Mars rover under pressure to reach mountain goal

Curiosity’s memory glitch prompts mission scientists to pick up the pace.

Credit: SOURCE: NASA/JPL-Caltech/ESA/DLR/FU Berlin/MSSS

Seven months after it hurtled to a landing on Mars, NASA’s Curiosity rover has rolled just 738 metres across the surface. It remains about 10 kilometres from its primary goal: Aeolis Mons, a 5-kilometre-high mountain thought to contain layers formed in ancient ponds. With the mission nearly one-third of the way through its allotted two years, the science team is beginning to feel the pressure to get moving.

If Curiosity were to die tomorrow, “we could certainly say we achieved a lot”, says science-team member Laurie Leshin, a planetary geochemist at Rensselaer Polytechnic Institute in Troy, New York. “But none of us would be satisfied.”

It took two months just to unfurl the array of scientific instruments on the US$2.5-billion Curiosity — the biggest, most expensive and most lavishly equipped rover ever sent to Mars. It is also planetary exploration’s most complicated robot ever, with about 400 scientists working on ten different instruments: a social environment that can slow things down. But the first serious glitch of the mission — a memory malfunction on 28 February that forced operators to use the rover’s back-up computer — has reminded Curiosity’s handlers that the machine is mortal.

From the start, however, mission scientists have found plenty of intriguing distractions. Soon after touching down in Gale Crater on 6 August last year, the rover found evidence of a dried-up stream bed near the base of Peace Vallis, an 80-square-kilometre fan of sediments that washed down from the walls of the crater.

In October, after heading to Glenelg, a junction where three terrains come together, the rover stopped for almost two months at a drift of sand dubbed Rocknest. Here, Curiosity plunged its sampling scoop into the sand and tipped the material into its two main analytical instruments, CheMin (for Chemistry and Mineralogy) and SAM (Sample Analysis at Mars). On 19 March, an entire session of the Lunar and Planetary Science Conference at the Woodlands, near Houston, Texas, was devoted to the findings at Rocknest. The dune turns out to be chemically similar to soils analysed elsewhere on Mars, suggesting that materials such as water move between the soil and atmosphere in similar ways around the planet.

Also at the conference, scientist Chris Webster of NASA’s Jet Propulsion Laboratory in Pasadena, California, reported the latest on methane measurements taken by the rover’s atmosphere-sniffing, tunable laser spectrometer. The spectrometer team’s findings have lowered the upper limit for methane in Mars’s atmosphere — to as little as 3 parts per billion by volume. The scarcity of methane casts doubt on the possibility that Martian microbes are emitting the gas into the atmosphere (see Nature 491, 174; 2012). The instrument has been used just three times in the first 200 sols (Martian days), even though it can be activated at night when there is less demand from other science instruments on the rover. This is a sign of the intense competition for rover time: one of the reasons for the slow pace.

Since 23 January, the rover has more or less stayed in one place, snuggled up next to a reddish rock nicknamed John Klein, in a region called Yellowknife Bay. At John Klein, Curiosity used its drill for the first time, and analysis of the powdered drilling sample revealed clay minerals that formed in a watery environment, along with oxidized and reduced forms of sulphur. That suggests that Yellowknife Bay was once a benign environment for microbial life (see Naturehttp://doi.org/ktt;2013). Yellowknife “has been a great place to start”, says team member Roger Wiens of Los Alamos National Laboratory in New Mexico. “We wouldn’t have wanted to miss this for anything.”

But Jorge Vago, project scientist for the European Space Agency’s ExoMars mission, says that he is already thinking about how he will need to do things faster with his rover, which is scheduled for launch in 2018. “Clearly, we couldn’t afford to run ExoMars in the way [Curiosity] is doing the mission,” he says. Instead, ExoMars is likely to have a shorter mission length, so might need to perform its science at a pace somewhere between the tortoise speed of Curiosity and the hare-like rate of NASA’s Spirit and Opportunity rovers, which landed on Mars in 2004 with primary missions of a little over three months.

Just as Curiosity’s science team is getting itchy to move the rover again, however, it will have to take another long break. For most of April, Mars will be behind the Sun as seen from Earth, and no spacecraft on or around Mars will be able to radio home. After Mars emerges, the team aims to drill into the John Klein rock once more, to repeat the measurements. Then the rover will finally hit the road to Aeolis Mons, also known as Mount Sharp.

Curiosity will follow a seemingly flat, unobstructed path around a set of sand dunes (see ‘A long road’) at speeds of up to 100 metres a day, says Raymond Arvidson, a planetary geologist at Washington University in St Louis, Missouri. “I call it the rapid transit route,” says Arvidson. “There’s general agreement that we have to get to the base of Mount Sharp before the primary mission ends, with a lot of time to spare.”