UNIGE/PlanetS: An Exoplanet Inflated Like a Balloon

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bystander
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UNIGE/PlanetS: An Exoplanet Inflated Like a Balloon

Post by bystander » Thu Dec 06, 2018 10:01 pm

Exoplanet Inflated Like a Balloon
National Centre for Competence in Research PlanetS
University of Geneva | 2018 Dec 06

Researchers from UNIGE and members of PlanetS have found helium in the atmosphere of an exoplanet, swollen like a balloon.

unige_111760.jpg
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.
(Credit: Denis Bajram)

Although helium is a rare element on Earth, it is ubiquitous in the Universe. It is, after hydrogen, the main component of stars and gaseous giant planets. Despite its abundance, helium was only detected recently in the atmosphere of a gaseous giant by an international team including astronomers from the University of Geneva (UNIGE) and members of PlanetS. The team, this time led by Genevan researchers, has observed in detail and for the first time how this gas escapes from the overheated 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 tracers of the atmospheres of exoplanets, these planets orbiting around other stars than the Sun, it took astronomers 18 years to actually detect it. It was hard to spot due to the very peculiar observational signature of helium, located in the infrared, out of range for most of the instruments used previously. 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 Centre for Competence in Research PlanetS, had the idea of pointing another telescope equipped with a brand-new instrument – a spectrograph called Carmenes.

A spectrograph decomposes the light of a star into its component colours, like a rainbow. The “resolution” of a spectrograph is a measure indicating the number of colours that can be revealed. While the human eye cannot distinguish any colour beyond red without an adapted camera, the infrared eye of Hubble is capable of identifying hundreds of colours there. This proved sufficient to identify the coloured signature of helium. The instrument Carmenes, installed on the 4-metre telescope at the observatory of Calar Alto in Andalusia, Spain, is capable to identify more than 100’000 colours in the infrared!

This high spectral resolution allowed the team to observe the position and speed of helium atoms in the upper atmosphere of a gaseous Neptune-size exoplanet, 4 times larger than the Earth. Located in the Cygnus (the Swan) constellation, 124 light-years from home, HAT-P- 11b is a “warm Neptune” (a decent 550°C!), twenty times closer to its star than the Earth from the Sun. ...

Helium Exoplanet Inflated Like a Balloon
University of Exeter | 2018 Dec 06

Spectrally resolved helium absorption from the extended
atmosphere of a warm Neptune-mass exoplanet
~ R. Allart et al
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