That's a long way to go without having the right sort of shower. A Martian selfie: NASA's Curiosity rover in the Gale crater on Mars. Credit:NASA "All of our spacecraft carry microbes from Earth," Swinburne University astronomer, Alan Duffy, told Fairfax Media. "We try our best to sterilise them by putting them in an ultraviolet tanning salon - but a very intense one." When preparing spacecraft for Mars missions, scientists have to get the balance right between this sterilisation and protecting the delicate electronics on board.

"In order to be completely sterile, they'd have to use really powerful ionising radiation or heat, both of which would damage the electronics," UNSW astrobiologist Malcolm Walter told Fairfax Media. "So they go as far as they dare." A photo from NASA's Mars Reconnaissance Orbiter shows the dark, narrow streaks on the surface of Mars. Credit:NASA/JPL On Tuesday NASA announced that dark, narrow gullies on the Martian surface contain water-bearing salts that formed from flowing water flowing during warmer periods. While it wasn't part of the study published in Nature Geoscience on Tuesday, very similar slope activity has been identified about 50 kilometres from the Mars Curiosity rover. The 'recurring slope lineae' emanating out of the walls of Garni crater on Mars. NASA says the dark streaks are evidence of flowing, briny liquid water. Credit:NASA/JPL

Dr Zurek said: "There are no confirmed brine flows (RSL) near Curiosity nor Opportunity [rovers]. There are in Gale crater some interesting slope streaks but they are several km away from the Curiosity's present path." The Curiosity rover has been exploring the Gale crater on Mars since it landed three years ago. Dr Zurek's revelation that the Mars Curiosity rover might be contaminated with Earth-origin microbes caused a flurry of questions on the Reddit AMA. "If the rovers haven't been properly sterilised already, will this throw doubt upon any possible future discovery of Mars-based microbes? Wouldn't detractors be able to claim that they are microbes that somehow survived from Earth?" asked one participant. Dr Zurek's response should satisfy most, except the most ardent conspiracy theorists: "The rovers have been sterilised for their particular landing sites where there's been no evidence of present day liquid water. To go to the RSL [sites] rovers will be required to be sterilised to a higher level. We also take samples of microbes that might be on the spacecraft before they're launched, so we can compare with any future discoveries."

Two other problems mean Curiosity can't go taste the water to test for life. The slopes are too steep and, anyway, there are no DNA sequencers on board. "These features are on steep slopes, so our present rovers would not be able to climb up to them," Dr Zurek told Reddit. He also said: "The Curiosity rover does not have life-detection instruments." The next generation of NASA's Mars rovers are due to be sent to the red planet in 2020. New Scientist reported that some astrobiologists have criticised NASA for not including DNA sequencers and other life-detecting instruments in its plans for these planetary explorers. Professor Malcolm Walter is the founding director of the Australian Centre of Astrobiology at the University of NSW. He told Fairfax Media that it's too late to modify the 2020 missions to take into account Tuesday's announcement. But he said of the discovered water locations: "They'd have to be high-priority sites now."

The European Space Agency's ExoMars mission in 2018 will launch a Mars rover with an organic molecule analyser to continue the hunt for life on Mars.