distant

  • An artistic representation of the exoplanet K2-18b. (Alex Boersma/) If you could pack a hot air balloon onto an interstellar spaceship and travel 110 light years to a certain planet orbiting a dim star in the constellation Leo, you’d have an experience not entirely unlike ballooning on Earth. The temperature, pressure, and moist air could feel quite pleasant, though you’d need an oxygen mask—and possibly an umbrella. “It could happen that you get rained upon,” says Björn Benneke, an exoplanet researcher at the University of Montreal. Telescopes hunting for flickering, wobbling stars have located more than 4,000 potential exoplanets in recent decades, some of which orbit in the not-too-cold, not-too-hot zone around their host star where water would have a shot at staying liquid. Others have even been found to harbor actual molecules of H2O. The exoplanet K2-18b, however, is the first to check both boxes, according to two studies published this week. Unfortunately, a few other decidedly unearth-like characteristics make K2018b an improbable home for life as we know it. But the discovery represents an important step toward finding planets we might actually consider hospitable. “It’s the closest we have come to detecting some kind of environment similar to the Earth,” says Benneke, who leads one of the two teams studying the planet. Everything scientists know about this alien world comes from the way it interacts with its star. The Kepler mission first spotted the star’s dimming in 2015, and follow-up observations with the Spitzer space telescope confirmed presence of a planet twice as large as Earth in 2017. A different instrument then weighed the planet by measuring the star’s wobble, finding it to be about eight times heavier than Earth. Another three years of observations with the Hubble Space Telescope managed to capture eight more flickers of light,...