structures placed in orbit around nearby
stars by alien civilisations.
"Artificial structures may be the best way for an advanced
extraterrestrial civilisation to signal its presence to an emerging
technology like ours," says Luc Arnold of the Observatory of
Haute-Provence in France. And he believes that the generation of
space-based telescopes now being designed will be able to spot them.
Arnold has studied the capabilities of space-based telescopes such as the
European Space Agency's forthcoming Corot telescope and NASA's Kepler.
These instruments will look for the telltale dimming of a star's light
when a planet passes in front of it. They could also identify an
artificial object the size of a planet, such as a lightweight solar sail,
says Arnold. His work will be published in The Astrophysical Journal
Arnold has determined the characteristic transit signal that differently
shaped objects would produce, including a Jupiter-sized equilateral
triangle and a louvre - parallel slats with gaps between them. Corot and
Kepler will be capable of distinguishing these objects from most planets,
though they could still be confused with a ringed planet like Saturn, he
To ensure the signal is unambiguous, an alien civilisation would have to
launch a number of objects into orbit around a star. As an example, Arnold
imagines 11 objects orbiting a star in groups of one, two, three and five
- the first prime numbers. The time interval between each group could also
encode prime numbers if the objects were powered rather than orbiting
freely. He thinks any civilisation that can engineer giant structures in
space would probably not find this a problem.
Arnold believes that this type of signalling is at least as effective as
broadcasting a message using a high-powered laser pulse or a radio signal,
which SETI is searching for.
The best place to begin looking for artificial structures could be around
dwarf stars. Their small size means they can be dimmed by the transit of a
relatively small object, making them the best bet for an advanced
civilisation wishing to announce itself.
But SETI researchers aren't changing tack just yet. "Arnold's proposal
falls within the category of SETT - the search for extraterrestrial
technology," says Paul Schuch, executive director of The SETI League in
New Jersey. "SETT is entirely complementary to SETI, which is narrowly
defined as the search for electromagnetic emissions from other
technological societies. The SETI League actively encourages and
enthusiastically endorses such research," he adds.
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Observatory of Haute-Provence
Printed on Thu Apr 07 20:58:20 BST 2005
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