Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

No signature of clear CO2 ice from the ‘cryptic’ regions in Mars' south seasonal polar cap


The seasonal polar ice caps of Mars are composed mainly of CO2 ice1,2. A region of low (< 30%) albedo has been observed within the south seasonal cap during early to mid-spring3,4. The low temperature of this ‘cryptic region’ has been attributed to a clear slab of nearly pure CO2 ice, with the low albedo resulting from absorption by the underlying surface4. Here we report near-infrared imaging spectroscopy of the south seasonal cap. The deep and broad CO2 absorption bands that are expected in the near-infrared with a thick transparent slab of CO2 ice are not observed. Models of the observed spectra indicate that the low albedo results from extensive dust contamination close to the surface of a CO2 ice layer, which could be linked to atmospheric circulation patterns5,6. The strength of the CO2 absorption increases after mid-spring, so part of the dust is either carried away or buried more deeply in the ice layer during the CO2 ice sublimation process.

This is a preview of subscription content, access via your institution

Access options

Rent or buy this article

Get just this article for as long as you need it


Prices may be subject to local taxes which are calculated during checkout

Figure 1: Reflectance spectrum of a region at 344° E, 59° S observed by OMEGA at L s 142°.
Figure 2: Albedo of the southern seasonal cap in mid-spring at 1.08 µm (continuum).
Figure 3: Reflectance spectra of representative regions within the southern seasonal cap.
Figure 4: Spectral evolution of a representative area in the cryptic region at 80° E, 82.5° S.


  1. Herr, K. C. & Pimentel, G. C. Infrared absorptions near three microns recorded over the polar caps of Mars. Science 166, 496–499 (1969)

    Article  ADS  CAS  Google Scholar 

  2. Larson, H. P. & Fink, U. Identification of carbon dioxide frost on the Martian polar caps. Astrophys. J. 171, L91–L95 (1972)

    Article  ADS  CAS  Google Scholar 

  3. Benson, J. L. & James, P. B. Yearly comparisons of the martian polar caps: 1999–2003 Mars Orbiter Camera observations. Icarus 174, 513–523 (2005)

    Article  ADS  Google Scholar 

  4. Kieffer, H. H. et al. Mars south polar spring and summer behaviour observed by TES: Seasonal cap evolution controlled by frost grain size. J. Geophys. Res. 105, 9653–9700 (2000)

    Article  ADS  CAS  Google Scholar 

  5. Colaprete, A. et al. Albedo of the south pole on Mars determined by topographic forcing of atmosphere dynamics. Nature 435, 184–188 (2005)

    Article  ADS  CAS  Google Scholar 

  6. Forget, F., Hourdin, F. & Talagrand, O. CO2 snowfall on Mars: Simulation with a general circulation model. Icarus 131, 302–316 (1998)

    Article  ADS  CAS  Google Scholar 

  7. Quirico, E. & Schmitt, B. Near-infrared spectroscopy of simple hydrocarbons and carbon oxides diluted in solid N2 and as pure ices: implications for Triton and Pluto. Icarus 127, 354–378 (1997)

    Article  ADS  CAS  Google Scholar 

  8. Grundy, W. M. & Schmitt, B. The temperature-dependent near-infrared absorption spectrum of hexagonal H2O ice. J. Geophys. Res. 103, 25809–25822 (1998)

    Article  ADS  CAS  Google Scholar 

  9. Hansen, G. B. Ultraviolet to near-infrared absorption spectrum of carbon dioxide ice from 0.174 to 1.8 µm. J. Geophys. Res. 110, E11003, doi:10.1029/2005JE002531 (2005)

    Article  ADS  Google Scholar 

  10. Bibring, J.-P. et al. Perennial water ice identified in the south polar cap of Mars. Nature 428, 627–630 (2004)

    Article  ADS  CAS  Google Scholar 

  11. Neumann, G. A., Smith, D. E. & Zuber, M. T. Two Mars years of clouds detected by the Mars Orbiter Laser Altimeter. J. Geophys. Res. 108(E4), 5023, doi:10.1029/2002JE001849 (2003)

    Article  Google Scholar 

  12. Piqueux, S., Byrne, S. & Richardson, M. I. Sublimation of Mars' southern seasonal CO2 ice cap and the formation of spiders. J. Geophys. Res. 108(E8), 5084, doi:10.1029/2002JE002007 (2003)

    Article  Google Scholar 

  13. Kieffer, H. H., Christensen, P. R. & Titus, T. N. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap. Nature doi:10.1038/nature04945 (this issue)

  14. James, P. B., Kieffer, H. H. & Paige, D. A. in Mars (eds Kieffer, H. H., Jakovsky, B. M., Snyder, C. W. & Mathews, M. S.) 934–968 (Univ. Arizona Press, Tucson, 1992)

    Google Scholar 

  15. Titus, T. N. & Kieffer, H. H. A comparison of the Mars south polar recession rates between 1999 and 2001. Lunar Planet. Sci. Conf. 33, abstr. 2071 (2002)

  16. Ockert-Bell, M. E., Pollack, J. B. & Forget, F. Absorption and scattering properties of the Martian dust in the solar wavelengths. J. Geophys. Res. 102, 9039–9050 (1997)

    Article  ADS  CAS  Google Scholar 

  17. Clancy, R. T., Wolff, M. J. & Christensen, P. R. Mars aerosol studies with the MGS TES emission phase function observations: optical depths, particle sizes, and ice cloud types versus latitude and solar longitude. J. Geophys. Res. 108(E9), 5098, doi:10.1029/2003JE002058 (2003)

    Article  Google Scholar 

  18. Drossart, P. et al. Martian aerosol properties from the Phobos/ISM experiment. Ann. Geophys. 9, 754–760 (1991)

    ADS  Google Scholar 

  19. Douté, S. & Schmitt, B. A multilayer bidirectional reflectance model for the analysis of planetary surface hyperspectral images at visible and near-infrared wavelengths. J. Geophys. Res. 103, 31367–31390 (1998)

    Article  ADS  Google Scholar 

  20. Eluskiewicz, J., Moncet, J.-L., Titus, T. N. & Hansen, G. B. A microphysically based approach to modelling emissivity and albedo of the martian seasonal caps. Icarus 174, 524–534 (2005)

    Article  ADS  Google Scholar 

  21. Prettyman, T. H. et al. Spatial deconvolution of Mars Odyssey neutron spectroscopy data: Analysis of Mars Southern seasonal cap. Lunar Planet. Sci. Conf. 36, abstr. 1384 (2005)

  22. Aharonson, O. et al. Depth, distribution, and density of CO2 deposition on Mars. J. Geophys. Res. 109, E05004, doi:10.1029/2003JE002223 (2004)

    Article  ADS  Google Scholar 

Download references


We acknowledge the support of CNES, which funded the development of OMEGA and its scientific exploitation. Author Contributions Y.L., J.-P.B. and B.G. were responsible for data reduction and observation planning; S.D., F.P. and B.S. contributed to the spectral modelling from optical constants; M.V. performed the modelling of the aerosol contribution; and F.F. provided input on the link with general circulation models.

Author information

Authors and Affiliations


Corresponding author

Correspondence to Yves Langevin.

Ethics declarations

Competing interests

Reprints and permissions information is available at The authors declare no competing financial interests.

Supplementary information

Supplementary Discussion

This file provides details on the procedures implemented for evaluating the contribution of aerosols, correcting for atmospheric absorption features and modelling spectra. (PDF 71 kb)

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Langevin, Y., Douté, S., Vincendon, M. et al. No signature of clear CO2 ice from the ‘cryptic’ regions in Mars' south seasonal polar cap. Nature 442, 790–792 (2006).

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing