Half of the stars in our galaxy that are similar to the sun could be home to an Earth-like planet capable of supporting life.
A team led by Steve Bryson at NASA’s Ames Research Center in California analysed data from the Kepler space telescope, searching for rocky planets within the habitable zone of stars the same size as our sun. The habitable zone is found at the distance from a star where it isn’t too hot or too cold for liquid water to exist.
Based on detections of 4034 exoplanet candidates and their frequency around sun-like stars, Bryson and his team simulated how Earth-like planets should be distributed across the Milky Way – and concluded there are more than we previously thought.
Advertisement
They found that 40 to 60 per cent of sun-like stars had rocky planets similar to Earth in their habitable zones, compared with previous estimates of 20 to 50 per cent. With 10 billion sun-like stars in the Milky Way, this could mean around 5 billion habitable planets in our galaxy.
“This is a really impressive work,” says Hugh Osborn at the Massachusetts Institute of Technology, who wasn’t involved in the study.
Bryson and his colleagues looked at exoplanets with a radius between 0.5 and 1.5 times that of Earth, narrowing in on those that are probably rocky. They also focused on stars similar in age and temperature, give or take about 800°C, to our sun.
“Outside of that temperature range, which is roughly centred on the sun’s temperature, stars start behaving very differently from our sun in terms of the amount of radiation they put out, and in what part of the electromagnetic spectrum, and also how long they live for, and also how hard it is to find planets around them,” says Jessie Christiansen at the California Institute of Technology, a co-author of the study.
There have been a lot of previous efforts to find the frequency of Earth-like planets, but this one is different, says Osborn. It used more data, simulated it in a new way, accounted for the possibility that some of Kepler’s candidates aren’t planets and only looked at small planets that receive a similar amount of light as Earth. “Taken together, these are all improvements over the various previous studies, and therefore all add credibility,” he says.
This isn’t the final result. In fact, the final number could be even higher, says Christiansen. “At this point our uncertainties are largely driven by the small number of candidates we truly have in the parameter space of interest,” she says. “So until we get more data it will be hard to truly reduce those error bars.”
Either way, it is an exciting result. “It suggests there are many Earth-like planets orbiting nearby stars that we will be able to study in detail in the coming decades,” says Osborn. “And it maybe lends weight to the idea that, if Earth-like planets are common, maybe life is common too.”
Reference:
Sign up to our free Launchpad newsletter for a voyage across the galaxy and beyond, every Friday
