Jueves 12 de Junio de 2008, Ip nš 233

Narrowing the search for ET
Por Kimm Groshong

If another advanced civilisation in the Milky Way is the proverbial needle, a group of researchers has suggested how we should narrow our search for it in the galactic haystack.

At a meeting of the American Astronomical Society in St Louis, Missouri, US, on Wednesday, Richard Conn Henry of Johns Hopkins University and colleagues proposed limiting the search for extra-terrestrial intelligence (SETI) to the ecliptic - the plane in which our solar system's planets orbit.

SETI begins with the hypothesis that another, more advanced civilisation in our galaxy is out there, trying to contact us. Assuming this is true, Henry says a search focused on the ecliptic "should lead rapidly to the detection of other civilisations".

That's because exoplanets in that plane would be able to see Earth passing in front of the Sun and dimming its light.

Such transits reveal all sorts of information about the transiting planets, including their radius, density and composition. They also shed light on the planet's atmosphere - so alien astronomers studying the Earth's spectrum could find indicators of life in our atmospheric oxygen, for example.

Henry and his colleagues hope to search the ecliptic for these civilisations with the Allen Telescope Array, a set of dozens of antennae in Hat Creek, California, US.

All of this begs the question - what kind of technology would alien astronomers in the ecliptic need to glean information from Earth transits?

Greg Laughlin, an astronomer and extrasolar planet hunter at the University of California, Santa Cruz, says it depends how distant the other planet is.

If we're lucky enough to have an advanced civilisation trying to communicate with us within 50 light years, its inhabitants could see the Earth as a bluish dot if they had an 8-metre space-based telescope with a good coronagraph. A set of space-based infrared telescopes would enable them to detect ozone and water vapour in our atmosphere.

That kind of technology is not so far-fetched. These are the underlying concepts behind NASA's Terrestrial Planet Finder missions, which would allow us to attempt this process in reverse, helping us to search elsewhere for habitable, Earth-like planets.

But budget woes have delayed TPF indefinitely, so we can only hope any alien astronomers on other worlds have evolved beyond such earthly concerns.

  05/06/2008. New Scientist Space Blog.