Anyone who has read H.G. Wells’ "War of the Worlds" knows the Martian invasion fails because Earth’s microbes attack the non-immune aliens. A recent study shows that Wells, who published the book in 1898, was correct in his science. reports on new study that shows Earth’s bacteria hitching a ride aboard any spacecraft would ultimately die on the Martian surface.

Scientists have long worried that errant bacteria could transfer from a landing spacecraft and contaminate the planet. Bacteria have been known to survive the trip through space, but until recently little was known about how long they could live after landing. Andrew Schuerger is a researcher at the University of Central Florida who recently looked at this issue. He concludes that it is unlikely bacteria could replicate and ultimately survive on Mars. 

As he told, "Without replication, terrestrial microorganisms are very unlikely to contaminate a landing site. Thus, it is unlikely that spacecraft microbes will compromise the search for organics or the search for life on Mars."

The study considered two strains of bacteria, Escherichia coli (E. coli) and Serratia liquefaciens (S. liquefaciens). These bacteria tolerate low-pressure systems and were thought to be able to survive Mars' climate. They re-created Mars in a lab using the planet's soil, atmosphere, pressure, temperature and UV irradiation. S. liquefaciens did not even make it to the Mars Simulation Chamber. But E. coli was so hardy that it was able to survive “Mars” for seven days, though it was not able to replicate.

NASA has a history of preparedness in protecting Mars from Earth’s microbes. NASA's Planetary Protection Program works to prevent cross-contamination. Just how clean a spacecraft needs to be depends on its type — lander or a rover. If a spacecraft is going to touch the planet’s surface, it needs to have fewer than 500,000 cells on it. Scientists point out that a gram of soil contains between 1 million and 100 million viable microbial cells. At present, NASA decrees that fewer than 300,000 viable microbial cells should be present on the entire spacecraft when it launches. Eventually, NASA hopes to develop standards that will render all spacecraft 100 percent microbe free.

But have previous missions to Mars already contaminated the planet? Not likely, says Karen Buxbaum of the Planetary Protection Manager for the Mars Program at NASA's Jet Propulsion Laboratory. As she told, "There's been a certain amount of microbes that may have gotten to the Martian surface … so the short answer is: yes, terrestrial microbes have been on spacecraft that have gone to Mars. But, the rest of the answer is that that was done in compliance with a conservative planetary protection policy intended to protect Mars from potential harmful contamination."

For further reading:

Mars likely to remain free of Earth's microbes
New study looks to see if Earth’s bacteria could survive on the red planet.