The Hubble Space Telescope has detected an extensive atmosphere of hydrogen enveloping and escaping from a newfound distant planet, according to the British journal "Nature" issued on Thursday.
The study, conducted by the European Space Agency and NASA, shows that the extrasolar planet is a huge gaseous body sharing many similarities in size and make-up to Jupiter in the solar system.
The research team said three separate observations by the Hubble telescope in 2001 revealed a hot and puffed-up hydrogen atmosphere surrounding a planet orbiting the star HD 209458, in the constellation Pegasus 150 light-years from Earth.
The most astonishing aspect, said the team leader, Dr. Alfred Vidal-Madjar of the Astrophysics Institute of Paris, is that the planet is so close to the searing heat of its parent star that thedense atmosphere is boiling off at a temperature of about 18,000 degrees Fahrenheit and evaporating at a rate of some 10,000 tons asecond. The escaping hydrogen was detected extending across 125,000 miles, trailing the planet like a comet's tail.
The scientists said analysis of the observations showed that hydrogen atoms in the extended atmosphere had high velocities relative to the planet. Thus, they concluded, the hydrogen "must be escaping the planetary atmosphere."
As a result, astronomers said, the planet may already have losta considerable amount of its mass. Much of it may eventually disappear, leaving only a dense core about 10 times the mass of Earth.
The newfound planet, designated HD 209458b, is one of over 100 extrasolar planets detected since 1995.