The Past and Present of Mars Look Wetter and Wetter

From salty streaks of flowing water to an ancient system of rivers and lakes, Mars seems more hospitable to life than previously thought

watery Mars
An artist's interpretation of what ancient Mars may have looked like Ittiz via Wikimedia Commons CC-BY-3.0

News that there’s water on Mars doesn't surprise many people anymore. The Red Planet’s surface isn't sopping with the stuff, but it is much wetter than anticipated. 

Now new data from Curiosity adds to the growing evidence, hinting at an ancient system of lakes, deltas, and rivers that endured for 100 to 10,000 years at a time, according to a study published today in the journal Science.

Scientists have long suspected that Gale crater once held a massive watery system, but lacked evidence for long-term lakes. Soon after it landed in Gale crater, NASA’s Mars Curiosity Rover spotted signs that Mars once harbored large ancient lakes and discovered evidence of salty liquids hidden in the soil. Just last month, the news buzzed with NASA's confirmation of flowing Martian water (albeit salty, temporary rivulets). 

The newest hints of Mars’ watery past suggest that a period of transient wetness could have lasted a millennium. That’s enough time to make the signs of water’s passage clear in the sediments lining Gale crater, and long enough to perhaps nurture or sustain life.​

Whether past or present, why do we care about water on Mars? Geologist Marjorie A. Chan explains for Science:

On Earth, it is likely that any and all near-surface waters for the past ~3.5 billion years have been literally “contaminated” with some microbial life. Would Mars have had pure, abiotic waters? The more the geology looks like Earth, the more likely it seems that some life-form(s) could have developed in the Martian waters.  

If there is life on Mars, it may be tricky to find it since Curiosity and Opportunity—the two active NASA rovers on the surface—are prohibited from areas most likely to harbor life. This isn't a mass conspiracy. It's because experts fear Earth bacteria hitching a ride on the rovers could infest the planet. 

“If we’re going to look for life on Mars, it would be really kind of lame to bring Earth life and find that instead,” Catherine A. Conley, NASA’s planetary protection officer tells Kenneth Chang in The New York Times. Her job is to keep Earth microbes from contaminating other planets. Mars is the one that needs protecting, not Earth.

“The environment on Mars…is basically one giant dinner plate for Earth organisms,” she tells Chang. Even the salty streaks of water announced last month might be enough for Earth microbes to live.

The Viking landers sent to Mars in 1976 were meticulously sterilized: First by cleaning until they carried fewer than 300 bacterial spore per square meter and then by a several-day-long "baking," to knock that count down by a factor of 10,000, reports Chang.

Before Curiosity launched, Mars appeared pretty lifeless, so this last baking step was skipped. Yet the ever-accumulating evidence of water on Mars means we may need to rethink how to keep our germs and bacteria to ourselves.

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