Could early life still exist on Mars? Some scientists say that, if life existed, it could have contributed to the Martian climate change that forced it underground in the same way that the “invention” of photosynthesis removed a lot of carbon dioxide (a greenhouse gas) from Earth’s atmosphere and caused a mass extinction.
Most scientists agree that Mars is likely a desolate, lifeless world — or, if they think there might be life, it’s probably simple life that resides deep enough underground to make it difficult for their probes to find. Scientists in the 1970s initially thought that the Viking rovers could have found signs of metabolism, but the readouts — while tantalizingly close — provided no clear evidence of life on Mars.
Now a research team used a simulation of conditions on Mars to describe a new way that early microbes could have survived longer than expected. If the microbes were desiccated, frozen, and adequately shielded from cosmic radiation and charged solar particles, there could still be something for future scientific missions seeking life on Mars to find. ExoMars’ Rosalind Franklin rover and the Mars Life Explorer could find biological remains.
The researchers took an especially close look at a microbe called Deinococcus radiodurans as a proxy for life-forms on Mars, which would have to be extremely radiation-resistant to survive on Mars. Supporters of Mars settlement have proposed covering habs with a few meters of regolith or turning lava tubes into habs to bring radiation down to a tolerable level. However, any microbes that are within range of the future Mars Life Explorer’s two-meter drills will be exposed to more radiation than we get on Earth due to Mars’ weaker protections against radiation.
In fact, researchers found that a microbe similar to Deinococcus radiodurans could have survived if it was buried ten meters underground if it was protected from the elements and their habitat was regularly stirred up and melted by meteorite strikes. They project that Deinococcus radiodurans could have survived for 280 million years under these conditions — likely long enough for a future Mars probe to find biological remains.
Some microbes that adapted to current conditions on Mars could have survived for even longer. As the NASA panel in the below video describes, the Mars Reconnaissance Orbiter did find evidence of intermittent liquid water on Mars — possibly meeting an important condition for life remaining on Mars.
Concerns About Cross-Contamination
The research team did express concern that future crewed exploration missions could contaminate Mars with their own germs. Even with the best decontamination protocols, a healthy human’s body mass contains 1-3% microbes, with most of them residing in the gut.
“Our model organisms serve as proxies for both forward contamination of Mars, as well as backward contamination of Earth, both of which should be avoided,” said lead researcher Dr. Michael J. Daly of the Uniformed Services University of the Health Sciences (USU).
The idea that future explorers could bring alien contaminates back to Earth has been around for nearly as long as crewed spaceflight has. The first few Apollo lunar landing crews had to put up with being in quarantine for a few weeks after they returned to the Moon to make sure they didn’t bring back any dormant germs that could cause a serious pandemic. (Luckily, they didn’t.)
Similar measures will likely be developed to protect Earth from potential contamination from Mars in a sample return mission, crewed or not. These measures would be required by Article IX of the United Nations Outer Space Treaty of 1967. As Ruth Hill described in the below presentation, the space domain has changed in the fifty-five years since the treaty was signed. However, it is still regarded as valid.
In fact, this research team received funding through a Defense Threat Reduction Agency (DTRA) grant to Dr. Michael J. Daly and a National Institutes of Health (NIH) grant to fellow research team member Dr. Brian M. Hoffman. The DTRA is normally focuses on defending against weapons of mass destruction but would naturally be interested in researching potential biothreats.
Despite the concerns, Daly claims that his research increases the chances that scientists can find life on Mars. That way, we’ll know for sure if cross-contamination from Mars to Earth will even be an issue.
“Mars was once similar to Earth, billions of years ago, and if life ever evolved there, it is likely still there,” he said.