A scoop of sandy soil analyzed by Curiosity's sophisticated chemistry laboratory contained water and a mix of chemicals, but not complex carbon-based molecules considered essential for life.
That the soil was not more hospitable did not surprise mission scientist Paul Mahaffy since radiation from space can destroy any carbon evidence.
"It's not unexpected necessarily," said Mahaffy of NASA's Goddard Space Flight Center, who is in charge of the chemistry experiments. "It's been exposed to the harsh Martian environment."
The latest findings were presented Monday at a meeting of the American Geophysical Union in San Francisco. The mission managed by the NASA Jet Propulsion Laboratory is trying to determine whether conditions on Mars could have been favorable for microbes when the red planet was warmer and wetter.
Hopes for a "Mars-shaking" discovery peaked two weeks ago after mission chief scientist John Grotzinger told National Public Radio: "This data is gonna be one for the history books. It's looking really good."
The Internet lit up with excitement. NASA later clarified that Grotzinger was referring generally to the mission and not a specific result. Days before the science gathering, the space agency sought to contain expectations and issued a statement insisting there'd be no big news.
So what did Curiosity find after baking the soil and analyzing the resulting gases?
Water, sulfur and perchlorate, a highly oxidizing salt that was also detected by one of NASA's previous spacecraft, the Phoenix lander, in the northern Martian latitudes.
"This is typical, ordinary Martian soil," said mission scientist Ralf Gellert of the University of Guelph in Canada.
The rover did detect hints of a simple carbon compound, but scientists don't yet know if it's native to the planet, came from space or hitchhiked from Earth.
Scientists think the best chance of finding complex carbon is at Mount Sharp, a mountain rising three miles from the center of Gale Crater near the Martian equator. Curiosity won't trek there until early next year. Images from space reveal intriguing layers at the base and many think it's the ideal place to search for carbon.
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"The real new science may have to wait until the rover gets to the ancient layered terrain at the base," said University of Arizona senior research scientist Peter Smith, who is not involved in the latest Mars mission.
The Curiosity team has been under pressure to announce a blockbuster find ever since the car-size Curiosity made its dramatic landing in early August using a never-before-tried technique that involved gently being lowered to the ground by cables.
The first month of a two-year mission was dominated by health checkups -- a requirement for every interplanetary spacecraft. Since then, it has been on the move, scooping up soil and hunting for its first rock to drill into.
While Curiosity has beamed back stunning panoramas of its surroundings, its major discovery so far is uncovering the remnants of an ancient streambed. Michael Meyer of NASA headquarters called Curiosity a "CSI laboratory on wheels" that has already revealed a lot about its surroundings.
At $2.5 billion, the Curiosity mission is the most expensive yet to Mars, which has been studied by various, less capable rovers and landers. Curiosity totes around high-tech tools designed to explore the Martian surface in unprecedented detail.
Press; By ALICIA CHANG]
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