May 11, 2019 - One question often asked is whether ... motion – is very minimal. So any age difference between the brothers would only be a few milliseconds....

July 13, 2016 - It really is all relative: Former NASA astronaut Scott Kelly's historic one-year mission aboard the International Space Station (ISS) made his identical twin Mark an even older brother.

July 23, 2024 - Radiation: Without Earth's atmosphere, an astronaut will take on more radiation which will definitely age them. No idea how much though, but it could very easily account for this. Exercise: This is honestly my pick for highest likelihood of the difference. With no gravity, astronauts exert little energy to do regular things, which can make it easy to put on a few pounds. Studies are pretty clear that being lean leads to a longer life. We also don't know from the picture if they looked the same ahead of the trip. Identical twins does not mean identical lifestyles.

August 29, 2016 - Here's something to wrap your head around: when astronaut Scott Kelly went into space and his slightly older twin brother Mark stayed on Earth, the age gap between them increased, thanks to Scott's time in orbit.

July 10, 2025 - The landmark Twins Study brought ten research teams around the country together to observe what physiological, molecular, and cognitive changes could happen to a human from exposure to spaceflight. This was accomplished by comparing retired astronaut Scott Kelly while he was in space, to his identical twin brother, retired astronaut Mark Kelly, who remained on Earth.

April 11, 2019 - Identical twin astronauts, Scott and Mark Kelly, are subjects of NASA’s Twins Study. Scott (right) spent a year in space while Mark (left) stayed on Earth as a control subject. NASA · NASA has big plans for the future of human spaceflight. The space agency’s proposals to send long-term, ...

April 11, 2019 - (Image credit: Courtesy NASA Twins Study) In a famous Einsteinian thought experiment called the twin paradox, a twin who embarked on a whirling flight through space would age more slowly compared to the twin left back home on Earth, a result ...

Reporting in the journal Science, the Twins Study team, which included several NIH-funded researchers, detailed many thousands of differences between the Kelly twins at the molecular, cellular, and physiological levels during the 340-day observation period. However, most of Scott’s measures returned to near pre-flight levels within six months of rejoining Mark on Earth. Over the past nearly 60 years, 559 people have flown in space. While weightless conditions are known to speed various processes associated with aging, few astronauts have remained in space for more than a few months at a time.

Although a year onboard the orbiting space station would produce an age difference of only ~ millisecond (one thousandth of a second), the question of aging associated with long-duration spaceflight, and possible increased risk of developing ...

October 11, 2018 - Scott Kelly is a 53-year-old American astronaut and a veteran of four space flights. He retired last year after spending 11 continuous months on the International Space Station. During his time on board the ISS, he orbited the Earth 5,440 times and made three space walks. He was also part of a study with his identical twin and fellow astronaut, Mark Kelly, to examine the genetic effects of spaceflight.

April 12, 2019 - The full NASA twins study was published Thursday in Science. ... NASA discovered that the telomeres of the Kelly brother who was in space got longer. Telomeres, which are the protective caps on the ends of chromosomes, get shorter as humans age.

April 11, 2019 - ... NASA’s identical-twin astronauts, Scott and Mark Kelly, are back to being nearly identical. That’s the verdict of a study that tracked how Scott’s body changed during a nearly year-long spaceflight in 2015-16, while Mark stayed on Earth.

February 20, 2024 - Expedition 45/46 commander and retired astronaut Scott Kelly (right), along with his twin brother, retired astronaut Mark Kelly (left), speak to media about the Twins Study and one-year mission.

Answer (1 of 9): The twin is space would look younger because he would be younger. It would not be the fact that he is is space, it would be the fact that he was accelerated into space.

On Earth, however, a whopping 30 years have passed between the spaceship’s departure and its return. Just like all other humans on the planet, the twin on Earth has aged by 30 years during that time. Seeing the two (ex?) twins side by side, the difference is striking.

September 3, 2022 - TIL there are twin astronauts, Mark and Scott Kelly, born on February 21 1964. Scott spent 340 days in the International Space Station. During and after Scott's year-long mission, the brothers were studied to find physical differences caused ...

Answer (1 of 9): It is not likely to be a significant difference unless the traveling twin went really, really fast (like half light speed). The “why” is not easily written in just a paragraph or two (it took the genius of an Einstein to figure it out), but I would point out that the “why ...