The Mars Astrobiology Explorer-Cacher (MAX-C), also known as Mars 2018 mission, was a NASA concept for a Mars rover mission, proposed to be launched in 2018 together with the European ExoMars rover. The MAX-C rover concept was cancelled in April 2011 due to budget cuts. The rover would have been solar powered, with a maximum mass of 300 kg and based largely on the Curiosity rover components, but would have entailed a system tailored to the specific payload. The MAX-C rover would have performed an in-situ astrobiological exploration, evaluate the habitability potential of various Martian environments, and it would have collected, documented, and cached samples for potential return to Earth by a future mission. The Mars 2020 mission with its Perseverance rover had similar scientific objectives as Mars 2018 and MAX-C.
History The essential energy, water, and nutrient requirements to support and sustain life on Mars are currently present, and the Martian geologic record offers tantalizing clue of many ancient habitable environments. If life emerged and evolved on early Mars then it is possible, and indeed likely, that physical or chemical biosignatures are preserved in the exposed rock record. These discoveries and inferences make a compelling case for a rover mission designed to explore for evidence of past Martian life. For over a decade, the Mars Exploration Program has pursued a strategy of "follow the water". While this strategy has been highly successful in the Mars missions of 1996-2007, it is increasingly appreciated that assessing the full astrobiological potential of Martian environments requires going beyond the identification of locations where liquid water was present. Thus, in order to seek signs of past or present life on Mars, it is necessary to characterize more comprehensively the macroscopic and microscopic fabric of sedimentary materials. This type of information would be critical to select and cache of relevant samples for addressing the life question in samples intended for study in sophisticated laboratories on Earth. The possible strategy of using rovers to collect and cache geological samples for possible subsequent return to Earth has been discussed as far back as at least the mid-1990s. In 2007 it was recommended sample caching on all surface missions that follow the Mars Science Laboratory Curiosity rover, in a way that would prepare for a relatively early return of samples to Earth. In mid-2007, NASA directed that a very simple cache be added to the Curiosity rover and, although they endorsed the potential value of sample caching, experts raised serious concerns regarding sample quality for this specific implementation. In November 2008, the cache was descoped to make room for tools to clean the rover's sample acquisition equipment, which were added due to sample handling problems encountered by the Phoenix lander. A mid-range rover concept was originally included in the planning work of the Mars Architecture Tiger Team (MATT). By the time of the MATT-3 report in 2009, the potential mission was referred to with several different working names, including both 'Mid-Range Rover' and 'Mars Prospector Rover', and the mission concept was generically envisioned as including a single Mars Exploration Rover or Mars Science Laboratory-class rover with precision landing and sampling/caching capability. To provide a name that fit the mission concept better, it was changed in August 2009 from the generic Mid-Range Rover (MRR) to Mars Astrobiology Explorer-Cacher (MAX-C).
In April 2011, because of a budgeting crisis, a proposal was announced to fly only one rover in 2018 that would be larger than either of the vehicles in the paired concept, ExoMars (ESA) and MAX-C (NASA). One suggestion was that the new vehicle be built in Europe and take on a combination of European and USA instruments. NASA proposed to provide a launch rocket and the "Sky Crane" landing system. In February 2012, NASA terminated its participation in ExoMars due to budgetary cuts, and when Congress reinstated funding for Mars exploration after a loud outcry from planetary scientists and enthusiasts, NASA announced in December 2012 the Mars 2020 rover and, later, that it would indeed prepare a sample cache.
Objectives
The main objective was at a site with high preservation potential for physical and chemical biosignatures, evaluate paleo-environmental conditions, characterize the potential for preservation of biosignatures, and access multiple sequences of geological units in a search for evidence of past life and/or prebiotic chemistry. Samples necessary to achieve the scientific objectives of the proposed future sample return mission would be collected, documented, and packaged in a manner suitable for potential return to Earth. The primary science objective was to land at a site interpreted to represent high habitability potential, and with high preservation potential for physical and chemical biosignatures:
Early Noachian astrobiology — Prebiotic environmental context in which life potentially arose. Noachian-Hesperian stratigraphy — Whether surface conditions before and after the decline in erosion, aqueous weathering, fluvial activity, and magnetic field were habitable. Astrobiology — Test life-related hypotheses in the context of another specific kind of geologic terrain. Sample collection that could have preserved evidence of prebiotic chemistry or life on Mars; characterize the potential for the preservation of biosignatures. Methane emission from subsurface. Radiometric dating Deep core drill — core samples from a depth of ~ 2m Polar layered deposits — Investigate potential record of recent global climate changes. Mid-latitude shallow ice — Investigate the habitability of mid-latitude ice, and how does perchlorate affect the present habitability of Mars. Could mid-latitude ice provide a resource for In-Situ Resource Utilization (ISRU)? A secondary science objective would have been to address the need for long-term atmospheric pressure data from the Martian surface. There were studies evaluating the possibilities for cooperative science between the MAX-C rover and the ExoMars rover if landed together at the same location.
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