Infrared Spectrum of the Cool Brown Dwarf Gl 229B

Spectroscopic measurements of a cool brown dwarf, GI 229B, reveal absorption features attributable to methane in the near infrared much like those of Jupiter. These features are not seen in any star. The presence of methane indicates that the surface temperature of GI 229B is below 1000 kelvin. Features attributed to water vapor also indicate that GI 229B is much cooler than any known star.