NASA's Curiosity could be followed by a simpler, but perhaps nimbler, rover. Credit: NASA/JPL-Caltech

NASA's next Mars explorer will be a leaner, meaner version of the Curiosity rover, with one major upgrade — the ability to store pieces of the red planet for later return to Earth, according to a plan released Tuesday.

Planetary scientists howled last year when budget cuts forced NASA to pull out of European-led Mars missions planned for 2016 and 2018. The US agency regrouped, announcing in December that it would launch another Martian rover in 2020 using the same body and landing system as Curiosity, which touched down on the planet in August 2012.

The agency asked a 19-person ‘science-definition team’ to determine which measurements the rover should be able to make to fulfil goals put forward by the US National Research Council (NRC).

The rover is intended to examine a region of Mars that may once have harboured liquid water, scanning the region for signs of any life that may have developed there. To do that, the team says, it should be able to capture detailed images and measurements of the mineralogical and chemical composition of its rock and soil targets — including their organic carbon content.

NASA, which estimates that the 2020 vehicle will cost about US$1.5 billion, asked the science team to limit the cost of the rover's scientific instruments to$100 million. That is much less than the \$1.8 billion spent developing Curiosity and its instruments.

Simple machine

As a result, the 2020 rover may have a simpler toolset than Curiosity’s pricey on-board sample-processing equipment — but it might be more nimble.

For example, the rover could use a technique known as ‘deep ultraviolet’ spectroscopy to look for signs of carbon in the spectra of sunlight reflected from rocks, says Jack Mustard, a planetary scientist at Brown University in Providence, Rhode Island, and the leader of the science-definition team. Deep ultraviolet spectroscopy provides less-detailed information than the equipment carried by Curiosity, which includes a laboratory that can detect the isotopic abundance of carbon in a sample to provide clues about whether it was produced by life. Deep ultraviolet spectroscopy cannot distinguish organic carbon that fell to Mars on a comet from organic carbon created by life, but it is relatively fast and cheap. “You have a trade-off there,” Mustard says.

But if the 2020 rover does find a particularly interesting sample, researchers on Earth might one day get to scrutinize it first hand. The team’s report says that the 2020 rover should be able to store, or cache, soil and rock samples for retrieval by a later mission — a capability identified in a 2011 NRC report as the top priority for Mars missions over the next decade.

Returning samples for study on Earth is the only way to rigorously test for signs of life, says Mustard. He says that the 2020 rover could be equipped to collect a total of 300–400 grams of material from more than 30 spots. But just when NASA might collect those samples is unclear.

“We’re not signing up to a timetable or a commitment for a follow-on mission,” John Grunsfeld, associate administrator for science at NASA in Washington DC, told reporters Tuesday.

Still, the fact that NASA is taking the first step towards sample return is reason for celebration, says Phil Christensen, a planetary scientist at Arizona State University in Tempe, who chaired the Mars panel for the 2011 NRC report. “I think those samples sitting on the surface are going to be this incredible magnet crying out, ‘Come get me!’”