U.S. astronauts Barry “Butch” Wilmore and Sunita “Suni” Williams splashed down to Earth on Tuesday after more than nine months in space.

But now, they have a new mission: recovery.

Why it matters: Muscle atrophy, bone density loss and even vision changes are expected side effects of long-duration space missions. And while some of the impacts of a layover hundreds of miles above Earth are quickly reversible, others can persist.

Wilmore and Williams splashed down Tuesday evening after undocking from the International Space Station early that morning.

Zoom in: One prominent effect of extended time in microgravity is muscle atrophy or weakening. The longer a space mission is, the more severe such atrophy would be, said Shenhav Shemer, a professor of biology at the Technion — Israel Institute of Technology who researches muscle loss.

Keep reading at axios.com.