A version of this article appears in the May 5 edition of Aviation Week & Space Technology.

As NASA managers refine their plans for transporting humans to the surface of Mars in 20 years or so, planetary scientists are polishing their strategies for using robots to answer some key questions about the red planet—and perhaps our blue one—before the astronauts arrive. One of those questions is eternal: How did life begin? Just as the ancient terrain of the Moon may

hold important clues to the geological history of Earth that has been obscured here by billions of years of plate tectonics and erosion, clays and sedimentary rocks a few meters below the surface of Mars may preserve primordial organic chemistry that could reveal how life first organized itself to begin evolving.

The problem on Mars is the blazing radiation that streams down from the pink sky, unhindered by a magnetic field that protects us here on Earth. Ongoing robotic exploration of Mars has indicated that the chemical building blocks of life are there, but the radiation so alters the surface chemistry that life’s secrets are erased. To get around that problem, the second of two upcoming European Space Agency (ESA) missions to Mars will drill below the surface to collect samples that it will analyze with a mini-chemistry lab (see graphic).

“The ExoMars 18 mission is actually that leap to the subsurface we’ve all been waiting for, to get below the depth where the ionizing radiation, the galactic cosmic radiation will modify the chemistry,” says Jim Garvin, chief scientist at NASA’s Goddard Space Flight Center.

An ESA science and engineering team has just narrowed the list of potential landing sites for ExoMars 18 to four, all of them at low enough elevation to be reachable by parachute in the thin Martian atmosphere, and believed to have been the sites of liquid water billions of years ago. All seem similar to the Gale Crater, where NASA’s Curiosity rover is picking its way across the rugged floor that was clearly shaped by flowing water (AW&ST Oct. 1, 2012, p. 16).

“That means the atmospheric pressure must have been much greater than it is today to be able to have liquid water on the surface,” James Green, director of NASA’s Planetary Science Div., told the Humans 2 Mars symposium at George Washington University April 22. “There have to have been clouds. It would have rained. It was more Earthlike than at any other time in its history.”

Tight budgets forced NASA to bail out of the ExoMars missions, which were originally planned as joint U.S./European endeavors. ESA has paired with Russia, which will provide Proton launches in 2016 and 2018, while NASA has started focusing on another Curiosity-class rover to be launched in 2020. Like ExoMars 18, that rover is likely to carry a drill to collect subsurface core samples, as well as internal robotic laboratory equipment like that inside Curiosity. The difference, as outlined by a science definition team last summer, will be the ability to preserve some of the cores for eventual analysis of its organic chemistry in laboratories on Earth.

Planetary scientists have long advocated for a sample return to give the full panoply of laboratory instruments—including some not yet invented—access to bits of Mars that have been protected from radiation since water flowed over them. A Mars sample return mission remains the top priority for experts polled in the National Academies of Science “decadal” survey for planetary science.

“We need our next mission to be able to drill and create cores, to be able to sample those cores with contact instruments, and to understand what happened in its past, cache those cores and bring them back,” says Green. “From that we will study what life may have started on Mars. And that might tell us how life started here on Earth.”

Once the samples are collected and cached, tentative plans call for a subsequent “fetch rover” to collect them from the 2020 model, and transfer them to a Mars Ascent Vehicle that will lift them from the surface to begin their trip to Earth. After that, the exact route becomes a little murky. It may involve astronauts working in what William Gerstenmaier, NASA’s human-exploration chief, terms the “proving ground” for exploration that he is trying to carve out in the vicinity of the Moon. A vehicle carrying the sample cores from the 2020 Mars rover could rendezvous with an Orion capsule operating in distant retrograde orbit around the Moon, where NASA wants to place a small asteroid for in-situ analysis, and transfer them to the human crew for entry into Earth’s atmosphere (AW&ST May 27, 2013, p. 20).

“We are on the precipice of some great discoveries on Mars, and the life question, I believe, is one of them,” says Green.