Possible Extent of Ancient Lake in Gale Crater, Mars (Pic:NASA/JPL-Caltech/MSSS)
NASA’s Curiosity rover on Mars is producing some extraordinary insights into our planetary neighbor. The latest findings as summed up in six separate papers published by scientists connected with the mission point to two particularly significant possibilities: 1) Early Mars was habitable and 2) Water flowed in many parts of the planet.
“In a little more than a year on the Red Planet, the mobile Mars Science Laboratory has determined the age of a Martian rock, found evidence the planet could have sustained microbial life, taken the first readings of radiation on the surface, and shown how natural erosion could reveal the building blocks of life,” NASA says.
Curiosity has drilled sites in an area of Mars NASA calls Yellowknife Bay. One rock in particular, christened ‘Cumberland’, which has been drilled by the rover is the first rock on another planet to be dated and analyzed for its mineral ingredients. The analysis is indeed telling us a lot. What jumps out at us is the inference that “habitable conditions in the Yellowknife Bay area may have persisted for millions to tens of millions of years.”
“During that time rivers and lakes probably appeared and disappeared. Even when the surface was dry, the subsurface likely was wet, as indicated by mineral veins deposited by underground water into fractures in the rock. The thickness of observed and inferred tiers of rock layers provides the basis for estimating long duration, and the discovery of a mineral energy source for underground microbes favors habitability throughout,” NASA says.
“Yellowknife Bay's clay-rich lakebed habitat offers the key chemical elements for life, plus water not too acidic or salty, and an energy source. The energy source is a type used by many rock-eating microbes on Earth: a mix of sulfur- and iron-containing minerals that are ready acceptors of electrons, and others that are ready electron donors, like the two poles of a battery,” according to NASA.
The idea that early Mars, as in between 3.5 billion to 4 billion years ago, was habitable is indeed an important finding. Whether that habitability led to microbial and even more complex life is debatable, particularly because of the high levels of radiation that Mars is lacerated with both because of extra-solar cosmic rays as well those emanating from our own sun. The Radio Assessment Detector (RAD) on Curiosity reveal high levels of radiation.
The relationship between high radiation and possibility of microbial life has also been explained by NASA. Curiosity’s drill can drill up to two inches in the Martial rocks. At that depth the kind of radiation Mars has been pounded with that possibility would be depleted 1000-fold in about 650 million years, according to NASA. Interestingly though, the Cumberland rock appears to have been exposed to cosmic rays for between 60 and 100 million years, which means that if there ever was organic material in it it can still detected because it would not have been stripped away by radiation yet.
One part of Curiosity’s mandate is to measure radiation levels for possible future human missions to the planet. Between August 2012 and June 2013 the RAD found that the surface at Gale Crater received average radiation of 0.67 millisieverts per day. “For comparison, radiation exposure from a typical chest X-ray is about 0.02 millisievert, “ NASA says. Their calculations show that a total round-trip radiation dose that astronauts would be exposed to would be 1,000 millisieverts, which represents a 5 percent increase in risk of cancer. NASA currently imposes a career limit of 3 percent increase in cancer risk. So this number will be a factor in any future human missions. Incidentally a Sievert is a measurement unit of radiation exposure to biological tissue.
I may be an uncritical admirer of all space missions but once you look at the quality of science that Curiosity is producing you might agree that from any angle it has been an astonishing accomplishment.