NASA / JPL-Caltech

NASA's Curiosity rover, shown in this artist's conception, is equipped to analyze chemicals on Mars.

Although NASA's Curiosity rover hasn't yet confirmed the detection of organic compounds on Mars, it's already seeing that the Red Planet's soil contains water and more complex chemicals — including signs of an intriguing compound called perchlorate.

The first soil sample analysis from Curiosity's Sample Analysis at Mars lab, or SAM, was the leadoff topic today at the American Geophysical Union's fall meeting in San Francisco. The findings were eagerly awaited because of rumors that the Curiosity team was on the verge of announcing major findings — and although NASA tamped down expectations, the scientists said they were overjoyed with the first round of analysis.

"We really consider this a terrific milestone," Paul Mahaffy, a NASA researcher who is SAM's lead scientist, said at the AGU briefing.

Mahaffy said in a statement issued by NASA's Jet Propulsion Laboratory that "we have no definitive detection of Martian organics at this point, but we will keep looking in the diverse environments of Gale Crater."

Curiosity landed in Gale Crater on Aug. 5, and since then it's been studying Martian rocks, soil and atmosphere with a suite of 10 scientific instruments. Its two-year, $2.5 billion primary mission is aimed at determining whether conditions in the crater were ever conducive for microbial life.

SAM is a key tool for that mission, because it can cook Martian samples in a mini-oven and then analyze the gases that are given off to identify the compounds contained in the sample. Other instruments — including the Chemistry and Mineralogy instrument, or CheMin — were used as well to study the initial soil samples, collected over the past several weeks from a drift of windblown sand and dust called Rocknest.

NASA / JPL-Caltech / MSSS

This Oct. 31 view from Curiosity's Mars Hand Lens Imager, or MAHLI, shows two of the trenches made by the rover's 1.6-inch-wide (4-centimeter-wide) sampling scoop. The dust and sand from a dune known as Rocknest were fed into Curiosity's onboard labs for analysis.

NASA said CheMin found that the composition of the Rocknest samples was similar to that of soil analyzed by other Mars rovers such as Pathfinder, Spirit and Opportunity — about half common volcanic minerals, and half non-crystalline minerals such as glass. SAM identified other ingredients in much lower concentrations, including water molecules that were apparently bound to the grains of sand and dust. Although the water wouldn't be enough to support any sort of life, the concentration was higher than expected.

SAM also identified a type of perchlorate, a compound that includes oxygen and chlorine. Perchlorate, which was also found by NASA's Phoenix Mars Lander in 2008, is considered a toxic substance and used as an ingredient in rocket fuel on Earth. But scientists say the compound could conceivably serve as an energy source for hardy microbes on Mars. Mahaffy said the particular type of compound detected by Curiosity appeared to be calcium perchlorate, but "we have to study that further."

Reactions with other chemicals in SAM's oven formed chlorinated methane compounds, which geologists consider organic chemicals because they contain carbon and hydrogen. Mahaffy said it was most likely that the chlorine came from a perchlorate-like compound in the soil. However, he said it wasn't yet clear whether the tiny amount of carbon in the compounds came from the Martian soil or was actually brought to Mars from Earth by Curiosity itself.

"We have to be very careful to make sure both the carbon and the chlorine are coming from Mars," he told reporters.

Caltech's John Grotzinger, the project scientist for Curiosity's mission, seconded that view. "We just simply don't know if they're indigenous to Mars or not," he said.

Grotzinger said the team would first have to confirm that the constituents of the organic compounds seen by SAM truly came from Mars. If the presence of organics is confirmed, then the scientists would have to look into whether they are merely part of the "background fall of cosmic material" onto the planet, or arose through chemical processes on Mars itself, he said.

It would take a step-by-step process to confirm the presence of truly Martian organic compounds, and reconstruct how those compounds were formed. "Then you have ... to decide whether or not those formation pathways are abiotic, or maybe in the end biologic," Grotzinger said. "So you see there's a complicated decision pathway there, and we have to explore each one systematically."

Grotzinger cautioned that there would be no "hallelujah moment" in the search for organic chemicals on Mars.

A couple of weeks ago, he was quoted as saying that the data set from Curiosity would be "one for the history books." That led to speculation that an earth-shaking discovery could be revealed at the AGU meeting. NASA later said Grotzinger was referring to the two-year mission as a whole, rather than any specific findings to be announced in the near term.

Today, Grotzinger said his original comments were misunderstood.

"What I've learned from this is that you have to be careful about what you say, and even more careful about how you say it." he told reporters. "We're doing science at the speed of science [but] we live in a world that's sort of at the pace of Instagrams. The enthusiasm that we had, that I had, that our whole team has about what's going on here ... I think it was just misunderstood."

Update for 3:05 p.m. ET: After discussing this report with my friends in the newsroom as well as on Twitter, I've turned the headline around to emphasize the detection of chlorinated methane compounds, even though the origin of those compounds has not yet been confirmed. Is that going too far the other way?

More about Mars Curiosity:

• Mars hype teaches science lessons
• Plastic beads on Mars: Rise and fall of a NASA spoof site
• Curiosity captures spooky self-portraits
• Mars rover driving through dried-up riverbed
• More news about Curiosity's mission

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.