Discovery
The water on Mars
By Massie Santos Ballon
Philippine Daily Inquirer
First Posted 23:03:00 05/30/2008
AT THE NORTH POLE OF THE PLANET Mars, on top of the Nasa (National Aeronautics and Space Administration) spacecraft Phoenix that landed a week ago, is a mini-DVD awaiting future “and presumably human” explorers of the red planet.
Titled “Visions of Mars,” the silica disc was compiled by the nonprofit organization The Planetary Society and was supposedly designed to last for centuries. It contains messages to Mars settlers or explorers from well-known futurists, Mars-inspired science fiction art and stories in written and audio form and the names of approximately 250,000 people who signed up to have their names sent to the red planet.
While the information stored on that disc waits to be accessed, its carrier is studying Mars’ subsurface ice to see if the frozen water might once have been able to support life.
Phoenix’s mission is part of Nasa’s “Follow the Water” reasoning, which says that since Earth’s species need water to live, water must also be a basic requirement for life on Mars.
Even as the spacecraft gets ready to dig into the frozen soil to collect samples of the ice believed to be just underneath ground level though, a new study suggests that the water on the red planet might have been too salty to support life as we know it.
Geoscientists Nicholas Tosca and Andrew Knoll from Harvard University and Tosca’s former mentor Scott McLennan at the State University of New York-Stony Brook authored the study, which appeared in the May 30 issue of the journal Science.
The researchers based their conclusions on the calculated water activities of rocks collected by the Mars Rover named Opportunity on an area of Mars known as the Meridiani Planum.
Last, best places for life
“Meridiani Planum,” Tosca and his colleagues wrote in their paper, “may have been among the last, best places for life on the early martian surface.” The area has hematite, which suggested there were hot springs in the area once.
Water activity refers to the chemical availability of the liquid for life processes; human bodies can take in freshwater from a river, for example, but not saltwater from the sea. Pure water has a water activity of 1.0, and most of Earth’s organisms thrive in water activity environments above 0.9.
In contrast, the Meridiani waters are estimated to have had water activities in the 0.78-0.86 range. Some parts of Mars, the researchers noted, might have even held liquids up to 100 times saltier than the environments Earth’s halites or high-salt-tolerant organisms called home.
Extreme salinity
“On this basis,” the study authors wrote, “the identification of halite at the martian surface indicates extreme salinity and brines that would not be inhabitable by known terrestrial creatures.”
Does this study mean the Phoenix’s nine-month journey from Florida to Mars and its successful landing on the red planet’s surface was useless? Not necessarily. According to study co-author Knoll, who is also part of the science teams for the Mars Rovers Spirit and Opportunity, the results don’t rule out the possibility that life existed. Instead, the study contradicts the long-held belief that the planet could once support life like Earth does.
“This result suggests quite strongly that even as long as four billion years ago, the surface of Mars would have been challenging for life,” Knoll said in a statement. “No matter how far back we peer into Mars’ history, we may never see a point at which the planet really looked like Earth.”
Mars’ past was so inhospitable to Earth’s organisms that it seems unlikely to change its ways. Long-term human colonies on Mars may therefore only ever exist in science fiction. That’s still not a guarantee, however, that the “Visions of Mars” disc will lie forever unused in its case.
E-mail the author at massie@massie.com.
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