Planets that are too close to its star will have a runaway greenhouse gas effect similar to Venus, while those that are too far have frozen waters.
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The boundaries of the habitable zone are critical.
The study took three years and required examining all 4,000 of the exoplanets that Kepler has since discovered in astonishing detail.
To find out if a planet can host life or not the team must understand some specific physical characteristics regarding every planet like size, orbit and distance from its star.
“What we can do is focus our efforts on the planets most likely to yield evidence of extraterrestrial life, and that is what we hope our work will provide”, Dr. Stephen Kane, an astronomer at San Francisco State University and the study’s lead author, told The Huffington Post in an email. But if it’s too far, any water will freeze, as is seen on Mars.
The research also determined that the distribution of Kepler planets is the same both within and outside the habitable zone, suggesting that the universe is teeming with potential moons and planets that can possibly hold life.
From these, the researchers figured out which planets had the best chance of being just like Earth, with the most flawless position in the habitable zone, a rocky composition, and an Earth-like size.
The 20 planets in the most restrictive category – rocky surface and a conservative habitable zone – are the most likely to be similar to Earth.
The catalogue, which is divided into four categories, is meant to help astronomers focus their research.
From those 4000 exoplanets, Kane and his team identified 216 planets located within the “habitable zone” of their star, where the conditions make it technically possible for liquid water to exist on the surface. Those looking for moons that could potentially hold life can study exoplanets in the gas giant categories, for example.
In addition to isolating 216 terrestrial planets from the Kepler catalog, they also devised a system of four categories to determine which of these were most like Earth.
The worldwide team was made up of researchers from NASA, San Francisco State University, Arizona State University, Caltech, University of Hawaii-Manoa, the University of Bordeaux, Cornell University and the Harvard-Smithsonian Center for Astrophysics.
Professor Kane is renowned for being one of the world’s leading “planet-hunters”. He is contributing his scientific knowledge to two upcoming satellite missions – NASA’s Transiting Exoplanet Survey Satellite (TESS) and the European Space Agency’s Characterizing ExOPLanet Satellite (CHEOPS) – that will benefit from the information contained in his latest research.
In a report in San Francisco News, Kane said that there are a lot of planetary candidates that can be studied across the galaxy.
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ASU’s School of Earth and Space Exploration postdoctoral scholar and research team member Natalie Hinkel, said, “Finding new Earth-like planets that could perhaps be habitable to human beings or even inhabited by other life forms is such a tantalizingly wonderful idea that you can’t help but have your curiosity piqued”.
