Space changes you in ways you wouldn’t expect, an extraordinary new study claims. As we reported recently, NASA has been comparing twin brothers Mark and Scott Kelly, the latter of whom spend time on the International Space Station, and they were stunned at the results. A video describing the findings is embedded at the end of this post.

NASA found that space actually alters the process that is responsible for regulating gene expression known as methylation. But just what is methylation, and why is this finding important? It’s because it could have huge implications for future manned missions in space, particularly for the long journey to Mars.

DNA methylation refers to the process by which methyl groups are added to the DNA molecule, which alters the DNA segment’s activity without changing the fundamental sequence itself. It works by taking a single carbon and three hydrogens and then applying it to your body’s functions, and it is instrumental in everything from thinking to repairing DNA to fighting off inspections. Problems with methylation can lead to tons of diseases, so this discovery is critical for scientists hoping to pave the way for a future mission to Mars.