Where are Mars' Hypothesized Ocean Shorelines? Large Lateral and Topographic Offsets Between Different Versions of Paleoshoreline Maps.

Mars' controversial hypothesized ocean shorelines have been found to deviate significantly from an expected equipotential surface. While multiple deformation models have been proposed to explain the wide range of elevations, here we show that the historical locations used in the literature and in these models vary widely. We find that the most commonly used version of the Arabia Level does not follow the originally described contact and can deviate laterally by ∼500 km in Deuteronilus Mensae. A meta‐analysis of different published maps shows that, globally, the minimum lateral offsets between the locations of the putative Arabia and Deuteronilus shorelines vary by an average of 141 ± 142 km and 180 ± 177 km, respectively. This leads to mean elevations of the Arabia Level that vary by up to 2.2 km between different mappings, and topographic ranges within each global mapping ranging from 2.7 to 7.7 km. The younger Deuteronilus Level has less topographic variation as it largely follows a formal contact (the Vastitas Borealis Formation) within the relatively flat northern plains. Given the high variance in position (spatial and topographic) of the maps, the use of such data and conclusions based on them are potentially problematic. Plain Language Summary: Whether oceans ever existed on Mars is controversial, with support largely coming from hypothesized ancient shorelines. As with modern shorelines on Earth, possible ancient martian shorelines are expected to be approximately level, but past studies found that the two main global shoreline mappings have elevation ranges from about one to several kilometers, respectively. Here, we remap segments of the proposed shorelines based on their original geomorphic definitions and find that modern maps vary laterally by hundreds of kilometers from our segments mapped using higher‐resolution data. Additionally, we compare maps of potential shorelines over time. We find that maps are both inconsistent and inaccurate with their placement of hypothesized shorelines. Lateral offsets between different maps locally exceed a thousand kilometers. This disagreement with the poorly understood location of the potential shorelines can explain, in part, the observed elevation differences. Our results question the usefulness of putative shorelines as evidence for ancient martian oceans and implies the need for more detailed, revised mappings and scrutiny. Key Points: Remapping segments of the putative Mars shorelines finds modern interpolated maps diverge up to 500 km from original geomorphic mapsPublished maps of the Arabia and Deuteronilus Levels have similar mean lateral offsets of 140 and 180 km with 1,000 km max offsetsA large portion of the topographic disparity of the Arabia Level may be explained through these inconsistent mappings over time [ABSTRACT FROM AUTHOR]