ESA Hubble Science Release | 2015 Jun 24
Astronomers using the NASA/ESA Hubble Space Telescope have discovered an immense cloud of hydrogen dispersing from a warm, Neptune-sized planet orbiting a nearby star. The enormous gaseous tail of the planet is about 50 times the size of the parent star. The findings will be published in the 24 June issue of the journal Nature.
A phenomenon this large has never before been seen around such a small exoplanet. It may offer clues as to how hot super-Earths — massive, hot versions of Earth — are born around other stars.
"This cloud of hydrogen is very spectacular!" says David Ehrenreich... "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."
The planet, named Gliese 436b, is considered to be a "warm Neptune", because it is similar in size to Neptune, but much closer to its star Gliese 436 than Neptune is to the Sun. Although in this case the planet is in no danger of having its atmosphere completely stripped away — leaving just a solid, rocky core — this behaviour could explain the existence of hot super-Earths, which orbit very close to their stars and are typically more massive than Earth, although smaller than the seventeen Earth masses of Neptune.
Hot super-Earths could be the remaining cores of more massive planets that have completely lost their thick, gaseous atmospheres to the same type of evaporation that Hubble observed around Gliese 436b. ...
Hubble Sees a 'Behemoth' Bleeding Atmosphere Around a Warm Neptune-Sized Exoplanet
NASA | STScI | HubbleSite | 2015 Jun 24
A giant comet-like cloud of hydrogen escaping the warm Neptune-mass exoplanet GJ 436b - David Ehrenreich et al
- Nature 522(7557) 469 (25 Jun 2015) DOI: 10.1038/nature14501 (pdf)
Red dwarf burns off planet’s hydrogen giving it massive comet-like tail
University of Warwick, UK | 2015 Jun 24
Giant comet-like tail discovered on small exoplanet
University of Exeter, UK | 2015 Jun 24
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