An international team of astronomers working with NASA's Kepler spacecraft have discovered two new planets, one of which might support flowing water, according to the findings published Tuesday by Monthly Notices of the Royal Astronomical Society Letters.
The planets are orbiting Kapteyn's Star, the 25th nearest star to our sun—just 13 light years away. That means it is close enough to be seen from Earth with an amateur telescope.
"Finding a stable planetary system with a potentially habitable planet orbiting one of the very nearest stars in the sky is mind blowing," Pamela Arriagada, a Carnegie Institution postdoctoral researcher and author on the study, said in a statement announcing the discovery. "This is one more piece of evidence that nearly all stars have planets, and that potentially habitable planets in our galaxy are as common as grains of sand on a beach."
Kapteyn's Star, named after Dutch astronomer Jacobus Kapteyn who discovered it at the end of the 19th century, is the fastest-moving star in the sky. It is thought to have been born in a dwarf galaxy that was long ago "cannibalized" by the Milky Way. That event would set the age of Kapteyn's Star and its newly discovered planets at 11.5 billion years old, fully 2.5 times older than Earth.
"It does make you wonder what kind of life could have evolved on those planets over such a long time," says Guillem Anglada-Escude, a former Carnegie postdoc now the Queen Mary University of London and lead author on the study.
The planet that might support water is called Kapteyn b, and is at least five times the mass of that of Earth. It orbits its star every 48 days, putting it in the range of warmth suitable for flowing water on its surface. The second planet, Kapteyn c, orbits its star much farther away, once every 121 days, making it likely too cold to support liquid water, according to the report.
Approximate masses, orbital periods and distances from Kapteyn's star are the only known facts about the new planets so far, but plans to measuring their atmospheres "using instruments that are currently under development" will be able to verify whether or not Kapteyn b truly has water flowing on its surface.
Meanwhile, the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo keeps a running list of the exoplanets that might be habitable. A paper published last month in the journal Challenges found that 1 percent of all planets in our galaxy—or roughly 100 million planets—might be suitable for complex life.
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