A principal scientific objective for sending spacecraft to Mars has been to explore its geology as interpreted from data returned to Earth (see Chapter 2 for a review of the history of Mars exploration). This exploration was spurred on when early spacecraft revealed a surface reflecting a long-lived, dynamic interplay of geologic forces, in many ways similar to those evident in our own Earth–Moon system. Thus, scientific investigation has focused on topics such as: What are Martian rocks made of, and how old are they? What do volcanic and tectonic features reveal about the interior of the planet? What is the history of impact bombardment? How much water has there been at or near the surface, and were there times of abundant surface water on the planet? Have there been gradual or sudden changes in the planet’s climate? Is Mars geologically active today? Could life survive in environmental niches on the surface or below the surface, now or in times past?

Memnonia occurs on the western margin of the Tharsis volcanic province and on the southern margin of Amazonis Planitia. Its elevation ranges from a few kilometers above datum in Terra Sirenum to a few kilometers below datum along the northern edge of the map sheet. The cratered and faulted terrain of Terra Sirenum gives way to Tharsis lava flows to the east within Daedalia Planum. Valleys and channels mark the northern margin of the highlands, where they grade into low regions interrupted by elongate plateaus like Amazonis Mensa and the broader Lucus Planum.

This map spans diverse highland to lowland terrains from west to east. The western smooth region is the margin of the Tharsis rise that is centered to the west of the map, descending from 2 km to near datum. The elevated Lunae Planum and southern part of Tempe Terra occupy the central third of the map area. Lunae Planum rises to 3,500 m elevation along the southern border of the map as it approaches the Valles Marineris canyon system (south of the map area, MC-18). East of the planum lies the heavily cratered Xanthe Terra and Xanthe Montes. Cutting into these highlands are the large outflow channels Maja Valles and Kasei Valles. The latter originates from the irregular Echus Chasma depression that lies near datum. In the northeastern corner is Chryse Planitia, part of the vast northern lowlands, more than 3000 m below datum, and the destination for channel outflow as well as the Viking 1 lander.

The Mare Australe quadrangle is dominated by the south polar plateau, Planum Australe (Figure 30.A), rising to about 4,800 m in elevation on its highest part, Australe Mensa (Figure 30.B). Planum Australe is roughly circular, with horizontal dimensions of 1,100 km by 1,400 km. The plateau is dissected by the large troughs Chasma Australe, Promethei Chasma, and Ultimum Chasma, which divide parts of the plateau into the tongue-shaped forms of Australe Lingula and Promethei Lingula. Also present are systems of lower relief, concentrically and obliquely trending troughs, and asymmetric ridges (Figure 30.A). The surrounding cratered highlands lie at 1–3-km elevations and include some rather exotic terrains, unique to the south polar region. Cavi Angusti form depressions tens of kilometers across and reaching depths of a kilometer. Branching ridges form Dorsa Argentea and other ridge systems that cover Argentea, Promethei, and Parva Plana, surrounding Planum Australe.

The MC-1 quadrangle includes the north pole of Mars, which is covered by a 1,000-km-diameter plateau, Planum Boreum. This plateau rises 2–3 km above the surrounding northern lowland plains of Vastitas Borealis, which lie 3–5 km below datum. Planum Boreum is dissected by a large canyon, Chasma Boreale, which sets apart a secondary plateau, Gemina Lingula. These plateaus are dissected by the swirling, spiral troughs of Borealis and Gemini Scopuli. On the opposite side from Chasma Boreale, Olympia Planum forms a kidney-shaped rise that is partly buried by the Olympia Undae dune sea. These dunes also overlap the pancake-shaped rises of Scandia Tholi and the irregular depressions that form Scandia Cavi. The lowest parts of the northern plains occur around the tholi and at the mouth of Chasma Boreale. Dense fields of low knobs make up Scandia Colles. The Phoenix Lander site (see Chapters 4 and 5) lies in Vastitas Borealis.

Amazonis Planitia occupies the north-central part of the map region. The east-central and northeastern parts of the map are dominated by the western margin of Olympus Mons (MC-9) and its associated aureole deposits. This forms one of the most pronounced changes in relief in the solar system when considering a topographic transect, and involves more than 25,000 m in elevation change from the summit of the giant volcano to the regionally flat, lava-flow-covered plains of Amazonis Planitia. Olympus Mons is the only part of the quadrangle above datum. The aureole deposits, which extend up to 750 km west from the flank of the volcano and lie 1–3 km below datum, are marked by the Lycus Sulci ridge systems (see Figure 8.A), which make up broad lobes, hundreds of kilometers across. In the southern part of the map, near the highland–lowland boundary, pronounced mesas, Gordii and Eumenides Dorsa, mark the landscape. Just south of the mesas is the debouchment site of Mangala Valles (MC-16). In the southwestern part, knobby-looking terrain marks a transitional boundary that separates the northern plains, including Amazonis Planitia at –3 km to –4 km, from the cratered highlands to the south. Included in this rugged terrain, located in the west-central part of the map, is Marte Vallis, a distinct but shallow valley system that connects Elysium (MC-15) and Amazonis Planitiae.

The western two-thirds of the Noachis quadrangle is dominated by the heavily cratered highlands of Noachis Terra (1–3 km elevation), which are bordered to the east by Hellas Planitia. The latter, as low as –7 km, forms the floor of the ~2,300-km-diameter Hellas basin. The highland–basin margin is marked by the arcuate Hellespontus Montes, composed of basin-ring ridge systems, hundreds of kilometers long. The southern part of the quadrangle consists of the high, ridged plains of Malea and Sisyphi Plana. Broad, lengthy but relatively subtle trough systems occur west of and concentric to Hellas basin.

The Amenthes quadrangle contains parts of the Martian southern highlands and northern lowlands, as well as the transition between the two. In the southern part of the quadrangle, Cimmeria and Tyrrhena Terrae form rugged, cratered plateaus as high as 1 km above datum, which are gouged by the long, linear depressions of Amenthes Fossae. Highland terrae in this quad are separated by Amenthes Planum, an elongate, topographic basin that is located as much as 1 km below the highlands. The northern part of the Amenthes quadrangle consists of southern Utopia Planitia, over 4 km below datum. The western part of the quadrangle is made up of eastern Isidis Planitia, which is nearly as low in elevation. Both Utopia and Isidis Planitiae – which are centered outside of the Amenthes quadrangle – are plains of sediments that fill very ancient impact basins. Various scarps and depressions mark the surface of these lowland planitiae. From south to north, the highland–lowland boundary is defined by distributed fields of knobs and intervening plains of Nepenthes Mensae, rolling plains of Nepenthes Planum, and isolated and coalesced depressions of Amenthes Cavi.

The Cebrenia quadrangle is mostly covered by the plains of eastern Utopia and western Arcadia Planitiae, which are split by the prominent, north-trending Phlegra Montes ridge belt. The south-central margin of the quadrangle includes the northern part of the Elysium rise, upon which Hecates Tholus forms a domical mountain that includes the highest point in the quadrangle, more than 8,000 m above the adjacent plains to the north. This edifice includes a series of nested summit calderas and extensive fluvial valleys (Figure 7.A). Lesser ridge and scarp systems in the plains include north-trending Phlegra Dorsa in Arcadia and northwest-trending Panchaia Rupēs and northeast-trending Cydnus Rupēs in Utopia. Several systems of sinuous channel systems, including Tinjar, Granicus, Apsus, and Hrad Valles, extend hundreds of kilometers northwestward from the Elysium rise into the deeper, central floor of Utopia basin, where the lowest regional elevations (~5,000 m below the Martian datum) occur. The most prominent crater, 100-km-diameter Mie, occurs near the quadrangle’s center. The Viking 2 landing site is more than 150 km west of Mie.

This quadrangle, most of which lies 1–3 km above datum, consists of northern and central Hesperia Planum, a wrinkle-ridged volcanic plain, bordered by the cratered highlands of Tyrrhena Terra to the west and Terra Cimmeria to the east. In the center of Hesperia Planum lies the broad Tyrrhenus Mons shield. The northern part of Hadriacus Mons and a few outer massifs of Hellas basin, Ausonia Montes, crop out in the southwest corner of the quadrangle. Herschel crater forms a 275-km-diameter double-ring impact basin along the eastern margin of the quadrangle.

Phobos is the larger of the two moons of Mars, with a mean diameter2 of about 22 km and an orbital radius of 9,376 km. Phobos orbits faster than Mars rotates, so it rises in the west and sets in the east as viewed from the planet’s surface. The low orbit has made it a target for robotic spacecraft orbiting Mars. Images show craters along with numerous grooves (Figure M.1). Explanations proposed for their origin include tidal-stress induced fracturing and secondary impacts from larger craters, such as Stickney, on Phobos. Study of recent, better-resolution images suggests that the grooves, which are absent on the trailing end of Phobos, may be chains of secondary impacts caused by debris from impacts on Mars (Murray and Heggie, 2014), or debris from impacts on Phobos that orbited the moon before impacting it (Nayak and Asphaug, 2016). Lineations within Stickney (Figure M.2) may be from landslides in the moon’s weak gravity. Study of the thermal properties of the surface may determine whether the surface material is loose or relatively coherent, as these would show different rates of heating and cooling (Figure M.3).

The Phoenicis Lacus quadrangle shows the heart of the Tharsis region that dominates the western hemisphere of Mars. Elevations are high: except for the floor of Valles Marineris, essentially the entire quadrangle lies above datum. Arsia Mons rises over 11 km from the surrounding plain and is more than 400 km across. It marks the southwest end of the northeast-trending Tharsis Montes, which also include Pavonis Mons and Ascraeus Mons (MC-9). The eastern half of the map is dominated by Syria, Sinai, and Solis Plana, high plateaus that are capped by a broad field of dozens of smaller volcanic shields. From Arsia Mons across Syria Planum the elevation is 6,000 m or more, descending to 2,000 m at the southwest corner of the map. Wrapping for 1,000 km around the north and west margin of Syria Planum is the Noctis Labyrinthus, where numerous canyons and depressions intersect in a maze-like pattern (see Figure 2.3 in Chapter 2). A large, rugged promontory, informally referred to as Claritas rise, lies along the southern margin of the quadrangle and east of Claritas Fossae (Dohm et al., 2009a). Valles Marineris extends east of Noctis Labyrinthus for several thousand kilometers (across MC-18).