An international team of astronomers has detected helium escaping from the upper atmosphere of HAT-P-11b, a Neptune-mass exoplanet located in the constellation of Cygnus, about 122 light-years away. The inert gas is in an extended cloud that is escaping from HAT-P-11b, just as a helium balloon might escape from a person’s hand.
An artist’s impression of the exoplanet HAT-P-11b with its extended helium atmosphere blown away by the star, an orange dwarf star smaller, but more active, than the Sun. Image credit: Denis Bajram.
Discovered in 2009, HAT-P-11b is about 4 times the radius of Earth and about 26 times Earth’s mass.
The giant planet orbits very close to its host star, a K-type star called HAT-P-11, and therefore is incredibly hot, with temperatures around 1,100 degrees Fahrenheit (605 degrees Celsius).
Using the Carmenes spectrograph on the 4-m telescope at Calar Alto in Spain, University of Geneva astronomer Romain Allart and co-authors detected helium atoms and measured their speed in the upper atmosphere of HAT-P-11b.
“We suspected that its close proximity to the star could impact the atmosphere of the exoplanet,” Allart said.
“These new observations are so precise that the exoplanet atmosphere is undoubtly inflated by the stellar radiation and escapes to space.”
This artist’s concept shows what the sky may look like on the exoplanet HAT-P-11b. Image credit: NASA / JPL-Caltech.
The observations are supported by a state-of-the-art computer simulation used to track the trajectory of helium atoms.
“Helium is blown away from the day side of the planet to its night side at over 6,200 mph (10,000 km an hour),” said Dr. Vincent Bourrier, an astronomer at the University of Geneva.
“Because it is such a light gas, it escapes easily from the attraction of the planet and forms an extended cloud all around it.”
“It is this phenomenon that makes HAT-P-11b so inflated, like a helium balloon.”
“This is a really exciting discovery, particularly as helium was only detected in exoplanet atmospheres for the first time earlier this year,” said Dr. Jessica Spake, an astronomer at the University of Exeter.
“The observations show helium being blasted away from the planet by radiation from its host star.”
“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.”
The findings were published in the journal Science.
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R. Allart et al. Spectrally resolved helium absorption from the extended atmosphere of a warm Neptune-mass exoplanet. Science, published online December 6, 2018; doi: 10.1126/science.aat5879
