Astronomers using the Hubble space telescope have spied a distant, Neptune-sized planet throwing off a massive cloud of hydrogen gas that makes it look something like a super-comet in close orbit around its red dwarf star, Gliese 436.
X-rays firing off of the star are burning off the upper atmosphere of its exoplanet, GJ 436b, creating the gaseous cloud that then absorbs the light of the star, reflecting ultraviolet rays that are visible from Hubble.
"Around 1000 metric tonnes of hydrogen are being burnt off from GJ 436b's atmosphere every second; which equates to only 0.1% of its total mass every billion years," said Dr. Peter Wheatley, from the University of Warwick. "The same process is likely to be much stronger on other exoplanets, where the entire atmosphere could be removed or evaporated to destruction."
Wheatley is one of the co-authors on a paper about the findings published online Wednesday by the journal Nature.
The observed ongoing loss of a close-orbiting gas giant's atmosphere suggests that hot rocky planets like Mercury might have started out as gas giant planets, the paper's summary states, but notes that "no confident measurements have hitherto been available."
The size of the planet's trailing cloud makes it a landmark find, estimated to be 50 times the size of the system's star.
"This cloud of hydrogen is very spectacular!" lead author David Ehrenreich of the Observatory of the University of Geneva said in a statement. "Although the evaporation rate doesn't threaten the planet right now, we know that the star, a faint red dwarf, was more active in the past. This means that the planet's atmosphere evaporated faster during its first billion years of existence. Overall, we estimate that it may have lost up to 10 percent of its atmosphere."
Members of the research team expect that the discovery could be a "game-changer" when it comes to characterizing certain exoplanet atmospheres, and that GJ 436b could be just the first of thousands of planets like it soon to be discovered.
