Long-duration spaceflight does weird things to the human body, even at the molecular level, but so far there’s no reason to think humans couldn’t survive a two-and-a-half-year round-trip journey to Mars. That was the bottom-line message Friday from a NASA official and two scientists as they revealed more results from the agency’s “Twins Study,” which examined physiological changes in astronaut Scott Kelly during his nearly year-long sojourn in space while his twin brother, Mark Kelly, stayed on Earth.