According to the US-based National Aeronautics and Space Administration (NASA), our galaxy is filled with nearly 300 million potentially habitable planets.
Before running out of fuel in 2018, the US Space Agency’s Kepler Space Telescope spent nine years on a planet-hunting mission, successfully discovering thousands of exoplanets in our galaxy. But the central question of the original mission remained, which is how many of these planets are habitable?
For years, scientists around the globe have poured over Kepler’s data and they believe they have found the solution. There are approximately 300 million potentially habitable worlds in our galaxy, according to studies reported in The Astronomical Journal. This means that there are that many rocky planets that can support liquid water on their surface.
This is a rough estimate on the conservative side, and “there may be several more,” NASA said in a news release. Some of these planets may be close enough to be called “interstellar neighbors” with the closest one being 20 light-years away.
“Kepler has already told us that there are billions of planets, but now we know that a decent chunk of those planets may be rocky and habitable,” NASA’s lead author and researcher Mr. Steve Bryson said in the statement.
“While this outcome is far from the final value, and water on the surface of the planet is just one of several life-supporting factors, it is extremely exciting that we have estimated that these worlds are so common with such high confidence and accuracy,” he added.
The study
The study was an international partnership between NASA scientists working on the Kepler project and international agency researchers, ranging from Brazil to Denmark.
According to reports from NASA, there are around 100 to 400 billion stars in our solar system. Each star in the sky is likely to host at least one planet meaning there are likely trillions of planets out there, just a few thousand of which we have found and confirmed.
A number of factors, including its atmosphere and chemical composition, influence whether a planet can support life. But the researchers in this study focused on a few specific criteria in order to narrow down from the trillions.
Criteria
In terms of age and temperature, they looked for stars comparable to our own Sun, so it wouldn’t be too hot or active. They also explored exoplanets with a radius similar to that of Earth, singling out any that were likely to be rocky.
They also took into account the distance of each planet from its star because if it’s too near, the heat could vaporize any water and if it is too far away any water could freeze.
To sustain liquid water on its surface, a habitable planet needs to be in the’ just right’ zone or the so-called Goldilocks zone.
Previous estimates of the number of habitable planets did not reflect how those planets could absorb the temperature and energy of a star, the NASA release said. But this time, thanks to additional data obtained by the Gaia project of the European Space Agency, which is mapping a three-dimensional map of our galaxy, scientists were able to factor temperature into their study.
“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 Mr. Ravi Kopparapu in the release. “Gaia’s data on stars allowed us to look at these planets and their stars in an entirely new way.”
Researchers used a conservative estimate that 7 percent of Sun-like stars could host habitable worlds after measuring these factors. But scientists said the figure could be as high as 75 percent.
NASA and other space agencies have said that the estimate will continue to be refined in future studies, which will help form plans for the next phases of exoplanet and telescope discoveries. NASA’s TESS (Transiting Exoplanet Survey Satellite) project is currently the latest planet-hunter in the pursuit of exoplanets.
