EXPLAINER

Nine months in space can permanently alter the body, leaving astronauts Sunita Williams and Barry Wilmore with possible long-term health effects.

It was a mission that lasted far longer than planned.

United States astronauts Sunita “Suni” Williams and Barry “Butch” Wilmore went to space on board the Boeing Starliner Calypso on June 5, 2024. They were meant to spend eight days on the International Space Station (ISS).

But as the spacecraft was approaching the station, its thrusters malfunctioned, and NASA ordered them to remain on the ISS while figuring out how to bring them back.

That lasted nine months, or 288 days, making Williams and Wilmore two of the longest-serving NASA astronauts in space on a single mission.

Who has spent the longest time in space?

The ISS orbits at an altitude of 354km (220 miles) while the average distance to Mars from Earth is a staggering 225 million kilometres (140 million miles).

Astronaut Frank Rubio holds the record for NASA’s longest space mission, spending more than a year on the ISS.

The overall record for a single spaceflight belongs to Russian Valeri Polyakov, who spent 437 days on board the Mir space station.

When did the SpaceX Crew-9 mission return to Earth?

The SpaceX Dragon spacecraft with Williams and Wilmore on board splashed down about 5:57pm local time (21:57 GMT) off the coast of Florida, after undocking from the ISS at 05:05 GMT.

On board with Wilmore and Williams was Roscosmos cosmonaut Aleksandr Gorbunov.

NASA provided live coverage of the lead up to the splashdown.

Now back on land, the crew will have to adjust to being back on Earth both physically and mentally.

How does living in space harm the body?

Spending months in microgravity is brutal on the body. Without the Earth’s gravitational pull, muscles shrink, bones weaken and bodily fluids shift.

Astronauts lose muscle mass rapidly because they do not use their legs to support their weight. Their bones become fragile, and they lose 1 percent of their bone mass per month – equivalent to an entire year of ageing on Earth.

Radiation is another major concern. Although the ISS is shielded by Earth’s magnetosphere, astronauts on missions lasting six months or longer receive over ten times the radiation than what’s naturally occurring on Earth. Prolonged exposure is linked to higher cancer risks and potential cognitive decline.

• Body mass and fluids: Astronauts lose about 20 percent of their body fluids and about 5 percent of their body mass while in space.
• Muscle: Microgravity causes muscle atrophy, but exercise for two hours a day, six days a week and supplements can reduce muscle loss.
• Skin: Skin thins, tears easily and heals more slowly in space.
• Eyes: Microgravity impairs vision while radiation increases cataract risk.
• DNA: Most genes reset after returning to Earth, but about 7 percent remain disrupted.
• Psychosomatics and cognition: Radiation may cause brain damage and onset of Alzheimer’s. Space disrupts orientation, causing motion sickness.
• Cardiovascular system: Blood circulation slows down and production of red blood cells decreases. Cardiac arrhythmia is common.
• Immune system: The immune system weakens. Radiation exposure from six months in space equates to 10 times the annual exposure on Earth.
• Bones: Skeletal deformation and bone loss are likely with 1 percent of bone mass lost every month. Astronauts become taller because their spines expand while in orbit.

How does the body recover back on Earth?

Returning to Earth doesn’t immediately undo months of strain on astronauts’ bodies. As their bodies readjust to gravity, they experience balance issues, dizziness and weakened cardiovascular function.

Even months after landing, not everything recovers. They face long-term health risks, including cancer, nerve damage and degenerative diseases.

• Arrival from space: The spine returns to normal size. Flatulence is no longer an issue, and blood pressure normalises.
• One week later: Motion sickness, disorientation and balance issues disappear. Sleep returns to normal.
• Two weeks later: The immune system recovers, and body fluids lost are regained. The production of red blood cells returns to normal.
• One month later: Muscle reformation is almost complete and near pre-flight levels.
• Three months later: Skin redevelopment is complete. Body mass returns to Earth levels, and problems with eyesight no longer exist.
• Six months later: The risk of bone fractures remains as well as an increased risk of cancer. Ninety-three percent of genes return to normal, but 7 percent remain disrupted.