Last week, on June 14, National Science Foundation (NSF) officials announced that Canadian pilots would embark on a daring rescue mission to the South Pole’s isolated Amundsen-Scott research station. There, they planned to evacuate two sick scientists in the middle of an Antarctic winter. Despite the dangerous odds, CBS News reports, the trip was a success: The ailing researchers, both U.S. contractors with Lockheed Martin, have safely arrived at a clinic in southern Chile.

Due to privacy reasons, nobody knew who the contractors were, or why they needed medical attention. According to CBS News, a hospital nurse said that one of them is a man who suffered a heart attack, and the other is a woman with complicated gastric problems. As of 10:30 a.m. on Thursday, July 23, NSF officials and other media outlets hadn’t verified these reports.

The entire rescue mission took place in several stages. Two winter-proof bush planes traveled south from Calgary, Canada, on Tuesday, June 14. One of them landed at the British research station Rothera on Adelaide Island, where they laid in wait to perform any necessary search-and-rescue operations. The second plane flew 1500 miles to the Amundsen-Scott research station, where they safely landed on Tuesday, June 21, amid total darkness and wind chill surpassing 100 degrees below 0.

After a 10-hour layover to let the pilots rest, the sick researchers were transported some 1500 miles to the Rothera Research Station. They finally researched their midway destination during the afternoon of Wednesday, June 22, and boarded another plane that took them another 1000 miles away to Punta Arenas, Chile. They arrived safely last night, on June 22.

This is only the third rescue mission that has occurred in the Amundsen-Scott station’s six-decade history. Due to the region’s black skies and sub-zero temperatures, it’s nearly impossible for planes to fly in and out of the Amundsen-Scott research station during the winter. Typically, no flights take place between February and October, and people have to wait until it’s summer in Antarctica to safely leave the region via aircraft.

There are medical personnel on site at the Amundsen-Scott station, but in a few rare instances people have gotten so sick that they required further treatment at a mainland hospital. In 2001, a physician named Ron Shemenski had pancreatitis and was airlifted from the Amundsen-Scott station. And in 2003, an environmental health and safety officer named Barry McCue developed a gallbladder infection and needed to be evacuated from the premises. However, these individuals are exceptions to the rule: Other people who have had strokes or cancer have stayed at the research station for months until a scheduled cargo plane safely arrived.

[h/t CBS News]