Oleg Kononenko Becomes 0.025 Seconds Younger After 1,110 Days in Space

Q: How much 'younger' is the record-holding astronaut than if he had never left Earth?

The record-holding astronaut, Russian cosmonaut Oleg Kononenko, is a little over **0.025 seconds younger** than he would have been had he stayed on Earth. That difference comes from **time dilation** during his cumulative time in orbit. As of 2026, Kononenko has logged more total time in space than earlier record holders, surpassing Sergei Krikalev’s widely cited **0.02-second** figure. In low Earth orbit, an astronaut’s high speed slows onboard time slightly more than the weaker gravity at ISS altitude speeds it up, producing a net effect in which the astronaut ages more slowly than people on Earth. The effect is real but tiny on a human scale. For ISS-class missions, the net difference is on the order of **tens of microseconds per day**, which adds up over years in orbit to only **hundredths of a second**. So while Kononenko is technically younger because of relativity, the amount is far less than a blink. If the question is instead about the single-mission record holder, **Valeri Polyakov**, who spent **437 days** in space on one continuous mission, he would be younger by only **a few milliseconds** compared with staying on Earth.

Q: Will future Mars colonists actually age at a different rate than we do on Earth?

Yes. Future Mars colonists would age at a slightly different rate than people on Earth, and the best estimate is that they would age very slightly faster. The reason is relativity. Time is affected both by speed and by gravity. On the International Space Station, cosmonauts such as Sergei Krikalev aged a tiny bit less than people on Earth because their very high orbital speed slowed their clocks more than weaker gravity sped them up. That effect added up to about 0.02 seconds over 803 days. For people living on Mars, the balance is different. Mars has weaker gravity than Earth, and under general relativity, clocks in a weaker gravitational field run a little faster. A colonist standing on the Martian surface would therefore experience time passing slightly more quickly than someone at Earth’s surface. Mars’s motion around the Sun and its rotation also matter, but for everyday life on the surface, the gravity difference is the key effect. The change would be real but extremely small—far too small for a person to notice biologically. It would show up only with very precise clocks, much like the tiny relativistic differences already measured for astronauts and satellites. So the practical answer is that Mars settlers would not feel themselves aging differently, but physics says they would. Over long periods, the difference would accumulate, making Mars colonists ever so slightly older than their Earth-bound counterparts after the same shared interval.

1 articles · Updated · spacedaily.com · Jun 23

Kononenko has accumulated more than 1,110 days across five spaceflights, making him about 0.025 seconds younger than people born at the same time as him.
ISS orbital speed of about 7.66 km per second slows an astronaut’s clock, while weaker gravity at roughly 400 km altitude speeds it up; the net effect still leaves astronauts aging about 22 to 23 microseconds less per day.
That cumulative edge has overtaken Sergei Krikalev’s long-cited mark of about 0.02 seconds from 803 days in orbit, though Krikalev remains the figure most associated with the popular example.
The tiny gap is imperceptible in daily life but serves as a human-scale demonstration of relativity, the same physics already verified by atomic clocks, particle experiments and GPS systems.