Nasa astronauts Sunita Williams and Butch Wilmore (ANI and AP images)

Nasa astronautsButch Wilmore and Sunita Williamshave finally returned to Earth on Tuesday, marking the end of nine-months extended and unplanned stay in the space.
Their SpaceX capsule successfully splashed down in the Gulf of Mexico off the coast of Tallahassee, Florida, just hours after their departure from the ISS.
According to Dr. Joe Dervay, a Nasa flight surgeon who spoke to CNN, the astronauts were in good health before their return journey.
Research continues into the extended effects of space travel on human health. Data collected over several decades indicates that astronauts undergo physical alterations even during brief space missions, with most changes reversing shortly after Earth return.
“There is some individual variability on how quickly they recover, but it is pretty impressive to see how they will turn the corner and really adapt quickly,” Dervay said. “Oftentimes, if you look at them a couple days later, you really have no idea what they’ve just done for the last several months.”
What physiological changes astronaut experience?
The absence of gravity causes numerous physiological changes in astronauts. Their bone density decreases, muscles deteriorate, and they face issues with motor control, coordination and balance. The absence of gravity impacts their immune system, cardiovascular functions, vision and DNA structure.
Most health effects are temporary, with only a few persistent issues noted. Upon return to Earth, astronauts undergo rehabilitation exercises to restore their bone and muscle strength.
“We don’t see any need for any special precaution,” Dina Contella, deputy manager of Nasa’s International Space Station Program, said Friday. “Like any astronauts coming back, there is an acclimation period, and so that will vary by crew member.”
Without Earth’s gravity, astronauts can lose up to one-third of their muscle fibre size within two weeks. Bone mass reduction can reach 1.5% monthly, comparable to annual bone loss in untreated postmenopausal women. This increases fracture risks and potential early osteoporosis.
In space, astronauts experience a 3% height increase during the initial three to four days of weightlessness. For instance, Astronaut Kate Rubins grew from 5’6″ to 5’7″ in space. Upon returning to Earth, gravity restores their original height.
The absence of gravity affects bodily fluids, which constitute 70% of the human body. Unlike on Earth where fluids settle below the heart, space causes even fluid distribution throughout the body, leading to unusual accumulation patterns.
This fluid redistribution causes what Nasa personnel refer to as “puffy face syndrome” and “chicken legs.” These conditions typically resolve within three days of returning to Earth. The phenomenon increases the risk of spinal issues, with astronauts being 4.3 times more likely to experience disc problems than Earth-bound populations.
Vision changes occur due to Spaceflight Associated Neuro-Ocular Syndrome, causing eye flattening and retinal nerve fibre layer thickening. Dr Michael Harrison from Mayo Clinic explains that approximately 16% of astronauts experience globe flattening post-flight, with varying degrees of vision changes.
Space affects immune function, with altered white blood cell behaviour increasing susceptibility to infections. DNA modifications occur, though studies comparing astronaut Scott Kelly with his twin brother Mark showed these changes normalised upon Earth return.
How astronauts will readjust to gravity?
Prior to their return, Williams and Wilmore increased their fluid intake using salt tablets and water to compensate for losses during space flight, according to Dervay. They utilised compression garments extending from feet to waist to redistribute bodily fluids.
“Every crew that comes back comes through a fluid loading protocol, just to make sure when they get back that their body is conditioned properly,” Steve Stitch, manager Nasa’s commercial crew program, said Friday. “There’s nothing beyond what we’ll normally do.”
Post-landing procedures require astronauts to remain at Johnson Space Center in Houston for several days under medical supervision before receiving clearance to return home.
“Almost every organ system in the body is impacted to some degree – whether it’s the skin, the neurovestibular, the bone, muscle, the immunological system, the cardiovascular system – so we have programs that our human health and Performance team focuses on to try and make sure that we’re covering all those areas,” Dervay said.
Health monitoring continues from training through retirement. Increased space missions provide researchers better insights into long-term effects on human health, crucial for future extended missions to the Moon and Mars.