Exoplanets that are most likely to host life have eluded detection, until now. As far as we understand, the most likely place to find extraterrestrial life outside of our solar system is on a planet that is similar in size to Earth and located within the habitable zone of its host star where temperatures are just right for the abundance of liquid water.
|Comparison of Earth and Kepler 186f. To the right you can see the orbit of Kepler 186f compared to the other four exoplanets in the system that orbit closer to the star. Credit: NASA Ames/SETI Institute/JPL-Caltech|
Today, a group of scientists announced that with Kepler they have discovered the very first Earth-sized planet in a habitable zone. Before now, scientists have observed Earth-sized exoplanets that were too close to their host star and therefore too hot for liquid water. Scientists have also observed a healthy amount of planets within their habitable zone, but the planets are too large to likely contain a rocky surface on which life could exist.
Up to this point, either exoplanets were the right size but too close or they were the right distance but too large. But Kepler 186f is both the right size and distance to potentially harbor life. It would be “just right” in Goldilocks’ eyes.
“We can now say other potentially habitable worlds similar in size to Earth can exist, and it’s no longer in the realm of science fiction,” said Elisa Quintana earlier today at a NASA teleconference. Quintana is a research scientist at the SETI Institute in Moffett Field, California and lead author of the paper detailing the team’s results. The paper is scheduled to be published tomorrow in Science.
Kepler 186f is about ten percent larger than Earth and orbits a cooler star about half the mass of our Sun located approximately 500 light years away. So, it’s not in our immediate neighborhood. The star that Kepler 186f revolves around is what astronomers call an M-dwarf, which means there might be more planets like Kepler 186f that are nearby said second author of the paper, Tom Barclay during the teleconference.
|Artist's rendition of Kepler 186f. Credit: NASA Ames/SETI Institute/JPL-Caltech|
Because Kepler 186f orbits a cooler star, the planet’s habitable zone is at a smaller radius than Earth’s – more comparable to the orbital distance of Mercury. The exoplanet orbits its star every 130 days, which makes it easier for Kepler to detect.
Kepler 186f is not the sole exoplanet in this system. In fact, four other planets are known to orbit much closer to the same host star. None of these planets scientists expect to have the same potential for life as Kepler 186f.
There are still many questions to be answered about Kepler 186f. For example, scientists still do not know its mass, temperatures or atmospheric composition. The latter of which will be the most likely piece of information that will divulge the presence of life. For this, scientists will likely have to wait for the James Webb Space Telescope.
Moreover, the system in which Kepler 186f resides is very different from Earth's. The size of its host star and the distance at which the planet revolves means that the exoplanet receives about one-third the heat radiation that Earth receives from the Sun. The stronger gravitational pull from the host star might mean the planet is in an asynchronous rotation with its star, which would mean that only one side would receive heat year-round.
These factors do not automatically rule out the possibility of life, the scientists explained during the teleconference. This finding is the closest we've come to finding a planet that might host life and because the system is different simply means the pictures is more complex and further observations are needed.