How can you prepare to leave Earth's atmosphere? By first exploring below the planet's surface.
Six astronauts from all over the world were sent more than 2,625 feet down into the caves of Sardinia, Italy, this week as part of a training program with the European Space Agency (ESA).
“Caves offer a dark and alien underground environment with many analogies to space,” according to ESA.
The latest class of astronauts to take the cave course include NASA astronauts Jessica Meir and Richard Arnold, ESA astronaut Pedro Duque, Japanese astronaut Aki Hoshide, Chinese astronaut Ye Guangfu, and cosmonaut Sergei Korsakov.
“Not in my wildest dreams did I imagine such a spectacular underworld existed below the surface,” Meir wrote on Twitter.
Even though the caves aren't completely similar to space — there is gravity down there, after all — they do remove the astronauts from their regular environment for five days, giving them opportunities to practice skills (like repelling) they'll need when they're high above Earth.
The purpose of the cave expedition is to immerse the astronauts in a situation where they must trust each other, and get “a better understanding of how they function in a multicultural team and what they are skilled at.” Meir is the first female astronaut to participate in the program, and Hoshide is the first “taikonaut.”