Butch Wilmore and Suni William have been stuck in the orbiting lab of the International Space Station for nine months.

A Space X capsule yesterday delivered a crew of four astronauts to the ISS in a crew-swap mission which means Butch and Suni will finally return to Earth. 

Australian National University Astrophysicist Brad Tucker told Sofie Formica on 4BC Breakfast, "It's something like six months in space, the equivalent of 20 years worth of bone density loss."

"They will come back down, not with bones of a late 40, early 50 year old, but of a bones of a 70 year old and that doesn't really go back," Mr. Tucker said.

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