New research, using Kepler spacecraft data, suggests there are about 300 million habitable planets just in the Milky Way.
Kepler Space Telescope spent nine years on a planet-hunting mission. It successfully identified thousands of exoplanets in our galaxy before running out of fuel in 2018. But people have always wondered about how many of these planets are habitable!
Using Kepler data, researchers estimate there are about 300 million potentially habitable worlds in our galaxy, the Milky Way.
Some of these planets could be close enough, with several likely within 30 light-years of our Sun.
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“Kepler already told us there were billions of planets, but now we know a good chunk of those planets might be rocky and habitable,” said astronomer Steve Bryson of NASA’s Ames Research Center.
“Though this result is far from a final value, and water on a planet’s surface is only one of many factors to support life, it’s extremely exciting that we calculated these worlds are this common with such high confidence and precision.”
To create a reasonable estimate for the number of habitable exoplanets, scientists looked for rocky Earth-sized worlds. They also searched for planets orbiting Sun-like stars that are the same age as our Sun and have similar temperatures. Another consideration for habitability is whether the planet could have the conditions necessary to support liquid water.
Previous estimates of the number of habitable planets did not reflect how a star’s temperature and energy could be absorbed by its planets, said the NASA release. But this time, scientists were able to factor temperature into their analysis. That’s thanks to additional data gathered by the European Space Agency’s Gaia mission, which is charting a three-dimensional map of our galaxy.
“We always knew defining habitability simply in terms of a planet’s physical distance from a star, so that it’s not too hot or cold, left us making a lot of assumptions,” said NASA scientist and study author Ravi Kopparapu in the release.
By taking both Kepler and Gaia data into account, the results better reflect the diversity of stars, solar systems, and exoplanets in our galaxy.
“Gaia’s data on stars allowed us to look at these planets and their stars in an entirely new way.”
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After calculating these factors, researchers used a conservative estimate that 7% of Sun-like stars could host habitable worlds. But the rate could be as high as 75%, scientists said.
One of Kepler’s main goals was to help determine how many exoplanets within these parameters exist in the Milky Way. Bryson and his team used all four years of the original Kepler mission data, from May 2009 to May 2013, to make the best estimate yet of this number.
However, scientists will need to do more research to understand the role a planet’s atmosphere has on its capacity to support liquid water. In this analysis, researchers used a conservative estimate of the atmosphere’s effect to estimate the occurrence of Sun-like stars with rocky planets that could have liquid water.
The Kepler mission, which officially ceased collecting data in 2018, has identified over 2,800 confirmed exoplanets. There are also several thousand more unconfirmed candidates. So far, researchers have identified several hundred planets in the habitable zone of their star in Kepler data. It may take a while to find all 300 million.
NASA said it and other space agencies will continue to refine the estimate in future research. That will help shape plans for the next stages of exoplanet discoveries and telescopes. Currently, NASA’s TESS mission is the latest planet-hunter seeking out exoplanets.
The study was a global collaboration between NASA and researchers from international agencies ranging from Brazil to Denmark.
Scientists published their research in The Astronomical Journal.