Finding those compounds wouldn't prove the existence of life, either, because they can come from other sources. But the appearance of organic molecules would suggest that the environment is good at preserving them.
The release of chlorine and oxygen when the rover heated up soil suggests the presence of a chemical called perchlorate, at a 0.5% level in the soil, Leshin said. This substance can destroy organic carbon in a chemical reaction when the rover heats up soil. And so far, Curiosity has not directly detected organics in the soil.
Potentially the rover could avoid this problem using alternative techniques, which wouldn't heat the soil so much that perchlorates break down.
"Perchlorate is reacting with some organic compound to produce these simple molecules," Grotzinger said. "It leaves us asking the question: Is this from Mars, or is it something we brought with us? And right now we don't know."
Perchlorate in the planet's abundant dust could present a toxicity problem to humans on Mars; on Earth, it's known to cause thyroid problems, Leshin said.
The dust could generally pose a health problem as well -- both physically interfering with respiration and being a chemical hazard. Mars is known to have massive dust storms.
"It's one of the significant concerns to human exploration," Webster said.
Still no methane
Scientists are interested in whether Mars has methane gas, which could be an indicator of the planet's habitability. About 90% to 95% of the methane in Earth's atmosphere is biologically derived, said Sushil Atreya, a University of Michigan researcher and co-investigator for SAM, said in November 2012.
But the rover still has not detected methane gas, as scientists noted in Science earlier in September.
Even if there were methane, nonbiological sources such as volcanic activity can produce it.
It's still possible that methane will turn up in future measurements, however, Webster said.
Where it's going now
Curiosity is about one-fifth of the way to Mount Sharp, its final destination, where it will climb while testing the peak's sedimentary layers that have formed over time. Mount Sharp is 3.4 miles high, and its rock layers represent a series of chapters of the planet's history and the environmental conditions present in various eras.
Along the way, the rover stopped at a location called Waypoint 1, where scientists found a conglomerate rock that would have been found in an ancient stream bed. The rock with the pebbles has strange veins, filled with material that scientists don't quite understand.
"The implication of that is that again we're seeing the involvement of water, and it looks like this water was very widespread across the landing area," Grotzinger said.
It appears that the river would have extended from the rover's landing site all the way to Waypoint 1. The entire area that Curiosity has been driving across would have been covered by a stream bed, at one point or another, in the ancient history of Mars.
Curiosity isn't the only moving human-made object on Mars. The Opportunity rover, which launched in 2004, is still chugging along.
In 2020, NASA plans to send an even more advanced rover to "explore and assess Mars as a potential habitat for life, search for signs of past life, collect carefully selected samples for possible future return to Earth, and demonstrate technology for future human exploration of the Red Planet."
NASA recently announced a competition for proposals of what instruments the 2020 rover could carry.
It, too, may get humans closer to drinking water, and possibly even showering, on Mars.