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Coevolution of Mars’s atmosphere and massive south polar CO₂ ice deposit

Buhler, P. B. and Ingersoll, A. P. and Piqueux, S. and Ehlmann, B. L. and Hayne, P. O. (2020) Coevolution of Mars’s atmosphere and massive south polar CO₂ ice deposit. Nature Astronomy, 4 (4). pp. 364-371. ISSN 2397-3366. doi:10.1038/s41550-019-0976-8.

[img] Image (JPEG) (Extended Data Fig. 1: Energy balance model schematic and model output comparison to data) - Supplemental Material
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[img] Image (JPEG) (Extended Data Fig. 2: Examples of metre- to 10-metre-scale polygonal patterning (white arrows) on the H2O ice layer overlying the MCID, adjacent to and beneath mesas of RSPC CO2 (black arrows)) - Supplemental Material
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[img] Image (JPEG) (Extended Data Fig. 3) - Supplemental Material
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[img] Image (JPEG) (Extended Data Fig. 4: Effect of varying obliquity on absorbed insolation due to albedo dependence on insolation) - Supplemental Material
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[img] Image (JPEG) (Extended Data Fig. 5: Regional context of textures in topmost H2O ice layer, timing of seasonal exposure of topmost H2O ice layer, and topmost H2O ice layer seasonal thermal profile) - Supplemental Material
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[img] Plain Text (Source Data Fig. 3) - Supplemental Material
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A massive CO₂ ice deposit overlies part of Mars’s primarily H₂O ice south polar cap. This deposit rivals the mass of Mars’s current, 96% CO₂, atmosphere. Its release could substantially alter Mars’s pressure and climate. The deposit consists of alternating CO₂ and H₂O ice layers to a depth of up to approximately 1 km (refs. 1,7,8). The top layer is an enigmatic 1–10 m covering of perennial surface CO₂ ice called the residual south polar cap. Typical explanations of the layering invoke orbital cycles. Up to now, models assumed that the H₂O ice layers insulate and seal in the CO₂, allowing it to survive high-obliquity periods. However, these models do not quantitatively predict the deposit’s stratigraphy or explain the residual south polar cap’s existence. Here we present a model in which the deposit’s near-surface CO₂ can instead exchange with the atmosphere through permeable H₂O ice layers. Using currently observed albedo and emissivity properties of the Martian polar CO₂ ice deposits, our model predicts that the present massive CO₂ ice deposit is a remnant of larger CO₂ ice deposits laid down during periods of decreasing obliquity that are ablated, liberating a residual lag layer of H₂O ice, when obliquity increases. Fractions of previous CO₂ deposits remain as layers because the amplitudes of the obliquity maxima have been mostly decreasing during the past ~510 kyr (ref. 17). Our model simultaneously explains the observed massive CO₂ ice deposit stratigraphy, the residual south polar cap’s existence and the presence of a massive CO₂ ice deposit only in the south. We use our model to calculate Mars’s pressure history and determine that the massive CO₂ ice deposit is 510 kyr old.

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URLURL TypeDescription ReadCube access
Buhler, P. B.0000-0002-5247-7148
Ingersoll, A. P.0000-0002-2035-9198
Ehlmann, B. L.0000-0002-2745-3240
Additional Information:© 2019 Nature Publishing Group. Received 01 November 2018; Accepted 15 November 2019; Published 23 December 2019. P.B.B. was supported by NASA Earth and Space Sciences Fellowship NNX16AP38H and the NASA Postdoctoral Program. Early work by B.L.E., P.B.B. and A.P.I. was partially supported by the NASA Mars Fundamental Research grant NNX14AG54G to B.L.E. and C. Pilorget. Part of this work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. Government support acknowledged. Data availability: The radar and image datasets that support the findings of this study are publicly available from the NASA Planetary Data System ( Source data for Fig. 3 are provided with the paper. Code availability: The code that produces the figures and numerical results stated in the text is available from the corresponding author on reasonable request. Author Contributions: P.B.B. conceived of the study, performed the numerical modelling and data analysis, and wrote the paper. Substantial discussions with A.P.I., S.P., B.L.E. and P.O.H. refined the results of the study and the manuscript presentation. The authors declare no competing interests.
Group:Astronomy Department
Funding AgencyGrant Number
NASA Earth and Space Science FellowshipNNX16AP38H
NASA Postdoctoral ProgramUNSPECIFIED
Issue or Number:4
Record Number:CaltechAUTHORS:20191106-121635863
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Official Citation:Buhler, P.B., Ingersoll, A.P., Piqueux, S. et al. Coevolution of Mars’s atmosphere and massive south polar CO2 ice deposit. Nat Astron 4, 364–371 (2020).
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:99698
Deposited By: George Porter
Deposited On:23 Dec 2019 17:43
Last Modified:16 Nov 2021 17:48

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