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Astronomy News - Planets and the Sun

Discovery of an extra-solar planet with Earth-like temperature - 20th April 2010


A recent article in Nature has detailed the discovery of a planet over 1500 light years away that may have a surface temperature conducive to supporting life. The planet, designated CoRoT-9b, is believed to be of a similar size to Jupiter and is orbiting its parent star at a distance similar to Mercury. Because the star in this system is much cooler than our sun, the temperature of the planet is thought to be in the range -20C to 160C, despite having a much smaller orbit than Earth; this could mean that liquid water is present on the surface. The planet, which has a year lasting around 95 days, was discovered using what is known as the transit method which works by measuring a slight dip in the amount of light detected from a star as a planet passes infront of it.

CoRoT (COnvection Rotation and planetary Transits) is a satellite dedicated to nding planets in other systems throughout the galaxy, with the ultimate aim being to nd a planet similar to Earth. Over 400 planets beyond our solar system have been discovered to date, although the majority have been of a type known as 'hot Jupiters'. These are planets which are of a similar size to Jupiter but are extremely close to their parent stars, completing orbits within a handful of days. As well as using the transit method, most planets have been detected by other means such as the radial velocity method, where the presence of a planet causes the star to 'wobble'. From this wobble the presence of a planet can be inferred. Another method, which has detected some of the lowest mass planets to date, is gravitational microlensing. This method works by observing the light from a far away star, and any orbiting planets, being bent around another star between that system and Earth.

Another reason that scientists are so excited about CoRoT-9b is that it has a near-circular orbit and is not believed to be tidally locked. Many of the planets discovered so far have highly eccentric orbits causing them to be very hot at certain points in their orbits and very cool at others. Planets that are tidally locked always have the same side facing the star they are orbiting, and therefore there are no days or nights; this is the case with our own moon. Neither of these conditions seem likely to be able to support life, so finding other planets similar to CoRoT-9b is the next step on the road to finding a second Earth.

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