Scientists are proposing splitting an ambitious multibillion-dollar mission to return samples from Mars into three pieces to ease budget concerns, officials said this week.

Artist's concept of a Mars sample return mission. Credit: NASA/JPL

Speaking to reporters from an astrobiology conference in Houston, researchers said the next round of robotic missions to explore the solar system will be better equipped to hunt for past or present life.

The holy grail of those missions is a project to collect soil samples from Mars and return them to Earth. Officials did not disclose a predicted cost for the mission, but it will be expensive enough to warrant a joint endeavor between NASA and the European Space Agency.

A joint Mars exploration initiative finalized last year between NASA and ESA calls for a cooperative sample return mission some time in the 2020s. The sample return effort would follow joint orbiters and landers launching in 2016, 2018 and 2020.

"It is a hellishly difficult mission," said Steve Squyres, principal investigator of the Mars rovers now exploring the Red Planet. "It always has been and always will be. The difficulty is part of why it's been 20 years in the future for the past 20 years."

NASA and ESA are carefully planning the missions to search for potential concentrations of organic material, the building blocks of all life.

"That would be a really good finding on Mars because if we can find the organic matter, then we have a real reason to think that there might once have been life there," said Bill Schopf, a researcher at the University of California, Los Angeles.

Squyres is also chairman of the National Research Council's Decadal Survey culling concepts for the next phase of planetary exploration. The NRC survey will recommend several missions to NASA next year.

The panel of independent scientists is considering 28 proposals, and many of the would-be probes will focus on the search for life or habitable conditions.

One of the concepts is a Mars sample return mission that would be divided into three separate missions to select, gather and launch material back to Earth.

The first component in the piecewise approach would be a rover to choose the most scientifically-rich samples and collect the material. A lander would next be dispatched to Mars to pick up the samples and launch them into orbit around the Red Planet. The final mission would rendezvous with the orbiting canister and return the soil to Earth.

"Those three parts always had to be there," Squyres said. "You always need a rover to find the right rocks, you always need something to blast them into orbit, and you always need something to bring them home."

Credit: ESA

Officials say the Mars sample return project would be the most costly and complex robotic mission ever launched into the solar system.

"What we're saying is it's possible to string those out in time, with gaps of potentially years between each one," Squyres said. "It makes the overall program more affordable because it spreads the cost out over time."

Material brought back from the Martian surface would give scientists unrivaled insight into whether the planet has ever harbored life. Officials say one-way missions to Mars can only do so much.

"I think we're going to need to study the samples here on Earth, rather than robotically," Schopf said. "I think if we had the rocks back tomorrow morning, and I had them in my lab, I think we could solve this problem."

Scientists also announced this week a crucial discovery in northern Italy, where researchers found microscopic fossils of primitive life forms embedded in gypsum.

The gypsum, a mineral left behind when water dries up, formed when part of the Mediterranean Sea evaporated about six million years ago, according to Schopf.

"Why does that matter? First of all, there's been almost no work ever done here on Earth looking for fossils in gypsum because we all assumed there wouldn't be anything in there, and we were wrong," Schopf said.

The finding gives scientists "great hope that sulfates on Mars might harbor a similar kind of suite of fossils," said Jack Farmer, a scientist at Arizona State University.

Gypsum is present at the Martian north pole and near Valles Marineris, a giant canyon that would stretch across the width of North America on Earth.

The Opportunity rover landed in 2004 on sulfate material similar to gypsum at Meridiani Planum, a sweeping plain with a smooth surface.

"There isn't a silver bullet for finding life," said Mary Voytek, the astrobiology senior scientist at NASA Headquarters. "It has to be put into context. We need photographs, we need information about the mineralogy, and we need information about organics."