Their names are Scott and Mark Kelly, and they are not just brothers, they are identical twins. However, genetics are not the only feature they have in common. They are both astronauts, and it is these two things together that makes them the ideal candidates for an ambitious study to be carried out in the space: the effects of spaceflight on the human body in comparison to Earth-based environments.

In a few days Scott Kelly will arrive at the International Space Station, where he will spend a year. During that period, a group of research teams will study his body, focusing on four areas: physiology, behavioral health, microbiology and molecular health. At the same time, his brother Mark, who is already retired, will be performing the same test, but on Earth.

Ten proposals by 10 institutions in seven states, University of Pennsylvania among them, were selected (out of the 40 that were submitted) to create the "Human Exploration Research Opportunities — Differential Effects on Homozygous Twin Astronauts Associated with Differences in Exposure to Spaceflight Factors” study.

“We realized this is a unique opportunity to perform a class of novel studies because we had one twin flying aboard the International Space Station and one twin on the ground,” says Craig Kundrot, deputy chief scientist of NASA’s Human Research Program. “We can study two individuals who have the same genetics, but are in different environments for one year.¨

Despite the fact that NASA admits this investigation is not expected to provide definitive data about the effects of spaceflight on individuals —they will collect the data from just two people— they see this research as a pilot project. One small, but great, step for science.