New tool to spot planets
2008-04-03 13:46
Paris - Astronomers looking for Earth-like planets orbiting distant stars have been given a tool that should hugely help their quest, a study published on Wednesday in Nature said.
A total of 277 planets beyond our solar system, known as exoplanets, have been spotted since the first one was detected 13 years ago.
But almost all of them have been gas giants the size of our own uninhabitable Jupiter or even larger.
Just a tiny number have been rocky planets, and none as inviting as Earth. In general, they are big, and orbit so searingly close to massive stars that if they had any atmosphere, it must have boiled into space long ago.
The search is now widening to cooler stars and to the so-called Goldilocks zone, where the temperature is not too hot, not too cold but just right to let a small rocky, Earth-sized planet have liquid water, an ingredient for life.
But to do this requires a twelve-fold refinement in the search technique, which measures a "wobble" in starlight, as seen from Earth, that occurs when a planet exerts a gravitational tug on the star.
The breakthrough may have been found in a device called the astro-comb, in which a pulsed laser is used to filter the sample of starlight before feeding the signal into a spectrograph to measure the frequency of the light "wobble".
The gadget is put forward by a team led Chih-Hao Li of Harvard University.
The first astro-comb will be installed in 2009 or 2010 with the William Herschel Telescope on the Canary Islands, they say.
"Astro-combs should revolutionise astrophysical spectroscopy," they claim.
In theory, the astro-comb could boost present spectrograph performance by nearly a hundred-fold, although there also remain problems such as sunspots that could distort the data at very fine sensitivities, said commentator Gordon Walker, a professor of physics and astronomy at the University of Columbia, Canada.
Meanwhile, British astronomers on Wednesday reported that they had spotted the earliest known "embryonic" planet - a distant, orbiting ball of gas and dust that typically develops, after millions of years, into a fully-fledged planet.
The "protoplanet", called HL Tau b after its parent star, HL Tau, lies in the constellation of Taurus about 520 light years away, and could be as young as a few hundred years old.
The discovery, made by a team led by Janes Greaves of the University of St Andrews in Scotland, was to be unveiled at a meeting of the Royal Astronomical Society in Belfast.
"The planet will probably take millions of years to settle down into its final form of something like Jupiter. So we really are seeing it very early - even a bit like the first cells that make up a human embryo in the womb," said Greaves.