On the Cover: Starkly beautiful, Antarctica is the coldest, driest, windiest continent on Earth. Thanks to the Antarctic Treaty, it is also a protected ecozone that supports ongoing scientific research by more than 4,000 scientists from around the world. Here, otherworldly towers of ice appear (about 9 meters, or 30 feet, high) to march up the slopes of Mount Erebus, Antarctica’s only active volcano. Some scientists speculate that geologically active, watery moons such as Europa and Enceladus might also sport features like these. Michael Carroll
6 Wonderfully Habitable Worlds? Franck Marchisexpounds on what we know—and don't know—about the TRAPPIST-1 planetary system.