Scientists have studied how some tiny living things, called microorganisms, can survive in space. These studies have used both laboratory simulations and experiments in space near Earth. In 1960, a Russian satellite carried bacteria such as Escherichia coli, Staphylococcus, and Enterobacter aerogenes into orbit. Since then, many types of microorganisms have been tested in space experiments, as shown in the table below.

Experiments on how microbes adapt to space conditions have produced unexpected results. Sometimes, the microorganisms become weaker, but in other cases, they may become more dangerous by increasing their ability to cause disease.

These microorganisms can be divided into two groups: those that live on humans and those that survive in extreme environments. Studying human-related microbes is important for protecting human health and planning future space missions. Extremophiles, which live in harsh environments on Earth, help scientists understand how life might survive in space. NASA has noted that the average adult has ten times more microbial cells in their body than human cells. These microbes are found nearly everywhere and can form slimy layers called biofilms, even though they are usually invisible.

Extremophiles live in some of the most extreme places on Earth, such as very salty lakes, dry deserts, the deep ocean, acidic areas, cold and dry polar regions, and frozen soil. Their ability to survive in such conditions has led scientists to think that microbes might also survive in space or on other planets. Many experiments focus on whether organisms could live inside rocks (a theory called lithopanspermia) or on Mars, to learn more about the possibility of life there. Because microbes are common and hard to remove from spacecraft, bacterial spores are considered a possible risk for contaminating Mars during robotic missions. Testing how well these microbes can survive in space helps scientists create better ways to clean spacecraft.

Studying microorganisms in space might one day help with ideas like sending microbes to other planets (directed panspermia) or changing the environment of another planet to make it suitable for life (terraforming).