Skywatch

  • March 8, 2007

    Episode 87: Planet Leaks Hydrogen

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    A large planet, the size of Jupiter, orbits the star HD 209458. The planet, creatively called HD 209458b, has been studied extensively since its discovery in 1999. Its orbit periodically brings the planet between its star and us, allowing astronomers to detect it using a technique called spectroscopy. The planet's orbit is short, about 3.5 days, because the planet is very close to the parent star. Observations by Hubble found sodium, carbon and oxygen in the planet's atmosphere. Newer observations show that the star is heating up the outer atmosphere of HD 209458b so much that hydrogen is streaming off of it into space.