Illustration of WASP-121b, an exoplanet which lies about 900 light-years away from Earth. This hot Jupiter orbits very close to its host star and temperatures in its upper atmosphere reach 2500 degrees Celsius. Using Hubble Space Telescope Imaging Spectrograph, astronomers have witnessed magnesium and iron gas escaping from the planet's atmosphere and far away from the exoplanet. This is caused by ultraviolet light from the host star heating WASP-121b's upper atmosphere. The planet is so close to its host star that it's shape has been stretched by gravitational forces and these forces could be destroyed the exoplanet.