NASA astronauts Suni Williams and Butch Wilmore might have a few symptoms after their ninth-month stay in space, including muscle waste or a mental condition called the "overview effect"Despite their prolonged stay, Williams previously said that she and Wilmore were doing "pretty darn good"The pair are due to splash down in Florida with fellow American astronaut Nick Hague and Roscosmos cosmonaut Aleksandr Gorbunov just before 6 p.m. local time on Tuesday As astronauts Suni Williams and Butch Wilmore prepare to return to Earth after nine months in space, experts are sharing what might happen to their bodies as they enter our atmosphere again. Williams, 59, and Wilmore, 61, have been at the International Space Station since June 2024 after their spacecraft experienced mechanical issues and was eventually sent home without them. The pair started their journey back to Earth at 1:05 a.m. EST on Tuesday, March 18, undocking from the International Space Station "right on time" — four days after a new crew arrived at the ISS. NASA astronaut Nick Hague and Roscosmos cosmonaut Aleksandr Gorbunov — who have been in space since last September — joined Williams and Wilmore on the return flight home. The astronauts, known as SpaceX Crew-9, are expected to splash down shortly before 6 p.m. local time on Tuesday. Although scientists and doctors are still studying what happens to the human body in space, there are already a few known symptoms that astronauts experience when they re-enter Earth's atmosphere. According to the space agency, visitors to space are at higher risk for loss of bone density and strength in the hip and spine because of the lack of gravity. Astronauts can lose up to 1% to 2% of bone density per month, and they are then more at risk of bone fracture and risk of early-onset osteoporosis because of spaceflight. Additionally, the lack of gravity in space causes muscle waste, in areas like the arms, legs and even the heart, according to The Guardian, because it doesn’t have to pump blood against gravity, and has to work much less. Speaking with high schools students over video in January, Williams even shared that she's going to have to relearn how to walk. "I've been up here long enough right now I've been trying to remember what it's like to walk," she told the students. “I haven't walked. I haven't sat down. I haven't laid down. You don't have to. You can just close your eyes and float where you are right here." While NASA said it's rare for astronauts to actually become sick in space, Wilmore and Williams may feel like they've just recovered from a cold, as fluid often builds up in a person's head because the lack of gravity doesn't allow for blood and other fluids to flow as they normally would. Alan Duffy, an astrophysicist at Swinburne University, told The Guardian that the buildup of fluid can result in a loss of smell, "which is probably a good thing, by the way, because it reeks up there," due to the completely closed ecosystem built up on the ISS, undisturbed for 20 years. The pair may struggle to walk, become dizzy easily, and have bad eyesight as the built-up fluid in their head can change the shape of their eyeballs and make their vision worse. Astronauts returning to non-zero gravity also cause some unusual side effects, Duffy told the outlet — including for human skin. Because people in spaceflight are so used to their clothing and hair not touching their skin all the time, they gain an almost "baby-like sensitivity" to touch and can develop rashes just from their clothes touching them. Never miss a story — sign up for PEOPLE's free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer​​, from celebrity news to compelling human interest stories. "In general, the environment in space causes an accelerated model for disease, and what we kind of say is an accelerated model for aging," Dr. Afshin Beheshti, director of the Center for Space Biomedicine at the University of Pittsburgh, told Salon. “But you don’t age faster, it’s just that all of the things associated with aging, like cardiovascular risk or cognitive issues … Everything is kind of sped up in space because of that environment." One of the greatest risks to astronauts is radiation, as rays from Earth’s magnetic field, solar energetic particles from the sun, and finally galactic cosmic rays become much stronger in space without the protective ozone layer to shield humans from harmful rays. According to Salon, this radiation can impact people at the cellular level. The European Space Agency even says that one week of radiation on the ISS is one year's worth of exposure to radiation on Earth (depending on the number of solar flares and other sun phenomena that occur). Brad Tucker, an astrophysicist at Australian National University told The Guardian that Wilmore and Williams might experience a cognitive shift called the "overview effect" — causing some astronauts to report feeling an overwhelming sense of connection to humanity and the Earth after viewing the planet at a distance for so long. “Some people call it a feeling of inspiration. Some people call it feelings of inadequacy in terms of just how big the world is," Tucker says of the condition, adding that adjusting back to civilian life makes the sensation even stranger. "It is a huge transition from living in a very inspiring environment." Despite the health issues that can arise from prolonged spaceflight, Williams and Wilmore have shared that they haven't minded their extra time in orbit. During the astronauts’ recent CNN interview from space, Williams said that she and Wilmore were doing "pretty darn good." "We got food, we got clothes," she told CNN's Anderson Cooper. "We got great crew members up here. Of course, it’s been a longer stay than we expected, but both of us have trained to live and work on the International Space Station and I think we made the most of it."