Potential existence and preservation of subsurface ice in the Athabasca Valles region, Mars.
Authors: Mansilla Nuñez Federico , Zorzano María-Paz , Ruiz Javier 
Published: July 2024

Previous research has suggested that large floods in the Elysium mons region, Mars, may have melted significant amounts of ice in the late Amazonian epoch. &#160;Recent work has proposed that there may be remnants of ice-rich layers in the subsurface of the Medusa Fossae Formation (Watters et al., 2024), close to Elysium mons, see Figure 1.&#160; In this work we investigate the plausible presence of ices in Athabasca Valles region, which is located at the southern flank of Elysium Mons and close to the Medusa Fossae Formation (MFF).&#160;Figure 1. Situation map of the area of interest considered in this study.Athabasca Valles consists of a group of subparallel valleys with NE-SW orientation and SW vergence whose source area is located at 10&#186;N, 157&#186;E. This area has a consistent slope that stops at Cerberus Palus, see Figure 1. There are currently two different models to explain the recent geological history of Athabasca Valles: one of them postulates the existence of considerable amounts of ice in the subsurface that interacted with magma (Cassanelli and Head, 2018), whereas&#160; the other one considers only volcanic activity (Ryan and Christensen, 2012; Miller et al., 2023).We have investigated the Athabasca Valles region to evaluate the possible presence of ice in the recent past. Using MOLA, THEMIS, HRSC, CTX and HiRISE observations, we find grooved surfaces at the bottom of the valleys, hills with nunatak like shapes, potential drop stones, surface features like polygonal patterned floors and pingo-like landforms, see Figure 2, as well as some other periglacial related landforms (Balme and Gallagher, 2009; Yakovlev et al., 2021). All of these features are caused by the sustained presence of ice.Figure 2. CTX and HiRISE view. Top left: Eroded impact crater surrounded by grooved surfaces and possible dropstones, in the MurrayLab_CTX_V01_E152_N08 tile. Top right: Pingo like features and polygonal patterned floors in the HiRISE HI_046690_1900_063437_1900 image. Bottom left: Possible moraines and grooved surfaces observed in MurrayLab_CTX_V01_E156_N08 tile. Bottom right: nunatak-type mount observed in MurrayLab_CTX_V01_E156_N08 tile. All images have the same orientation.We also observe the existence of a platy region with fractures that may be attributed to lava-ice interaction, see Figure 2. Using crater counting chronology methods, we have dated the platy surface structures and estimated an age of 29 Ma.&#160; We propose that the existence of ices under the surface 29 Ma ago caused the movement of the platy surface structures downstream of Athabasca Valles because of the lava-ice interaction. The valley has a consistent slope that stops at Cerberus Palus, and it is reasonable to think that ice or melted ice may have moved along this slope accumulating at Cerberus Palus.Figure 3. THEMIS Thermal image of a fractured plate structure, where the plates show low thermal inertia whereas the inter-plate regions show high thermal inertia. These two differentiated parts have been dated using crater counting methods (see inset).Using SHARAD data, we find bright radar reflectors in the accumulation area of Cerberus Palus, which we interpret as potential preserved subsurface layers of ice pore-filling materials, remains of previously existing ices, see Figure 4. We have modelled the temperatures of an hypothetical ice sheet under the surface of this region using the same methodology described by Egea et al. 2022 (Egea-Gonz&#225;lez et al., 2022) for the North Pole region.&#160; Our analysis shows that subsurface ice can be thermally stable under the present-day thermal environment.Our observations are consistent with the possible interaction of lava and ices in Athabasca Valles around 29 Ma ago, and the present-day preservation of ice in the subsurface at the end of the valley, in Cerberus Palus.Figure 4. Example of one radargram where we can observe the existence of subsurface reflectors at the end of the basen.&#160;AcknowledgementsM.-P.Z. and F. M. were supported by grant PID2022-140180OB-C21 funded by MCIN /AEI /10.13039/501100011033 / FEDER, UE. The work of F. Mansilla is supported by the grant PRE2020-09170, founded by MCIN/AEI/10.13039/501100011033.ReferencesBalme, M. R. and Gallagher, C.: An equatorial periglacial landscape on Mars, Earth Planet. Sci. Lett., 285, 1&#8211;15, https://doi.org/10.1016/j.epsl.2009.05.031, 2009.Cassanelli, J. P. and Head, J. W.: Large-scale lava-ice interactions on Mars: Investigating its role during Late Amazonian Central Elysium Planitia volcanism and the formation of Athabasca Valles, Planet. Space Sci., 158, 96&#8211;109, https://doi.org/10.1016/j.pss.2018.04.024, 2018.Egea-Gonz&#225;lez, I., Lois, P. C., Jim&#233;nez-D&#237;az, A., Bramson, A. M., Sori, M. M., Tendero-Ventanas, J.-&#193;., and Ruiz, J.: The stability of a liquid-water body below the south polar cap of Mars, Icarus, 383, 115073, https://doi.org/10.1016/j.icarus.2022.115073, 2022.Miller, R. C., Grima, C., Gulick, S. P. S., Goudge, T. A., Russell, A. T., Perry, M. R., Putzig, N. E., and Campbell, B. A.: Dynamic development of the Athabasca Valles outflow system from volcanic facies and 15 m scale roughness, Icarus, 115691, https://doi.org/10.1016/j.icarus.2023.115691, 2023.Ryan, A. J. and Christensen, P. R.: Coils and Polygonal Crust in the Athabasca Valles Region, Mars, as Evidence for a Volcanic History, Science, 336, 449&#8211;452, https://doi.org/10.1126/science.1219437, 2012.Watters, T. R., Campbell, B. A., Leuschen, C. J., Morgan, G. A., Cicchetti, A., Orosei, R., and Plaut, J. J.: Evidence of Ice&#8208;Rich Layered Deposits in the Medusae Fossae Formation of Mars, Geophys. Res. Lett., 51, e2023GL105490, https://doi.org/10.1029/2023GL105490, 2024.Yakovlev, V., Horelik, S., and Lytvynenko, Y.: On the cryogenic nature of the large hills of Mars, Planet. Space Sci., 208, 105340, https://doi.org/10.1016/j.pss.2021.105340, 2021.