In Search of Missing Worlds, Hubble Finds a Fast Evaporating Exoplanet
Release date: Dec 13, 2018 10:00 AM (EST)
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.
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