Mars Astrobiological Cave and Internal habitability Explorer (MACIE): A New Frontiers Mission Concept

Abstract

Mission Concept for Mars Subsurface Life and Habitability 1. Martian lava tubes are one of the best places to search for evidence of life The Mars Astrobiological Cave and Internal habitability Explorer (MACIE) mission concept is named for Macie Roberts, one of NASA's 'human computers' (Conway 2007). MACIE would access the Martian subsurface via a lava tube. Lava tube caves are compelling subsurface astrobiological targets because they have their own relatively stable microclimates, are shielded from radiation and harsh surface conditions, and may contain water ice (Blank et al., 2020). They may also provide access to materials vital to future human exploration and in situ resource utilization (ISRU) activities (Sam et al., 2020). A cave mission represents a compelling next-step in Mars astrobiology and habitability exploration, because it would examine the deeper subsurface (>20x deeper than prior surface craft) without the cost and risk associated with a deep drilling payload. Subsurface Mars among the best places to look for post-Noachian habitable environments Post-Noachian Mars (<3.1 Ga) near-surface habitability rapidly degraded, making near-surface environments inhospitable to life as we know it. Organics observed on Mars to date are oxidized due to radiation making it challenging to search for unambiguous biosignatures in near-surface environments (Eigenbrode et al., 2018). Additionally, transient liquid brines may form at the surface, but may not persist long enough to be habitable (Rivera-Valentin et al., 2020). In contrast, modelling of subsurface environments indicates metastable water ice (Williams et al., 2010) and brines (Burt and Knauth, 2003) may be present over extended time periods and have chemical disequilibria necessary to support life. Thus, subterranean Mars may be the best place to look for habitable environments and evidence of life. NASEM's Astrobiology Strategy (2019) recommends targeting the Martian subsurface habitability, which has yet to be the focus of a planetary mission. Tharsis lava tubes may have been habitable in the Amazonian Hundreds of lava tube entrances are located within Hesperian-Amazonian terranes in the Tharsis region (Cushing et al., 2015) and are expected to host metastable water ice (Williams et al., 2010). Mapping of the Tharsis region demonstrates both glacio-volcanism (Cassinelli and Head, 2019) and hydrothermal fluvial activity (Hargitai and Guilick, 2018), which may have occurred into the late Amazonian. This suggests hydrothermal fluid fluxes from the surface to the subsurface may have occurred as they do in modern volcanic systems, as well as melting of glaciers associated with glaciovolcanic activity, similar to Iceland. The Tharsis region also hosts vast fracture networks, which would provide means to transport surface waters and nutrients into the subsurface (Bouley et al., 2018). Thus, lava tube caves may represent a modern and/or recently habitable environment on Mars. Detection of habitable conditions in the subsurface of Amazonian Mars would fundamentally change our view of Mars' habitability and astrobiological potential through geologic time. 2. MACIE will determine the Habitability and Astrobiological Potential of a lava tube cave MACIE focuses on two key questions: (1) how long were habitable conditions maintained within a Martian cave? and 2) did life ever colonize a Martian cave? These questions are translated into two primary goals: 1) assess the present and past habitability of a Martian lava tube and (2) search for evidence of past or present life in a Martian lava tube. MACIE would address multiple goals of Summary of Key Points 1. Martian subsurface habitability and astrobiology can be evaluated via a lava tube cave, without drilling. 2. MACIE addresses two key goals of the Decadal Survey (2013-2022) and three MEPAG goals. 3. New advances in robotic architectures, autonomous navigation, target sample selection, and analysis will enable MACIE to explore