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Mars' polar layered deposits (PLD) are comprised of layers of varying dust-to-water ice volume mixing ratios (VMR) that may record astronomically-forced climatic variation over Mars' recent orbital history. Retracing the formation of these layers by quantifying the sensitivity of deposition rates of polar material to astronomical forcing is critical for the interpretation of this record. Using a Mars global climate model (GCM), we investigate the sensitivity of annual polar water ice and dust surface deposition to various obliquities and surface water ice distributions at zero eccentricity, providing a reasonable characterization of the evolution of the PLD during recent low-eccentricity epochs. For obliquities between 15{\deg} - 35{\deg}, predicted net annual accumulation rates range from -1 to +14 mm/yr for water ice and from +0.003 to +0.3 mm/yr for dust. GCM-derived rates are ingested into an integration model that simulates polar accumulation of water ice and dust over 5 consecutive obliquity cycles (~700 kyrs) during a low eccentricity epoch. A subset of integration simulations predict combined accumulation of water ice and dust in the north at time averaged rates that are near the observationally-inferred value of 0.5 mm/yr. Three types of layers are produced per obliquity cycle: a ~30 m-thick dust-rich (~25% dust VMR) layer forms at high obliquity, a ~0.5 m-thick dust lag forms at low obliquity, and two ~10 m-thick dust-poor (~3%) layers form when obliquity is increasing/decreasing. The ~30 m-thick dust-rich layer is reminiscent of a ~30 m feature derived from visible imagery analysis the north PLD, while the ~0.5 m-thick dust lag is a factor of ~2 smaller than observed "thin layers". Overall, this investigation provides further evidence for obliquity forcing in the PLD climate record, and demonstrates the importance of ice-on-dust nucleation in polar depositional processes., Comment: 71 pages (pre-proof version), 7 figures

In its polar layered deposits (PLD), Mars possesses a record of its recent climate, analogous to terrestrial ice sheets containing climate records on Earth. Each PLD is greater than 2 ​km thick and contains thousands of layers, each containing information on the climatic and atmospheric state during its deposition, creating a climate archive. With detailed measurements of layer composition, it may be possible to extract age, accumulation rates, atmospheric conditions, and surface activity at the time of deposition, among other important parameters; gaining the information would allow us to “read” the climate record. Because Mars has fewer complicating factors than Earth (e.g. oceans, biology, and human-modified climate), the planet offers a unique opportunity to study the history of a terrestrial planet’s climate, which in turn can teach us about our own planet and the thousands of terrestrial exoplanets waiting to be discovered. During a two-part workshop, the Keck Institute for Space Studies (KISS) hosted 38 Mars scientists and engineers who focused on determining the measurements needed to extract the climate record contained in the PLD. The group converged on four fundamental questions that must be answered with the goal of interpreting the climate record and finding its history based on the climate drivers. The group then proposed numerous measurements in order to answer these questions and detailed a sequence of missions and architecture to complete the measurements. In all, several missions are required, including an orbiter that can characterize the present climate and volatile reservoirs; a static reconnaissance lander capable of characterizing near surface atmospheric processes, annual accumulation, surface properties, and layer formation mechanism in the upper 50 ​cm of the PLD; a network of SmallSat landers focused on meteorology for ground truth of the low-altitude orbiter data; and finally, a second landed platform to access ~500 ​m of layers to measure layer variability through time. This mission architecture, with two landers, would meet the science goals and is designed to save costs compared to a single very capable landed mission. The rationale for this plan is presented below. In this paper we discuss numerous aspects, including our motivation, background of polar science, the climate science that drives polar layer formation, modeling of the atmosphere and climate to create hypotheses for what the layers mean, and terrestrial analogs to climatological studies. Finally, we present a list of measurements and missions required to answer the four major questions and read the climate record. 1. What are present and past fluxes of volatiles, dust, and other materials into and out of the polar regions? 2. How do orbital forcing and exchange with other reservoirs affect those fluxes? 3. What chemical and physical processes form and modify layers? 4. What is the timespan, completeness, and temporal resolution of the climate history recorded in the PLD?

Mars Polar Science is a subfield of Mars science that encompasses all studies of the cryosphere of Mars and its interaction with the Martian environment. Every 4 yr, the community of scientists dedicated to this subfield meets to discuss new findings and debate open issues in the International Conference on Mars Polar Science and Exploration (ICMPSE). This paper summarizes the proceedings of the seventh ICMPSE and the progress made since the sixth edition. We highlight the most important advances and present the most salient open questions in the field today, as discussed and agreed upon by the participants of the conference. We also feature agreed-upon suggestions for future methods, measurements, instruments, and missions that would be essential to answering the main open questions presented. This work is thus an overview of the current status of Mars Polar Science and is intended to serve as a road map for the direction of the field during the next 4 yr and beyond, helping to shape its contribution within the larger context of planetary science and exploration.