MARK GARLICK / SCIENCE PHOTO LIBRARY MARK GARLICK / SCIENCE PHOTO LIBRARY
Brown dwarf Gliese 229b in orbit around its parent star Gliese 229 (upper left), artwork. Gliese 229b was the first brown dwarf to be directly imaged when it was found in 1995. A brown dwarf is an intermediate object between a gas giant planet (like Jupiter) and a star. Gl229b has a mass between 20 and 50 times that of Jupiter, but is still too small to sustain the nuclear reactions characteristic of stars. It is relatively cool, enough to allow the formation of molecular methane in its atmosphere. The identification of methane in Gl229b's atmosphere was the crucial evidence that it was a brown dwarf rather than a dim star. The Gliese 229 system lies around 19 light years from Earth in the constellation Lepus.
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