NASA’s planet hunting Kepler Mission has been extended for a period of up to four years after its initial 3 and half year mission came to an end. The space based telescope searches for planets that exist outside our solar system, known as exoplanets or extrasolar planets.

Since its launch in March 2009 the mission has been highly successful in detecting planets orbiting distant stars, with over 2,000 candidates and over a hundred confirmed discoveries. Kepler will now focus on finding Earth sized planets with one year orbital periods around sun like stars.

The Kepler Space Telescope scans over 150,000 stars simultaneously looking out for rare events called transits, where a planet passes between its star and Earth. This causes light from the star to dim very slightly which can be measured by the telescope’s sensitive instrumentation. The dimming reveals the radius of any potential planet but not its mass.

Kepler has found several potentially Earth like planets some of which orbit in the habitable zone around their host star, a region where temperatures would allow for the presence of liquid water on the planet’s surface. Perhaps the most promising of these is Kepler 22b, a planet with a radius only 2.4 times that of Earth, if it possesses a similar atmosphere and composition to our own planet it could have surface temperatures of around 22C (72F).

The main finding of the Kepler Mission’s data so far is that planetary systems are extremely common in our galaxy. It is estimated that at least a third of the 200 billion stars in the Milky Way are orbited by one or more planets, meaning there are many billions of planets in our galaxy.

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