title: Two years at Meridiani Planum: results from the Opportunity Rover.
abstract: The Mars Exploration Rover Opportunity has spent more than 2 years exploring Meridiani Planum, traveling approximately 8 kilometers and detecting features that reveal ancient environmental conditions. These include well-developed festoon (trough) cross-lamination formed in flowing liquid water, strata with smaller and more abundant hematite-rich concretions than those seen previously, possible relict "hopper crystals" that might reflect the formation of halite, thick weathering rinds on rock surfaces, resistant fracture fills, and networks of polygonal fractures likely caused by dehydration of sulfate salts. Chemical variations with depth show that the siliciclastic fraction of outcrop rock has undergone substantial chemical alteration from a precursor basaltic composition. Observations from microscopic to orbital scales indicate that ancient Meridiani once had abundant acidic groundwater, arid and oxidizing surface conditions, and occasional liquid flow on the surface.
authors.affiliation: Department of Astronomy, Space Sciences Building, Cornell University, Ithaca, NY 14853, USA.
authors.forename: S W
authors.initials: SW
authors.lastname: Squyres
authors.forename: A H
authors.initials: AH
authors.lastname: Knoll
authors.forename: R E
authors.initials: RE
authors.lastname: Arvidson
authors.forename: B C
authors.initials: BC
authors.lastname: Clark
authors.forename: J P
authors.initials: JP
authors.lastname: Grotzinger
authors.forename: B L
authors.initials: BL
authors.lastname: Jolliff
authors.forename: S M
authors.initials: SM
authors.lastname: McLennan
authors.forename: N
authors.initials: N
authors.lastname: Tosca
authors.forename: J F
authors.initials: JF
authors.lastname: Bell
authors.forename: W M
authors.initials: WM
authors.lastname: Calvin
authors.forename: W H
authors.initials: WH
authors.lastname: Farrand
authors.forename: T D
authors.initials: TD
authors.lastname: Glotch
authors.forename: M P
authors.initials: MP
authors.lastname: Golombek
authors.forename: K E
authors.initials: KE
authors.lastname: Herkenhoff
authors.forename: J R
authors.initials: JR
authors.lastname: Johnson
authors.forename: G
authors.initials: G
authors.lastname: Klingelhöfer
authors.forename: H Y
authors.initials: HY
authors.lastname: McSween
authors.forename: A S
authors.initials: AS
authors.lastname: Yen
mesh_terms: D000143:Acids; D005118:Extraterrestrial Environment; D005290:Ferric Compounds; D019015:Geologic Sediments; D018535:Mars; D008903:Minerals; D017640:Silicates; D018531:Spacecraft; D013431:Sulfates; D013995:Time; D014867:Water
chemical_list: D000143:Acids; D005290:Ferric Compounds; D008903:Minerals; D017640:Silicates; D013431:Sulfates; C060346:basalt; D014867:Water; C000499:ferric oxide