How living in outer space changes the human body

By Kate The Chemist,

Published November 20, 2024 at 4:00 AM CST

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Gravity is the universe’s most important fundamental force. It dominates every moment of our existence on this planet, and yet we really don’t appreciate gravity as much as we should.

NASA astronaut Kate Rubins, though, knows that “life is hard without gravity.” After all, she’s spent 300 days on the International Space Station (ISS) conducting hundreds of science experiments in microgravity.

What is the difference between microgravity and gravity?

Gravity is the force that pulls everything toward the center of our planet (or any other large body of mass). It was discovered thanks to the work of Isaac Newton and his laws of motion and universal gravitation.

Microbiologist and NASA astronaut Kate Rubins has spent 300 days in space experiencing microgravity.

People tend to think astronauts experience “zero gravity” while orbiting the planet, but that's not true. There is in fact still gravity at work, which is why NASA prefers the word "microgravity" to describe the environment in space.

“So zero gravity means no gravity whatsoever,” Rubins says. “And there are small, they're very small, but there are measurable, gravitational effects on the space station.”

We don’t know how much a human body can handle in microgravity

Russian cosmonaut Oleg Kononenko currently holds the record for the most time spent in space: 1,111 days, or over three years, of his life without gravity. He accomplished this by participating in five different stays on the ISS.

NASA Astronaut Kate Rubins was the first person to sequence DNA in space.

Kononenko is basically donating his living body to science, because living without gravity really messes up your systems.

“There's a lot of things that we're still learning about humans in space. You know, our bodies have evolved with this constant downward force,” says Rubins.

Rubins was the first person to sequence DNA in space. She also championed the Cardinal Heart Experiment, a study that investigated what happened to engineered human heart tissue when it underwent changes in gravitational force.

One of the things Rubins and her team learned is that space affects our blood flow! She found that astronauts either have stagnant, or sometimes even reversed, blood flow.

Expedition 64 NASA astronaut Kate Rubins is helped out of the Soyuz MS-17 spacecraft just minutes after she, and Roscosmos cosmonauts Sergey Kud-Sverchkov and Sergey Ryzhikov landed in a remote area near the town of Zhezkazgan, Kazakhstan on Saturday, April 17, 2021. Rubins, Ryzhikov and Kud-Sverchkov returned after 185 days in space having served as Expedition 63-64 crew members onboard the International Space Station. Photo Credit: NASA/Bill Ingalls — Expedition 64 NASA astronaut Kate Rubins is helped out of the Soyuz MS-17 spacecraft just minutes after she, and Roscosmos cosmonauts Sergey Kud-Sverchkov and Sergey Ryzhikov landed in a remote area near the town of Zhezkazgan, Kazakhstan on Saturday, April 17, 2021. Rubins, Ryzhikov and Kud-Sverchkov returned after 185 days in space.

“Our vascular system has evolved all these cool little pumps that start pumping the blood back up and, you know, this maintains your blood pressure and everything,” she says. “But when you take out the downward force side of that equation, the fluid shifts towards your head.”

There’s a name for this phenomenon: “Puffy Face and Bird Legs.” The liquid in astronauts’ legs travels up to their heads, causing their cheeks to swell and their legs to shrink. Rubins says astronauts always have a stuffy nose while they’re in space.

Astronauts are exploring other long term health effects like how microgravity affects bone loss, muscle atrophy, vision, and the immune system.

How could this impact a human’s mission to Mars?

It’s projected it would take an astronaut a minimum of 21 months to journey to the Red Planet and back.

The first nine months are just to travel there, but they then have to wait a few months for the planets’ orbits to sync up before they can even attempt to take the journey back to Earth. Plus, while on Mars, the gravity is 62.5% less than on Earth!

In 2020, NASA announced that Kate Rubins, along with 17 other astronauts, had been selected for their 1st Artemis Team. One of the goals of the Artemis program is to put the first woman and the first person of color on the Moon.

“You’re going to keep losing bone,” Rubins says of that time spent in space. “And so we have to develop countermeasures against that.”

She’s confident that they’ll be able to come up with some solutions to deter the adverse health effects to make Mars travel happen within the next 20 years.

To hear more about Kate Rubins’ lessons from microgravity and about the challenges of conducting science experiments in space, check out the latest episode of Seeking A Scientist.

Additional sources from Seeking A Scientist:

Seeking A Scientist is a production of KCUR Studios. It's made possible with support from the Stowers Institute for Medical Research, where scientists work to accelerate our understanding of human health and disease.

It's hosted by Dr. Kate Biberdorf, AKA Kate the Chemist. Our senior producer is Suzanne Hogan. Our editor is Mackenzie Martin. Our digital editor is Gabe Rosenberg.

This episode was mixed by Suzanne Hogan with support from David McKeel, Byron Love and Genevieve DesMarteau.

Our original theme music is by The Coma Calling. Additional music from Blue Dot Sessions.