A tiny but incredibly tough creature called the tardigrade has been identified as the Earth-dweller most likely to hitch a ride to Mars and survive once there—indicating that our methods for sterilizing Mars rovers may not be up to snuff. The millimeter-long creature, also known as the water bear, and a single-celled micro-organism from briny saltwater in Mexico were the only ones to survive 40 days in an environment designed to mirror conditions on Mars, Wired reports. The creatures were exposed to extreme temperatures, soil full of harsh chemicals, and ultraviolet radiation.
Some creatures in the experiment, including bacteria from Siberian permafrost, died off fairly quickly, but scientists believe the tardigrades could have lasted up to 300 days. "We threw a lot of organisms at the experiment,” the lead researcher says. “A lot of studies just focus on one, but we really just threw the kitchen sink at it." The experiment was designed to find a way to prevent alien life from Earth from contaminating Mars and "points out the need for ongoing re-examination and updating of sterilization and detection methods used for planetary protection purposes during cleaning and preparation of spacecraft,” said one of the paper's co-authors. “We are continuing to find microorganisms that surprise us in their hardiness."