Available online at www.sciencedirect.com Planetary and Space Science 52 (2004) 11–21 www.elsevier.com/locate/pss Selecting landing sites for the 2003Mars Exploration Rovers John A. Granta;∗, Matthew P. Golombekb, Timothy J. Parkerb, Joy A. Crispb, Steven W. Squyresc, Catherine M. Weitzd aCenter for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, 6th St. and Independence Avenue SW, Washington, DC 20560-0315, USA bJet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA cDepartment of Astronomy, Space Sciences Bldg., Cornell University, Ithaca, NY 14853, USA dNASA Headquarters, Code SE, 300 E St. SW, Washington, DC 20546, USA Received 15 January 2003; received in revised form 4 June 2003; accepted 29 August 2003 Abstract A two-plus year process of identifying and evaluating landing sites for the NASA 2003Mars Exploration Rovers began with deÿnition of mission science objectives, preliminary engineering requirements, and identiÿcation of ∼ 155 potential sites in near-equator locations (these included multiple ellipses for locations accessible by both rovers). Four open workshops were used together with ongoing engineering evaluations to narrow the list of sites to four: Meridiani Planum and Gusev Crater were ranked highest for science, with southern Isidis Basin and a “wind safe” site in Elysium following in order. Based on exhaustive community assessment, these sites comprise the best-studied locales on Mars and should possess attributes enabling mission success. Published by Elsevier Ltd. Keywords: Mars; Landing sites; Rovers; 2003; Exploration; Selection 1. Introduction (Squyres et al., 1998). The MER mission will use the Mars Pathÿnder airbag system for landing (Crisp, 2001), though The process of identifying and evaluating landing sites scaled up considerably due to the higher mass of the MER for the 2003Mars Exploration Rovers (MER-A and lander. After landing and deployment, at least one rover must MER-B) began in September of 2000 and has involved a traverse up to 600 m to achieve mission success (Weitz, broad cross-section of the planetary science community. 2001). Activities built upon the premise that all engineering re- quirements (e.g., acceptable surface rock abundances and slopes) must be met in order to maximize the probability 2. Guiding principles and participants of landing safely; given that these constraints are satisÿed, then locations were evaluated where the scientiÿc objec- Landing site selection activities built on unchanging tives of the mission could best be achieved. Outcomes guiding principles that include the recognition that: (A) included a shortlist of four sites with generally high science identifying optimal sites within the limits enabled by potential. data and resources (e.g., suDcient solar energy for oper- The MER mission consists of two identical rovers to be ations) is critical to mission success, and (B) the assis- launched in June, 2003. The ÿrst MER will land on January tance of the science community is crucial in identifying 4, 2004 and the second will land on January 25, 2004. Each optimal science sites. Nevertheless, ÿnal site recommen- rover will conduct science operations for a minimum of dation was the job of the Athena Science Team and MER 90 Martian days (sols) using the Athena Science Payload Project at the Jet Propulsion Laboratory (JPL), whereas site selection was made by the Associate Administra- tor for Space Science at NASA Headquarters. Finally, there was no predetermined outcome to any aspect of the ∗ Corresponding author. Tel.: +1-202-633-2474; fax: +1-202-786-2566. landing site selection process and participants were kept E-mail address: [email protected] (J.A. Grant). up-to-date on activities via posting of materials at two 0032-0633/$ - see front matter Published by Elsevier Ltd. doi:10.1016/j.pss.2003.08.011 12 J.A. Grant et al. / Planetary and Space Science 52 (2004) 11–21 Table 1 Table 2 NASA Mars landing site steering committee Summary of landing site engineering constraintsa ADliation MER mission engineering Requirement for MER mission parameter landing sites Co-Chairs John Grant Smithsonian Institution Altitude 6 − 1:3km relative to MOLA Matthew Golombek Jet Propulsion Laboratory deÿned Geoidb Approximate ellipse ∼ 155 km × 16 km at 11◦N, Members dimensions ∼ 96 km × 19 km at 15◦S Michael Carr US Geological Survey, Menlo Park Approximate ellipse orientation ∼ 94◦ at 11◦Nto76◦ at 15◦S Philip Christensen Arizona State University (w/respect to north) Jack Farmer Arizona State University Site separation latitude (MER Solid angle ∼ 37◦ 5◦N–15◦S Virginia Gulick NASA Ames Research Center A and MER B) and 10◦N–10◦S, respectively Bruce Jakosky University of Colorado 1 km length-scale slopes Must be less than 2◦ Michael Malin Malin Space Science Systems 100 m length-scale slopes Must be less than 5◦ George McGill University of Massachusetts 10 m length-scale slopes Must be less than 15◦ Richard Morris NASA Johnson Space Center Minimal local high relief Hazard-free in Viking MDIMc Timothy Parker Jet Propulsion Laboratory Rock abundance Should be ¡ 20% (from ther- Roger Phillips Washington University mal inertia) Michael Shepard Bloomsburg University Minimal hazardous rocks Should be ¡ 1% larger than Kenneth Tanaka US Geological Survey, FlagstaJ 0:5 m high TraDcability Minimal decimeter-scale roughness from radar Horizontal winds Generally 6 0:9 6 2:1 (being (shear/turbulence) reÿned) open URL’s: http://marsoweb.nas.nasa.gov/landingsites/ Horizontal winds Must impact surface at ¡ 16– and http://webgis.wr.usgs.gov/. (sustained mean) 20 m=s To ensure a robust, comprehensive process, multiple Acceptable vertical winds Must impact surface at ¡ 12– groups were solicited for input in evaluating potential land- 15 m=s ◦ ing sites. Activities were led by a Steering Committee that Minimum temperature at site Warmer than −97 C Thermal inertia Greater than 200–250 SI units was responsible for approving modiÿcations to the process (see albedo) and adjudicating if community consensus was not achieved Albedo Less than 0.18 and 0.26 (see (never required). The Steering Committee was co-chaired thermal inertia) by the ÿrst two authors of this paper, and both were selected Local dust environment Relatively dust free from MGS d via NASA peer- review. Other Steering Committee members TES and albedo Surface must be load bearing Deÿned on basis of radar and were appointed by NASA Headquarters to ensure breadth geology of science expertise and mission involvement (Table 1). In Radar reNectivity Must be ¿ 0:05 addition, the broader science community and investigators a in the NASA Mars Data Analysis Program were targeted, Engineering constraints remain under evaluation at the time the paper was accepted for publication and the actual values may diJer. thereby enlisting individuals developing and applying new bAs described in Smith and Zuber (1998) and Smith et al. (1999). data analysis techniques relevant to evaluating site safety. cSecond generation Viking Mars Digital Image Map. Finally, additional members of the science and spacecraft dThermal Emission Spectrometer. engineering community and NASA ex-oDcios were invited to provide mission experience, provide feedback, and en- able access to data collected by the Mars Global Surveyor Mission science objectives are tightly coupled to the (MGS) Mars Orbiter Camera (MOC) and Mars Odyssey NASA Mars Program objectives and relate to deÿning the Thermal Emission Imaging System (THEMIS) imagers. aqueous, climatic, and geologic history on Mars in loca- tions where conditions were favorable for preserving clues to environmental conditions when liquid water was present 3. Basis for site selection (Crisp, 2001; Weitz, 2001). Proposed landing sites include locations possessing evidence for surface processes involv- Requiring that any recommended site must satisfy all ing water and examples of how the Athena instruments can mission engineering/safety and science requirements placed be used to achieve the objectives via hypothesis testing. strict constraints on the regions accessible to landing dur- ing the MER mission (Golombek et al., 2001, 2002, 2003). For example, latitude, altitude, and temperature constraints 4. The ÿrst two landing site workshops (Table 2) limited potential landing sites to a discontinuous equatorial band that covers approximately 5% of the planet. Deÿnition of the landing sites for the 2003Mars Ex- Application of all remaining mission engineering constraints ploration Rovers began in earnest following deÿnition of (Table 2) further reduced potential landing areas. preliminary engineering constraints in September, 2000. J.A. Grant et al. / Planetary and Space Science 52 (2004) 11–21 13 Fig. 1. Map of the equatorial region of Mars showing location of initial ∼ 155 landing ellipses (white and green) for the MER rovers. Areas in grey are outside of the elevation requirements. Colored regions represent potentially acceptable regions and display MOLA topography. Using site requirements as a guide, ∼ 155 landing (99% identiÿed coarse-grained hematite deposits in Meridiani probability) ellipses were identiÿed (including multiple el- Planum (Christensen et al., 2000, 2001), locations in Valles lipses for some sites accessible by both rovers) to provide Marineris (e.g., in Melas and Eos Chasmata, see Weitz access to terrains ranging from Noachian highland dissected, et al., 2003; Greeley et al., 2003a), putative paleo-crater- hilly, cratered, and subdued cratered units; to Hesperian lake deposits (e.g., in Gale and Gusev Craters, see Cabrol ridged plains, channel materials, and the Vastitas Borealis and Grin, 1999), and locations with access to in situ (Merid- Formation; to Amazonian smooth plains, channel materials, iani Highlands) or transported (Isidis Basin) highlands volcanics, knobby materials, and the Medusae Fossae For- materials. The Meridiani Planum site received the strongest mation (Fig. 1, see Table 3 for speciÿc ellipses in each ter- support and includes multiple sites to permit some choice rain type as deÿned in Scott and Tanaka, 1986; and Greeley related to future safety concerns or targeting the most inter- and Guest, 1987).