text: View Images NASA's Curiosity rover has delivered some cool findings from its trips across the red planet. 
   
   Photograph courtesy NASA/JPL-Caltech/MSSS 
   
   NASA's Curiosity rover, which has been on Mars for almost a year and a half now, just delivered its largest and most important downlink so far of findings, discoveries, and conclusions. (Also see video: "Mission to Mars.") 
   
   While the six papers released by the journal Science report on different aspects of Mars and do it from different scientific perspectives, together they present the beginnings of a new understanding of the red planet, especially in its early epochs, three to four billion years ago. 
   
   Early Mars, it has become increasingly apparent, was in many important ways similar to Earth. (See also "Did Life on Earth Come From Mars?") 
   
   "If you put together all that we're learning about Gale Crater and Mars, you really begin to chip away the rock and the sculpture inside emerges," said Pan Conrad, an astrobiologist with NASA's Goddard Space Flight Center and a co-author on several of the papers. 
   
   As described in the six Science papers, that hidden but slowly materializing landscape looks something like this: 
   
   1. Early Mars was habitable, perhaps for a long time. 
   
   After concluding that rivers and streams once flowed into Gale Crater, the Curiosity team has now reported that a lake existed there as well. That surface water, as well as groundwater that likely went down hundreds of meters, possessed all that was needed to support microbial life. 
   
   The period when Gale Crater was warmer, wetter, and habitable was broadly between 3.5 and 4 billion or more years ago. That period is when life on Earth is understood to have arisen. 
   
   Was Mars once home to primitive extraterrestrial life? Curiosity can't and won't make that determination, but its discoveries have made the possibility of Martian life significantly more plausible. 
   
   2. Water once flowed on many parts of Mars. 
   
   And that water was there at times and in forms that scientists didn't believe to be possible not long ago. 
   
   One of the major achievements of Curiosity so far has been to "ground-truth" observations made in recent years by the satellites orbiting the planet. Those instruments found strong hints that Mars had a watery past, and at Gale Crater they were found to be on target. 
   
   As a result, the mission has given greater credibility to the view that thousands of additional fossil formations of what appear to be ancient streams, channels, deltas, and lakes likely are just what they appeared to be. 
   
   3. "Follow the carbon" has been vindicated. 
   
   The search for Martian carbon-based organic compounds—one of the major goals of the Curiosity mission—has been and will continue to be complicated and trying. 
   
   While as many as six different organic compounds have been identified so far by the miniature chemistry lab called Sample Analysis at Mars (SAM), their origin remain unclear. 
   
   "There's no doubt that SAM has identified organics, but we can't say with confidence yet that they are Martian in origin," said Douglas Ming of NASA's Johnson Space Center, and author of one of the six Curiosity papers in Science. 
   
   There are at least two sources of the confounding results: The presence on Mars of a chlorine-based compound that, when heated in the SAM oven with any organic material, largely destroys the compounds. And the leak into the SAM ovens of an organic solvent brought to Mars as part of a wet chemistry experiment. 
   
   The search for Martian organics is nonetheless making progress. With each collection of Martian sand or rock, the number of organics found and their concentration has increased—suggesting that different samples of Martian material are leading to different results. If the organics were all contaminants from Earth, those concentrations would likely be more steady. 
   
   "SAM is probably the most complex and important instrument ever brought to another planet," Ming said. "Inevitably, it has taken time to figure out how best to work with it." 
   
   4. Mars gets pounded by radiation. 
   
   Galactic cosmic rays and solar eruptions bombard Mars, and their high-energy particles break the bonds that allow organisms to survive. The Radiation Assessment Detector on Curiosity has made the first measurements ever of radiation on the surface of Mars, and the results are sobering. 
   
   In another Science paper, RAD principal investigator Donald Hassler reports that the radiation would almost certainly be fatal within a few million years to any microbial life on the surface or less than several meters deep. 
   
   The RAD team used as their model the terrestrial bacteria Deinococcus radiodurans, which is capable of withstanding enormous doses of radiation, to make that assessment. 
   
   Notwithstanding the high levels of radiation, Hassler reported that life could theoretically still survive on Mars today under special circumstances. If a bacteria similar to D. radiodurans appeared when early Mars was wetter, warmer, and had a more protective atmosphere, he wrote, it could have survived over the epochs through long periods of dormancy. 
   
   5. Mars radiation also damages normal chemistry. 
   
   Many on the Curiosity team point to radiation damage of all carbon chemistry on Mars as a major reason why it has been so difficult to identify organics on the surface. 
   
   That effort, however, may have gotten a significant boost from one of the most unexpected developments to come out of the mission so far―a method to date how long surfaces have been exposed to the sky on Mars. 
   
   Using measurements of radioactive decay also employed on Earth, Kenneth Farley of the California Institute of Technology reports that the surface of Yellowknife Bay has been exposed for some 80 million years. 
   
   The discovery points to a method for finding places for the rover to drill where there has been less chemistry-damaging radiation exposure. 
   
   Essentially, Farley said, the team has to look for cliffs or overhangs being undercut by the surface wind―as happened in Yellowknife Bay―and where radiation would be blocked by the rocks above. "If we find that kind of formation," he said, "drill there." 
   
   6. Detours sometimes turn out to be interesting. 
   
   The Curiosity rover was scheduled to head for the scientifically alluring Mount Sharp in the center of Gale Crater soon after landing. More than 480 days into the mission, the rover is still months away from its prime destination. 
   
   The detour to Yellowknife Bay is the main reason why, and it has turned out to be a gold mine of data. But now the rover is on what is called the "rapid transit route" to three-mile-high Mount Sharp, driving most of the time and passing many potentially interesting sites. ||||| Mastcam mosaic of the Yellowknife Bay formation. This is a view from the base of an exposed section up through Sheepbed, Gillespie Lake, and basal Glenelg members. Locations of drill holes and Alpha Particle X-Ray Spectrometer (A PXS) measurements are shown. Image released Dec. 9, 2013. 
   
   NASA's Curiosity rover has found evidence of an ancient Martian lake that could have supported life as we know it for long stretches — perhaps millions of years. 
   
   This long and skinny freshwater lake likely existed about 3.7 billion years ago, researchers said, suggesting that habitable environments were present on Mars more recently than previously thought. 
   
   "Quite honestly, it just looks very Earth-like," said Curiosity lead scientist John Grotzinger, of the California Institute of Technology in Pasadena. [Ancient Mars Could Have Supported Life (Photos)] 
   
   "You've got an alluvial fan, which is being fed by streams that originate in mountains, that accumulates a body of water," Grotzinger told SPACE.com. "That probably was not unlike what happened during the last glacial maximum in the Western U.S." 
   
   The lake once covered a small portion of the 96-mile-wide (154 kilometers) Gale Crater, which the 1-ton Curiosity rover has been exploring since touching down on the Red Planet in August 2012. 
   
   
   
   Yes - The Red Planet is teeming with tiny microbes, we just haven't found them yet. 
   
   Yes - An advanced civilization lives below the surface, where we can't detect them. 
   
   No - Life never existed on Mars. 
   
   No - Mars once had life, but those organisms are long dead. 
   
   
   
   The main task of Curiosity's $2.5 billion mission is to determine whether Gale Crater could ever have supported microbial life. The rover team achieved that goal months ago, announcing in March that a spot near Curiosity's landing site called Yellowknife Bay was indeed habitable billions of years ago 
   
   The new results, which are reported today (Dec. 9) in six separate papers in the journal Science, confirm and extend Curiosity's landmark discovery, painting a more complete picture of the Yellowknife Bay area long ago. 
   
   This picture emerged from Curiosity's analysis of fine-grained sedimentary rocks called mudstones, which generally form in calm, still water. The rover obtained powdered samples of these rocks by drilling into Yellowknife Bay outcrops. 
   
   The mudstones contain clay minerals that formed in the sediments of an ancient freshwater lake, researchers said. Curiosity also spotted some of the key chemical ingredients for life in the samples, including sulfur, nitrogen, hydrogen, oxygen, phosphorus and carbon. 
   
   The lake could have potentially supported a class of microbes called chemolithoautotrophs, which obtain energy by breaking down rocks and minerals. Here on Earth, chemolithoautotrophs are commonly found in habitats beyond the reach of sunlight, such as caves and hydrothermal vents on the ocean floor. 
   
   "It is exciting to think that billions of years ago, ancient microbial life may have existed in the lake's calm waters, converting a rich array of elements into energy," Sanjeev Gupta of Imperial College London, co-author of one of the new papers, said in a statement. 
   
   NASA's Curiosity rover — the centerpiece of NASA's $2.5 billion Mars Science Laboratory (MSL) mission — landed on Mars Aug. 5. How much do you know about Curiosity and its mission? Start the Quiz 0 of 10 questions complete 
   
   A 'Curiosity' Quiz: How Well Do You Know NASA's Newest Mars Rover? NASA's Curiosity rover — the centerpiece of NASA's $2.5 billion Mars Science Laboratory (MSL) mission — landed on Mars Aug. 5. How much do you know about Curiosity and its mission? 0 of questions complete 
   
   The shallow ancient lake may have been about 30 miles long by 3 miles wide (50 by 5 kilometers), Grotzinger said. Based on the thickness of the sedimentary deposits, the research team estimates that the lake existed for at least tens of thousands of years — and perhaps much longer, albeit on a possibly on-and-off basis. 
   
   Taking into account the broader geological context, "you could wind up with an assemblage of rocks that represent streams, lakes and ancient groundwater systems — so for times when the lake might have been dry, the groundwater's still there. This could have gone on for millions or tens of millions of years," Grotzinger said. 
   
   The lack of weathering on Gale Crater's rim suggests that the area was cold when the lake existed, he added, raising the possibility that a layer of ice covered the lake on a permanent or occasional basis. But such conditions wouldn't be much of a deterrent to hardy microbes. 
   
   "These are entirely viable habitable environments for chemolithoautotrophs," Grotzinger said. 
   
   Researchers still don't know if the Gale Crater lake hosted organisms of any kind; Curiosity was not designed to hunt for signs of life on Mars. But if chemolithoautotrophs did indeed dominate the lake, it would put an alien twist on a superficially familiar environment. 
   
   "You can imagine that, if life evolved on Mars and never got beyond the point of chemolithoautotrophy, then in the absence of competition from other types of microbes, these systems might have been dominated by that type of metabolic pathway," Grotzinger said. "And that's an un-Earth-like situation." 
   
   Follow Mike Wall on Twitter @michaeldwall and Google+. Follow us @Spacedotcom, Facebook or Google+. Originally published on SPACE.com.
target: – The Curiosity rover has discovered evidence of an ancient freshwater lake on Mars that was brimming with the key chemicals necessary to support microbial life, and its findings suggest that it could have held that life more recently than we thought—and possibly for millions of years before that. "Quite honestly it just looks very Earth-like," the Curiosity's lead scientist said, according to Space.com. The lake, located in the Gale Crater, would have been about 30 miles long and 3 miles wide. The lake's mudstones—which form in calm, still water—contain traces of sulfur, nitrogen, hydrogen, oxygen, phosphorus, and carbon, meaning it could have supported chemolithoautotrophs, a kind of microbial that obtains energy by breaking down rock minerals. The lake was revealed today amidst a barrage of papers on the Rover's progress. National Geographic breaks down some of the other key take-aways, including one that's less promising for Martian life hunters: Curiosity's first radiation measurements indicate levels that would be fatal, within a few million years, to anything within several meters of the surface. Though the researchers did note that some classes of bacteria might have been able to survive through long periods of hibernation.