Hubble finds planets

The Hubble Space Telescope appears to have found 16 extrasolar planets - planets orbiting stars other than the Sun - that are all around 26,000 light years away from the Earth near the centre of our Galaxy. That is a pretty amazing feat and, if they are all confirmed, will add to the ever increasing list of exoplanets which currently stands at 208.

Hubble spots planets
HST view of the Sagittarius Window. The field contains approximately 150,000 stars, down to 30th magnitude. Green circles identify stars orbited by planets CREDIT: NASA, ESA, K. Sahu (STScI) and the SWEEPS science team
The latest slew of planets were found by the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS) in the central bulge of our galaxy. The region of sky covered by SWEEPS has an angular area less than two percent of that of the full Moon and contained 180,000 stars! The planets that were found were not actually directly imaged; they were found by the transit method which spots the slight dip in light from the parent star when a planet passes in front of it. Of course, this method only finds those planets which happen to pass between us and their star which is a very small fraction of the total number that are likely to be out there.

Taking into account the difficulty in detecting planets at that distance and the tiny fraction that can be found using the transit method, the team claim that this supports the hypothesis that the Milky Way contains around 6 billion Jupiter-sized planets. That is about one for every 30 or so stars. I don't know what the uncertainty on that extrapolation is and I wouldn't have thought you could be too confident extrapolating from 16 to 6 billion. I'll have to wait until the results are published in the journal Nature tomorrow to find out what the uncertainty on that figure is. Still, finding 16 planets is good going.

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Posted in astro blog by Stuart on Wednesday 04th Oct 2006 (19:04 BST) | Permalink
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