Hydrogen. Carbon. Oxygen. Nitrogen. Sulfur. Phosphorus. These elements account for more than 96% of the stuff life on Earth is made from — and all six have been found in a rock sample on Mars.
NASA scientists said Tuesday that the Curiosity rover discovered these basic building blocks of life in the very first rock it has drilled from beneath the Martian surface — along with signs that the Red Planet was once capable of hosting primitive microbes.
"It definitely has all the indications of being a habitable environment at one point in time," Michael Meyer, lead scientist for NASA's Mars Exploration Program, said at a news conference in Washington.
The rover's results are filling in a picture of what increasingly appears to have been a very inviting environment — low acidity, full of water, with signs of chemically complementary compounds.
"We have found a habitable environment that is so benign and is so 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 Grotzinger, lead scientist for the Mars Science Laboratory mission, as Curiosity is officially known.
Grotzinger, a geologist at Caltech, was quick to add that "we're not a life-detection mission." Curiosity's analytical machinery isn't built to find life's metabolic remnants, and its cameras wouldn't be able to resolve an image of a fossil microbe if it were staring the rover in the face, he added.
Still, the findings fired up the imaginations of NASA officials.
"I feel giddy," said John Grunsfeld, a former astronaut who now serves as an administrator for the space agency's Science Mission Directorate. "I have an image now of possibly a lake, a freshwater lake, on a Mars with probably a thicker atmosphere."
The discovery fulfills the primary purpose of Curiosity's mission just seven months after its landing on the Red Planet. It also provides a major coup for the Jet Propulsion Laboratory in La Cañada Flintridge, which is managing the mission.
Among the first hints that Curiosity's first drilled sample would reveal a wealth of information was its color. Rather than rusty red, the powder drilled last month showed up as shades of gray — indicating that the rock underneath, protected from the atmosphere, could still contain vital information about the planet's mineral history.
"If there was organic material present there, it could have been preserved," said David Blake of NASA's Ames Research Center in Moffett Field, the scientist in charge of Curiosity's Chemistry and Mineralogy instrument.
Analysis revealed that the rock was 20% to 30% clay, which forms in the presence of water, Blake said.
That sign of water may sound like no big deal — after all, the Opportunity rover that landed on Mars in 2004 found signs of water in Meridiani Planum.
But water is just part of the picture. Rock from Meridiani had magnesium and iron sulfates, salts that indicated a highly acidic environment.
The sample Curiosity drilled from a rock in Mars' Gale Crater, on the other hand, bore calcium sulfate and halite. Those are signs of a much more neutral environment — and one far more conducive to life.
In addition, the rock, named John Klein in honor of a JPL engineer who died in 2011, lies in a former river system or a lake bed that once held enough water to host life, scientists said.
Meridiani, on the other hand, had so little water that all of the fluids in a hypothetical microbe would have been sucked right out by the salt in the environment (rather like table salt on an unfortunate slug).
In Gale Crater, many of the compounds Curiosity detected — such as sulfates and sulfides, for example — seem to occur in pairs with positive and negative charges, like the two sides of a battery.
"These are the kind of things that tell you that there could have been a flow of electrons in the environment," Grotzinger said, a sign that life's battery was running.
The trove of key elements also serves as validation for Grotzinger and other mission scientists who lobbied for Gale Crater to be the rover's landing site.
In Yellowknife Bay, less than half a mile from where Curiosity touched down, the Mars scientists have already found much of what they were looking to uncover at Mt. Sharp, the 3-mile-high mound in the middle of Gale Crater whose layers may reveal the various chapters of the Red Planet's geologic history.
As the rover makes its way there, it will now take more time to analyze the geological cues it encounters along the way.
"We'll be trying to figure out how the rocks we're at now at Yellowknife Bay relate to Mt. Sharp," Grotzinger said. "That's how we get the relative age of all this stuff."
