An article in the journal “Nature” describes a research about the planet GJ 436b, whose mass is similar to that of Neptune. Using the Hubble Space Telescope, a team of astronomers led by David Ehrenreich of the Observatory of the University of Geneva in Switzerland discovered that it leaves behind a huge tail of the estimated size of about 50 times that of the star it orbits. Those are hydrogen emissions ripped from the planet which make it looke like a huge comet.