In search of lost worlds: an exoplanet is discovered that quickly evaporates

Most well-known Neptunes are rather considered as 'warm', since they are more distant from their host star in the region where the Neptunes would be expected to be hot. The mysteries deficit of this type of exoplanet suggests that such worlds are rare, or that, being abundant at the time, they have now disappeared.

In a recent work published in the magazine A stronomy & amp; Astrophysics, an international team of astronomers, with the participation of the Center for Astrobiology (CAB, CSIC-INTA), has detected a second 'very warm' Neptune, called GJ 3470b, which is losing its atmosphere at a rate 100 times greater than GJ 436b. Both planets are very close to their host star, about 3.7 million km away, a tenth of the distance between Mercury and the Sun.

For Jorge Sanz-Forcada, CAB researcher and co-author of the study," the particularity of this planet lies in that it is on the edge of the evaporation desert, as it reinforces the most accepted explanation that this desert is due to the fact that planets with a mass like Neptune, when they orbit too close to their host star, receive a huge amount of radiation that evaporates the planet's atmosphere. "

The host star of GJ 3470b has an estimated age of only 2 billion years, considerably less than that of GJ 436b, estimated between 4,000 and 8,000 million years ago. The youngest star is, therefore, more energetic, and bombards the planet GJ 3470b with more radiation than GJ 436b receives. Both stars are red M-type dwarfs, which are smaller and longer than the Sun.

The discovery of these hot Neptunes evaporating reinforces the idea of that the hottest version of this kind of worlds can be a kind of "transient" planet, whose final destiny is to become a more common type of exoplanet known as mini-Neptunes: planets with dense atmospheres composed mainly of hydrogen, greater than the of the Earth, but smaller than that of Neptune. Eventually, these planets can further reduce their size to become Super-Earths, rocky planets like Earth, but with greater mass.

Observations are part of the PanCET project (Panchromatic Comparative Exoplanet Treasury), a pan-chromatic comparison of a collection of exoplanets, a Hubble program to observe a sample of 20 exoplanets, most of which are hot Jupiters, which constitutes the first Large scale comparative study of exoplanets in the ultraviolet, visible and infrared ranges. The researchers used the spectrogram of the Hubble Space Telescope to detect the hydrogen signal in ultraviolet light, in the exosphere that surrounds the planet, as it transited eclipsing its star.



Figure: artistic illustration showing the nine hydrogen giant around GJ 3470b, whose atmosphere is evaporating. © NASA / ESA and D.Player (STScl).


 

Fuente: UCC-CAB

 

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