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Several billion years ago, Mars may well have been a pleasant place for tiny microbes to live, with plenty of water as well as minerals that could have served as food, NASA scientists said Tuesday at a news conference on the latest findings from their Mars rover. But they have yet to find signs that actual microbes did live in that oasis.
“We have found a habitable environment that is so benign and supportive of life that probably if this water was around and you had been on the planet, you would have been able to drink it,” said John P. Grotzinger, the California Institute of Technology geology professor who is the principal investigator for the NASA mission.
In drilling into its first rock, a fine-grained mudstone, the scientists said, the rover Curiosity — a self-contained science laboratory about the size of a Mini Cooper — sent back to Earth convincing evidence that Mars was once awash in water.
Plus, the Curiosity scientists identified elements in the rocks — sulfur, nitrogen, hydrogen, oxygen, phosphorus and carbon — that are some of the key ingredients of life, as well as minerals, like sulfates and sulfides, that primitive microbes could eat for food. Dr. Grotzinger said these minerals are “effectively like batteries” and can provide an energy source for life.
This included the presence of clays, one of the main things that scientists were hoping that Curiosity would find on its two-year, $2.5 billion mission. Clays form in waters that have a neutral pH.
“What we have learned in the last 20 years of modern microbiology is that very primitive organisms, they can derive energy just by feeding on rocks,” Dr. Grotzinger said.
Even so, the Curiosity scientists said they had not yet definitively found the carbon building blocks needed to come together to give rise to living organisms. Two earlier NASA rovers, Spirit and Opportunity, also found strong evidence of liquid water on the Martian surface, but in places on the planet that were highly acidic and salty — far harsher for any hypothetical organisms.
About three billion years ago, the conditions on Mars changed. With just one-tenth the mass of Earth, Mars was unable to hold on to most of its atmosphere. The inside of the planet cooled, and the volcanoes stopped erupting. The water froze or evaporated and escaped into space. Mars became cold and dry.
Curiosity landed in August in a 96-mile crater named Gale, gouged long ago by a meteor, and has been roaming in the area since then. The rover’s ultimate destination is a three-mile-high mountain at the center of the crater that caught the eye of scientists because they detected the presence of clays in observations taken by orbiting spacecraft. Now, long before getting to the mountain, scientists have already found the clays, and these rocks would be prime candidates to look for organics.
The scientists and engineers have been taking a deliberate, careful approach to checking the rover’s systems. The last instrument to be tested was the drill, which ground up its first rock a month ago. A bit of the powder was then scooped up and dropped in a sophisticated chemistry laboratory for analysis.
The surface of Mars today is cold, dry and battered by radiation from space. But planetary scientists think young Mars, more than three billion years ago, was a far more hospitable place, with a thicker atmosphere, warmer weather and water flowing at the surface. Some scientists believe that if life ever took hold there, it might persist even today beneath the surface.
Curiosity is not carrying any instruments that can detect Martian life, past or present, but it can identify so-called organic molecules, which contain carbon and hydrogen atoms. The presence of organic molecules would not prove the presence of life, since many nonliving chemical reactions can produce organic molecules. But organic molecules are a necessary prerequisite for life — at least, life as we know it.
So far, the Curiosity scientists cannot say that the rock contained organics, but neither can they rule out the possibility. Rather, since their instruments did measure some simple organics, the researchers are sorting out whether the organics came from the Martian rock, from contamination brought from Earth or were formed in chemical reactions as the rock powder was heated.
Still, the scientists are excited by the possibilities.
“I have an image now of possibly a lake, a fresh water lake, on Mars with a thicker atmosphere,” said John M. Grunsfeld, NASA’s associate administrator for science.
The answers will take a while to discern. Science operations are delayed as engineers work to diagnose and fix what went wrong with the rover’s computer last week when Curiosity failed to send back science data and then failed to go to sleep as scheduled.
Part of the rover’s computer memory had become corrupted, and the engineers switched operations to an identical backup. They are also figuring out whether the corrupted memory may clear up when the computer is restarted or whether the errors are permanent, requiring modification of computer programs to avoid that part of the memory.
In addition, the Sun will be in the way between Mars and Earth for most of April, making communications impossible. Limited science work is expected to resume in a few days, but further drilling of rocks will wait until May.
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