27/09/2006. Contributed by Jessica Martin
Wide-eyed telescope finds its first transiting planets around distant stars.
Finding planets that pass in front of their parent stars is so important to understanding how planets form that the European Space Agency will shortly launch the €35M COROT satellite to find them. But a team of UK, French and Swiss astronomers is already paving the way from the ground, with today's announcement of the discovery of two new Jupiter-sized planets around stars in the constellations of Andromeda and Delphinus. They are among the hottest planets yet discovered. Their atmospheres are slowly being whipped away into space by the searing radiation from their parent stars.
These planets are the first to be found during the UK-led SuperWASP (Wide Angle Search for Planets) programme. Using wide-angle camera lenses, backed by top-quality CCD cameras, the SuperWASP team have been repeatedly surveying several million stars over vast swathes of the sky, looking for the tiny dips in the starlight caused when a planet passes in front of its star. This is known as a transit.
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 French-built instrument at the Observatoire de Haute-Provence. SOPHIE was able to detect a slight wobble in each star's motion as the planets orbited around them. Together the two types of observation confirmed the existence and nature of the planets.
"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 (Queen's University Belfast), the SuperWASP Project Scientist.
"We're delighted that in its first 4 nights of operation, SOPHIE has detected SuperWASP's first two new planets," said Professor Andrew Collier Cameron (University of St. Andrews), who led the international follow-up campaign.
Approximately 200 planets around other stars are now known, but almost all of them were discovered using large telescopes costing tens of millions of pounds. This requires laborious study of one star at a time, in the hope of finding stars with planets around them.
In contrast, the SuperWASP telescopes look at hundreds of thousands of stars at a time, allowing all those with transiting planet candidates to be identified in one go.
In only a dozen or so of the known systems, has a planet been observed to pass in front of its star. Although the number of known 'transiting exoplanets' is still very small, they hold the key to the formation of planetary systems, and an understanding of the origin of our own Earth. They are the only planets whose sizes and densities can be determined reliably.
The stars around which the new planets are orbiting are both similar to the Sun. One is a little hotter, brighter and bigger, whilst the other is a little cooler, fainter and smaller. The larger star, in the constellation of Andromeda, is over 1,000 light years away. The smaller star, in the constellation of Delphinus, is only about 500 light years distant. Although both stars are too faint to be seen with the naked eye, they are easily detectable with a small telescope.
The planets themselves, known as WASP-1b and WASP-2b, are of a type known as 'hot Jupiters'. They are both giant gas planets, like Jupiter, the largest planet in our solar system, but they are much closer to their parent stars. Whilst Jupiter is nearly 800 million km from the Sun and orbits it once every 12 years, WASP-1b is only 6 million km from its star and orbits once every 2.5 days, WASP-2b is only 4.5 million km from its star and orbits once every 2 days. The very close orbits mean that these planets must be even hotter than the planet Mercury in our solar system, which is nearly 60 million km from the Sun and has a surface temperature of over 400°C. WASP-1b's temperature is estimated to be over 1800C. Both planets show signs that they are losing their atmospheres to space.
The SuperWASP team are currently planning follow-up observations of the two new planetary systems with the Hubble Space Telescope and the Spitzer Space Telescope in order to measure more accurately the sizes and temperatures of the planets, and also to look for indications of any other planets in these systems.
SuperWASP is expected to find dozens more transiting planets over the next few years. A paper detailing these results has been submitted to the journal Monthly Notices of the Royal Astronomical Society.
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