How long it could take stranded NASA astronauts to recover now they've returned back to Earth

The two astronauts who were stranded in space have finally returned to Earth, but now, they have to overcome the many health risks they face.

On Tuesday (March 18), SpaceX Crew Dragon essentially rescued NASA astronauts Barry 'Butch' Wilmore and Sunita 'Suni' Williams and brought them back to Earth from the International Space Station.

The pair were only meant to be on the station for just over a week, but their stay ended up being extended to 9 months.

The pair were 'stranded' in space, as the Boeing vessel intended to bring them home was determined not safe enough to carry them.

But while Williams and Wilmore may be happy to be back on solid ground, with gravity and all the other pleasures of home, they aren’t exactly out of the woods yet. Being in space for such a long period of time takes quite a toll on the body and the pair will now have to undergo significant rehab to get themselves up and running.

The crew are expected to undergo a program that could last up to 45 days.

Pulmonologist and Air Force veteran Vinay Gupta spoke to the Mail Online and revealed what is the point of it all.

Astronauts bracing as they land on planet Earth from the ISS (NASA)

He said as well as regaining strength, the two astronauts will have to have a good exercise regime and nutritional plan. The first steps are expected to focus on walking, flexibility, and muscle strengthening.

But why do they need it in the first place?

Well, as well as being infinitely vast, space isn’t exactly hospitable to the human body, even if you are in a state-of-the-art space station.

Astronauts can start to lose bone density as quickly as a month after being in space, and they're also likely to lose muscle mass.

As well as this, the human body is mostly liquid, and tends to shift downwards due to gravity, but in zero gravity, these fluids move up the body.

The pair now have a lengthy rehab program ahead of them (MIGUEL J. RODRIGUEZ CARRILLO/AFP via Getty Images)

They can also lose basic motor skills, and both Butch and Suni will be unable to walk on their own for a long time due to being in low gravity for so long.

And to top it all off, a lack of gravity can also negatively impact the body's ability to run the immune and cardiovascular system as efficiently.

So, while it is probably great to be back, the astronauts won't quite be going back to their normal lives before they left for space just yet.