Mark and Scott Kelly are identical twin brothers who are both NASA astronauts. Identical twins have exactly the same genes and very similar bodies. In 2015, Scott Kelly was launched on a record 340 day mission to the International Space Station.

Biomedical researchers studied Scott and his earthbound brother Mark for comparison during and after Scott's mission. The massive studies involved ten research teams and 84 researchers.

NASA needs to understand the physiological effects of long spaceflights because a Mars mission could be three years long.

Scott showed an unexpected change in the structure of his chromosomes; his telomeres got longer in space. Telomeres are regions at the ends of chromosomes that are noted as biomarkers of aging because they generally get progressively shorter with age.

When he returned to Earth, his telomeres rapidly shortened, but then took several months to return to normal. By contrast, Mark's chromosomes remained stable. Researchers also observed changes in the expression of Scott's genes. These mostly returned to normal back on Earth, but a few changes were lasting.

Overall the results highlighted the resiliency of the human body to prolonged exposure to conditions in space, including weightlessness and radiation. But researchers want to understand the changes better before drawing definite conclusions. Although NASA doesn't have any other twin pairs, they plan to send ten more astronauts on one year space station missions to learn more.

Sources and Further Reading

• Garrett-Bakelman, F. E., et al. (2019). The NASA Twins Study: A multidimensional analysis of a year-long human spaceflight. Science. 364 (6436).Â
• Rehm, J. NASA's Twins Study reveals effects of space on Scott Kelly's health. ScienceNews.com, April 11, 2019.