Astronaut twin Scott Kelly begins #YearInSpace: Why that long?

American astronaut and twin Scott Kelly is now aboard the International Space Station, beginning his one-year mission in space. How will this year affect him and his twin brother, and what will the implications be for future missions?

It’s official: The first American to spend a #YearInSpace has arrived.

Astronaut Scott Kelly joined two Russian cosmonauts on Friday in a rocket bound for the International Space Station. They left Kaikonur Cosmodrome in Kazakhstan at 3:42 p.m. ET, and arrived at 9:36 p.m., taking less than six hours. Yes, it takes less time to fly to the International Space Station than it normally does to fly from New York to London.

Kelly will stay at the International Space Station (ISS) until March 2016, along with Russian cosmonaut Mikhail Kornienko, who will be the fifth Russian to spend a year in space. The other cosmonaut, Gennady Padalka, will spend about six months at the station.

What is the purpose in having humans spend a year in space?

One of the main reasons space missions are opting for longer periods of time in orbit is to study the effects space has on the human body. Living in tight quarters in a different gravitational environment could have implications over a period of time. Discovering and addressing these effects may give astronauts the answers needed to prepare for longer space expeditions, such as a manned mission to Mars that could last as long as three years.

“This is an important step forward to start utilizing ISS more effectively in preparation for human missions to Mars,” Chris Carberry, executive director of Explore Mars, told FoxNews.com.  “We look forward to more ambitious missions at ISS and beyond that help achieve human landings on Mars in the 2030s.”

Ambitions to travel to – or even colonize – Mars have been on the rise in recent years. In February, Netherlands-based nonprofit Mars One narrowed its 100,000 applicants for a one-way trip to Mars down to 100. The finalists will spend the next decade training and learning how to work efficiently as a team. The final pool will be narrowed to 24 people, who will break into four groups of six to be launched every two years, starting in 2025. If they make the trip, there are no plans for them to return.

This private venture mission is an indication of the widespread curiosity in a mission to start colonization elsewhere in the solar system – and that a large number of individuals want to space travel even if it means they'll never return to earth. However, there are many flaws with the Mars One plan, including funding and the ability to even colonize Mars, a planet that has yet to have a manned expedition.

And without spending long periods in space, it is difficult to know the possible side effects of a three-year Mars trip, and how they can be prevented.

Kelly may be one of the best choices for someone to spend a year in space to study the effects on the body. Not only is he a decorated space explorer – he is a veteran of three space flights and has logged over 180 days in space – but he also has an identical twin brother, former astronaut Mark Kelly, who will remain on earth and serve as a baseline to study the effects.

Comparing the brothers may be more public relations than new science, since Scott has spent significantly more time in space than Mark, therefore already providing a comparison. But still, Mark’s blood samples, exercise, and overall physical status will be monitored alongside of Scott’s with the hope of gaining insight into the impact of space on the body.

Scott will leave behind his two daughters, ages 20 and 11, his girlfriend, and family to partake in this mission. Mark, who travelled to central Asia to witness his brother’s departure, said that what Scott is doing is invaluable.

“This mission will push the limits of what Americans can do in space,” Mark Kelly said, reported USA Today. “I hope it will advance our understanding of what happens when people leave the planet for a long time and help pave the way for sending Americans beyond low-earth orbit.”