This puzzling discovery was made by scientists from the Instituto de Astrofísica de Canarias (IAC) in the Canary Islands, Spain, who scoped out the planet’s atmosphere with the help of the 3.5-meter telescope stationed at the Calar Alto Observatory in Almeria. The study, published in the journal Science on Dec. 6, was able to calculate a numerical simulation for how helium moves and why, from humans’ point of view, this gas became like a tail trailing a star or other cosmic bodies. The results of such studies could confirm that extreme radiation from the host star can strip the gaseous envelope of giant planets (similar to Jupiter or Neptune) and turn them into rocky planets with densities similar to Venus or Earth. It is also the second most common element in the universe and was long- predicted to be one of the most readily-detectable gases on giant exoplanets. For this new study, the research team used the spectrograph, Carmenes, to pull apart the star's light into its component colours, like a rainbow, to reveal the presence of helium. The 'rainbow' data, called a spectrum, also tells us the position and speed of helium atoms in the upper atmosphere of HAT-P-11b, which is 20 times closer to its star than the Earth is from the Sun. “We suspected that this proximity with the star could impact the atmosphere of this exoplanet,” said Romain Allart, first author on the study and Ph.D. student at the University of Geneva. “The new observations are so precise that the exoplanet atmosphere is [undoubtedly] inflated by the stellar radiation and escapes to space.”

The research team believes that this detection, combined with the other one from earlier in the year, will open up a new way to observe the extreme atmospheres of some of the hottest exoplanets — and that these observations can be done using ground-based telescopes outfitted with innovative instruments. "Helium is blown away from the day side of the planet to its night side at over 10'000 km/h because it is such a light gas, it escapes easily from the attraction of the planet and forms an extended cloud all around it,” Vincent Bourrier, co-author of the study, explained.
Scientists from the University of Geneva announce that a previously-known Neptune-sized exoplanet, HAT-P-11b, has a slowly-escaping helium atmosphere.