A Planet with a Tail Nine Million Miles Long
A planet outside of our solar system is losing its atmosphere, which is dissipating into a giant cloud, according to a new study. GJ 436b is so close to its parent star 33 times as close as the Earth is to the sun that its atmosphere is evaporating, creating a large cloud around the planet, said David Ehrenreich, an astrophysicist at the University of Geneva and one of the study’s authors. “What we see is the planet kind of turning into an enormous monster much bigger than its star,” Dr. Ehrenreich said.
The star is much fainter than our sun, and the evaporating gases are not swept away. Instead, the star “allows the huge cloud to gather,” Dr. Ehrenreich said. He and his colleagues report their findings in the current issue of the journal Nature. The researchers analyzed ultraviolet observations of the Neptune-mass exoplanet, located 33 light years from Earth. The planet orbits a small red dwarf star in the constellation Leo.As the planet loses mass, the cloud of hydrogen atoms continues to grow. Stellar radiation has given the cloud a long tail nine million miles in length trailing the planet.
The discovery could help scientists learn more about the rocky, Earth-size planets discovered by NASA’s Kepler Space Telescope. “It has always been a mystery how these rocky planets so close to their stars could form,” Dr. Ehrenreich said. “One possibility is that they are the remnants that have lost mass because of atmospheric evaporation.”