Rejoice!

The world is buzzing with the news that European Space Agency (ESA) scientists have found water on a planet outside the solar system.

The planet, affectionately called HD 189733b, was discovered in 2005 at 63 light-years away and is classified as a ‘hot Jupiter’. Such planets are large and have extensive atmospheres because heat from the nearby star gives them energy to expand. Indeed, HD 189733b is 1.15 times the mass of Jupiter and its diameter is 1.25 times that of Jupiter. It is a mere 4.5 million km from its star; Earth is 150 million km from the Sun and Mercury, the innermost planet, is 70 million km away. Because of its orbit, one hemisphere of HD 189733b constantly faces the star, heating the planet only on one side to reach over 700 degrees C, or higher.

So just how do we figure out there is water in the atmosphere? It’s quite simple actually. As the planet moves around its sun, it hides parts of it from us (much like a lunar eclipse, but hiding a much smaller area). This means that the planet and its atmosphere are between it sun and our telescopes. We can measure what kind of light comes through from the planet’s sun, through the planet’s atmosphere, and onto Earth. How the light behaves through the atmosphere tells us a lot about its composition. What the ESA found is one infra-red band of light changed in a way that can only be explained by the presence of water.

The research is published in [review=http://www.nature.com/nature/journal/v448/n7150/abs/nature06002.html]Nature[/review].

Image credit: ESA - C.Carreau