Oxia Planum: The Landing Site for the ExoMars “Rosalind Franklin” Rover Mission: Geological Context and Prelanding Interpretation

Abstract

The European Space Agency (ESA) and Roscosmos ExoMars mission will launch the “Rosalind Franklin” rover in 2022 for a landing on Mars in goals of the mission are to search for signs of past and present life on Mars, investigate the water/geochemical environment as a function of depth in the shallow subsurface, and characterize the surface environment. To meet these scientific objectives while minimizing the risk for landing, a 5-year-long landing site selection process was conducted by ESA, during which eight candidate sites were down selected to one: Oxia Planum. Oxia Planum is a 200 km-wide low-relief terrain characterized by hydrous clay-bearing bedrock units located at the southwest margin of Arabia Terra. This region exhibits Noachian-aged terrains. We show in this study that the selected landing site has recorded at least two distinct aqueous environments, both of which occurred during the Noachian: (1) a first phase that led to the deposition and alteration of ∼100 m of layered clay-rich deposits and (2) a second phase of a fluviodeltaic system that postdates the widespread clay-rich layered unit. Rounded isolated buttes that overlie the clay-bearing unit may also be related to aqueous processes. Our study also details the formation of an unaltered mafic-rich dark resistant unit likely of Amazonian age that caps the other units and possibly originated from volcanism. Oxia Planum shows evidence for intense erosion from morphology (inverted features) and crater statistics. Due to these erosional processes, two types of Noachian sedimentary rocks are currently exposed. We also expect rocks at the surface to have been exposed to cosmic bombardment only recently, minimizing organic matter damage.

Morphology, Morphometry and Distribution of Isolated Landforms in Southern Chryse Planitia, Mars

“…Despite this, individual examples of mounds show evidence of being embayed and buried by the dark plains material (Figures 8a, 8c and 8e), suggesting that, in general, the mounds pre-date the dark plains material. A clear contact between a mound and the clay-bearing unit of Oxia Planum is observed (Figure 8f), showing that the mounds post-date the clay-bearing unit, which is in agreement with the interpretation in Quantin-Nataf et al (2021).…”

“…Hence, the Mawrth-like compound mounds may be genetically equivalent to the wider circum-Chryse mound population. This inference suggests that the wider mound population is older than 3.8 Ga, but younger than the 4.0 Ga lower limit controlled by the age of the Oxia Planum clays (Quantin-Nataf et al, 2021), assuming that, as our data shows, all of the mounds belong to the same population.…”

Periodic Bedrock Ridges at the ExoMars 2022 Landing Site: Evidence for a Changing Wind Regime

“…In 2023, the mission will land in Oxia Planum (18.2° N; 24.3° W) to search for signs of past or present life on Mars and to perform long‐term atmospheric investigations (Rodionov et al., 2017; J. L. Vago et al., 2017). Oxia Planum shows large outcrops of Noachian‐aged phyllosilicates (a light‐toned sedimentary/clay bearing unit) and a fan delta enriched in hydrated silicates, which record two distinct alteration environments and events (Carter et al., 2016; Lakdawalla, 2019; Pajola et al., 2017; Quantin‐Nataf et al., 2016, 2021; J. L. Vago et al., 2017). The clay bearing unit is unconformably overlain by a Amazonian dark resistant unit (Adru or Capping Unit; Quantin‐Nataf et al., 2016, 2021; J. L. Vago et al., 2017), which was interpreted to be remnants of an Early Amazonian (2.6 Ga) volcanic material suggesting an intense and prolonged erosion by wind (Carter et al., 2016; Pajola et al., 2017; Quantin‐Nataf et al., 2016, 2021).…”

“…Oxia Planum shows large outcrops of Noachian‐aged phyllosilicates (a light‐toned sedimentary/clay bearing unit) and a fan delta enriched in hydrated silicates, which record two distinct alteration environments and events (Carter et al., 2016; Lakdawalla, 2019; Pajola et al., 2017; Quantin‐Nataf et al., 2016, 2021; J. L. Vago et al., 2017). The clay bearing unit is unconformably overlain by a Amazonian dark resistant unit (Adru or Capping Unit; Quantin‐Nataf et al., 2016, 2021; J. L. Vago et al., 2017), which was interpreted to be remnants of an Early Amazonian (2.6 Ga) volcanic material suggesting an intense and prolonged erosion by wind (Carter et al., 2016; Pajola et al., 2017; Quantin‐Nataf et al., 2016, 2021). Aeolian bedforms, such as megaripples or transverse aeolian ridges (TARs; Balme et al., 2008; Foroutan & Zimbelman, 2016; Hugenholtz et al., 2017; Zimbelman, 2010), are also widespread, testifying the key role played by the wind in shaping the surface of Oxia Planum (Balme et al., 2017; Bhardwaj et al., 2019; Ivanov et al., 2020; Pajola et al., 2017; J. L. Vago et al., 2017).…”

“…PBRs formative winds can be investigated even if landing will be far from double-crested ridge structures, by looking for aeolian grooves over a specific ridge slope (Hugenholtz et al, 2015). In addition, being eroded into the bright clay-rich unit (Carter et al, 2016;Quantin-Nataf et al, 2021), PBRs provide an easily accessible window into the first 1-2 m of this astrobiologically promising rock unit. Furthermore, the lander instruments will provide a better assessment on the present-day aeolian environment at the surface (Martín-Torres et al, 2020;Mongelluzzo et al, 2019;Rodionov et al, 2017;Soria-Salinas et al, 2020).…”