Astronomers have long known that Earth isn't alone in the galaxy—but just how many neighbors are out there? In 2009, NASA launched a space-traveling observatory to find out. Now, the agency is announcing the craft’s newest sighting: 104 planets outside of our solar system.
In a release, NASA writes that scientists have confirmed the exoplanets after analyzing 197 candidates spotted by the craft. That brings Kepler’s total planet-finding count to a whopping 2453.
Like Johannes Kepler, the 17th-century astronomer after whom the craft is named, the observatory's purpose is to describe the planets of the universe. The mission is focused on finding Earth-sized planets that orbit other stars with the goal of figuring out where Earth fits in a larger context. To do so, Kepler points its telescope at far-away stars, then watches as they brighten and dull as their orbiting planets pass in front of them. By measuring these planetary transits, Kepler can both find planets and help scientists learn more about their orbits, temperatures and mass.
Four of the planets Kepler spotted orbit around K2-72, a cool red dwarf star 181 light years away. This star is less than half the size of the sun and much dimmer, writes the agency in the release. Yet the planets rotate around K2-72 in a tight orbit, placing some of them in the star's habitable zone—a region where liquid water can exist. Though the planets themselves are all larger than Earth, two seem to have comparable radiation exposure. And the possibility of life "cannot be ruled out," according to the press release.
It’s been a bumpy road for Kepler, which has experienced a number of close calls and near-misses while in space. But scientists hope the laboratory will reveal even more deep-space finds. In the paper announcing the new planets, researchers write that if the mission continues, “based on current discoveries we would expect a planet yield roughly 4-5 times as great as currently produced.” When it comes to planets, persistence matters—and great discoveries are the best reward.