Apparently, extroverts will have to sit out the initial exploration of Mars:
[E]xtroverts tend to be talkative, but their gregarious nature may make them seem intrusive or demanding of attention in confined and isolated environments over the long term, the researchers say.
"You're talking about a very tiny vehicle, where people are in very isolated, very confined spaces," said study researcher Suzanne Bell, an associate professor of psychology at DePaul University in Chicago. "Extroverts have a little bit of a tough time in that situation."
In one study of a spacecraft simulation, an extroverted team member was ostracized by two other members who were more reserved, Bell said. "They thought he was too brash, and would speak his mind too much, and talk too much," Bell said.
The new findings don't mean that extroverts can't go to Mars. More specific studies are needed to look at how extroverts fare on these teams, and whether certain kinds of training could help prevent problems, Bell said.
Seriously, though. Imagine six people confined in an El car for nine months. Forgetting how Sartrian that situation is on its face, it seems obvious that if there were more introverts than extroverts, the extroverts would be sent to play outside. Reverse the demographics and the introverts would kill themselves.
All right, perhaps it wouldn't be that dire. But one can see the difficulties.