NASA's (National Aeronautics and Space Administration/NASA) Mars rover "Perseverance" is collecting and analyzing rock samples on Mars. Astronomers are searching the universe for planets that might have Earth-like atmospheres. We are also listening to radio signals from space, hoping to pick up signals that may be coming from distant planets in the Milky Way.
These complex missions all have a common goal: to find out whether life exists, or has ever existed, beyond Earth.
Humans have been searching for signs of life beyond Earth for decades, but any alien life won't necessarily look like the green aliens in the movie. In fact, astrobiologist and author Dr Michaela Musilova says they are likely microorganisms. She has collaborated on research with NASA and the European Space Agency (ESA; European Space Agency), among others.
However, if we do find microbes in space, could they make us sick? As humans travel farther and farther from Earth, will we in turn be the ones carrying these microbes into space?
Harsh environment
Musilova told the BBC podcast CrowdScience that simple organisms such as bacteria are most likely to survive in the harsh environment of space.
Some bacteria on Earth can survive in space for long periods of time because they can form spores and enter a dormant state that withstands radiation, she said.
She explained: "They form a thick protective shell in the cell, and the DNA is tightly wrapped and protected by special proteins. These proteins act like safety belts in a way."
"They hold the DNA in place because radiation tends to break DNA into tiny pieces."
Some theories suggest that bacterial spores might survive in space for thousands of years, Musilova said. However, she pointed out that these theories are still hypothetical because scientists have not been conducting experiments in this area on the International Space Station for a long time.
from space to earth
An important question that scientists need to answer is whether microbial life that may exist in outer space will be brought back to Earth - that is, "reverse contamination." Could they be harmful to humans?
Expert panels have said in the past that the risk of harm to Earth from samples from the Martian surface is "extremely low." But Musilova said space agencies such as NASA still take the threat "quite seriously."
For example, the currently suspended "Mars Sample Return" project was a joint project between NASA and the European Space Agency that was originally scheduled to bring Mars samples back to Earth for the first time. The authorities have formulated contingency plans for this.
"They do plan to set up special isolation laboratories on Earth where they will first store these samples and test them," Musilova said.
One of the scientists who worked on the project was Silvio Sinibaldi, the planetary protection officer of the European Space Agency.
He noted that researchers consider threats beyond the samples themselves.
"We also looked at some particles that could cross-contaminate the exterior of the spacecraft," Sinibaldi explained. They didn't even want the particles to "get close to the Earth's atmosphere."
Will we pollute space?
But if microbes can survive in space, we must also think about what humans are taking into space. Dr. Kate Rubins, a former NASA astronaut and microbiologist at the University of Pittsburgh, said this.
When humans go to space, they will inevitably bring microorganisms with them. Rubins pointed out that one of the characteristics of microorganisms is their ability to sense their surrounding environment.
"They are very sensitive to factors such as pressure, and the space flight environment and microgravity environment are full of various pressures," she said.
Research has found that some bacteria, when exposed to a microgravity environment, turn on genes related to "virulence," which is their ability to cause disease.
"It's definitely a bit concerning...that they may become slightly more pathogenic," Rubins said.
Some studies have also shown that space flight may have a negative impact on the human immune system.
NASA has observed that some latent viruses, including those related to shingles, appear to reactivate in space under certain circumstances. "It could mean that the immune system is suppressed... and the virus wakes up and becomes active again," Rubins said.
Taking microbes into space could also threaten our own scientific research, Musilova said, because we could contaminate what we wish to study.
"We've been sending different probes to Mars to study whether the environment on Mars was ever suitable for life in the past," she said.
"It is almost certain that some microorganisms have successfully 'hitchhiked' all the way to Mars... If we really find life on Mars one day, we must first confirm that it is not a pollutant from the Earth."
Sinibaldi added that reducing this risk would also prevent us from bringing organisms that might "reproduce" on other planets.
Spacecraft design can play a role in this.
The European Space Agency's ExoMars "Rosalind Franklin" Mars rover is expected to be launched in 2028 and is designed to minimize the risk of contamination.
The European Space Agency said the rover was assembled in an ultra-clean environment. Engineers also used methods such as dry heat microbial reduction, ultraviolet light and gamma rays to minimize the number of bacteria, but they were still unable to completely eliminate them.
"The number of bacterial spores on the entire surface of the rover must not exceed 10,000, which is typically found in an area one-eighth the size of a pinhead," said ExoMars engineer Paul Meacham.
"What we actually achieved was only 10% of this upper limit."
Why is this important?
This article is based on an episode of the BBC World Service program CrowdScience, with additional reporting by Daisy Stephens.
