The astronauts may be back on Earth, but they still have one more mission, fully regaining their health.

Spending an unexpected nine months in space in zero gravity has inevitably taken a toll on Butch Wilmore and Sonny Williams.

Dr. Thomas Mashburn is a former astronaut and M.D. with three flights into space.

When an astronaut comes back from space, number one, they're instructed don't do anything before we tell you to do it, like don't try to stand up and go run.

You're going to hurt yourself.

He says initially they can't even shower alone.

Hot water being dehydrated can make people pass out.

Jack Fisher is also a former astronaut who knows what the return to planet Earth feels like.

Your flexibility is just awful, so you really need to work on stretching and getting that back.

Butch and Sonny's immune systems are being closely monitored since the return to Earth will expose them to germs.

Another battle, bone and muscle loss.

When you saw them return to Earth yesterday, you must have thought to yourself, well, now their journey here starts, right?

Absolutely.

I went to Burke Rehabilitation Hospital in White Plains, New York, to learn about the exercises Butch and Sonny will almost certainly be doing to get back into shape, beginning with walking on a treadmill while wearing a harness.

It will allow them to more slowly feel the effects of gravity again while they're walking.

Exercising on a half-balance ball is also recommended.

It's a weight-bearing activity, so helping to improve your muscle strength and your bone density.

Butch and Sonny's splashdown made for a breathtaking news event as all the Big 3 broadcast networks and cable news went live.

That joyous welcome home by a pod of dolphins was the icing on the cake.

Wow, we got a cute little pod of dolphins.

It wasn't just one or two.

And Butch's daughter did a happy dance dressed as an astronaut.

She'll be able to give him a hug in the next day or so.