NASA's Mars rover Curiosity is set to fire its rock-vaporizing laser for the first time this weekend, shortly before the 1-ton robot's maiden drive on the Red Planet.
Once it starts driving, which could be within a week, the rover will begin by heading for one of four scars that its own landing gear scoured into the soil.
The Sky Crane that lowered Curiosity into Gale Crater on 5 August hovered above the rover using four retro rockets, then used those rockets to propel itself to a crash landing about half a kilometre away. Before the jetpack flew off, the rockets singed the rusty Martian dust off the planet's surface, exposing bedrock beneath.
"That will be our first science target," project scientist John Grotzinger said in a press conference today. Assuming its wheels are in good driving condition, the rover will head towards a scar the team is calling Goulburn (named for ancient rock formations in Northern Canada).
But before it departs, Curiosity has to shoot itself in the back.
That's because the rover needs to check its own aim with the ChemCam instrument, a key tool for checking out rocks on the Red Planet.
ChemCam zaps rocks with a pinpoint of laser light to produce a small, hot puff of plasma and uses a telescopic camera and on-board spectrometers to get a quick read on its composition. Once it warms up, the laser tool will probably be one of the most-used instruments on the rover, set to make up to 14,000 individual analyses.
First, though, the team needs to make sure the instrument knows what it's looking for. The rover carries a palette of nine circles of material akin to what scientists expect to find on Mars - for instance, glass samples represent igneous rock formed in volcanoes, while ceramics represent sedimentary rock.
So far the camera has taken images of each individual calibration target.
"We have done basically everything with this instrument except turn the laser on," said ChemCam leader Roger Wiens of Los Alamos National Laboratory. In the next few days, the team will take another image of each target to be sure its aim is true.
"When we shoot the laser we want to make sure we're hitting that target assembly and not some other part of the rover," Wiens said.
Then they'll finally be ready to start shooting rocks. The first laser target currently has the unromantic name "N165", and was chosen for its banality and flat face rather than its scientific value.
"This is a sort of target practice," Wiens said. "It gives us something easy to start with."
ChemCam won't go easy on the rock, though: it shoots any target 30 times in 10 seconds. Wiens hopes that the barrage of laser shots will get underneath the Martian dust, to help figure out how deep it goes and what materials lie beneath.
Once it's fired up and calibrated, ChemCam will take aim at the bedrock exposed in Goulburn, which looks like it might be a conglomeration of different rocks cemented together.
The science team has four or five hypotheses for how it formed, Grotzinger said. "We're chewing through those."
The rocks at Goulburn appear to be loosely bound, so the team decided the scar wouldn't be a good place to try out another sampling instrument, the arm-mounted drill, for the first time.
Instead, they're heading for a place where three types of rock appear to come together. Dubbed "Glenelg" (also named for a Canadian rock), the site lies to the east of Curiosity's landing site.
The team doesn't yet know what those three materials are. "Glenelg simply looks distinctive and interesting," Grotzinger said. "Mostly it just looks cool."
Tey think the brightest terrain might represent bedrock that would be good for drilling and feeding into Curiosity's onboard chemistry suite. The middle terrain is pockmarked with craters and may be an older or harder surface. And sampling the terrain that Curiosity will drive through to get to Glenelg can tell scientists whether it's the same stuff that was uncovered at Goulburn.
It will be a while before Curiosity makes it out there, though. After the wheels are checked out, it could take three to four weeks of straight driving to make it to Glenelg. And if the team encounters some nice loose soil, they'll probably stop and dig it up to give the chemistry suite its first taste of Martian ground.
But of course, there's that mountain in the background spurring the science team forward. The rover will eventually head southwest towards a natural break in the dunes that will allow it to begin scaling the mountain's lower reaches.
"We always keep in mind that our real goal for having chosen this landing site is Mount Sharp itself," Grotzinger said.