Four NASA researchers descended to an undersea research base off the Florida Keys June 11, kicking off a 12-day mission designed to help future astronauts explore near-Earth asteroids.

The researchers entered the Aquarius research station — which sits 19 meters below the water and about 5.6 kilometers off Key Largo — at 12 p.m. EDT, NASA officials said.

Their arrival marked the start of the 16th expedition in the NASA Extreme Environment Mission Operations program, or NEEMO. Because NEEMO missions put participants in a hostile, alien environment, they are good analogs for expeditions to asteroids, planets, moons or other space destinations, officials said.

NEEMO researchers — called aquanauts — can simulate living on a spacecraft and test techniques for space missions. NASA also can weigh down the participants to varying degrees, to simulate different gravity environments.

NEEMO 16 will focus on ways to help future astronauts explore near-Earth asteroids, a key priority for NASA. In 2010, U.S. President Barack Obama instructed the space agency to work toward sending humans to a nearby space rock by 2025. “We’re trying to look out into the future and understand how we’d operate on an asteroid,” NASA astronaut Mike Gernhardt, NEEMO principal investigator, said in a statement. “You don’t want to make a bunch of guesses about what you’ll need and then get to the asteroid to find out it won’t work the way you thought it would. NEEMO helps give us the information we need to make informed decisions now.”

NEEMO 16’s undersea crew consists of astronaut Dottie M. Metcalf-Lindenburger, Japanese spaceflier Kimiya Yui, European Space Agency astronaut Timothy Peake and Cornell University professor Steven Squyres, who is also the lead scientist for NASA’s Spirit and Opportunity Mars rovers.

The crew members’ 12 days of activities will focus on three core areas — dealing with communication delays, figuring out optimum crew sizes and coming up with ways to attach to asteroids (and stay attached to a space vehicle during excursions).

Metcalf-Lindenburger, Yui, Peake and Squyres will stay underwater for the duration of NEEMO 16, which concludes June 22.

Aquarius is the world’s only undersea research station, according to NASA officials. It sits on a sandy patch of seafloor next to coral reefs in the Florida Keys National Marine Sanctuary. Aquarius is owned by the U.S. National Oceanic and Atmospheric Administration and managed by the University of North Carolina at Wilmington.

Aquarius measures 13 by 6 by 5 meters. The research station has six bunks and many of the comforts of home, including a shower, a toilet, hot water, a microwave, a refrigerator, air conditioning and computers with a wireless link to shore.