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Extra-solar planet snapped by galactic paparazzi
Ever wondered what a planet looks like from a distance of 225 light-years? No-one really knows, because no direct image has ever been taken before. But astronomers examining at data from the Very Large Telescope in Chile spotted a faint mark next to a young brown dwarf star.
On closer examination using Hubble's infrared cameras, they were able to classify it as a candidate planet, because it is only 100th the brightness of its stellar companion.
Hubble's Near Infrared Camera and Multi-Object Spectrometer (NICMOS) camera can make observations at wavelengths that would be invisible from the ground. Complementary images, taken at these shorter wavelengths, are important because they help characterise the physical nature of an object being observed.
The Hubble pictures were taken in August last year, and then compared with data from the earlier VLT observations. Astronomers needed to rule out the possibility that the planet candidate was merely a background object.
If the candidate planet does orbit the brown dwarf, then the pair will move across the sky together. Confirming this was made easier because the two objects are so far apart - approximately eight billion kilometres. This means the "planet" takes around 2,500 years to complete one orbit.
In four months of observation, this orbital movement would be so slight as to be undetectable from Earth. So any change in the relative positions of the two objects would immediately confirm the second object is in the background. The scientists did not detect any relative movement, providing reasonable evidence that the two bodies are companions.
Glenn Schneider of the University of Arizona says the measurements provide a "99 per cent level of confidence" that the planet candidate does orbit the brown dwarf. More observations with Hubble are planned to remove that remaining uncertainty, he says. ®
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