Hitchhikers May Have Thumbed A Ride to Mars

Ronald Crawford (shown above) believes that conditions on Mars may harbor endospores, a type of bacteria that could have been inadvertently transported to the red planet, hitchhiking on previous spacecraft sent from bacteria-rich Earth.
Credit: University of Idaho

A new Mars exploration mission is due to launch this summer, and scientists will be eagerly awaiting results from experiments conducted on the planet’s surface. These results may indicate – at long last – the possibility for life on the Red Planet. But new research published in the BioMed Central Microbiology journal suggests that any life we might discover could have an earthly origin.

According to Ronald Crawford and colleagues from the University of Idaho, conditions on Mars may harbor a form of bacteria known as endospores. These dormant bacteria could have been inadvertently transported to Mars, hitchhiking on previous spacecraft sent from bacteria-rich Earth.

Bacteria form endospores when they find themselves in a jeopardous situation – facing such dangers as extreme temperatures, disinfectants, radiation, or drying. Bacterial endospores can remain in this dormant state for thousands of years, and they can even survive the harsh vacuum of space.

Scientists have suggested that if there is life on Mars, it will be below the surface layer of soil. The soil on Mars is believed to be rich in superoxidizing chemicals that can destroy life, and the surface of the planet is exposed to high levels of damaging UV radiation.

Crawford and his colleagues investigated whether endospores of Bacillus subtilis could survive in a simulated Martian environment. They created an analogy of martian soil by mixing dry sand containing endospores with ferrate. Ferrates are iron-enriched soils, and they are considered to be the strongest of the oxidizing soils that make the surface of Mars self-sterilizing.

To replicate the conditions of the martian surface, the soil was kept under a carbon dioxide atmosphere and cooled to -20 degrees C (-4 F). The soil was exposed to high levels of ultraviolet (UV) light for six weeks. Subsequent analysis of the soil showed that endospores were still alive below a depth of 5 millimeters.

"Many types of bacteria from Earth could survive in dormant form in the martian soil, where even a thin layer of soil over them would protect them from UV."
-Christopher McKay
Credit: Metro Publishing, Inc.

The scientists also exposed their soils to liquid water. Although all the water on Mars appears to be frozen, many scientists have suggested that the ice may have melted during brief episodes in the past. Ferrates are highly reactive in water, where they alter into a less toxic soil. The scientists found that endospores were not killed by ferrate when liquid water also was present.

If life arrived on Mars by traveling on Earth-sent spacecrafts, that could compromise efforts to determine the past and present history of life on Mars. Researchers would not be sure whether any endospores found on Mars were native to the planet, or if they originated from Earth.

"The United Sates and other space faring nations are required by treaty to protect Mars and other non-earthly planetary systems from contamination by earthly microorganisms," the authors write. "(Our work suggests) that environmentally robust endospores, if delivered to Mars on spacecraft, could survive for very extended periods of time in the cold, dry, preserving environment of Mars, despite the presence of strong oxidants in the soil."

Christopher McKay, planetary scientist with the Space Science Division of NASA Ames Research Center, says the experiment results make sense.

"Many types of bacteria from Earth could survive in dormant form in the martian soil, where even a thin layer of soil over them would protect them from UV," says McKay. "At some point in the future we may want to go to Mars and retrieve all the old spacecraft that have landed or crashed there, and clean up the bacterial mess."

What’s Next

The experiment did not duplicate the Martian atmosphere exactly, because the scientists did not have a vacuum chamber. They hope to acquire more sophisticated equipment for future tests.

The Mars 2003 mission, consisting of two identical rovers, will launch in mid-2003 and arrive at Mars in January 2004. The rovers are designed to cover roughly 100 meters each martian day, and they will be equipped with many scientific instruments to gather data. The rovers will help determine if life ever arose on Mars, characterize the planetary climate and geology, and pave the way for future human exploration.

Related Web Pages

Original paper in BMC Microbiology Journal
Mars 2003 Mission