Live coverage: Rosetta’s final hours

Two NASA astronauts and an Italian flight engineer took shelter in the space station’s Russian segment Wednesday as mission control analyzed a possible leak of toxic ammonia coolant aboard the complex. Initial data indicated it was likely a false alarm.

The year ended with a deluge of big news, reminding us of the risks of spaceflight and the thin margins between success and failure on the final frontier. 2014 was also a year of breakthroughs in the exploration of the solar system and the future of human spaceflight.

Nearly six months after NASA’s New Horizons probe zoomed past Pluto, just one quarter of the data stored on board has made its way back to waiting scientists, revealing a surprisingly varied terrain that includes glacial flows and steep mountains of frozen water floating in a “sea” of slush-like nitrogen ice.