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  • Print publication year: 2016
  • Online publication date: March 2016

1 - Chronological sequence of missions and events Pages 1 to 205


2003: MER landing site selection

The Mars Exploration Rover (MER) mission was intended to land two identical rovers at different sites showing evidence of past water activity. This description of the landing site selection process is based on the extensive public documentation at the Mars Landing Site website at NASA Ames Research Center ( and a summary by Golombek et al. (2003). Maps and tables released at the time contain minor discrepancies, which are corrected here as noted.

MER landing site selection began in September 2000. Engineering considerations stipulated landings below −1.3 km elevation for the parachute system and between latitudes 15° S and 5° N (MER-A) and between latitudes 5° S and 15° N (MER-B) for solar power. Thermal inertia data further limited the available area by excluding very rocky or dusty regions. The entry procedure and accuracy defined the size and orientation of the landing ellipse. This varied from 80 by 30 km for MER-A at 15° S to 360 by 30 km for MER-B at 15° N. The orientation also varied with latitude. The two rover sites had to be at least 37° of longitude apart to minimize communication conflicts. A Landing Site Steering Committee headed by Matt Golombek (JPL) made an initial assessment of possible sites. Maps of the accessible area were overlaid with ellipses at every location free of hazards in Viking images. In this way 85 candidate ellipses were defined for MER-A and 100 for MER-B (Tables 1 and 2, Figures 1 and 2). Some pairs of sites have identical coordinates but different orientations.

Next, a shortlist of high-priority sites was assembled from abstracts submitted to the First Landing Site Workshop, augmented by sites for which team members requested new high-resolution images (Table 3). A region in Sinus Meridiani shown by Mars Global Surveyor (MGS) to be rich in hematite (Christensen et al., 2001) was a clear favorite from the start, as it had been for Mars Surveyor 2001. Crater lakes were the next most popular targets. Soon after that shortlist was circulated on 13 December 2000, new analyses of the landing process increased the length of the landing ellipses. Some ellipses that would no longer fit safely between obstacles were eliminated on 21 December. These sites are labeled (*) in Table 3.