Scientists dub exoplanet's bleeding atmosphere 'The Behemoth'

WASHINGTON, June 24 (UPI) -- Earth's atmosphere is expansive. But it's neatly packaged and sturdily structured, hemmed in by snug layers and a magnetic field. The whole package is held together by the inward pull of gravity.

Not all atmospheres are so well behaved. The Hubble Space Telescope recently spotted a wily collection of hydrogen gas surrounding an exoplanet called GJ 436b.

The planet is relatively small for its massive atmosphere, which is bleeding out into space. Astronomers have dubbed the atmosphere "The Behemoth."

The planet is close enough to the star that it's atmosphere is actively evaporated by stellar radiation. But the sun isn't able to heat up the upper atmosphere enough to eat away all of the excess, allowing the hydrogen to peel off into space like a comet's tail.

"This cloud is very spectacular, though the evaporation rate does not threaten the planet right now," David Ehrenreich, an astronomer the Observatory of the University of Geneva in Switzerland, explained in a press release.

"But we know that in the past, the star, which is a faint red dwarf, was more active," said Ehrenreich, lead author of a new study on The Behemoth. "This means that the planet evaporated faster during its first billion years of existence because of the strong radiation from the young star. Overall, we estimate that it may have lost up to 10 percent of its atmosphere over the past several billion years."

Researchers say the exoplanet might reveal the early evolution of Hot Super-Earths, a type of rocky exoplanet which are similar to Earth in size, but which lie much closer to their parent star and are without a thick atmosphere.

The star may also reveal details about Earth's past lives. Scientists believe Earth likely once hosted a large hydrogen-rich atmosphere, before it was burned away by the energy of the sun. If so, Earth may too have once featured a comet-like tail of gas trailing as it circled the sun.