Strictly speaking, Fred Calef III is geospatial information scientist for the Curiosity rover. But most people at Nasa’s Jet Propulsion Laboratory in Pasadena, California refer to Calef as ‘the Keeper of the Maps’.
“I’m in charge of the base map for the Curiosity mission so we can locate the geology, identify points of interest and track where the rover is,” Calef explains.
This is no ordinary road or hiking map but almost certainly the most detailed map ever produced of an alien world.
“Wherever the rover’s been we can literally map down to the scale of sand grains,” says Calef. “Although,” he admits, “it takes a little bit of work.”
In reality there is no physical map unfolded across a table at mission control for the rover drivers to pore over with compasses and protractors. Instead there is a series of virtual layers built up from many years of data.
The base map uses images from Nasa’s Mars Reconnaissance Orbiter (MRO), a satellite that has been circling the planet for the past eight years.
“Each pixel from MRO represents 25cm (10in) on the ground – that’s around the size of a dinner plate or laptop,” says Calef. “Considering it’s in orbit, that’s amazing detail.”
Next, the mapmakers add data from Curiosity itself. “With the rover we take images every day and we can reconstruct a 3D map of the surface,” says Calef. “With the navigation cameras we get down to a resolution of 3cm and with the other cameras and instruments on board we can resolve that to the size of sand grains.”
The maps are continuously updated and every Martian night, when the rover is asleep, the next day’s course is plotted. When the Sun rises on the Red Planet, the drivers upload the instructions and Curiosity wakes up to head off for another day’s exploring. The combination of detailed maps and the rover’s own built-in hazard avoidance features mean the Nasa drivers are confident that it will not fall over a cliff or get grounded on a boulder.
(For more on driving the rover, read our earlier story).
Since landing in August 2012, Curiosity has successfully travelled just under 9.5km (5.9 miles or 9,458m to be exact) to the base of Mount Sharp – a rounded 5.5 km (3.4 mile) peak at the centre of Gale Crater. Eventually, the six-wheeled robot will climb to the top of this mountain, having negotiated a formidable terrain of boulders, canyons and escarpments.
However, it seems Calef is not unduly worried about the climb ahead. “Sometimes things appear worse than they are,” he laughs. “What might at first look like a cliff turns out to be a doorstep – I’ve seen the rover in our test area climb over three boulders half-a-metre tall and it didn’t break a sweat, so it’ll be okay.”
In fact the primary target is not the summit of the mountain at all – “not particularly interesting” says Calef – but a zone about 400m (1,330ft) up. This is where geologists expect to find the boundary between an area that was once flooded with water and a dry upper section of the mountain. This ‘beach’ should reveal rich geologic pickings and give scientists an insight into Mars’ transition from wet planet to dry wasteland.
The mapping team has already been involved in plotting a “strategic path” to the area, which will mean 12km (7.5 miles) of driving over approximately four Earth years. “I don’t want to put too fine a number on how long it will take,” says Calef. “We’re discovery-driven, so if we find something of interest, we’re going to stop there and poke at it until we understand it well.”
“It’s like driving to a national park,” he says. “We’ve spent a lot of time driving to the park as fast as we can, now we’re going to pull over and spend time looking at the sights.”
Even at this relative speed of only three kilometres (1.87 miles) a year, the trek up Mount Sharp still has its dangers. Despite the relatively flat surface, the extraterrestrial terrain has already presented some unexpected challenges.
“We did find a point where the wheels were getting much more wear than we expected and we realised we were getting into a dangerous area,” says Calef. “The rocks were so hard that they were breaking up into shards and occasionally we would get a shard digging chunks out of the wheels.”
“Even with a big hole in a wheel, the driving performance doesn’t change,” says Calef. “In fact even if a wheel failed, it’d still be drivable and we don’t expect the performance to deteriorate for many years to come.”
Recently Curiosity has been trundling through a mix of sand and boulders. Once clear of them, it will head across smooth plains. After that, it gets more exciting.
“It’ll be challenging in terms of high slopes from hills, but also hill shadows which block sunlight that assist in keeping the rover warm as well as hinder communication with spacecraft in orbit,” says Calef. These are both hazards that could potentially stop the rover in its tracks. “Still,” he adds confidently, “we can handle it.”
As Curiosity begins its long slow climb, for the Keeper of the Maps, the best is yet to come. “I’m incredibly excited,” he says. “I think the things we’re going to see at the lower reaches of Mount Sharp will be stunning and, from a scientific perspective, incredible.”
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