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Last Updated: Tuesday, 26 September 2006, 10:19 GMT 11:19 UK
Planets have scientists buzzing
By Jonathan Amos
Science reporter, BBC News

Artist's impression of a "hot Jupiter" during transit (M.A.Garlick/markgarlick.com)
A planet passing in front of its star causes a dip in brightness
A new wide-field survey of the sky has made its first major discovery - two planets orbiting far-distant stars.

The SuperWasp project uses camera lenses and super-sensitive detectors to monitor stars for tiny dips in light that might betray a passing planet.

The UK-led project identified a number of "suspects" and then handed the data to a French observatory for checking.

It used an instrument to analyse the light from the stars in detail and confirm the presence of the planets.

"To get these two we had to survey about 1.1 million stars and then go though several stages of filtering. It's a bit like panning for gold," Professor Andrew Collier Cameron from the University of St Andrews told BBC News.

The two extrasolar (outside our Solar System) planets, now known as Wasp-1b and Wasp-2b, are in the constellations of Andromeda and Delphinus.

Very hot

One is about 1,000 light-years from Earth; the other is about half that distance.

They are what astronomers term "hot Jupiters" - very large planets like the gas giants in our own Solar System but orbiting much closer in to their parent stars.

Whilst our Jupiter is almost 700 million km from the Sun and takes some 12 years to complete an orbit, these planets are just a few million km from their stars and take only a couple of days to complete an orbit.

These planets should have dense cloud decks made essentially of 'rock snowflakes'
Prof Andrew Collier Cameron, University of St Andrews
This makes them extremely hot. Indeed, scientists think that of the 200 or so extrasolar planets detected to date, these may be among the hottest of the lot. Wasp-1b's temperature is estimated to be over 1,800C (3,300F).

SuperWasp (Wide Angle Search for Planets) is a new programme that puts eight lenses and top-quality CCD cameras on a robotic mount.

There are two set-ups: one is at La Palma observatory in the Canary Islands; the other is at the Sutherland Observatory in South Africa. Together they sweep the entire sky.

French detail

Night after night, the SuperWasp robots watch millions of stars for small deviations in brightness that might be the result of an orbiting planet passing across the stellar disc.

In normal circumstances, with just one narrow-field telescope, the chances of seeing such transits would be very small; but the odds rise dramatically for SuperWasp because its automated systems can filter a huge sample of stars.

The SuperWasp telescope (SuperWasp)
Comprises 8 scientific cameras; lenses just 11cm in diameter
Field of view 2,000x greater than conventional telescope
State-of-the-art detectors feed automated data analysis
System can monitor entire sky several times per night
Detects hundreds of thousands of stars in a single snap-shot
One night's observing run generates up to 60GB of data
SuperWasp based in Canary Islands and South Africa
Confirmation of the new finds came earlier this month when the team joined forces with the Swiss and French users of Sophie, a powerful new spectrograph sited at the Observatoire de Haute-Provence.

Sophie can detect if there is a slight change in a star's velocity - the result of an (unseen) extrasolar planet's gravity tugging the star in different directions as it makes an orbit.

In other words, the star appears to wobble under the influence of its smaller companion.

"The partnership between the two instruments is particularly powerful - SuperWasp finds candidate planets and determines their radii, and Sophie confirms their nature and weighs them," said Dr Don Pollacco, of Queen's University Belfast and the SuperWasp Project Scientist.

Ferocious weather

SuperWasp's goal is to find the planets that more specialist telescopic systems can then investigate more closely.

Once a target has been confirmed, astronomers can book time on the likes of the Hubble and Spitzer space observatories to examine the object at infrared wavelengths.

"This tells us quite a lot about the weather on them," said Professor Andrew Collier Cameron, who explained that these planets lived a ferocious existence.

"All the theoretical models tell us that these planets should have dense cloud decks made essentially of 'rock snowflakes'; the sorts of chemicals which condense to form clouds at these high temperatures are things that we normally think of on Earth as minerals - olivine, forsterite, all the magnesium silicates."

Professor Collier Cameron said astronomers wanted to try to find out how such weather systems transported intense heat around a planet.

The new worlds come from SuperWasp's inaugural five-month observing run in 2004. Over the next three years, the project hopes to identify all the transiting events in the vision range of the robots.

Later this year, French scientists will launch the Corot mission.

This space telescope will also look for transiting events, but it will see deeper into the sky than SuperWasp and detect lower-mass planets, ones that are perhaps just a little bigger than Earth.


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