Located 63 light years from Earth, HD 189733b is a gas giant planet with a hazy atmosphere mainly composed of hydrogen. Due to close proximity to its star – about 1/30th of the distance from the Earth to the Sun – its upper atmosphere receives a huge amount of energy in the form of ultraviolet and X-ray radiation.
The researchers initially observed the star in order to confirm a result obtained in 2003 with the Hubble for another exoplanet, HD 209458b, located in a different planetary system. They discovered that the hydrogen making up the topmost layer of the planet’s atmosphere was spreading out in a huge plume, providing evidence that its atmosphere was evaporating into space.
In fact, the researchers observed HD 189733b on two occasions. In April 2010 they saw nothing unusual. However, in September 2011 they detected a huge cloud of gas six times larger than the planet itself. This shows that the state of the atmosphere had changed in the meantime, and that the scientists had found a meteorological difference on HD 189733b.
Via Dr. Stefan Gruenwald