One of the coolest scientific advances of my lifetime has been the development of the ability to find exoplanets – planets around other stars. I remember Carl Sagan talking about the techniques astronomers planned to use to find such planets back in the 1980’s. Then, in 1995 these plans came to fruition with the first discovery of an exoplanet – 51 Pegasi b, a Jovian planet around a star 50 light years away.

This discovery was just the first. In the last 14 years a total of 339 exoplanets have been discovered, and this number is growing every week. Frequently we hear about the largest exoplanet, the hottest, the closest to its parent star, and the smallest. New superlatives are being made on a regular basis. It’s all very exciting.

The most common method used for discovering these exoplanets is called the radial velocity method. This looks for the wobbling of the star due to gravitational tugs from planets orbiting it. This method, however, favors large planets close to their stars. This new planet was discovered using the transit method – when a planet passes in front of its star as viewed from the earth, the total amount of light measured from that star dips a bit. This technique has been made possible by better telescopes and better computers able to process the information from those telescopes.

Now we have once again broken a new exoplanet record – the new smallest exoplanet yet discovered. The BBC reports:

“For the first time, we have unambiguously detected a planet that is ‘rocky’ in the same sense as our own Earth,” said Malcolm Fridlund, Corot project scientist from the European Space Agency (ESA).

“We now have to understand this object further to put it into context, and continue our search for smaller, more Earth-like objects with Corot,” he added.

Finding a planet just like earth is the holy grail of exoplanet astronomy.  This is partly for psychological reasons – humans are very egocentric – but also does have serious implications. Earth-like planets are more likely to support life similar to life on earth. Therefore we are interested in planets that are rocky and are a similar distance from their sun with similar average temperature.

This planet does not fit that bill. It is the smallest planet yet discovere, only about twice as big as earth. That size planet could plausibly harbor life. It is also rocky, so it has a surface and is not just a ball of gas. However, it is very close to it’s star. It orbits once every 20 hours and has a surface temperature of 1,000-1,500C.

As better telescopes go online we will soon be able to detect earth-size planets at hospitable distances from their stars.

So the cool is about to get even cooler.