In drilling a small hole into bedrock on the floor of Gale Crater and tucking the sample into a scoop, NASA's Mars rover Curiosity has made space-exploration history and passed a significant mission milestone.
It's the first time any rover has done more than scratch the surface of rocks on the red planet. And it's the first time a robotic craft has drilled on any planet other than Earth since the then-Soviet Union put two landers on the surface of Venus in 1981, each of which drilled into soils and returned data during their brief operation on the planet's harsh surface.
The test represented the final step in the rover's commissioning period, which began shortly after landing last August. As Curiosity slowly exercised its robotic arm and each of the other nine science packages it carries, researchers grew increasingly excited by the results – not just as confirmation that the experiments and tools were working, but that the evidence these tests gathered pointed to a landing zone where water once flowed.
The drilling "is a real big turning point for us," says John Grotzinger, a planetary geologist at the California Institute of Technology and the mission's lead scientist.
Like a teenager eager to slip behind the wheel of her first car, the scientists received the figurative keys to the rover last week from controllers overseeing these initial months of systems tests. Unless problems arise, destinations will now be picked more for their scientific interest than their value as a spot to test hardware.
"We're excited because from here on out what we're going to do is a repeat of something we've done before," Dr. Grotzinger says. "With that comes more confidence, a chance for fewer surprises, and increased efficiency."
Yet even the tests were a bit like movie trailers, giving researchers hints of discoveries to come – yielding evidence for an ancient stream bed and rock types paving parts of the crater floor that appear to have formed in the presence of water.
Geological models of the surface, based on data from Mars orbiters, pointed to Gale Crater's floor as a once-watery site.
"But we had no idea that we were going to find the rest of this stuff," he says, referring to the types of rocks and their flagstone-path-type layout at Curiosity's current location – a zone on the crater floor the team has dubbed Yellowknife.
If Curiosity had "gone long" and landed on the flank of Mt. Sharp instead of its planned landing site, "and we would have found stuff like this, we could have considered it to be very much the stuff we chose the landing site to go find," Grotzinger says.
Mt. Sharp is a towering summit inside Gale Crater. Its strikingly layered slopes hold the promise of revealing much about the early history of Mars's climate and the geological forces that built the mountain. Near the base, Curiosity will be hunting for signs that the crater might have been a suitable place for life to emerge shortly after Mars formed and its climate – it is believed – was warmer and much wetter.
The test hole is modest, even by Curiosity's standards. It measures about 0.6 inches across and is about 2.5 inches deep – roughly half the depth it's capable of reaching. The drill actually sank its first test hole on Feb. 9, but Wednesday's briefing confirmed that the rover had succeeded in transferring the soil into a scoop that delivers the samples to a pair of chemistry labs inside the rover's chassis.
Past rovers have scrapped beneath the dusty veneer on Mars to reveal water ice or have used a rasp to scrape the surface layers of a rock to get at more-pristine layers. But the drill represents a veritable time machine.
"We're able to get into the interior of these materials ... and really understand the environment these rocks were formed in" without the confounding effects of surface weathering, says Joel Hurowitz, Curiosity's sampling-system scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
Already the researchers are seeing color differences between the reddish dust that covers everything on Mars; the light, sandstone-toned rock that appears after the dust is swept away; and the gray, fine-grained material the drill brought to the surface.
At first blush, the rock appears to be siltstone or mudstone, Dr. Hurowitz says. The test rock, with the drill site prosaically labeled "Drill," sits nestled among other flat specimens that together resemble garden flagstones whose gaps are filled with silt. Over the next couple of weeks, the team aims to drill into adjacent rocks at locations dubbed Thundercloud, Werneke, and Brock Inlier.
The science team "is grappling with the explanation for why these are fractured in the way that they are," Hurowitz says.
The gaps could represent fractures triggered by water pressure, he says, or perhaps they represent once-moist areas that shrank as they dried – much like the cracking between plates of dried mud in a drought-dessicated lake bed.
As researchers puzzle over Curiosity's latest data, engineers are dealing with two glitches with the drill and sampling system that for now don't represent show-stoppers but may call for extra care in using the systems.
The drilling process ran more slowly than anticipated because of software glitches. But engineers were able to devise work-arounds. Potentially more troubling is the partial separation of a membrane welded to the top of a sieve on CHIMRA, the sample-delivery system on the end of Curiosity's robotic arm. Soil or drill samples pass through the membrane to ensure the grains are small enough for ChemIn, one of the rover's two internal chemistry labs, to ingest and analyze.
One of two test rovers at JPL also exhibited the separation, which appeared "well into the testing program," says Daniel Limonadi, JPL's lead systems engineer for the sampling and science gear.
"We got extensive use of the sieve even after the fault started all the way through what we would expect" during the length of the missions nominal research program and beyond, he says.
The second test device at JPL showed no signs of the problem after undergoing the same wear and tear as the other test unit.
During an upcoming drill session at the rock area, known as John Klein, the team will shorten the time the sieve runs and reduce "how many times we thwack the hardware" as part of the sieve process, he says.