Washington: Two super-Earth planets, which had been discovered by NASA`s Kepler mission along with a new planetary system that is home to five small planets around a slightly smaller star than the Sun, may sustain life after all.
Both the planets, most likely made of rock or ice mixed with rock, are located in the habitable zone of their host star.
This discovery is providing a target for the SETI search, since if life has thrived on these worlds and reached a point where civilization has developed complex technology, it may be detectable.
When the NASA Kepler mission was launched on March 9, 2007, the Delta II rocket was carrying the hope of a large community of scientists who dedicate their work to studying extra-solar planets, planets in orbit around other stars.
The Kepler mission`s main scientific objective is exploration of the structure and diversity of planetary systems. It accomplishes this goal by staring almost constantly at a large field composed of about 150,000 stars to detect small dips in brightness due to the transits of a planet.
Kepler has already been a successful NASA mission with the discovery of 2,740 planet candidates with estimated sizes from Mercury to larger than Jupiter.
A fifth of these planet candidates are also called "super-Earths," a new class of planets, without analog in our solar system, with a radius between 1.25 to 2 times the radius of our planet.
The Kepler team announced the discovery of a multiple planet system, composed of 5 Earth-sized and super-Earth planets orbiting a K-type star.
The detection of these planets was indirect since Kepler astronomers observed the attenuation of the host star`s brightness due to the passage of a planet in the line of sight, and not the planets themselves.
The authenticity of this multiple planet system was confirmed by a statistical analysis based on previous detections of multiple planets by Kepler.
"By estimating the rate of false-positives due the remote possibility of additional planet-hosting stars in the photometric aperture we have strong confidence that we have discovered two genuine transiting super-Earth planets in the habitable zone of their host star," Jason Rowe, Research Scientist at the Carl Sagan Center of the SETI Institute and co-author of the work said.
The outermost planet, named Kepler-62f (radius about 1.4 times Earth`s radius and a period of 267 Earth days) is located in the habitable zone of the star, a region around the star where a rocky planet with an atmosphere similar to Earth could host liquid water on its surface.
The team expanded the definition of the Habitable Zone by taking into account the evolution of the brightness of the host star. Their calculations suggest that Kepler-62e (radius about 1.6 times Earth`s radius and a period of 122 Earth days) was also in the habitable zone so that liquid water could have existed on its surface, too.
Similar to Venus and Mars that are believed to have lost their surface water 1 billion years and 3.8 billion years ago respectively, before our Sun was more luminous, the host star`s habitable zone was broader in the past.
The findings are published in Science magazine.