Researchers Have Discovered a Neptune-Sized "Balloon" Planet With a Helium-Filled Atmosphere

An international group of researchers led by a team at the University of Geneva have found an exoplanet with an atmosphere that is doing something you don’t see everyday, even if you have a powerful spectrograph with an insanely long name at your disposal.

Using the Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Échelle Spectrographs (CARMENES for short) installed on the 4-meter long telescope at Calar Alto, Spain, the researchers observed helium escaping from the atmosphere of a planet 124 light years away from Earth. According to reports, the exoplanet designated HAT-P-11b has an extended helium cloud around it that is “swollen” like a balloon. With CARMENES, the team was able to separate the light from the host star into a spectrum which revealed the helium atoms in the exoplanet’s atmosphere. “This is a really exciting discovery, particularly as helium was only detected in exoplanet atmospheres for the first time earlier this year,” Jessica Spake of the University of Exeter’s physics and astronomy department said in a statement. “The observations show helium being blasted away from the planet by radiation from its host star.” 

The data also shows that the planet is 20 times closer to its host than we are to our Sun, which may explain the effect on its atmosphere. “We suspected that this proximity with the star could impact the atmosphere of this exoplanet,” said Romain Allart, University of Geneva PhD student and first author of the study recently published in the journal Science. “The new observations are so precise that the exoplanet atmosphere is undoubtly [sic] inflated by the stellar radiation and escapes to space.” “Hopefully we can use this new study to learn what types of planets have large envelopes of hydrogen and helium, and how long they can hold the gases in their atmospheres,” Spake added.

Like a balloon losing its helium, we picture HAT-P-11b sputtering and flying around in space, but there is no evidence that supports that mental image.

Cover image adapted from ESO/L. Calçada –– CC BY 2.0