Last week, astronaut Scott Kelly returned to Earth after spending nearly a year in space, temporarily two inches taller due to zero-gravity conditions. But his height was only one way in which the long mission changed him. Dozens of researchers, including Penn’s Mathias Basner, are busy working to evaluate just how Kelly was affected, and the implications for an eventual manned voyage to Mars.

Basner, an associate professor of sleep and chronobiology in psychiatry at the Perelman School of Medicine, has spent his career studying how extreme conditions, such as severe sleep deprivation and noise exposure, influence cognitive performance. Along with David Dinges, chief of Penn Medicine’s  Division of Sleep and Chronobiology, and Ruben Gur, director of Penn Medicine’s Brain Behavior Laboratory, Basner has also studied astronauts for many years.

Kelly’s latest NASA mission, the longest space flight of any American astronaut, presented Basner and colleagues with a unique research opportunity. The fact that Scott Kelly has an identical twin brother, Mark Kelly, who is also an astronaut, is akin to winning the scientific Powerball, Basner says, as all of their experiments have the closest thing to a built-in control.

A few years ago, Basner and colleagues developed a battery of 10 different cognitive tests, designed specifically for high-performing, highly motivated astronauts. Scott Kelly took the tests repeatedly while in space, as did Mark Kelly, who remained on Earth.

Many astronauts, after their arrival in space, have reported feeling a kind of mental dizziness or fuzziness.

“Up to this point, this hasn’t been confirmed with objective measures of cognitive performance,” Basner says.

Among other cognitive domains, the researchers are interested in spatial orientation, which Basner says is very important “because in space you’re floating through a three-dimensional environment.”

The test battery also assesses an astronaut’s ability to recognize and interpret emotions from facial expressions.

“If you’re flying to Mars and can’t read your fellow astronauts’ facial expressions, that could lead to conflicts,” says Basner.

Other tests track risk tolerance around decision-making. “Even a tiny mistake in space could lead to a loss of human life and expensive equipment,” Basner notes.

Now that Kelly has returned, he will be evaluated for at least an additional six months to see how he fares.

The Penn researchers are also collaborating with nine other scientific teams studying other aspects of the astronauts’ health, including looking at changes in gene expression patterns and the microbiome.

As informative as Scott Kelly’s voyage has been, however, Basner notes that there is a long way to go before scientists understand the consequences of a mission to Mars on the human body and mind—a trip that is nearly three times longer than the one Kelly just completed.

“We cannot expect to answer all the questions after this one mission,” Basner says. “But it is a good first step.”