Hubble Finds a Fast Evaporating Exoplanet

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Hubble Finds a Fast Evaporating Exoplanet

Post by bystander » Thu Dec 13, 2018 5:53 pm

In Search of Missing Worlds, Hubble
Finds a Fast Evaporating Exoplanet

NASA | STScI | HubbleSite | 2018 Dec 13
STScI-H-v1852a_GJ3470b.jpg
This artist’s illustration shows a giant cloud of hydrogen streaming off a warm,
Neptune-sized planet just 97 light-years from Earth. The exoplanet is tiny compared
to its star, a red dwarf named GJ 3470. The star’s intense radiation is heating the
hydrogen in the planet’s upper atmosphere to a point where it escapes into space.
The alien world is losing hydrogen at a rate 100 times faster than a previously
observed warm Neptune whose atmosphere is also evaporating away.
Credits: NASA, ESA, and D. Player (STScI)

In nabbing exoplanets that are precariously close to their stars, astronomers have discovered a shortage of one type of alien world. It's a predicted class of Neptune-sized world that orbits just a few million miles from its star, much closer than the 93-million-mile distance between Earth and the Sun. Dubbed "hot Neptunes," these planets would have atmospheres that are heated to more than 1,700 degrees Fahrenheit (hot enough to melt silver).

However, the mysterious hot-Neptune deficiency suggests that these planets are rare, or, they were plentiful at one time, but have since disappeared. In fact, most of the known Neptune-sized exoplanets are merely "warm," because they orbit farther away from their star than those in the region where astronomers would expect to find hot Neptunes.

To date, astronomers have discovered two warm Neptunes that are leaking their atmospheres into space. The most recent finding, a planet cataloged as GJ 3470b, is losing its atmosphere at a rate 100 times faster than that of the previously discovered evaporating warm Neptune, GJ 436b.

These discoveries reinforce the idea that the hotter version of these distant worlds may be a class of transitory planet whose ultimate fate is to shrink down to the most common type of known exoplanet, mini-Neptunes — planets with heavy, hydrogen-dominated atmospheres that are larger than Earth but smaller than Neptune. Eventually, these planets may downsize even further to become super-Earths, more massive, rocky versions of Earth. If GJ 3470b continues to rapidly lose mass, in a few billion years, perhaps it, too, will dwindle to a mini-Neptune.

Hubble Finds Far-Away Planet Vanishing at Record Speed
Johns Hopkins University | 2018 Dec 13

The Hot Neptunes, Planets That Shrink
University of Geneva | 2018 Dec 13

Hubble PanCET: An Extended Upper Atmosphere of Neutral Hydrogen around the Warm Neptune GJ 3470b ~ V. Bourrier et al
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