Sex and romantic entanglements among astronauts could derail missions to Mars and should therefore be studied by NASA, warns a top-level panel of US researchers.

NASA plans to return astronauts to the Moon by 2018 and later on to Mars. But a round-trip mission to the Red Planet would probably last at least 30 months and carry six to eight people. That would be a hotbed for intense crew relationships, says a report by the US National Academy of Sciences (NAS).

"With the prospect of a very long-term mission, it's hard to ignore the question of sexuality," says Lawrence Palinkas, a medical anthropologist at the University of Southern California in Los Angeles....