An Insider’s Guide to the Galaxy

The Challenges of Life in Outer Space

Mars rover on the surface of Mars


This illustration depicts NASA’s Perseverance rover operating on the surface of Mars. Perseverance, which at the Red Planet’s Jezero Crater on February 18, 2021, will search for signs of life and test technologies that may help determine whether humans could one day inhabit the planet

Seeking signs of ancient life, NASA’s Perseverance rover (nicknamed “Percy”) landed on Mars on February 18th, 2021. Percy joins Curiosity, Spirit, Opportunity, and Sojourner as America’s fifth rover to explore Mars. When might humans be able to visit the red planet? The answer is complicated, as Mark Shelhamer and Christopher Wanjek explained in their virtual Demystifying Medicine lecture on February 23rd.

Shelhamer, a professor of otolaryngology at Johns Hopkins School of Medicine (Baltimore) and former chief scientist of the Human Research Program at NASA, is studying sensorimotor physiology, with an emphasis on vestibular and oculomotor systems, and how astronauts adapt to space flight and living in space. In particular he is interested in how weightlessness affects vision and balance.

Wanjek, a health and science journalist who writes regularly about astronomy and previously worked at NASA, described the psychological and physical challenges of traveling in space and settling on another planet.

A major risk of living in space or on another planet is having to survive without relying on Earth. Earth is more than 140 million miles—and seven months of space travel—away from Mars. If an emergency occurred on a mission to Mars or another planet, such as running out of supplies or having a medical crisis, the crew would be out of luck.

To illustrate that point, Shelhamer described a medical emergency that occurred on the International Space Station (ISS) a couple of years ago: An unidentified astronaut had a blood clot in their neck. Although there was no established method for treating them in a microgravity environment, the ISS did have a small supply of blood thinners on board. A doctor on Earth advised NASA how to ration the medication until the next cargo mission could bring more medication to the ISS. The astronaut was treated successfully and survived. What if the same dilemma arose on a trip to Mars, or on Mars itself? Earth wouldn’t be able resupply the mission as easily.

liveable modules on the surface of Mars


This artist’s concept depicts astronauts and human habitats on Mars. NASA’s Mars 2020 rover will carry a number of technologies that could make Mars safer and easier to explore for humans.

Both Wanjek and Shelhamer described other health issues associated with living in a near-zero-gravity environment including reduced bone density and muscle tone, and a shift of fluids upward that increases volume and pressure in the head. For example, Shelhamer explained, vision is affected as the eyes become slightly flattened and the retina swells. What’s more, our brains use gravity as a constant frame of reference to inform its sense of balance. The brain loses this reference after a person spends a long time in space or on the ISS, so astronauts have a very poor sense of balance when they return to Earth. Both issues are temporary, but could be detrimental when landing in a new environment such as Mars. If you can’t see or move very well, avoiding dangerous situations would be difficult.

Space travel can also affect mental health. Astronauts on the ISS, Shelhamer pointed out, reported increased stress during a six-month study conducted by researchers at the University of Pennsylvania (Philadelphia). Even though some astronauts may “thrive on [stress], it still may be impacting them physiologically,” said Shelhamer. There may be “alternations in immune system function and cardiovascular function.” That stress, along with other perils, such as radiation exposure, can be dangerous. “The thing that really [keeps] me up at night is the thing we haven’t thought of,” said Shelhamer. “It’s the funny combination of things that happen that we have no way of predicting.”

Shelhamer believes that a broad integrative approach that assesses medical, physiological, and psychological issues is a good way to maintain physiological and psychological fitness for long-duration space flights and life in outer space.

When humans have made it to Mars safely, what other hazards may await? The sun poses far more risk on Mars than on Earth, the speakers said. Earth’s atmosphere is thick enough that sunscreen is sufficient protection against the sun’s harmful rays. With the thinner Martian atmosphere, a little sunbathing would expose humans to life-threatening amounts of radiation. What’s more, the Martian soil contains perchlorates, chemicals poisonous to humans. You certainly wouldn’t want to grow potatoes in that soil as Matt Damon’s character in the movie The Martian did.

Mars may have a hostile environment, but some workarounds are possible, Wanjek explained. For instance, we could live in caves for radiation protection and use aquaponics with light-emitting diodes to grow plants and raise fish.

Still, we have much to learn about what it would take to be sure people could safely live on another planet. What would be the long-term effects of living in a microgravity environment? Could humans give birth to and raise healthy children in a space colony? Can Mars sustain a natural human settlement?

illustration of a structure for a space colony


Space colonies: Artist’s rendering of a cutaway view of NASA’s proposed Stanford torus design. This space habitat would be capable of housing 10,000 to 140,000 people; have a comfortable, artificial climate; would rotate to produce artificial gravity; and have a system of mirrors that would provide sunlight and solar energy.

Wanjek concluded his talk by raising an alternative possibility of living above planets—”in orbiting spheres [with] artificial climate with climate control with perfect gravity”—and visiting planets from there. He displayed a concept image showing modern architecture surrounded by lush trees. “I mean, look at this one; it has patio furniture,” he said, “Wouldn’t you want to live here [rather] than in some ice-fishing hut on Europa?”

To view the videocast of the February 23, 2021, Demystifying Medicine lecture “Biomedical Challenges in Space,” go to For Demystifying Medicine’s full schedule and links to past lectures, go to

megan kalomiris

Megan Kalomiris, a postbaccalaureate fellow in the Laboratory of Infectious Diseases in the National Institute of Allergy and Infectious Diseases, studies noroviruses. After completing her NIH training in 2021, she will be attending the Science Communications Master’s Program at the University of California at Santa Cruz (Santa Cruz, California). In her spare time, she enjoys taking walks in the woods and playing games (now, virtually) with her friends.