The mystery deepened as NASA's Mars Curiosity rover recorded a big spike in methane over the last few months. Since methane, which can be produced by bacteria or microbes even in environments with little or no oxygen, is a sign of life, scientists are taking note of this latest finding from the Martian surface.
Since Curiosity has been working on the surface of Mars since August 2012 to help scientists figure out if life, even in microbial form, ever existed on the Red Planet, the latest data from the robotic rover is particularly interesting.
Here on Earth, many microbes are known to produce methane. That leads scientists to think that if there is methane on Mars, there could be life.
Adding to the detection of what NASA said is a 10-fold spike in methane in the atmosphere around the rover, Curiosity also found organic molecules in a sample it took from drilling into a rock in May.
The space agency noted that organic molecules, which contain carbon and often hydrogen, are some of the chemical building blocks of life. However, they can exist without the presence of life.
Scientists are confident that the organics are Martian and were not accidentally transported there on the rover.
NASA's researchers pointed out that the organics don't necessarily mean that Mars ever sustained life. But they do show that it is a chemically active planet and that ancient Mars at one point sustained the conditions necessary for life.
"We will keep working on the puzzles these findings present," John Grotzinger, Curiosity project scientist, said in a statement. "Can we learn more about the active chemistry causing such fluctuations in the amount of methane in the atmosphere Can we choose rock targets where identifiable organics have been preserved"
Today's news comes after NASA said in September 2013 that the chances of finding life on the planet had grown slim because Curiosity had not, at that time, found any traces of methane.
NASA scientists had been testing the Martian atmosphere repeatedly for months for methane but had not found even a single trace of it.
Curiosity continued to "sniff" the Martian atmosphere, taking a dozen samples in a 20-month period. In two tests -- one late in 2013 and one early this year -- the rover's instruments measured spikes of 7 parts per billion, which was up from a 10th that level.
After the spikes were noted, the methane levels dropped back down.
"This temporary increase in methane -- sharply up and then back down -- tells us there must be some relatively localized source," said Sushil Atreya, a member of the Curiosity rover science team. "There are many possible sources, biological or non-biological, such as interaction of water and rock."