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An exoplanet inflated like a balloon – ScienceDaily

Although helium is a rare element on earth, it is everywhere in the universe. It is, after hydrogen, the main…

Although helium is a rare element on earth, it is everywhere in the universe. It is, after hydrogen, the main component of stars and gaseous giant planets. Despite its abundance, helium was only recently discovered in the atmosphere of a gaseous giant of an international law including astronomers from the University of Geneva (UNIGE), Switzerland. The team, currently led by Genevan researchers, has observed in detail and for the first time how this gas flies from the superheated atmosphere of an exoplanet literally inflated with helium. The results are published in Science .

Helium is the second most abundant element in the universe. Predicted since 2000 as one of the best possible tracks of the exoplanet’s atmosphere, these planets revolve around stars other than the sun, it took astronomers 1

8 years to actually discover it. It was difficult to get fit because of the very strange observational signature of helium, located in infrared, outside the measuring range of most of the instruments previously used. The discovery occurred earlier this year thanks to Hubble Space Telescope observations, which proved difficult to interpret. Team members from UNIGE, members of the National Center for Competence in Research PlanetS, had the idea of ​​pointing another telescope equipped with a brand new instrument – a spectrograph called Carmenes.

Discovering Colors of Planets with Carmenes

A spectrograph decomposes the star’s light in its component colors, like a rainbow. The resolution of a spectrograph is a measure indicating the number of colors that can be revealed. While the human eye can not distinguish any color beyond red without a custom camera, the infrared eye of Hubble can identify hundreds of colors there. This proved sufficient to identify Helium’s colored signature. The Carmenes instrument, installed on the 4 meter telescope at the Observatory of Calar Alto in Andalusia, Spain, can detect more than 100,000 colors in infrared!

This high-resolution resolution enabled the team to observe the position and velocity of helium atoms in the upper atmosphere of a gaseous Neptune magnitude exoplanet 4 times greater than the Earth. HAT-P-11b is in the Cygnus (swan) constellation, 124 light years from home, a “hot Neptune”, a decent 550 ° C!), Twenty times closer to the star than the sun from the sun. “We suspected that this proximity to the star could affect the atmosphere of this exoplanet,” said Romain Allart, PhD student at UNIGE and first author of the study. “The new observations are so accurate that the exoplanet atmosphere is undoubtedly blown up by the radiation and flies to space,” he adds.

A planet inflated with helium

These observations are supported by numerical simulation, led by Vincent Bourrier, co-author of the study and member of the European project FOUR ACES *. Thanks to the simulation, it is possible to trace the path of the helium: “Helium is blown away from the planet’s day to its night’s side at more than 10,000 km / h,” explains Vincent Bourrier. “Because it is such a light gas, it easily holds from the attraction of the planet and forms an expanded cloud around it.” This gives the HAT-P-11b the shape of a helium-inflated balloon.

This result opens a new window to observe the extreme atmospheric conditions of the hottest exoplanets. The Carmenes observations show that such studies, which were only long imaginable from space, can be achieved with greater precision by terrestrial telescopes equipped with the right type of instrument. “These are exciting times for the search of atmospheric signatures in the exoplanet,” says Christophe Lovis, University Lecturer at UNIGE, and co-author of the study. In fact, UNIGE astronomers are also heavily involved in the design and utilization of two new infrared spectroscopy with high resolution, similar to Carmenes. One of them, named SPIRou, has just started an observation campaign from Hawaii, while the AGE Department of Astronomy hosts the first tests of NIRPS, which will be installed in Chile by the end of 2019. “This result will increase the interest of scientific society for these instruments. Their numbers and their geographical distribution will enable us to cover the whole sky in search of displaced exoplanets, “concludes Lovis.

* FOUR ACES, Future of Upper Atmospheric Characterization of the Exoplanet with Spectroscopy, is a project funded by a European Research Council (ERC) Consolidation Grant under the European Union 2020 Research and Innovation Program (Grant Agreement No. 724427).

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