A team of astronomers from the United States and France has pinpointed which of 4,270 exoplanets discovered by NASA’s Kepler mission are most likely to be similar to Earth.
This artist’s concept depicts an exoplanet. Image credit: NASA / Ames / JPL-Caltech.
The team, led by San Francisco State University astronomer Stephen Kane, identified 216 Kepler planets located within the ‘habitable zone’ of their host stars.
“This is the complete catalog of all of the Kepler discoveries that are in the habitable zone of their host stars,” Dr. Kane said.
“That means we can focus in on the planets in this paper and perform follow-up studies to learn more about them, including if they are indeed habitable.”
The team’s research also confirms that the distribution of Kepler exoplanets within the habitable zone is the same as the distribution of those outside of it — additional evidence that the Universe is teeming with planets and moons where life could potentially exist.
The scientists sorted the planets by whether they were in a conservative or a more optimistic interpretation of the habitable zone.
Then they further sorted them by planet size: smaller, rocky planets versus larger gas giants.
The four categories are aimed at helping astronomers focus their research.
Those looking for moons that could potentially hold life can study exoplanets in the gas giant categories, for example.
The most restrictive category – a rocky planet with a radius less than two Earth radii within the conservative habitable zone – contains 20 exoplanets, including Kepler-62f, Kepler-186f, Kepler-283c, Kepler-296f and Kepler-442b.
This figure shows the habitable zone for stars of different temperatures, as well as the location of terrestrial size planetary candidates and confirmed Kepler planets described by Kane et al. Some of the Solar System terrestrial planets are also shown for comparison. Image credit: Chester Harman.
“There are a lot of planetary candidates out there, and there is a limited amount of telescope time in which we can study them,” Dr. Kane said.
“This study is a really big milestone toward answering the key questions of how common is life in the Universe and how common are planets like the Earth.”
“It’s exciting to see the sheer amount of planets that are out there, which makes you think that there is zero chance of there not being another place where life could be found,” added co-author Michelle Hill, also from San Francisco State University.
Details of the research have been accepted for publication in the Astrophysical Journal. The article is also publicly available at arXiv.org.
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Stephen R. Kane et al. 2016. A Catalog of Kepler Habitable Zone Exoplanet Candidates. ApJ, accepted for publication; arXiv: 1608.00620
