Researchers at the University of California at Berkeley working with researchers from the University of Hawaii at Manoa have found that planets similar to Earth may be more common than we believed. Their work, published in this week’s Proceedings of the National Academy of Sciences, used NASA’s Kepler telescope to estimate the number of Earth-sized planets that orbit stars similar to our sun and have years around the same length as ours. Based on their calculations, about 5.7% of all stars resembling our sun have planets like ours circling them.
The group used Kepler’s data to identify those planets that are about the same size as Earth based on how much they dimmed the light from their respective stars when their orbits cross in front of them. They then estimated how long it takes for said planet to fully orbit its star, focusing in particular on those planets whose orbits last between 200 and 400 days (a ballpark for our own 365 days per revolution year). Lastly, they examined how much stellar energy these planets would absorb, looking for those that occupy what is called the “habitable zone,” where liquid water would be able to exist on the planet’s surface.
Previous studies like this have come to some wildly disparate conclusions about how many Earth-like planets are out there, with estimates ranging from 1% of sun-comparable stars having them to a whopping 34%. The authors of this paper are confident in their math though, as their calculations take into account factors such as the incompleteness of Kepler’s data and the uncertainties inherent in using these high-powered telescopes, which other researchers have failed to consider.
So what does this mean, beyond that there are a good number of planets out there shaped like ours? Well it could mean a lot actually. The results this group got also show that smaller planets are much more common than larger ones, based on the number of Earth-sized planets spinning around out there compared to Jupiter-sized ones. This supports a timeline for planet formation that argues larger, gaseous planets form from atmospheric build-up around smaller, rockier planets (basically solids accumulate first, then gases later on). This timeline is widely debated and the exact details of how planets grow into what we now see them as are not well-known, and so studies like this could also help us to look back into the formative processes of our universe.
The group also found that, assuming their calculations hold true, the nearest Earth-sized planet, orbiting a star similar to our sun, lying within the delicately defined habitable zone, is only twelve light-years away. And it’s visible to the naked eye. That means that when you look up at the night sky you could see, with your own eyes, a planet where, maybe, there is some other eye, looking up at you.