A bunch of NASA researchers headed by Junji Morokuma just published an article describing how they sent flatworms to the International Space Station for 5 weeks.

Flatworms are cool because if you cut them in half each half will regenerate the missing part. And Morokuma & Co didn’t just send whole flatworms. They sent 15 “pre-amputated” flatworm segments from which they had chopped off both heads and tails. And one of these flatworm segments, when returned to earth, did not regenerate a head and a tail. Instead it grew two heads.

Then they cut both heads off the body again, and the body fragment still re-grew two heads. Whatever changes had been caused by the time in space remained in the organism.

Morokuma’s team also detected “physiological, behavioral, morphological, and microbiological changes” in the flatworms. For example, for unknown reasons the space worms had considerably less tendency to avoid light than the control worms who remained on earth.

Changes in microbiome are particularly fascinating, although they make a much less interesting headline than “double-headed space worm”. If an organism’s microbiome changes after only 5 weeks in space, what might happen to human microbiota in the nine months it will take for colonists to travel to Mars.

Research on the effects of extended periods in space have generally focused on the big things: muscle loss, blood pressure, affects of gravity loss etc. But humans carry 1kg of bacteria in their gut, and there are totally fascinating connections between gut biota and human social behavior (including a controversial association with autism). Humans like to think we have free will, but the more we understand ourselves as a giant cluster of interdependent cells, mitochondria, and bacteria the more we realize we’re fooling ourselves. We’re not human individuals deciding we want to watch Game of Thrones with a friend, we’re a fleshy “brain–gut–microbiome axis” responding to constant chemical signals that affect our social communication.

What if, after all that careful testing of astronauts before and during training, people with quite different behaviors and personalities landed on Mars? Elon Musk has sworn to attempt a Mars colony by 2022, so I guess we’re gonna find out.

I can’t wait.