The seven planets that could support life

One year on the Habitable Exoplanet Catalog has identified seven exoplanets in our Milky Way that are similar to Earth.

Extrasolar planets, also known as exoplanets, are planets discovered outside of our solar system. The Habitable Exoplanet Catalog (HEC) based at the University of Puerto Rico, Arecibo, is a project that aims to identify which of these worlds could support life. 

Since its launch exactly a year ago, the HEC has so far identified seven exoplanet worlds that could support life, far more than expected when the project began. In order of increasing size these planets are: Gliese 581g,Gliese 667Cc,Kepler 22b,HD 40307g,HD 85512b,Gliese 163c andGliese 581d.

The catalog also has a further 27 planets identified by Kepler, NASA’s planet-hunting spacecraft, waiting for confirmation.

“The main purpose is for research, but then I realized that also for the public, it was very important,” said Abel Mendez, who heads up the team at HEC told

“There are many press releases announcing discoveries of habitable planets … and that is confusing. So having a catalog that everyone can check what is available right now is useful.”

The list of seven planets includes the disputed exoplanet Gliese 581g, whose existence is still currently up for debate among astronomers. 

“There are two versions of the story, and the two versions can be supported by data,” says Mendez. 

“But because we think that there’s still the sense that planet could exist, we are including it.”

When the HEC was launched on December 5 2011, only two habitable exoplanets had been recorded. The team believe that the leap from two to seven in the space of one year could not have been predicted. The HEC uses several methods to assess the habitability of exoplanets such as the Earth Similarity Index (ESI) which is a measure of Earth-likeness in a scale from zero to one, one being identical to Earth.

All seven of the exoplanets are ‘superterrans’ meaning that they are much larger than Earth, but still have the potential to support life. The team are still hunting for a true earth analogue or an extrasolar moon that could be harbouring extra-terrestrial life.