What happens to the human body after nine months in space?

After spending nine months aboard the International Space Station (ISS), NASA astronauts Sunita Williams and Butch Wilmore are finally on track for their long-awaited return to Earth. A replacement crew launched on Friday evening, paving the way for the duo’s homecoming after what was initially expected to be a short-term mission.

SpaceX’s Falcon 9 rocket took off from NASA’s Kennedy Space Center at 7:03 pm ET, carrying four astronauts who will take over ISS operations. The incoming crew—NASA’s Anne McClain and Nichole Ayers, Japan’s Takuya Onishi, and Russia’s Kirill Peskov—will spend the next six months aboard the station while Williams and Wilmore prepare to return home.

But what does being in space for such an extended period do to your body?

Does space make you weaker?

After nine months in space—roughly the time required to reach Mars—astronauts experience profound transformations. One of the most noticeable changes is muscle and bone loss.

Without Earth’s gravitational pull, the body sheds bone density at a rate of about 1% per month, increasing the risk of fractures. Muscles, especially in the legs and back, weaken due to lack of use, despite rigorous exercise routines aboard the spacecraft.

Also Read: | Sunita Williams’s nine-month wait in space drags on as SpaceX scrubs return mission

To counteract these effects, astronauts engage in 2.5 hours of daily exercise and rigorous training while aboard the ISS. Their regimen includes squats, deadlifts, rows, and bench presses using a resistive exercise device installed in the station’s designated workout area. In addition, they perform regular treadmill sessions while tethered and use an exercise bike.

To support bone health, they also take dietary supplements.

This image taken from video posted by NASA shows the astronauts speaking during a news conference. (Photo: NASA via AP)

Why do astronauts have puffy faces?

In microgravity, bodily fluids, which are normally pulled downward by gravity, redistribute toward the upper body. This leads to puffy faces, increased intracranial pressure, and vision problems—some astronauts report blurred vision due to changes in the shape of their eyes.

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The cardiovascular system also adapts; the heart slightly shrinks and pumps less efficiently, posing potential risks upon return to Earth’s gravity.

Scientists are exploring ways to artificially induce gravity to prevent these issues, including rotating spacecraft modules to simulate Earth’s pull.

Can space mess with your mind?

Nine months in isolation, confined quarters, and a lack of real-time communication with Earth can take a psychological toll. The brain itself undergoes structural adaptations to compensate for the lack of gravitational orientation, which can affect balance and coordination upon return.

A recent study has pointed out at additional concerns about structural changes in the brain during long-duration space missions. Cavities in the brain, specifically the right lateral and third ventricles—responsible for storing cerebrospinal fluid, supplying nutrients, and removing waste—can expand and may take up to three years to return to their normal size.

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This image provided by NASA shows four astronauts completing a countdown dress rehearsal on March 9, 20295, at NASA’s Kennedy Space Center in Florida, ahead of their planned SpaceX launch. From left, Russia’s Kirill Peskov, NASA’s Nichole Ayers and Anne McClain, and Japan’s Takuta Onishi. (Photo: NASA via AP)

Could a long space mission increase cancer risk?

Beyond microgravity, cosmic radiation is one of the greatest dangers of deep-space travel. Without Earth’s protective magnetic field, astronauts are exposed to higher levels of radiation, increasing the risk of cancer and potential DNA damage.

Long-term effects on human genetics are still being studied, but shielding technologies are a major focus for future missions. Scientists are researching protective materials and even pharmaceutical interventions that could help mitigate radiation exposure.

What happens when astronauts return to Earth?

Long-term space travel also alters the immune system, making astronauts more susceptible to infections. Studies show that immune cells become less effective in microgravity, increasing the risk of illness.

Also Read: | Why Indian-origin astronaut Sunita Williams is stuck in space

Additionally, metabolic changes occur, affecting how the body processes nutrients and stores energy. Some astronauts experience unexpected weight loss or changes in appetite, which could pose challenges for long-duration missions where proper nutrition is essential.

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Returning to Earth after a nine-month journey means a difficult readjustment. Astronauts often experience dizziness, weakness, and difficulty walking due to changes in their vestibular and musculoskeletal systems.

Williams and Wilmore, like others before them, must undergo months of rehabilitation to regain normal function.

(With inputs from BBC)

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