The rocks were said to have been formed over 3.5 billion years ago in this ancient lake when the once abundant water source dried out.
Scientists also discovered that the amount of methane gas in the Martian atmosphere changes with the seasons, although the cause of these fluctuations was not clear. Living things produce numerous organic molecules and therefore, the finding of traces of organic matter on Mars suggests that there are conditions that may allow for the formation of life on the planet.
"This is a very exciting discovery, but we cannot confirm the origin of these molecules yet, it could be a previous life test, but they could also belong to a meteorite or other sources", said a cautious Mahaffy in the same presentation.
For the past six years, "the Curiosity has sifted samples of soil and ground-up rock for signs of organic molecules - the complex carbon chains that on Earth form the building blocks of life", according to Science. Those molecules are still very interesting though, because the radiation and chemicals found on the surface of the red planet will destroy organic molecules, so these somehow survived and did so in the top five centimeters of the surface.
"Curiosity has not determined the source of the organic molecules", said Jen Eigenbrode of NASA's Goddard Space Flight Center in Greenbelt, Maryland, who is the lead author of one of the two new Science papers. NASA calls Curiosity the "largest and most capable" rover ever to make contact with Mars.
The studies were conducted using evidence collected by NASA's Curiosity rover, which is now rolling around the Martian surface.
In a second paper in Science, NASA's Christopher Webster and an worldwide team describe how they have used instruments on-board Curiosity to measure a seasonal variation in methane levels in the Martian atmosphere.
NASA has not yet provided clues on what the new results are about, but it said that during the event, NASA scientists will have chats with the the public and media on the findings.
"Are there signs of life on Mars?" asks Michael Meyer, NASA Program Scientist for the Mars Science Laboratory mission.
Attention, however this does not mean that life exists or has ever existed on the Red planet! The organic molecules he found in 2012 are comparable to those found by Curiosity. The research hints that-just maybe-there was a life on Mars, or still is hiding somewhere underground.
However, ten Kate says that it is not surprising to find organic matter on Mars because it can not be compared to items like pieces of flesh, dead cells or tufts of grass. The study, which ran for three Martian years (about five Earth years), found that methane concentration in the summer was almost three times higher than in the winter.
"We have no proof that the methane is formed biologically, but we can not rule it out, even with this new data set", Webster said. "But it doesn't tell us that life was there".