Following the discovery that Mars was suited for microbial life, scientists with NASA's rover Curiosity mission will attempt what is expected to be a far more difficult task of looking for organic carbon.
A tantalizing clue already is in the ground-up rock sample that Curiosity processed to reveal that Mars, like Earth, has the chemical building blocks for life.
Scientists want to drill out another sample from inside the target rock, located in a low-lying and once water-rich region inside the rover's Gale Crater landing site.
The work, however, will have to wait until May when radio communications between Earth and Mars are restored after a month of blockage due to the position of the sun in April. Rover operations also currently are suspended due to an unrelated computer glitch, which scientists hope to resolve this week.
The rock, named "John Klein" after a mission manager who died in 2011, was the first place Curiosity drilled to obtain powdered samples from inside a Martian rock. From its greenish-gray color alone, scientists realized the material had been somewhat sheltered from the harsh radiation and oxidation processes on the planet's surface.
"If there was organic material there, it could have been preserved," said David Blake, principal investigator for Curiosity's Chemistry and Mineralogy, or CheMin, experiment.
The hunt for organic carbon is difficult because many of the same processes that create rock destroy organics.
"On Earth, finding organics in very, very ancient rocks is a difficult proposition," said Paul Mahaffy, principal investigator for Curiosity's Sample Analysis at Mars, or SAM, instrument.
Mars doesn't have Earth's destructive plate tectonics, but its thin atmosphere doesn't provide much shielding from organics-destroying ultraviolet and cosmic radiation. Mars also is apparently flush with chemicals like perchlorates that consume organic molecules.
"The search for organic carbon is an issue for this mission and you want to do this as deliberately as possible. You don't just want to wander around and try stuff out ... With the issue of habitability in the bag, we can undertake a more systematic search for a (strong) carbon signal," said lead Curiosity scientist John Grotzinger, with the California Institute of Technology.
"This is not a simple problem, but I think the mission is up to it and we're really excited to get started on that now," he added.
Scientists on Tuesday unveiled the first chemical analysis of the John Klein rock sample which turned out to contain six elements needed for life -- hydrogen, carbon, oxygen, nitrogen, sulfur and phosphorus -- plus water that was not too acidic or too salty.
The carbon was bound in carbon dioxide, which on Earth at least is not a problem for some well-adapted microbes.
"There does need to be a source of carbon somewhere, but if it's just CO2, (carbon dioxide) you can have chemoautotrophic organisms that literally feed on rocks and they will metabolize and generate organic compounds based on that carbon," Grotzinger said.
"You don't have to have (organic) carbon present in a geological environment that's habitable in order to have microbial metabolism occur," he added.
The $2.5 billion, nuclear-powered Curiosity rover landed inside the giant Gale Crater impact basin, located near the Martian equator, on Aug. 6 for a two-year mission to assess if the planet most like Earth has or ever had the ingredients for life.
Seven months after landing, in the first drill sample, scientists got their answer.
"This rock, quite frankly, looks like a typical thing that we would get on Earth," Grotzinger said. "The key thing here is this is an environment that microbes could have lived in and maybe even prospered in."