Sniffing an Exoplanet’s Atmosphere / The Transiting Exoplanet HD 209458 b
The exoplanet HD 209458 b was discovered in 1999 by the gravitational wobble it raised on its sunlike star, located 150 light-years from Earth in the constellation Pegasus. Measurements of the size and period of the wobble revealed the planet to be about 70 percent of the mass of Jupiter, in a scorching 3.5-day orbit of the star.....[ More ]
Sniffing an Exoplanet’s Atmosphere / The Transiting Exoplanet HD 209458 b
The exoplanet HD 209458 b was discovered in 1999 by the gravitational wobble it raised on its sunlike star, located 150 light-years from Earth in the constellation Pegasus. Measurements of the size and period of the wobble revealed the planet to be about 70 percent of the mass of Jupiter, in a scorching 3.5-day orbit of the star. The planet was so large, and in such a close orbit, in fact, that it had a good chance to transit—crossing the face of its star as seen from Earth and casting a shadow toward us here. Its transit was observed in 1999. In 2001 astronomers used Hubble to monitor four transits of HD 209458 b, delivering a “light curve” (above) that at the time was unprecedentedly pristine. Careful analysis of the Hubble data from the transit also revealed the spectral fingerprint of sodium, imprinted on the starlight shining through the . This was the very first detection of an exoplanet’s atmosphere, and it built the case for subsequent space-based transit surveys such as NASA’s Kepler mission, which launched in 2009 and has discovered thousands of worlds. Eventually, the same techniques pioneered by Hubble in 2001 will be used to examine the atmospheres of smaller, more Earth-like planets beyond the solar system.
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