Research outlines 216 Kepler planets located within ‘habitable zone’

ASU belongs to an international team that has indicated towards the exoplanets, out of the over 4,000 exoplanets found by NASA's Kepler mission, with the highest chances of being similar to our planet.

Explained in a recently published article in the Astrophysical Journal, the research has shed light on the 216 Kepler planets present within the ‘habitable zone’, region around a star wherein a planet's surface may hold liquid water. Among those, they have listed 20 best candidates that can be habitable rocky planets like our planet.

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”.

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.

In case a planet is very near to its star, it will face a runaway greenhouse gas effect, such as Venus. But, in case it’s too far, all water, if any, will freeze, as in the case of the Red Planet. The science team filtered the planets by checking if they were in a conservative or a more optimistic interpretation of the habitable zone. Thereafter, the team filtered them by planet size, including smaller, rocky planets opposite huge gas giants.

The researchers took over three years in studying and cataloging the over 4,000 exoplanets. The study’s main author Stephen Kane, an associate professor of physics and astronomy at San Francisco State University said that it was the complete list of all of the Kepler discoveries belonging to the habitable zone of their host stars.

According to a report in Tech Crunch by Darrell Etherington, "The international group of scientists behind the study examined the over 4,000 planets outside of our solar system (exoplanets for those In the know) to identify the ones most likely to harbor life based on the model of the only life-bearing planet we know of: Earth."

Coming up with a short list of Earth-like planets has very real value to the continued project of searching for signs of extraterrestrial life. Simply investigating every exoplanet identified by Kepler just isn’t feasible in terms of available resources, but a core group of 20 with characteristics that greatly increase the likelihood of finding Earth-like life is manageable.

“There are very limited resources available for studying the atmospheres of terrestrial planets and so the Habitable Zone is used to select those planets most likely to have liquid water on the surface,” Kane explained in an interview. “This will become increasingly important once new facilities, such as the James Webb Space Telescope, are deployed.”

A report published in Hawaii revealed, "A team of astronomers known as the Kepler Habitable Zone Working Group, including Nader Haghighipour of the University of Hawai’i Institute for Astronomy, has identified which of the more than 4,000 exoplanets discovered by the NASA Kepler mission are most likely to be similar to our rocky home."

The research also confirms that the distribution of Kepler planet sizes within the habitable zone is the same as the distribution of those outside of it. Said Haghighipour, “Given that many of these planets are as large as gas-giant planets in our solar system, there is a high possibility that these planets may harbor large moons that could also be habitable.”

The 20 planets in the most restrictive category — rocky surface and a conservative habitable zone — are the most likely to be similar to Earth. “These are the prime targets for our studies with large ground-based telescopes such as the Keck, Subaru and Gemini telescopes – and in the future, the Thirty Meter Telescope,” said Haghihgipour.