An 'aquanaut' admires the fish off the coast of Florida, USA. The 21st NASA Extreme Environment Mission Operations, or NEEMO, sortie enacted a mission to Mars to test equipment for astronauts. The six aquanauts spent 16 days 20 m underwater in their habitat and performed ‘waterwalks’ – by adjusting their buoyancy, aquanauts can simulate Mars gravity.
It takes over 16 hours to decompress and return to the surface – when the mission ended the crew Tweeted: "So long and thanks for all the fish!"