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


A massive CO2 ice deposit overlies1 part of Mars’s primarily H2O ice2,3,4 south polar cap5. This deposit rivals the mass of Mars’s current, 96% CO2, atmosphere6. Its release could substantially alter Mars’s pressure and climate1. 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 enigmatic9,10,11 1–10 m covering of perennial surface CO2 ice12 called the residual south polar cap. Typical explanations of the layering invoke orbital cycles1,7. Up to now, models assumed that the H2O ice layers insulate and seal in the CO2, allowing it to survive high-obliquity periods7,13. 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 albedo14,15 and emissivity16 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.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1: Overview of geologic context and representative model outputs.
Fig. 2: Schematic of the onset of lag layer formation during increasing mean annual absorbed polar insolation, labelled by southern season.
Fig. 3: Model input and results.
Fig. 4: Long-term model-predicted pressure evolution.

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.


  1. 1.

    Phillips, R. J. et al. Massive CO2 ice deposits sequestered in the south polar layered deposits of Mars. Science 332, 838–841 (2011).

    ADS  Google Scholar 

  2. 2.

    Ingersoll, A. P. Mars—the case against permanent CO2 frost caps. J. Geophys. Res. 79, 3403–3410 (1974).

    ADS  Google Scholar 

  3. 3.

    Nye, J., Durham, W. B., Schenk, P. M. & Moore, J. M. The instability of a south polar cap on Mars composed of carbon dioxide. Icarus 144, 449–455 (2000).

    ADS  Google Scholar 

  4. 4.

    Titus, T. N., Kieffer, H. H. & Christensen, P. R. Exposed water ice discovered near the south pole of Mars. Science 299, 1048–1051 (2003).

    ADS  Google Scholar 

  5. 5.

    Byrne, S. The polar deposits of Mars. Annu. Rev. Earth Planet. Sci. 37, 535–560 (2009).

    ADS  Google Scholar 

  6. 6.

    Hess, S. L., Ryan, J. A., Tillman, J. E., Henry, R. M. & Leovy, C. B. The annual cycle of pressure on Mars measured by Viking Landers 1 and 2. Geophys. Res. Lett. 7, 197–200 (1980).

    ADS  Google Scholar 

  7. 7.

    Bierson, C. J. et al. Stratigraphy and evolution of the buried CO2 deposit in the Martian south polar cap. Geophys. Res. Lett. 43, 4172–4179 (2016).

    ADS  Google Scholar 

  8. 8.

    Putzig, N. E. et al. Three-dimensional radar imaging of structures and craters in the Martian polar caps. Icarus 308, 138–147 (2018).

    ADS  Google Scholar 

  9. 9.

    Byrne, S. & Ingersoll, A. P. A sublimation model for martian south polar ice features. Science 299, 1051–1053 (2003).

    ADS  Google Scholar 

  10. 10.

    Thomas, P. C. et al. Mass balance of Mars’ residual south polar cap from CTX images and other data. Icarus 268, 118–130 (2016).

    ADS  Google Scholar 

  11. 11.

    Malin, M. C., Caplinger, M. A. & Davis, S. D. Observational evidence for an active surface reservoir of solid carbon dioxide on Mars. Science 294, 2146–2148 (2001).

    ADS  Google Scholar 

  12. 12.

    Kieffer, H. H. Mars south polar spring and summer temperatures: a residual CO2 frost. J. Geophys. Res. 84, 8263–8288 (1979).

    ADS  Google Scholar 

  13. 13.

    Manning, C. V., Bierson, C., Putzig, N. E. & McKay, C. P. The formation and stability of buried polar CO2 deposits on Mars. Icarus 317, 509–517 (2019).

    ADS  Google Scholar 

  14. 14.

    Paige, D. A. & Ingersoll, A. P. Annual heat balance of martian polar caps: Viking observations. Science 228, 1160–1168 (1985).

    ADS  Google Scholar 

  15. 15.

    James, P. B., Kieffer, H. H., and Paige, D. A. in Mars (eds Kieffer, H. H., Jakosky, B. M., Snyder, C. W. & Matthews, M. S.) pp. 934–968 (Univ. Arizona Press, 1992).

  16. 16.

    Hayne, P. O. et al. Carbon dioxide snow clouds on Mars: south polar winter observations by the Mars Climate Sounder. J. Geophys. Res. 117, E08014 (2011).

    ADS  Google Scholar 

  17. 17.

    Laskar, J. et al. Long term evolution and chaotic diffusion of the insolation quantities of Mars. Icarus 170, 343–364 (2004).

    ADS  Google Scholar 

  18. 18.

    Guo, X., Richardson, M. I., Soto, A. & Toigo, A. On the mystery of the perennial carbon dioxide cap at the south pole of Mars. J. Geophys. Res. Planets 115, 1–13 (2010).

    Google Scholar 

  19. 19.

    Haberle, R. M. et al. The effect of ground ice on the Martian seasonal CO2 cycle. Planet. Space Sci. 56, 251–255 (2008).

    ADS  Google Scholar 

  20. 20.

    Fanale, F. P., Salvail, J. R., Banerdt, W. B. & Saunders, R. S. Mars: the regolith-atmosphere-cap system and climate change. Icarus 50, 381–407 (1982).

    ADS  Google Scholar 

  21. 21.

    Jakosky, B. M. & Haberle, R. M. Year-to-year instability of the Mars south polar cap. J. Geophys. Res. Solid Earth 95, 1359–1365 (1990).

    Google Scholar 

  22. 22.

    Brown, A. J., Piqueux, S. & Titus, T. N. Interannual observations and quantification of summertime H2O ice deposition on the Martian CO2 ice south polar cap. Earth Planet. Sci. Lett. 406, 102–109 (2014).

    ADS  Google Scholar 

  23. 23.

    Byrne, S., Zuber, M. T. & Neumann, G. A. Interannual and seasonal behavior of Martian residual ice-cap albedo. Planet. Space Sci. 56, 194–211 (2008).

    ADS  Google Scholar 

  24. 24.

    Haberle, R. M. et al. Preliminary interpretation of the REMS pressure data from the first 100 sols of the MSL mission. J. Geophys. Res. Planets 19, 440–453 (2014).

    ADS  Google Scholar 

  25. 25.

    Hu, R., Kass, D. M., Ehlmann, B. L. & Yung, Y. L. Tracing the fate of carbon and the atmospheric evolution of Mars. Nat. Commun. 6, 10003 (2015).

    ADS  Google Scholar 

  26. 26.

    Jakosky, B., Henderson, B. & Mellon, M. Chaotic obliquity and the nature of the Martian climate. J. Geophys. Res. 100, 1579–1584 (1995).

    ADS  Google Scholar 

  27. 27.

    Leighton, R. B. & Murray, B. C. Behavior of carbon dioxide and other volatiles on Mars. Science 153, 136–144 (1966).

    ADS  Google Scholar 

  28. 28.

    Murray, B. C. & Malin, M. C. Polar volatiles on Mars—theory versus observation. Science 182, 437–443 (1973).

    ADS  Google Scholar 

  29. 29.

    Byrne, S. & Ingersoll, A. P. Martian climatic events on timescales of centuries: evidence from feature morphology in the residual south polar ice cap. Geophys. Res. Lett. 30, 2–5 (2003).

    Google Scholar 

  30. 30.

    Giauque, W. F. & Stout, J. W. The entropy of water and the third law of thermodynamics. The heat capacity of ice from 15 to 273°K. J. Am. Chem. Soc. 58.7, 1144–1150 (1936).

    ADS  Google Scholar 

  31. 31.

    Slack, G. A. Thermal conductivity of ice. Phys. Rev. B 22, 3065–3071 (1980).

    ADS  Google Scholar 

  32. 32.

    Phillips, R. J. et al. Mars north polar deposits: stratigraphy, age, and geodynamical response. Science 320, 1182–1185 (2008).

    ADS  Google Scholar 

  33. 33.

    Ruiz, J., López, V. & Dohm, J. M. The present-day thermal state of Mars. Icarus 207, 631–637 (2010).

    ADS  Google Scholar 

  34. 34.

    Schubert, G., Solomon, S. C., Turcotte, D. L., Drake, M. J. & Sleep, N. H. in Mars (eds Kieffer, H. H., Jakosky, B. M., Snyder, C. W. & Matthews, M. S.) pp. 147–183 (Univ. Arizona Press, 1992).

  35. 35.

    Zuber, M. T. et al. Internal structure and early thermal evolution of Mars from Mars Global Surveyor topography and gravity. Science 287, 1788–1793 (2000).

    ADS  Google Scholar 

  36. 36.

    Dehant, V. et al. Future Mars geophysical observatories for understanding its internal structure, rotation, and evolution. Planet. Space Sci. 68, 123–145 (2012).

    ADS  Google Scholar 

  37. 37.

    Montabone, F. et al. Eight-year climatology of dust optical depth on Mars. Icarus 251, 65–95 (2015).

    ADS  Google Scholar 

  38. 38.

    Hourdin, F., Le Van, P., Forget, F. & Talagrand, O. Meteorological variability and the annual surface pressure cycle on Mars. J. Atmos. Sci. 50, 3625–3640 (1993).

    ADS  Google Scholar 

  39. 39.

    Houben, H., Haberle, R. M., Young, R. E. & Zent, A. P. Modeling the Martian seasonal water cycle. J. Geophys. Res. Planets 102, E4 (1997).

    Google Scholar 

  40. 40.

    Richardson, M. I. & Wilson, R. J. Investigation of the nature and stability of the Martian seasonal water cycle with a general circulation model. J. Geophys. Res. Planets 107, 5031 (2002).

    ADS  Google Scholar 

  41. 41.

    Montmessin, F. et al. On the origin of perennial water ice at the south pole of Mars: a precession-controlled mechanism? J. Geophys. Res. 112, E08S17 (2007).

    Google Scholar 

  42. 42.

    Clancy, R. T. et al. Water vapor saturation at low altitudes around Mars aphelion: a key to Mars climate? Icarus 122, 36–62 (1996).

    ADS  Google Scholar 

  43. 43.

    Kelly, N. J. et al. Seasonal polar carbon dioxide frost on Mars: CO2 mass and columnar thickness distribution. J. Geophys. Res. Planets 112, 1–12 (2007).

    Google Scholar 

  44. 44.

    Paige, D. A. The Annual Heat Balance of the Martian Polar Caps from Viking Observations. PhD thesis, California Institute of Technology (1985).

  45. 45.

    Hapke, B. Combined Theory of Reflectance and Emittance Spectroscopy 2nd edn (Cambridge Univ. Press, 2012).

  46. 46.

    Alwarda, R. and Smith, I. B. Mapping and characterization of the bounding layers of the CO2 deposit in Planum Australe, Mars. In 50th Lunar and Planetary Science Conference 2132 (2019).

  47. 47.

    Piqueux, S. & Christensen, P. R. A model of thermal conductivity for planetary soils: 2. Theory for cemented soils. J. Geophys. Res. 114, E09006 (2009).

    ADS  Google Scholar 

Download references


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.

Author information




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.

Corresponding author

Correspondence to P. B. Buhler.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Peer review information Nature Astronomy thanks Isaac Smith and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1 Energy balance model schematic and model output comparison to data.

Left. Schematic of the energy balance model (Equation 1). Right. One-year model outputs with incoming flux (orange), outgoing flux (red dashed), and modelled accumulated CO2 (purple line), compared to observed accumulated CO2 (purple points; Kelly et al. (2006)43). LS is solar longitude. Apparent line-width of incoming flux is due to daily insolation oscillations, which are not resolved at plot resolution. The small fluctuations in the incoming flux curve are due to seasonal variations in the atmospheric opacity (Extended Data Fig. 3). Model runs for current orbit (obliquity = 25.19°, eccentricity = 0. 0934, longitude of perihelion = 251°). H2O layer thickness = 15 m. A. Latitude = 89.5°S, pressure = 1.0 × Peq,0, elevation = 4750 m, \({\it{\epsilon }}_{CO_2}\)= 0.8. B. Same, but with pressure = 0.95 × Peq,0, \({\it{\epsilon }}_{H_2O}\) = 1.0, \(A_{H_2O}\) = 0.4. C. Latitude = 89.5° N, pressure = 1.00 × Peq,0, elevation = −2000 m, \({\it{\epsilon }}_{CO_2}\)= 0.485, \({\it{\epsilon }}_{H_2O}\) = 0.55, \(A_{H_2O}\) = 0.4.

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).

Locations of panels are indicated in Extended Data Fig. 5A. HiRISE images A. ESP_014179_0930 B. ESP_058543_0930 C. PSP_003716_0930 D. ESP_058527_0940 E. ESP_058896_0910 F. ESP_058119_0940 G. ESP_041120_0920 H. ESP_014182_0960.

Extended Data Fig. 3

Opacity data from Montabone et al. (2015) from 87–90° S, -90-0° E from Mars Years 27–33, with mean (black) and median (grey) values.

Extended Data Fig. 4 Effect of varying obliquity on absorbed insolation due to albedo dependence on insolation.

(Blue) Total annual incident insolation at 89.5°S normalized to maximum annual incident insolation (at 90° obliquity); (Orange) total absorbed insolation, normalized to maximum annual absorbed insolation (at 36° obliquity); (Green) equivalent mean annual albedo. The equivalent mean annual albedo is calculated from one minus the ratio of the sum of the absorbed insolation at each 30-minute time step throughout one Mars year divided by the sum of the incident insolation at each 30-minute time step throughout one Mars year. At each time step the albedo is calculated from Equation 4 at 89.5° S and zero eccentricity. Nonzero eccentricities slightly modify the obliquity at which peak annual absorbed insolation occurs and are taken into account when we calculate the instantaneous albedo at each time step in our model.

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.

Top Left. CTX mosaic context for top right panel (black rectangle) and panels in Extended Data Fig. 2 (blue dots labelled A–H). Top Right. Regions of dark H2O layer are exposed by LS 297 (HiRISE image ESP_013775_0931). The regions correspond to kilometre-scale depressions in the H2O layer1. Bottom panels show time progression of modelled thermal profile for a 20 m thick H2O layer overlying a semi-infinite CO2 layer that becomes exposed at LS 301. The basal temperature of the H2O reaches the CO2 sublimation temperature between LS 335 and LS 183 the following year. LS 300: last day of seasonal CO2 coverage. LS 301: first LS bare H2O is exposed. LS 316: maximum surface temperature reached. LS 335: basal temperature of H2O layer reaches CO2 sublimation temperature. LS 355: surface CO2 condenses. LS 90: winter solstice; thermal wave decaying. LS 183: last LS basal temperature of H2O layer is at CO2 sublimation temperature. LS 270: summer solstice; basal temperature of H2O layer ~1 K below CO2 sublimation temperature.

Source data

Source Data Fig. 3

Model pressure history for Fig. 3b.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

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).

Download citation

Further reading

  • The Holy Grail: A road map for unlocking the climate record stored within Mars’ polar layered deposits

    • Isaac B. Smith
    • , Paul O. Hayne
    • , Shane Byrne
    • , Patricio Becerra
    • , Melinda Kahre
    • , Wendy Calvin
    • , Christine Hvidberg
    • , Sarah Milkovich
    • , Peter Buhler
    • , Margaret Landis
    • , Briony Horgan
    • , Armin Kleinböhl
    • , Matthew R. Perry
    • , Rachel Obbard
    • , Jennifer Stern
    • , Sylvain Piqueux
    • , Nicolas Thomas
    • , Kris Zacny
    • , Lynn Carter
    • , Lauren Edgar
    • , Jeremy Emmett
    • , Thomas Navarro
    • , Jennifer Hanley
    • , Michelle Koutnik
    • , Nathaniel Putzig
    • , Bryana L. Henderson
    • , John W. Holt
    • , Bethany Ehlmann
    • , Sergio Parra
    • , Daniel Lalich
    • , Candice Hansen
    • , Michael Hecht
    • , Don Banfield
    • , Ken Herkenhoff
    • , David A. Paige
    • , Mark Skidmore
    • , Robert L. Staehle
    •  & Matthew Siegler

    Planetary and Space Science (2020)