Rover Reveals Unexpected Martian Landscapes
Less than a month after its touchdown, NASA's Curiosity rover is already revealing a wealth of new detail about Mars—even before driving for any significant distance.
Moreover, scientists are confident the startling high-definition images of inclined strata and other significant geological phenomena transmitted late last month from Curiosity are merely the tip of the iceberg as it begins its trek toward the base of nearby Mount Sharp, the central feature of the Gale Crater in which it landed. The rover, which landed on Aug. 5, is tasked with assessing the past and present habitability of Mars (see p. 28).
Following two short moves to check its mobility and test bedrock exposed at the landing site by one of the sky crane's thrusters, Curiosity began its first major drive on Aug. 28 to a science destination about a quarter-mile (400 meters) away. Covering approximately 52 ft. on its 22nd sol (Martian day) after landing, the first leg of Curiosity's journey will terminate several weeks from now at a spot named Glenelg, where operators at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif., have spotted a promising conjunction of three terrain types.
The target-rich zone will mark the first significant opportunity for the rover's 7-ft.-long robotic arm and drill to study sedimentary rocks for signs of organics. The arm supports a 73-lb. turret, which houses a percussive drill as well as an Alpha Particle X-ray Spectrometer and a sample processing Collection for In-Situ Martian Rock Analysis subsystem. Also mounted is a dust-removal tool for brushing the surfaces of sample rocks, and a close-up Mars Hand Lens Imager.
The study of accumulated rock-forming sediments is among the key targets for the mission, which hopes to interpret the planet's environmental record preserved within the layers. Clues to climate change, and the possible transitions from habitable to non-habitable conditions, are expected to be found in these layers.
This was all the more reason for the excitement caused on Aug. 27 when JPL unveiled a newly processed mosaic of high-definition images from Curiosity that showed “unexpected” geological features including multiple sequences of exposed, tilted strata of a sort never before seen on Mars.
“The cool thing is the cameras have discovered something we were unaware of,” says mission chief scientist John Grotzinger. “This thing jumped out at us as being very different to what we expected,” he adds. Situated in the low-lying foothills beyond the dune field between the rover and the base of Mount Sharp, the inclined layers are a “spectacular feature” that could only be viewed clearly from low angles.
NASA says it is too early to comment on the mechanics of the processes that created the landform, which Grotzinger describes as a type of clinoform. On Earth such features are typically driven by or related to tectonic, volcanic, sub-aqueous or wind-driven processes (sand dunes and the like).
Mission scientists are particularly intrigued by images from the same feature that appear to show an unconformity, or a missing piece in the geological record, where a sedimentary layer does not line up with those above it. The image shows “a transition from the strata that are . . . full of the hydrated minerals, to strata above them, which do not obviously contain the hydrated (formed in the presence of water) minerals,” says Grotzinger.
“The striking thing about it, [is that] everything above that is steeply inclined with respect to everything below it. This is a spectacular feature that we are seeing very early on that you only had the slightest hint [of] from orbit,” Grotzinger says. The features “clearly are the result of the exhumation of the larger sequence of strata that created Mount Sharp. One day we hope—toward the end of our mission—to get up and go across that to check it out,” he adds.
The precise angles of the strata will be measured through triangulation by comparing the first set of images captured by Curiosity's stereoscopic mast cameras (Mastcam) with a new set taken from a few meters away on Aug. 28. The images were collected by the rover's 100-mm telephoto lens and 34-mm wide-angle lens, and will also provide a three-dimensional guide to the rover's navigators.
The following day, “We will execute a series of increasingly long drives in excess of 100 meters,” Grotzinger adds. This will be “well away from the area we think was affected by the thrusters, and then we will head east as quickly as possible.” Prior to starting off on the longer drive, the rover demonstrated its ability to maneuver during a series of short moves around its present site—dubbed 'Bradbury Landing' by NASA as a tribute to the late science fiction author Ray Bradbury, who died in June.
On Aug. 27, mission planners also conducted the first science drive to study the bedrock exposed by the impingement made by one of the sky-crane's thrusters as it lowered the rover to the surface. Although the science team was concerned about potential contamination from rocket chemical and heating effects, the scoured-out depression was sampled with Curiosity's Dynamic Albedo of Neutrons (DAN) instrument. It fired neutrons into the ground to a measurable depth of around 20 in. below the rover in search of hydrogen atoms, and indicating signs of water. The results will be compared with readings already taken by the DAN over soil-covered areas in Bradbury Landing.
Preparations also continue for taking the first sample of the Martian atmosphere. “We are the nose of Curiosity” says SAM (Sample Analysis at Mars) principal investigator Paul Mahaffy. During initial check-out tests of SAM, scientists discovered the amount of air from Earth's atmosphere remaining in the instrument after launch was more than expected. As a result, a difference in pressure on either side of the tiny pumps led SAM operators to stop pumping out the remaining air as a precaution. The pumps subsequently worked, and a chemical analysis was completed on a sample of Earth air.
The inadvertent air sample provided an unscheduled test of the instrument, but was “a beautiful confirmation of the sensitivities for identifying the gases present,” says Mahaffy. The initial indication of methane sparked a brief flurry of excitement until the terrestrial origins of the gas were recognized, he noted from NASA's Goddard Space Flight Center, where he is based. “A few sols down the road we're looking forward to getting our first sniff of Mars atmosphere,” he adds.
The SAM system is a key tool in Curiosity's search for signs of life and is more sensitive and sophisticated than the sensors on the Viking landers in the 1970s, which failed to confirm any organic traces. The system is designed, for example, to examine a wider range of organic compounds and can therefore check a recent hypothesis that perchlorate—a reactive chemical discovered by the Phoenix Mars Mission—may have masked organics in soil samples taken by Viking.
Rover Reveals Unexpected Martian Landscapes