Using the Hubble Space Telescope, astronomers have discovered a Neptune-sized planet that's literally disappearing in front of our eyes. The exoplanet is fairly close to the star and is losing mass at a rate never seen before. The findings are reported in Astronomy & Astrophysics.
The planet in question is called GJ 3470b and is 97 light-years from Earth. It is evaporating at a rate 100 times faster than the similarly sized planet GJ 436b. This staggering rate could explain the lack of detection of a potential class of planets known as hot Neptunes as well as other aspects of how planetary systems evolve.
Astronomers have so far discovered roughly 4,000 exoplanets. Among those orbiting closest to their star, we've found Earth-sized planets or slightly bigger, the so-called super-Earths, and infernally hot gas giants (hot Jupiters). Mid-sized gas planets appear to be missing.
This research provides some damning evidence that the evaporation is enough to significantly downsize a planet. These Neptunes get stripped of their atmosphere by the intense light of their star, reducing them to a much smaller planet.
“This is the smoking gun that planets can lose a significant fraction of their entire mass. GJ 3470b is losing more of its mass than any other planet we seen so far; in only a few billion years from now, half of the planet may be gone,” co-author David Sing, Bloomberg distinguished professor at Johns Hopkins University, said in a statement.
The team estimates that GJ 3470b has already lost 35 percent of its original mass, and since it's orbiting such a young active star, they expect it to be reduced to a rocky core in just a few billion years. The work is part of the Panchromatic Comparative Exoplanet Treasury (PanCET) program, the largest exoplanet observation program using Hubble.
“We’re starting to better understand how planets are shaped and what properties influence their overall makeup,” Sing said. “Our goal with this study and the overarching PanCET program is to take a broad look at these planets’ atmospheres to determine how each planet is affected by its own environment. By comparing different planets, we can start piecing together the larger picture in how they evolve.”
The team plans to look for more of these evaporating hot Neptunes, especially as upcoming observatories like the James Webb Space Telescope will hopefully help astronomers discover many more.