USGS Scientists Exploring Mars as Part of NASA’s Mars Science Laboratory
Three U.S. Geological Survey (USGS) researchers—astrogeologist Ken Herkenhoff, Shoemaker Postdoctoral Fellow Ryan Anderson, and sedimentary geologist David Rubin—were among the jubilant scientists at NASA’s Jet Propulsion Laboratory in Pasadena, California, on August 5, 2012, as incoming data showed that the rover Curiosity had landed safely on Mars. Having survived an intricate series of landing maneuvers—referred to by some NASA engineers as “7 minutes of terror”—Curiosity was poised to begin its mission: exploring and assessing the region around the landing site as a potential habitat for life, past or present.
Curiosity landed in Gale crater near Mars’ equator. The site was chosen partly because data from Mars orbiters show evidence of past water there, increasing the chances that the rover might find evidence of past life. Scientists working with Curiosity are particularly interested in Aeolis Mons, known informally as Mount Sharp. This mountain of layered material in the middle of the crater may be the eroded remnant of sedimentary layers that once filled the crater completely. Some of these layers may have originally been deposited on a lakebed. With an array of scientific instruments for observing its surroundings and for acquiring and analyzing samples of rock, soil, and atmosphere, the rover will gradually make its way to and up the mountain, studying the makeup and structure of the layers to investigate how they formed.
Living on Mars Time
Directing the rover’s activities are Herkenhoff, Anderson, Rubin, and the many other scientists working on Mars Science Laboratory—the name of the mission using Curiosity to explore Mars (http://mars.jpl.nasa.gov/msl/). For approximately 3 months after the landing, the scientists will be living on “Mars time.” Although they are directing the rover’s daylight operations, their work shift is during Mars night. In Mars afternoon, the rover starts sending its data to Earth, where the scientists study the incoming images and analyses. (The time it takes information to travel between Earth and Mars at the speed of light varies with the distance between the two planets; when Curiosity landed on August 5, data transfer from Mars to Earth took about 14 minutes.) Each of three groups of scientists—focused on geology, environment, and mineralogy—comes up with a plan for what it would like the rover to do on the following day. The plans are discussed and integrated into a single plan, which the rover drivers convert into a list of commands to be sent to the rover by Mars dawn.
Days on Mars, called “sols,” are 24 hours, 39 minutes, and 35.2 seconds long—not much different from days on Earth, but different enough that each Earth day the scientists start work about 40 minutes later than the day before, and so sometimes they are working in the middle of Earth’s night. As the mission progresses—it is expected to last at least 1 Martian year, or 687 Earth days—the MSL scientists will transition to “Earth shifts” that allow them to consistently work during Earth’s daylight hours.
Eyes on Mars—Specialized Cameras
Ken Herkenhoff is a research geologist from the USGS Astrogeology Science Center in Flagstaff, Arizona, with a particular interest in using specialized cameras to study landforms and surface processes on Mars (see http://astrogeology.usgs.gov/people/ken-herkenhoff). During 7 years as a research scientist at the Jet Propulsion Laboratory, Herkenhoff took part in numerous Mars exploration and mapping projects, including the 1997 Mars Pathfinder mission, the first U.S. mission to put a rover (Sojourner) on Mars. After joining the USGS in 1998, Herkenhoff continued his Mars work, including leading the Microscopic Imager team for the Mars Exploration Rover (MER) mission, which landed two rovers, Spirit and Opportunity, on Mars in 2004. A Co-Investigator on the current mission since instruments were selected in December 2004, Herkenhoff works with several instruments on Curiosity: the Mastcam, MAHLI, and MARDI cameras and the ChemCam spectrometer and remote microscopic imager.
The Mastcam (short for Mast Camera) takes high-definition videos of the Martian terrain, as well as color photographs, including stereopairs—photographs taken from slightly different angles whose combination produces three-dimensional views. These images will be used to study the Martian landscape, rocks, and soils; to view frost and weather phenomena; and to support the rover’s driving and sampling operations.
The MAHLI, or Mars Hand Lens Imager, functions like a geologist’s hand lens, providing closeup views of the minerals, structures, and textures in Martian rocks and dust. MAHLI is similar to the Microscopic Imager used by Spirit and Opportunity but has more capabilities; for example, MAHLI takes color rather than monochrome images, and it has its own light sources, enabling it to take images in shadow and even at night. In addition to white-light sources, like the light from a flashlight, MAHLI has ultraviolet-light sources, like the light from a tanning lamp. The ultraviolet light is used to induce fluorescence in order to help detect carbonate and evaporite minerals, both of which would indicate that water helped shape the landscape. MAHLI’s lens has a focusing mechanism that allows images to be acquired at a range of target distances, from less than an inch (resolution better than the MER Microscopic Imager) to infinity.
The MARDI, or Mars Descent Imager, took color video during the rover’s descent, providing an “astronaut’s view” of the landing site to help Curiosity’s drivers steer it around loose debris, boulders, cliffs, and other potential obstacles, as well as to provide geologic context for the rover’s early investigations. Shot at 4 frames per second, the video supplements high-resolution digital topographic models of the study area prepared by USGS astrogeologist Randy Kirk (see related article, this issue). The video frames, which have very large file sizes, are gradually being transferred to Earth; some of them have been combined into a movie posted at http://www.youtube.com/watch?v=e1ebHThBdlY&feature=channel&list=UL. Although MARDI has completed its main task—imaging the ground during the rover’s descent—it can still take useful pictures of Mars, looking straight down at the surface just behind Curiosity’s left front wheel. Eventually the scientists hope to use MARDI to take images as the rover drives.
The ChemCam (short for Chemistry and Camera) fires a laser at rocks and soils and analyzes the elemental composition of vaporized materials from surface areas smaller than 1 millimeter. From as far away as 7 meters (23 feet), the ChemCam can rapidly identify rock types (for example, determine whether rocks are volcanic or salty), measure the abundance of most chemical elements, recognize ice and minerals with water molecules in their crystal structures, and much more. The ChemCam contains a remote microscopic imager to capture detailed images of the spot analyzed by the laser and the surrounding area. If Curiosity cannot reach a rock or outcrop of interest, the ChemCam will enable scientists to analyze it from a distance.
Herkenhoff is using data from all these instruments to study rocks and fine regolith (loose materials) in the study region. He is particularly interested in eolian (wind-formed) features and the geologic history recorded in the layers exposed on Aeolis Mons. Making use of his previous mission operations experience, Herkenhoff is serving in various MSL operational roles, including Chair of the Science Operations Working Group, which meets daily to discuss and decide what the rover will do the following sol. Other tactical roles include Payload Uplink Lead, which involves preparing instrument command sequences for transmission to the spacecraft (“uplink”). He is also refining the calibration of some of Curiosity’s cameras and planning coordinated observations by multiple instruments. Read Herkenhoff’s sol-by-sol updates at http://astrogeology.usgs.gov/news/.
Communicating with Curiosity
Ryan Anderson is a Shoemaker Postdoctoral Fellow who works with Herkenhoff at the Astrogeology Science Center (http://astrogeology.usgs.gov/people/ryan-anderson). His use of data from Mars orbiters to study landforms and layered deposits in Gale crater contributed to its selection as Curiosity’s landing site (see technical paper posted at http://dx.doi.org/10.1555/mars.2010.0004). A Collaborator on the MSL project, Anderson is a ChemCam science-team member and a Payload Downlink Lead for ChemCam. “Downlink” is the transfer of data from Curiosity to Earth. As these data arrive, Anderson and his group check to see that the rover’s instruments are functioning properly and performing the scientific tasks as commanded; then they translate the data into information that can be examined by the science teams. Anderson has uplink responsibilities as well. His observations about being part of MSL are posted on his blog “The Martian Chronicles.”
Sediments Past and Present
Dave Rubin is a research geologist from the USGS Pacific Coastal and Marine Science Center in Santa Cruz, California, with a particular interest in sediments, both modern and ancient, and how they are moved and deposited by water and wind (https://profile.usgs.gov/drubin). His computer animations depicting the formation of bedding structures, particularly cross-beds (layers within a bed that are at an angle to the main bedding plane), have proved extremely valuable in the interpretation of complex bedding patterns exposed in outcrops (http://walrus.wr.usgs.gov/seds/bedforms/animation.html). Rubin’s work on the orientation of ripples and dunes in multidirectional flows has been applied to bedforms on Earth, Mars, and Saturn’s moon Titan. In 2004, he was asked to review NASA scientists’ interpretations of sedimentary structures in images of a Martian outcrop taken by the rover Opportunity (see “USGS Sedimentologist David Rubin Serves As External Expert During NASA Announcement of Evidence for Flowing Water on Mars,” Sound Waves, April 2004). Rubin joined the Mars Science Laboratory in November 2011, when he was selected as a Participating Scientist. He has three roles in the mission: Geology Theme Group Member, Geology Science Theme Leader, and Surface Properties Scientist.
Rubin is examining images of sedimentary structures taken by Curiosity’s cameras and comparing them with terrestrial analogs to reconstruct past geologic processes—particularly flowing water and wind—that may have produced them. For example, cross-beds in an outcrop can indicate the shape and motion of ripples along an ancient streambed or lakebed. In the case of complex structures, three-dimensional computer modeling and animation will be used to aid in this reconstruction. (View “Ripples to Rocks on Mars,” a video using computer animation to illustrate the process that likely formed cross-beds in an outcrop imaged by Opportunity in 2004).
Curiosity may have to drive over sand dunes or other loose sediment on its journey to Aeolis Mons, and so mission leaders assembled a Surface Materials and Mobility Working Group to help keep the rover from getting stuck. As a Surface Properties Scientist in this group, Rubin works with the rover drivers to pick the safest routes for the rover to drive and the safest outcrops for the rover to drill.
Like any epic production, MSL has a “cast of thousands.” Here are some USGS personnel who, though not official members of the mission, are supporting the project from the Astrogeology Science Center:
Mark Rosiek is leading the analysis of MAHLI calibration data to determine the modulation transfer function (image sharpness) of the camera at various target distances.
Ella Lee is assisting Rosiek in the processing of MAHLI calibration data.
Bob Sucharski set up and maintains the USGS subscription to the Mars Science Laboratory File Exchange Interface, allowing secure transfer of data between the Astrogeology Science Center in Flagstaff and the Mars Science Laboratory project at the Jet Propulsion Laboratory in Pasadena.
Scientist and cartographer Ken Tanaka of the Astrogeology Science Center served on the landing-site selection committee. (See additional USGS contributors in “High-Resolution Digital Topographic Maps Help Curiosity Navigate Mars,” this issue.)
in this issue: