Long ago, Mars had the conditions and ingredients to support life.

That conclusion—the first ever made about another celestial body—was announced today by the Curiosity rover team after a wildly successful drilling campaign into what may have once been the bed of a Martian lake. (Related: "Mars Rover Curiosity Completes First Full Drill.")

"We have found a habitable environment," said John Grotzinger, project scientist for the Curiosity mission. "The water that was here was so benign and supportive of life that if a human had been on the planet back then, they could drink it."

Their finding is based in part on the discovery of both clays and sulfate minerals in the powered sample drilled out of the rock named after deceased mission project manager John Klein. Both materials only form in water, and only in water that is low in potentially life-killing acids. (Related: "Mars Rover Finds Intriguing New Evidence of Water.")

At a press conference at NASA headquarters in Washington, D.C., the team also announced that simple organics had been detected by the Sample Analysis at Mars (SAM) instrument.

Principal investigator Paul Mahaffy said, however, that it remained unclear if the organics are of purely Martian origin or if they were formed by interactions with organics inadvertently brought from Earth by Curiosity. (Related: "Mars Rover Detects Simple Organic Compounds.")

Jackpot

The low depression where Curiosity has been exploring for several months is called Yellowknife Bay, and Grotzinger and others described it excitedly as a "jackpot" for their mission.

Curiosity will drill another hole in the John Klein rock in May, after communication between Earth and Mars is safely restored following a conjunction—when the sun will come between the two planets.

The head of the NASA Science mission directorate, John Grunsfeld, said at the end of the press conference that he felt "giddy" about the results and the possibility that Curiosity is now drilling in an ancient lakebed.

"This has been a huge science question: Did Mars once have a habitable environment?" Grunsfeld said. "Now we have an answer."

Although the determination of "habitability" is considered a major breakthrough, it does not mean that Mars was necessarily once home to microbes or any other form of life.

But having earlier determined that Mars was once much wetter and warmer, and now that it had the kinds of minerals that are formed only in the kind of water that can support life, the possibility that organisms once existed on the planet is certainly greater.

Gray Is Good

The initial breakthrough came when the Chemical and Mineralogy Instrument (CheMin) detected a type of clay called smectite at the John Klein site, and found it in large concentrations. It is the kind of clay that—on Earth—often forms in still, basic (non-acidic) water.

Not only is the smectite discovery a scientific gold mine because of those qualities, said CheMin principal investigator David Blake, but the mineral is also capable of preserving ancient organic compounds, which are the building blocks of life.

The Curiosity team had grown excited about the drilling results as soon as they saw that the inside of the rock wasn't red, but rather was gray. The red color of Mars is a function of the presence of iron compounds, which are acidic and can destroy traces of organics.

"A gray Mars suggests habitability," Grotzinger said.

Productive Detour

The SAM instrument has also found evidence in the drill sample of life-supporting carbon in the form of carbon dioxide. If the carbon was available to any potential living organisms, that would lend further support for the habitability of ancient Mars. (Related: "Meet One of Mars Rover Curiosity's Earthbound Twins.")

Asked if this period of habitability coincided with the period some 3.8 billion years ago, when life is believed to have begun on Earth, Grotzinger said it appeared to be in the same range.

Mars is cold, dry, and hostile now, and the likelihood of life existing on its surface is considered vanishingly slim. But with its portable chemistry and mineral labs—the first ever to be used on Mars—the rover team is now finding the long-expected evidence of a once warmer and wetter Mars. This was made possible by use of the drill, also a first for a rover on Mars.

But in addition to upcoming delays as a result of the conjunction, Curiosity hasn't been able to conduct any science experiments for almost two weeks due to an "anomaly" in the rover's main onboard computer that caused a shutdown and a switch to a backup computer.

Curiosity troubleshooters have suggested that the computer malfunction may have been the result of a cosmic ray strike. It is because of this delay that the second hole won't be drilled at Yellowknife Bay until May.