International Space Station faces a squeaky challenge—it's too clean! -

The most isolated place on Earth isn't the depths of Antarctica, but rather, the International Space Station (ISS). It's been home to a few animals and, historically, a cumulative 270 humans. Yet, the ISS is not only one of the most isolated places, but also one of the cleanest. Turns out, this is likely a tribulation in terms of objectives to inhabit Earthly life on other planets. The microbial diversity of the ISS and achieving a delicate balance to address this issue is making headlines around the world. Want to learn more about the issue? Click on. 

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Microbial diversity on the ISS -

A three-dimensional map of the International Space Station’s (ISS) microbial diversity was published in March 2025 in Cell.

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Low-Earth orbit -

The ISS is located in the “near vacuum of low-Earth orbit,” approximately 400 kilometers (248 miles) above Earth.

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Reflects sunlight -

It’s visible from Earth due to its proximity, but also because it reflects sunlight. So it appears as a big white light in the sky.

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Bright white object -

For novice skygazers, it can be confused for the North Star, as the ISS will appear nearly as bright as the moon. Approximately 90% of the Earth’s population can track the ISS by just looking up. It's pictured here flying over Brazil.

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Speed -

The ISS makes its way around the Earth at a speed of 28,000 kilometers per hour (17,500 miles per hour), making 16 rounds around the Earth every day. Here, it transits the sun, as seen from Kuwait. 

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Space widget and app -

Want to know when the ISS will be passing you by? NASA has a space widget and an app to locate its trajectory and make it possible for you to catch sight of it.

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Massive structure -

The ISS consists of a massive structure akin to a six-bedroom home. It is equipped with a gym (its inhabitants work out two hours a day to prevent significant muscle and bone loss), two bathrooms, and a huge window that gives astronauts a 360-degree view.

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Every 90 minutes -

As of February 2025, there are seven people living and working on the structure, taking a quick ride around Earth every hour and a half.

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Home to 270 people and animals -

Over the course of just over 25 years, the ISS has been home to approximately 270 people and a few animal guests, too. But it has also hosted people’s microbes.

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Extreme environment -

A bioengineer at the University of California deems what we all likely agree with: The ISS is certainly an extreme environment.

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Study -

To understand more about astronaut health in space, and therefore, human health in space, a study was conducted to understand more about the ISS’s microbes.

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Swab samples -

Astronauts took about 1,000 sample swabs all over the ISS to help scientists understand more about this. Back on Earth, the data was analyzed and produced a three-dimensional map of the ISS’s microbial diversity.

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ISS is too clean -

What they found was that the ISS is too clean. So why is that a problem? Humans need to interact with bacterial life for the sake of our well-being.

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More microbes -

Therefore, scientists concluded that there needs to be more microbes in space. This revelation offers a serious challenge for Earthly science.

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Skin -

Initial samples were analyzed in 2021. Researchers detected that the majority of the bacteria on the ISS was from human skin.

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Staphylococcus -

The microbial species, called Staphylococcus, dominated the samples that the researchers were able to analyze. This is not unlike our Earthly environments. Humans are constantly shedding skin, therefore, your city office might generate a similar swab.

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Soil and water -

On Earth, we interact with a great deal of bacteria. But the most worrying types of bacteria missing were those that are from Earth’s soil and water.

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Previous study -

In a previous study, swabs taken from homes in a remote Amazonian village were compared with those taken from city homes in Manaus, Brazil.

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Natural environments -

That study argued that the farther we live from natural environments, the amount of microbes in our living spaces decreases.

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Extreme low end -

While the ISS is even more isolated than remote villages, when compared to swabs of a number of isolated, even continuously sterilized locations (such as hospitals), the ISS was “on the extreme low end of microbial diversity.”

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Akin to isolation dorm -

The closest comparison that researchers were able to make between the ISS and an Earthly dwelling is “an isolation dormitory used during COVID-19.”

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Impact -

The impact of low microbial diversity on astronaut health is still unclear, but there is now a theory emerging regarding the immune issues that astronauts sometimes face in-flight.

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Thriving under artificial environments -

The more artificial the environment, whether that’s the ISS or an isolation dormitory amidst a pandemic, it’s clear that humans are not intended to live or thrive in such environments.

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Exposure and evolution -

This is because our own evolutionary process has required a certain level of microbial exposure that our immune systems require to stay resilient.

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Immune system -

Simply put, our immune systems have not evolved to the point where they are able to deal with the absence of microbial diversity.

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Human life outside Earth -

While this issue isn’t so pressing for the astronauts who spend several hundred days in space, as ambitions for humans to inhabit non-Earthly sites continue to grow, this is a major cause for concern.

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Survival -

Will humankind be able to survive in space without the microbial diversity it has evolved to depend on here on Earth? That’s the question that researchers are asking themselves now.

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Antimicrobial resistance -

It seems that for humans to thrive outside of Earth, we’ll need to counter antimicrobial resistance instead of provoking more of it.

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Rich diversity -

This doesn’t mean we need to take harmful bacteria to space, but it does indicate that our environments have a rich diversity of microbes that are important for our health, on and off Earth.

Sources: (NASA) (Scientific American)

See also: Life in orbit: the International Space Station

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