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NASA will examine how a year of zero gravity will affect the human body when Scott Kelly blasts off for an extended stay on the International Space Station.

But NASA isnt just going to look at Kelly and fellow astronaut Mikhail Kornienko. The team also will be following Scott Kellys identical twin brother, Mark Kelly, as an earthbound control group.

Officials hope to understand what exactly happens to a human body hundreds of miles above Earth's surface.

We need to figure out how people are going to live in space for really long periods of time, especially if we want to send somebody to Mars or maybe we want to build a base on the moon," Mark Kelly told ABC News' David Kerley.

There are a number of studies being conducted, with collaborations among various universities, including Stanford University, Colorado State University, Johns Hopkins University and Cornell University.

The astronauts will be subject to a battery of tests looking at things such as muscle mass, bone loss and even the shape of their eyeballs. In a previous NASA study, some astronauts reported a change in vision after the physical shape of their eyeballs changed.

NASA medical officer Dr. Steven Gilmore said being able to compare samples between identical twins would be helpful for the research.

You can look at, in detail, how the genes and the proteins that are made from them change as a result of this unique environment," he told ABC News.

Researchers will look at how genes go "on and off" during space flight and if being away from Earth in the vacuum of space affects proteins in the body.

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What NASA Can Learn About Space Health From the Kelly Twins