Kepler-438b

 

Kepler-438b has an Earth Similarity Index of 0.88. Prior to its discovery, the two most Earth-like exoplanets known were Gliese 667Cc and Kepler-296e.

“With each new discovery of these small, possibly rocky worlds, our confidence strengthens in the determination of the true frequency of planets like Earth,” said team member Dr Doug Caldwell of NASA’s Ames Research Center at Moffett Field, California, who is a co-author of the paper accepted for publication in the Astrophysical Journal (arXiv.org preprint).

“The day is on the horizon when we’ll know how common temperate, rocky planets like Earth are.”

“This announcement is important because it shows that we are finding many planets in the habitable zone around other stars,” added Prof Lisa Kaltenegger of Cornell University and the Institute for Pale Blue Dots, who was not involved in the discovery.

“Now that we are probing the entire habitable zone around cool stars, we are starting to see the fascinating diversity of such potential Earths.”

Artistic representations of all known potentially habitable exoplanets (including newly-discovered Kepler-438b, Kepler-440b, Kepler-442b, and Kepler-443b), ranked from best to worst by the Earth Similarity Index – a measure of Earth-likeness based on stellar flux and planet size. Our planet, Mars, Jupiter, and Neptune are shown for scale. Image credit: PHL / UPR Arecibo.

According to the astronomers, Kepler-438b is 12 percent bigger than Earth and orbits its parent star, Kepler-438, once every 35.2 days.

The star, also known as KOI-3284, is a red dwarf located in the direction of the constellation Lyra, about 470 light-years away. It is smaller and cooler than our Sun.

To be in the habitable zone, an exoplanet must receive about as much sunlight as Earth. Too much, and any water would boil away as steam. Too little, and water will freeze solid.

Kepler-438b receives about 40 percent more light than Earth. In comparison, Venus gets twice as much solar radiation as our planet.

As a result, Dr Torres and his colleagues calculate it has a 70 percent likelihood of being in the habitable zone of its star. It has also a 70 percent chance of being rocky.

“Each result from the planet-hunting Kepler mission’s treasure trove of data takes us another step closer to answering the question of whether we are alone in the Universe,” said Dr John Grunsfeld of NASA’s Science Mission Directorate.