1. Geology Investigations on Mars

This article, Martian Geology Investigations, is Part 2 of the results of the Human Exploration of Mars Science Analysis Group (HEM-SAG) which are presented in five papers in this issue of the Journal of Cosmology (Levine et al., 2010a,b,c,d,e).

The geology of Mars poses a number of fundamental questions. While current and future robotic Mars missions would provide insight regarding the geology of Mars, HEM-SAG which was chartered by the Mars Exploration Program Analysis Group (MEPAG) in 2007, concluded that the top-level questions would likely remain broadly the same over the next 20 years. Among those questions are:

1. What is the volcanic history of the planet, and is Mars volcanically active today?

2. What was the nature and evolution of the Martian magnetic field?

3. What is the climate history of Mars?

4. What is the hydrologic history of Mars?

5. Is Mars hydrologically active at the present time?

These questions have wide-ranging implications with regard to the evolution of the Solar System, the nature and evolution of Earth’s surface and climate, and the feasibility and likelihood of biology on another planetary body. The complex history of the Mars, and the evolution of Mars from the potentially “warm and wet” periods of its early Noachian history to the later “cold and dry” period of the Amazonian, strongly suggest that an exploration strategy that addresses the characteristics and processes of the three major periods would be required (Fig. 1).

Thus, none of these questions could be answered by a focused study on just one landing site. The diversity of surface morphology and composition of the Martian surface demands an array of landing sites that spans the geologic history of Mars. As a preliminary exercise, we specified 58 distinct landing sites that would address these issues and would specifically benefit from the presence of human explorers (Fig. 2). A brief discussion of each of the 58 landing sites is found in Appendix 1. From these 58 sites, we chose three sample sites (Jezero Crater, Mangala Valles and Arsia Mons Graben) for more detailed examination and traverse selection, which we plan to use as reference missions after further outlining the major questions with regard to the geology of Mars.

All of the investigations outlined by MEPAG Goal III could be addressed by human exploration at carefully chosen exploration sites, such as those at the here proposed reference missions outlined above. Table 1 shows the methods and instrumentation that would be used at the various exploration sites.

2. Planetary-Scale Geologic Processes that Could be Addressed by Human Exploration

The absolute ages of surface units on Mars has been deciphered through indirect methods; samples returned from the Moon in the Apollo Program were used to provide constraints on the crater-size-frequency distribution of the lunar surface, and this has been applied to Mars, among other terrestrial planetary bodies. While this has provided a general history of Martian surface processes (Figure 1), it does not allow for detailed study of specific Martian periods, in particular the Hesperian and Amazonian, when the impact flux greatly decreased. While Martian meteorites have been analyzed and dated, not knowing their geologic context makes their incorporation into the geologic history of Mars difficult. And while a Mars Sample Return mission would yield surface samples with known context, a robotic mission would not yield the array of optimal samples that would address a wide range of fundamental questions. A human mission would allow for greater access to samples that a robotic rover might not get to, and the capacity for real-time analysis and decision-making would ensure that the samples obtained would be the optimal samples available.

Human explorers would also have greater access to the near-subsurface of Mars, which would yield insights into climate and surface evolution, geophysics, and potentially biology. Humans would be able to navigate more effectively through blocky ejecta deposits that would provide samples that were excavated from great depth and provide a window into the deeper subsurface. Humans could trench in dozens of targeted locations and operate sophisticated drilling equipment that could sample the top ~1 km of the crust. Our current understanding of the crust of Mars is limited to the top meter of the surface, so drilling experiments would yield unprecedented and immediate data. Drilling in areas of gully formation could also test the groundwater model by searching for a confined aquifer at depth.

3. Human Science Reference Missions (HSRM): Geology

We have analyzed three different exploration sites in detail as potential reference missions for the first program of human Mars exploration. The sites would span the geologic history of Mars (one site for each period of Martian history; Fig. 1) and allow for exploration traverses that would examine a variety of surface morphologies, textures and mineralogies to address the fundamental questions posed by MEPAG.

Jezero Crater. Jezero crater is a ~45 km impact crater on the northwest margin of the Isidis impact basin, in the Nili Fossae region of Mars (Figs. 3 and 4). This region is a very important area for understanding the formation of the Isidis basin, the alteration and erosion of this Noachain basement, and subsequent volcanism and modification (e.g., Mustard et al., 2007; Mangold et al., 2007). The rim has been breached in three places: twice where channels from the neighboring highlands to the west have drained into the crater from the northwest (Figs. 3, 4), and once on the eastern margin where the crater has drained eastward towards the Isidis basin (Fassett and Head, 2005) (Fig. 5). Each input channel deposited deltas on the crater floor that have been preserved and reveal sedimentary structures (Fig. 6) and clay deposits (Fig. 7) in highresolution images and spectral data (Fassett et al., 2007). Other parts of the crater floor appear to have been resurfaced by lava.

A 500-day mission at this site would reveal considerable data regarding the early Martian environment. Jezero crater itself is Noachian in age and the preserved rim would provide access to ancient bedrock material (rich in low-calcium pyroxene) exposed by the impact. The delta deposits are likely to be Noachian in age and HiRISE data show that the sedimentary record in the deposit has been preserved as a series of thin layers (Fig. 6). On the basis of the fact that a standing body of water existed within the crater for an extended period of time, this would be an ideal site to search for extinct biology. Humans would also be able to examine the structure and deposits within the channels associated with the deltas, which would be applicable to the other vast valley networks on Mars.

Extended traverses would be able to access and study the entire Jezero crater system (Fig. 3). To the southwest of Jezero are Hesperian lava flows from Syrtis Major, a principle volcano in the northern hemisphere of Mars providing a key constraint on the geological timescale of the region. This would also shed light on the evolution of magma composition on Mars. To the east of Jezero is the floor of Isidis basin, which is topographically connected to the northern plains and which would allow for detailed study of major impact events. Samples collected from all of these sites would allow for enhanced geochronology and a more detailed understanding of the hydrology, sedimetology, volcanology, and habitablity of the region.

Mangala Valles. Mangala Valles is an Hesperian-aged outflow channel which has received considerable attention on account of its role in global cryosphere/hydrosphere interactions, as well as the possibility that it contains icy near-surface deposits (Levy and Head, 2005; Leask et al., 2007a,b; Hanna and Phillips, 2006; Ghatan et al., 2005; Wilson and Head, 2004; Head et al., 2004). Mangala Valles emanates from a graben that is radial to the Tharsis volcanic complex (Fig. 8). Massive release of water from the ground at the graben was accompanied by phreatomagmatic eruptions (Wilson and Head, 2004) and caused catastrophic flow of water to the north, carving streamlined islands. There are also young glacial deposits along the rim of the graben (Head et al., 2004) and evidence for glacial scour having modified the surface of the outflow channel.

This site shows evidence for fluvial, volcanic, tectonic and glacial activity and complicated interactions among them. A landing site in the smooth terrain at the center of the outflow channel would provide access to a variety of sites of interest. Traverses to the channel head and the graben would allow direct observation of cryosphere-breaching geological activity. Traverses along the floor of the outflow channel, as well as on the scoured plains would provide insight into outflow flood hydrology and erosion processes, as well as provide an opportunity for sampling ice-rich deposits which may contain ancient flood residue. A traverse to the vent-rim glacial deposits would provide access to landforms created by volcano-ice interactions, as well as to samples of distal Tharsis volcanic deposits. On the basis of the likelihood that if life exists on Mars, it is most likely to inhabit the subsurface, a site such as Mangala would offer a unique opportunity to sample for evidence of such activity.

Arsia Mons Graben. All three of the major Tharsis Montes shield volcanoes and Olympus Mons exhibit expansive late-Amazonian glacial deposits on their northwestern flanks. The broadest of these deposits are the ones found on Arsia Mons, which show glacial deposits ~400 km to the west of the accumulation zone and cover an area of about 170,000 km³ (Head and Marchant, 2003). These glacial deposits are found among classic volcanic and tectonic structures, so an extended mission at this location would provide a wealth of information concerning several of the fundamental questions of Martian geology during the Amazonian period.

We designed several traverses from a potential base camp set up at 8°S, 124°W (Fig. 9) that would analyze the glacial and volcanic deposits, and the complicated relationship between them. Using extended rovers human explorers would be able to ascend the western flank of the shield and systematically obtain targeted samples that elucidate the recent volcanic history of Arsia. Another traverse from the same base camp would provide access to a ~5 km wide graben that appears to have been a major accumulation zone for much of the observed glacial deposits (Shean et al., 2007). A systematic sampling strategy at this location would provide a history of the flow regime at this site, and drilling at targeted locations could provide the recent climate record for Mars.

Recent General Circulation Models (GCMs) based upon global topography have revealed the Tharsis Montes to be significant cold traps for the accumulation of volatiles on the surface (Forget et al., 2006). Fieldwork at this site used in conjunction with remote sensing data would have global implications for recent climate change on Mars.

Below we assess the detailed activities that might be undertaken during these extended exploration periods, and show how they might link to MEPAG Goals and Objectives.

4. Graben and Surrounding Smooth Plains — 5 months

Geological Analysis. Analysis of glacial landforms and glacial and climatic history. Analyze the multiple drop moraines and assess sedimentary fabric, lithologic variations, search for erratics from further up the volcano. Study the processes producing drop moraines and assess similarities and differences between moraines. Dig for buried ice for ancient ice samples, and assess for ice cores for climate history. Examine the relationship to any exposed bedrock, searching for any evidence that the glacier was ever wet-based (scou in rock, drumlins, etc.). Examine thickness and fabrics of sublimation tills. Enter the major graben from the north, and traverse the ridges to the apparent base of the accumulation zone. Sample the volcanic rock suite and look for diversity and evidence of different eruption styles. Assess wall stratigraphy and gather representative samples in sequence for radiometric dating. (MEPAG investigations IA1, IA2, IA3, IIA2, IIB4, IIB5, IIIA1, IIIA3, IIIA4, IIIA5, IIIA6).

Shallow Seismic Survey. Measure thickness of sublimation tills and graben fill deposit at distal and proximal locations; assess presence of ice beneath till on graben floor. (MEPAG investigations IA1, IA2, IIB5, IIIA1, IIIA2).

Sediment Drilling. Analyze contributions from Arsia (tephra and bedrock) and from regional climate system (dust and ice) (MEPAG investigations IA1, IA2, IIB5, IIIA1, IIIA2).

GPR Ice-sounding. Determine high-resolution layering of valley-ill deposit, and document lenses of near-surface ice. (MEPAG investigations IA1, IA2, IIB5, IIIA1, IIIA2).

Shallow Excavations. Sample near-surface ice and permafrost deposits. (MEPAG investigations IA1, IA2, IIB5, IIIA1, IIIA2).

Electrical Resistivity. Determine permafrost depth in valley fill deposit and on surrounding plains. (MEPAG investigations IA1, IA2, IIB5, IIIA1, IIIA2).

Rock Sampling. Systematic sampling to provide constraints on flow rates and evolution with implications for recent climate change. (MEPAG investigations IA3, IIIA2).

Mapping. Features of interest would include accumulation zone at the south-eastern extent of the graben and parallel ridges throughout the graben. Detailed maps of the extent of each of the major drop moraines. (MEPAG investigations IA1, IA2, IIB5, IIIA1, IIIA2).

5. Eastern Flank of Arsia Mons — 3 months

Geological Investigations of the Flank of a Major Shield Volcano on Mars. Analysis of mineralogy and petrology of lava flows, pyroclastic edifices and tephra deposits. Examine evidence for volcano-ice interactions and document geologic effects and chemical/mineralogic alterations. Look for evidence of the highest topographic levels of ice accumulation on the edifice and document the nature of such deposits. (MEPAG investigations IIIA4). Mapping of the Flanks of a Representative Tharsis Volcano. (MEPAG investigations IA1, IA2, IIB5, IIIA1, IIIA2). Installation of sensitive seismometers to detect current magmatic and deeper subsurface activity and to study the internal structure of the volcanic edifice. (MEPAG investigations IA1, IA2, IIB5, IIIA1, IIIA2).

Rock Sampling. Systematic sampling of Amazonian volcanic units to provide insight into present Mars composition. (MEPAG investigations IA3, IIIA2).

6. Southern Young Glacial Deposits — 3 months

Geological Analysis. Study the nature of the youngest glacial deposits in and around the small graben and assess the drop moraines and their stratigraphic relationships. Assess the ages of these in relation to the rest of the Arsia tropical mountain glacier deposits. Traverse the broad Arsia lava flows that appear to be superposed on the glacial deposit and assess their ages in detail, sampling for radiometric ages. Look for evidence for volcano-ice interactions and document these effects, including generation and fate of any meltwater. Assess impact craters for deeper material and subglacial deposits. (MEPAG investigations IIIA3, IIIA4).

Shallow Seismic Survey. Determine relative contributions of glacial and volcanic deposits. (MEPAG investigations IA1, IA2, IIB5, IIIA1, IIIA2).

Sediment Drilling. Examine sediment for compositional analysis. (MEPAG investigations IA1, IA2, IIB5, IIIA1, IIIA2).

GPR Ice-sounding. Determine high-resolution layering of smooth glacial units, and document lenses of near-surface ice. (MEPAG investigations IA1, IA2, IIB5, IIIA1, IIIA2).

Shallow Excavations. Sample near-surface ice and permafrost deposits. (MEPAG investigations IA1, IA2, IIB5, IIIA1, IIIA2).

Electrical Resistivity. Determine permafrost depth in young glacial deposits. (MEPAG investigations IA1, IA2, IIB5, IIIA1, IIIA2).

Ice Coring. Drill to reveal ice composition and trapped atmosphere for recent climate change analysis.

7. Western Deposits — 4 months

Geologic Analysis. Traverse to major graben within the fan-shaped tropical mountain glacier deposit. Compare these glacial deposits to relatively younger deposits higher on the edifice. Assess proportions of sediment sources and determine depth to ice. Look for evidence of wetbased glacial activity. Traverse to graben: Analyze theories of origin. Compare evidence for simple glacial-passive graben interaction and the possibility of dike intrusion into the ice and phreatomagmatic explosions and eruptions. Look for country rock blocks and juvenile magmatic material on the rim and floor of the graben. Assess wall stratigraphy. (MEPAG investigations IA1, IIIA4, IIIA7). Detailed Mapping of Glacial/Volcanic Interactions. (MEPAG investigations IIIA4, IIIA6, IIIA7).

Shallow Seismic. Record depth measurements of distal smooth facies. (MEPAG investigations IIIA4, IIIA5, IIIA6, IIIA7).

Rock Sampling. Dating of distal units to provide context for duration of glacial flow. (MEPAG investigations IIIA4, IIIA5, IIIA6, IIIA7).

Application to MEPAG Goal III. Determine the evolution of the surface and interior of Mars.

Compiled by HEM-SAG with specific site suggestions and contributions by Jim Head, James Dickson, Caleb Fassett, Joseph Levy, Jim Rice, Francois Poulet, Jeff Moersch, Jen Heldmann, Charles Cockell, Peter Doran, Ralph Milliken and Rick Elphic. Initial biology prioritization also included: (Score: 1-5. EL = Extinct Life, PL = Present life. WG = biologist’s 'wild guess’). See map for locations, separate entries at each site description for gamma ray spectrometer and neutron spectrometer data on hydrogen/water content. RM is one of three HEM-SAG Reference Mission sites (red dots on map). All sites would include full complement of geophysical instrumentation (active and passive seismometers, magnetometers, heat flow probes, etc.) and the selection of sites should consider how the selection would contribute to the most effective seismic networks, obtaining heat flow measurements from different terrains and terrains of different ages, and be sure to sample the full range of known magnetic anomalies. Most sites contain the average Water Equivalent Hydrogen (WEH) in weight %, courtesy of Rick Elphic. Three reference mission sites provide seismic profile from edge to middle of Tharsis (38 and 34) and opposite sides of the globe for deep seismic structure (38/34 and 1).

1. Impact Crater Near Nili Fossae: (18.4°N, 77.7°E) (WEH wt% = 4.02) Valley networks forming deltas and water-filled impact crater near edge of Isidis Basin. Valley networks, layered sediments, ancient crater walls, Isidis basin deposits, volcano or basin peak ring structure near crater rim, mineralogical alteration revealed by OMEGA and CRISM (phyllosilicates, olivine). EL 5 (valley network means water — and ancient crater might have ponded water). PL1 (unless there is geological activity there now, this looks like a place most promising for past life). RM

2. Newton Crater gully sites: (40.5°S, 157.9°W) (WEH wt% = 4.03) Potentially ice-rich lineated valley fill on crater floor, gullies, crater stratigraphy. Highest concentration of gullies in one region anywhere on Mars. EL4 (crater hydrothermal systems?). Crater might have hosted life in hydrothermal system. PL5 gullies might be sites of present-day water seeps and therefore extant life.

3. Meridiani Region: (2.0°S, 5.5°W) (WEH wt% = 7.67) MER site to investigate context and the nature of early water-rich deposits. Easily traversable terrain would enhance regional study. Mineralogically unique region of the planet. EL5 early sediments/water suggest site of high priority for early life. PL1 Now dry and geologically inactive — not so likely to harbour present-day life

4. Gusev Crater-Columbia Hills: (14.6°S, 175.4°E) (WEH wt% = 8.42) Complex stratigraphy and explosive volcanic deposits in Columbia Hills, at the MER Gusev site. Lies on the crustal dichotomy, with fluvial input from the southern highlands and volcanic deposits related to Hr (Hesperian ridged plains). EL3 crater may have hosted hydrothermal systems/ponded water for early life, although it is a large crater and the site would have to be selected carefully. PL1 Doesn’t look very geologically active for present-day life.

5. Chasma Boreale:(82.6°N, 47.3°W) (WEH wt% = 41.45) North polar layered deposits and pre-PLD basal unit. Assessment of polar stratigraphy and relations to pre-polar deposits; orgin of Chasma Boreale and relationship to the northern extent of Vastitas Borealis. EL5 – If chasma was formed by water flood may be site of potential habitability early on and site of sustained water. Ice cap may have provided water. PL4 Near water ice (polar cap). Changes in obliquity may have created regions suitable for life even in recent times with oases sustained today?

6. South polar layered deposits and the Dorsa Argentea Formation:(71.8°S, 67.3°W) (WEH wt% = 35.71) Polar stratigraphy, comparison to MARSIS radar data showing ice-like layering, exploration of Hesperian DAF and possible ancient ice record. Close proximity to Amazonian ice flow features along the margins of the present day polar cap. EL5 – ancient terrains may have hosted water during the Noachian. PL4 Site of ancient permafrost – possible preservation/habitats of recent life?

7. Gale Crater: (5.1°S, 137.5°E) (WEH wt% = 6.48) Ancient crust, valley networks, central mound of volatiles. Stratigraphic analyses of crater wall material as well as sedimentary layers within the central mound, possibly of fluvial origin. EL4 Crater may have hosted hydrothermal systems/ponded water for life, particularly given evidence for volatiles. PL1 If it’s not geologically active now it’s unlikely to be a site for present life.

8. Floor of Valles Marineris: (7.0°S, 72.7W) (WEH wt% = 4.49) Interior layered deposits, stratigraphy and mineralogy; VM wall talus and stratigraphy. Examination of regional connection to circum-Chryse outflow channels. EL3 May have layers of sediments with early biology? PL3 Depth may create pressures suitable for transient liquid water even today?

9. Holden-Eberswalde Craters: (24.0°S, 33.6°W) (WEH wt% = 2.47) Late Noachian-Early Hesperian Valley network deltas and stratigraphy. Well-preserved and accessible sedimentary deposits. Ancient crust preserved along crater walls. EL4 See site 7 – same rationale. PL1.

10. Eastern Olympus Mons: (17.7°N, 128.2°W) (WEH wt% = 4.34) Recent volcanic, tectonic and fluvial activity, perhaps within the last few tens of millions of years. EL3 Not clear what the potential is for fossil life, but fluvial activity and volcanic activity would be promising. PL4 recent tectonic activity may suggest geothermal hot spots for present-day life?

11. Elysium Planitia: (5.0°N, 150°E) (WEH wt% = 3.05) Late Amazonian volcanic lava flows and outflow channels deposits. High biological interest. Testing of pack-ice hypothesis for platy units; could yield recent ice activity in the equatorial region of Mars. EL5 Sustained liquid water and lava, i.e. geochemically active and nutrients. PL2 Not geologically/aqueous today.

12. Western Olympus Mons Scarp: (19.6°N, 139.7°W) (WEH wt% = 5.79) Late Amazonian piedmont glacial deposits, stratigraphy of Olympus Mons lava flows and talus deposits. Access to Olympus Mons aureole deposits. EL4 Glacial deposits may be places for early life – if they had melted and provided liquid water. PL2 Not geologically active today to provide habitats for extant life.

13. Eastern Hellas Basin Massifs: (38.7°S, 97.0°E) (WEH wt% = 4.21) Hellas basin rim mountain rings for Noachian stratigraphy; Late Amazonian ice-rich deposits. Late Amazonian gullies, including the Centauri Montes “active gully” site (See 29), EL3 Ice and noachian terrains may have been good for early life – no obvious sustained habitats though? PL2 Not geologically active today?

14. Nili Fossae: (24.2°N, 79.4°E) (WEH wt% = 3.75) Hesperian ridged plains, OMEGA mineralogical anomalies (clays), possible ancient basin impact melt and olivine deposits. EL5 clays and impact melts suggest weathering/water/geochemical activity. May be good microenvironments for life. PL1 Not geologically active today and not obvious where extant life would be sustained.

15. Lyot Crater central deposits: (50.3°N, 29.1°E) (WEH wt% = 4.62) Largest crater in the northern lowlands, crustal stratigraphy, evidence for penetration of the cryosphere. Potential access to Late Amazonian high-latitude volatile-rich mantling deposits. EL5 Penetration of cryosphere may have provided conduit for liquid water into crater hydrothermal system. Good habitat for life. PL2 Not geologically active now, but the crater is in permafrost and contains ice — may have basal ice habitats for life?

16. Coloe Fossae Dichotomy Boundary: (41.3°N, 54.2°E) (WEH wt% = 3.86) Stratigraphy of dichotomy boundary scarp, Amazonian lobate debris aprons and lineated valley fill. Accessing the plateaus that are interspersed amongst the lineated valley fill can allow for testing as to whether potential glaciation was local or regional. WG EL3 Not a site of ancient water, but there was obviously geological activity, which may benefit life?? PL1 Not geologically active/water rich now?

17. Utopia Planitia: (28.5°N, 134.4°E) (WEH wt% = 5.49) Examine the deposits on the floor of Utopia, including the lahar-like deposits and related materials. Access to volcanic and fluvial deposits; high concentration of polygonally patterned ground in Utopia. EL2 Dead desert in the past? May have been more water rich in the very early history of Mars? PL1 Dead today.

18. Aram Chaos: (2.6°N, 21°W) (WEH wt% = 4.35) Outflow channel processes. Examine the nature of a range of mineralogical anomalies and investigate the OMEGA-based mineralogy sequence, testing the stratigraphic relationships. EL3 Outflow channels may have been good for life, but probably very transient water availabilities? PL1 Not a geologically active site today for life

19. Arsia Mons Glacial/Volcanism: (4.8°S, 126.3°W) (WEH wt% = 5.41) Examine site of late stage volcanism extruded from dikes cutting Late Amazonian glacial deposit on the northwest flank of Arsia Mons. Meteorological analysis of local climate at high elevations. EL2 If the volcanism wasn’t in an environment of high water content maybe not interesting? PL1 Not active today?

20. Slope Streaks: (14.4°N, 118.2°W) (WEH wt% = 4.31) Examine the nature and origin of slopes streaks and their characteristics, including searching for subsurface water, springs, landslide deposits, etc. EL4 Possible regions of past water, springs etc. PL4 Possible regions of present-day water, springs etc?

21. Atlantis Chaos: (34.8°S, 177.4°W) (WEH wt% = 4.99) Examine the nature of Atlantis Chaos and assess the large pluvial lake hypothesis. Extended traverses to assess the major magnetic anomalies in this area. Access to Noachian stratigraphy and fluvial processes, with potential connection to deposition within Gusev Crater. EL4 Area of water ponding??? PL1 Not very geologically active today?

22. Central Alba Patera: (40.7°N, 109.6°W) (WEH wt% = 6.85) Examine the range of Hesperian and Amazonian volcanic activity associated with Alba Patera, the young (Late Amazonian) latitude-dependent mantle deposit, and ancient (Hesperian) valley networks on the northern flanks. EL4 Valley networks and volcanism suggest strong potential for habitats for life (water/mineral supplies). PL1 Geologically inactive today.

23. Chryse Planitia: (27.0°N, 41.0°W) (WEH wt% = 3.35) Examine over a wide area the mineralogy, petrology and biology of outflow channel effluent. Examine the “ocean” hypothesis. Study underlying Hesperian ridged plains at impact craters. Provide greater context for the results from Viking Lander 1 and Pathfinder. EL3 Outflow channels may provide transient water availability, but not sustained for life. Impact craters of potential biological interest. PL1 Geologically inactive today.

24. Medusae Fossae Formation: (1.6°N, 173.2°W) (WEH wt% = 6.39) Examine the areas where interfingering of Tharsis lava flows and the MFF are observed. Establish nature and origin of MFF and stratigraphy, age and interactions with lava flows. WG EL4 Lava flows and past water? PL1 Geologically inactive today.

25. Hellas Basin Floor: (41.9°S, 69.6°E) (WEH wt% = 3.92) Study the effluent of the Eastern Hellas outflow channels, and assess the Hellas “ocean” hypothesis. Meteorologic analyses could address the unique climate of Hellas at a low elevation and relatively high pressure. Very important site for biology. EL5 depth of hellas and evidence of sediments suggests sustained liquid water. PL3 May be a place where transient liquid water (above triple point) could be sustained today at bottom of basin?

26. Northeast flanks of Arsia Mons: (7.4°S, 121.2°W) Cave skylight site (see Cushing et al., 2007 – LPSC #1371). Site of high biologic interest if subsurface water resources are available. Accessiblity to Arsia lava flows.

27. Walls of Dao Vallis: (33.7°S, 92.5°E) These are classic, well-developed gully systems and also some of the gullies are associated with the “pasted-on” terrain which Christensen (2003) has hypothesized to be melting snowpacks. High relief throughout the valley could yield excellent insight into local micro-climate-related surface processes. From Jen Heldmann.

28. Terra Sirenum:(39.3°S, 161.7°W) Site of high-albedo deposit that formed within the last decade in the proximity of gullies (Malin et al., 2006). Classic Noachian highland terrain with Hesperian lava flows and small-scale Amazonian fluvial activity.

29. Centauri Montes: (38.7°S, 96.7°E) Site of high-albedo deposit that formed within the last decade in the proximity of gullies and more extensive volatile-rich deposits (see site 13) (Malin et al., 2006). Meteorologic stations could provide insight into the local climate of eastern Hellas and the regional climate of Hellas as a whole.

30. Terra Cimmeria: (70.0°S, 180.0°E) A suggested drill target is at 180W between 60-80S which is a region of preserved crustal magnetism (indicating old terrain) and ground ice (GRS measurement, but also crater morphology indicative of underlying deeper ice).

31. Mawrth Vallis:(25.3°N, 19.3°W) Fluvial geomorphology with heavy weathering. Stratigraphic analysis and access to the northern lowlands.

32. Olympia Planitia: (75.0°N, 180.0°E) Sulfate-rich dunes around the north pole (very recent alteration product(?)). Access to the southern-most extent of the residual polar caps, and access to polar troughs to reveal Amazonian climate history.

33. Valles Marineris: (6.2°S, 70°W) Sulfate-rich deposits only accessible by human operations. Extensive stratigraphic analysis and access to landslides/talus piles.

34. Arsia lobate glacial deposit: (7.4°S, 123.8°W) Evidence for Late-Amazonian glacial activity. Assess the interaction of late-stage glaciation and volcanism, analyze climate history and sample possible residual ice. Assess various moraines, obtain ice cores, sample lava flow stratigraphy to assess volcano and glacial chronology. RM

35. North Polar Cap: (86.0°N, 79.0°E) Accessibility to Late-Amazonian ice deposits, through drilling and stratigraphic analysis of polar troughs.

36. South Polar Cap: (88.0°S, 30.0°E) Accessibility to Late-Amazonian ice deposits, through drilling and stratigraphic analysis of polar troughs.

37. Syrtis Major Planum: (7.0°N, 69.0°E) Possible SNC-meteorite ejection locale, Hesperian lava flows and silicate-rich deposits in caldera. Interactions with Isidis and the northern lowlands. From Joe Levy.

38. Mangala Valles: (18.0°S, 149.4°W) Outflow Channel Floor: Residual ice-rich deposits remaining on the floor of an outflow channel. Hesperian-aged (?) outflow channel. Dike-related vents; evidence for phreatomagmatic eruption and rim glacial deposits at the graben. Examine floor and evidence for multiple events and role of groundwater. Possible residual ice on the floor of the channel. From Joe Levy. RM

39. Nilosyrtis Mensae: (35.0°N, 71.0°E) Complex LVF/LDA stratigraphy along the dichotomy boundary. Evidence for multi-stage formation of extensive glacial deposits; sampling could provide chronology for recent climate change and resulting glacial landforms.

40. Olympus Mons Caldera Floor: (18.3°N, 133.0°W) Age of Tharsis volcanism; Caldera wall stratigraphy, chronology, atmospheric dust stratigraphy, ash deposition. Landslide deposits along the caldera wall. Seismic studies and mass spectrometer for possible gas venting.

41. Milankovic Crater: (55°N, 146.5°W) Rare large impact crater within the northern lowlands (> 40 km); Analysis of excavated material from the northern lowlands and adjacent high-latitude volatile-rich mantling and related deposits.

42. Kasei Valles: (21.0°N, 73.8°W) Massive streamlined morphology gives access to Noachian/Hesperian fluvial deposits; Stratigraphic analysis of channel walls; Channel is sourced from the northern extent of Vallis Marineris, which could yield insight into more regional processes. Evidence for fluvial activity, glacial scour, and subsequent lava flows.

43. Vastitas Borealis Formation: (65.7°N, 20.2°E) Classic northern lowlands terrain; Possible sublimation residue for outflow channel effluent; extensive polygon development; Latitude-dependent mantling deposits; Context for Mars Phoenix analysis.

44. T-Shaped Valley: (37.6°N, 24.0°E) Massive glacial deposits along the dichotomy boundary; Multiple converging flows from various localized sources; Meteorological study could address the recent conditions along the dichotomy boundary; Possible Late Amazonian glacial ice preserved.

45. Isidis Basin Floor: (12.0°N, 88.5°E) Possible flooding remnants from a Noachian and Hesperian northern ocean; Volcanic input from Syrtis Major; Was this a major part of a northern lowlands ocean?

46. Utopia Basin Floor: (43.8°N, 117.0°E) Extensive access to patterned ground and nearsurface volatiles; Examine distal parts of the Elysium lahar deposits; Corroborative studies to go along with VL2 analyses; Possible preserved ice from Early Amazonian.

47. Hecates Tholus: (32.0°N, 150.3°E) Unique concentration of young (Hesperian/Amazonian) valley networks, in the proximity of extensive Hesperian volcanic activity; Access to nearby northern lowlands; Some volcanism may be Amazonian.

48. Peak Magnetic Anomalies: (60.0°S, 175.0°E) Geophysical analysis could reveal details of an early Martian magnetic field; classic Noachian cratered terrain could yield insight into the composition of Mars in its first billion years; Major goal would be to link surface geology to any evidence of subsurface magnetism and magnetic carriers.

49. Hesperian Calderas: (59.4°S, 60.7°E) Volcanic record for middle-Mars history; Meteorological study could document interaction between Hellas and South Pole; Examine key part of Martian timeline; understand Hesperian volcanic processes and related valley networks.

50. Hesperia Planum: (23.3°S, 110.6°E) Potential comparison with classic lunar mare terrain; Structural investigation of wrinkle-ridge formation; Examination of classic unit of the Mars timeline.

51. Huygens Ridge: (12.3°S, 66.3°E) Access to exhumed dike/Potential Hesperian Ridged terrain; Geochemical analyses of intrusive volcanic material; This dike system may be feeder for major Hesperian ridged plains volcanism.

52. Argyre floor deposits: (51.5°S, 41°W) Potential analyses of volatile deposits from south polar ice sheet; primary impact record for large impact basin/large impact melt-sheet; Amazonian formation of small-scale fluvial features. Possible eskers in southern part of basin; Assess evidence for aqueous flooding and shorelines.

53. Thaumasia Valley Networks (Warrego): (38.6°S, 89.4°W) Post-emplacement modification of classic Noachian valley networks; Access to ice-rich crater-fill material; Geophysically probe classic thrust-like structure at edge of Tharsis rise.

54. Syria Planum: (7.7°S, 100.5°W) Structural evolution of Tharsis; Close proximity to western most extent of Valles Marineris; This region is highest point on Tharsis and key to its early volcanic evolution.

55. Proctor Crater: (47.5°S, 30.2°E) Extensive dune field on crater floor; Study of recent dune formation and migration and relation to climate change; Stratigraphic analysis of Noachian crust.

56. White Rock: (8.0°S, 25.2°E) Field analysis of high-albedo crater floor deposit; Eolian modification history of enigmatic surface unit; Thought to be key to early mineralogy and resurfacing.

57. Complex tectonic ridges: (66.0°S, 140.0°E) Structural analysis of Noachian terrain; Potential exposure of deep-crust from massive faulting; Enigmatic part of Noachian crustal deformation; Geophysical analyses.

58. Mie Crater: (48.5°N, 139.7°E) Rare large crater within the northern lowlands provides vertical sampling and stratigraphy; Fifty-year in-situ comparison of high-latitude present-day surface processes and climatic activity; Examination of condition of Viking 2 lander after ~50 years; Ground truth for major mid-latitude site that illustrates periglacial processes.