We’re used to meticulously designed space missions going far beyond their intended end date. But NASA’s Kepler exoplanet hunting satellite began suffering mechanical failures in 2012, right around the end of its original 3.5 year mission. In 2013, NASA began preparation for Kepler’s “K2” mission to extend its planet spotting, though in a more limited capacity. That’s proven sufficient to find many more exoplanets, including 104 newly confirmed planets in the latest round. Among them are four Earth-like rocky planets orbiting a nearby dwarf star.
Kepler uses the transit method for detecting exoplanets orbiting far away stars. This involved observing a star over time, watching for a regular dip in light that indicates a planet passing between the star and the telescope. This obviously requires that the telescope remain very stable, and that was Kepler’s problem. The failed components are called reaction wheels, and they are used to keep the telescope oriented as it swings around the sun. In its K2 phase, Kepler uses the solar wind and its remaining reaction wheels to balance itself for shorter observations at various points in its orbit.
Over Kepler’s life, it has identified nearly 5,000 potential exoplanets, more than 3,200 of which have been verified by ground-based telescopes. The latest batch of 104 exoplanets includes four that are between 20% and 50% larger than Earth (larger exoplanets are easier to detect). That means they’re most likely rocky, and all four are in the same solar system 181 light years away. Two of them are too far away from the systems’ small and cool dwarf star to support life, but two (K2-72c and K2-72e) are believed to be in the habitable zone where liquid water could exist. That means life is a possibility.
K2-72c is the closest to its star with an orbital year of just 15 days. It’s 10% warmer than Earth. Meanwhile, K2-72e is a little farther out with a 24-day year and temperatures about 6% colder than Earth. NASA expects Kepler to continue operating until the middle of 2018. By then, the Transiting Exoplanet Survey Satellite (TESS) is expected to be ready to take over. This satellite is scheduled for launch in late 2017 on a Falcon 9 rocket. It too will use the transit method to search for exoplanets.
NASA expects to use TESS to identify targets for the upcoming James Webb Space Telescope. The Webb telescope will be capable of focusing on individual exoplanets to characterize their atmospheres. This could tell us if they could actually support life as we know it.