NASA’s twin study, published in 2019, found that Scott Kelly’s 340‑day stay aboard the International Space Station (ISS) produced lasting changes in his DNA, telomeres, and cognitive skills, while his Earth‑bound broter, Mark, remained unchanged.

Scott Kelly’s 7% Gene Expression Shift Persists Six Months After Return

According to the NASA report, about 7% of Scott’s genes showed altered expression even six months after his return, a change that the study noted had not reverted to preflight levels. The study highlighted 811 immune‑related genes that remained altered, suggesting a permanent molecular imprint of microgravity.

Telomere Lengthening in Space, Shortening on Earth: An Unexpected Pattern

NASA’s findings revealed that Scott’s telomeres lengthened while in orbit but shortened after his return. The report calls this an unexpected pattern with unclear long‑term significance, underscoring the need for further research into cellular aging in space.

Decline in Cognitive Skills: A Common Side Effect of Long‑Duration Flight

The study documented a measurable drop in Scott’s cognitive performance during his stay, a side effect that NASA identifies as common among astronauts. The report stresses that such cognitive changes must be factored into safety protocols for future missions.

Who Will Benefit From New Safety Measures?

The NASA study urges the development of new safety measures to protect astronauts during extended missions. However, the report admits that it is unclear whether these changes are unique to Scott or apply to a broader population of space travelers.

Key Unknowns: Are These Changes Universal?

While the twin experiment provides compelling evidence, the source notes that further studies are needed to determine if the observed genetic and cognitive shifts are specific to Scott or represent a universal response to long‑duration spaceflight. the report also leaves unanswered whether the telomere dynamics observed will have lasting health impacts.