First ever evaporating alien planet caught

For the very first time, astronomers can observe a planet outside of our galaxy losing its atmospheric gas.

The study leader of this "leaking atmosphere" phenomenon, Alain Lecaveiler said "This discovery tells us that (atmospheric) evaporation is a genuine phenomenon for planets close to their stars". The planet in question similar to Jupiter is called HD 189733b and it's about 60-light years from Earth. The planet, like Jupiter, is composed of gas and because it orbits very close to its host star, it's also being referred to as a hot Jupiter.

Why is planet's HD 189733b atmosphere "leaking" anyway? Scientists believe, that evaporation of its atmosphere is caused or triggered by a forceful stellar flare. Stellar flare is an eruption of charged particles from a star, meaning a colossal mass of energy is being released into space. So it is possible that the stellar rays from the star reached the planet, making its atmospheric gas to heat up to tens of thousands of degrees Celsius. That huge amount of heat made the gas molecules to move faster or fast enough to escape the planet's gravitation. In the illustration above (courtesy of L. Calçada, ESA/NASA) we can see the planet HD 189733b passing its host star.

Some scientists also believe that atmospheric evaporation could explain the existence of some Earth-size planets, that have only recently been discovered. These planets could be left overs of  hot Jupiters that were passing by to close to their stars, so the heat made their atmospheres to evaporate and expose their cores made of rock. It's also believed that Jupiter (picture above) has a rocky core of heavier elements. The rest of the planet, is as said, composed of gas - mainly hydrogen.