Astrogeology Science Center

Lambert albedo (.3-3um) mosaics made from 11 days of data from April, 2001; the Martian mid-summer season
Lambert albedo (.3-3um) mosaics made from 11 days of data from April, 2001; the Martian mid-summer season
This is an artist's rendition of what the Cryptic region might look like if one was standing on the surface of the polar cap
This is an artist's rendition of what the Cryptic region might look like if one was standing on the surface of the polar cap
Side-by-side comparisons of TES data from 1998 and Viking IRTM from 1977, taken for approximately the current season on Mars
Side-by-side comparisons of TES data from 1998 and Viking IRTM from 1977, taken for approximately the current season on Mars

The Mars-Ice project is a joint project between the USGS Astrogeology Research Program (Flagstaff, AZ) and the Arizona State University Mars Space Flight Facilty (Tempe, AZ) to bring together a single resource for the exploration of martian ices. Much of this research is done at the USGS Flagstaff Science Center.

North Pole Cold Spots

In the 1970s, spacecraft observations of the polar regions of Mars revealed polar brightness temperatures that were significantly below the expected kinetic temperatures for CO2 sublimation. For the past few decades, we have speculated as to the nature of these Martian polar cold spots. Are the cold spots surface or atmospheric effects? Do the cold spots behave as blackbodies, or do they have emissivities less than unity? Two developments have allowed us to answer these questions: (1) the measurement of the optical constants of CO2 by Gary Hansen (1997) and (2) direct thermal spectroscopy of the north polar cap by MGS TES (Kieffer et al., 1998). 

With a few possible exceptions, cold spots are surface effects. The CO2 frost in cold regions of the polar cap show a strong absorption feature at 25 microns that is indicative of fine-grained CO2, thus explaining the low brightness temperatures observed by the Viking IRTM. Brightness temperatures at 18 microns are usually consistent with expected kinetic surface temperatures. In many cases, the brightness temperatures at 15 microns reveals an atmosphere that is too warm for CO2 condensation to occur. 

Cold spot formation is strongly dependent on topography, forming preferentially near craters and on slopes of the perennial cap. While cold spots are surface effects, the formation of the fine-grained CO2 deposits is not entirely restricted to surface formation. TES data, combined with MOLA cloud data (Ivanov and Muhleman, 1999), suggest that at least a few of these cold spots were formed from atmospheric condensates. 

Another major component to the north polar cap composition is slab CO2 ice. Slab ice has near unity spectral emissivity (Kieffer et al.,1999;Hansen, 1998) and appears to have a low albedo. Two explanations for the low albedo are that the slab ice is intrinsically dark or the slab ice is transparent and we are seeing through to the underlying substrate. Regions of the cap where T18-T25 < 5 degrees have slab ice. Slab ice is the dominant endmember of the polar cap at latitudes south of the polar night.

TES Observations of the South Pole

The Mars Polar Lander arrived at Mars on December 3, 1999. TES analysis of recent data from the mapping phase demonstrates that the spacecraft landing site was bare ground, free of -128° C (-200° F) dry ice that completely covered this region during the winter. The image to the left shows the 2pm and 2am temperatures of data within the landing site on December, 2, 1999. The plus sign marks the landing site. The thick white line shows the location of the polar layered deposits. Temperatures are given in Celsius. The temperature of CO2 frost (dry ice) on Mars is 145K (-128° C), approximately -200° F. Temperatures above 200K show the absence of CO2 frost. These temperatures were calculated from thermal radiation at a wavelength of 30µm.

The recession of the south polar cap has been observed telescopically and from spacecraft in both the visible and thermal regions. Although a simple cap-edge versus time plot has commonly been used, without regard as to the longitude of measurement, Mariner 9, Viking, and HST observations clearly show that the retreating edge is irregular and asymmetric. 

The data used in this analysis is from the Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES). Repeated TES coverage over the period Ls 185 through Ls 270 acquired much of the cap recession. 

During this period of time, TES was taking data in the array normal spin (ANS) mode, scanning acrossed the planet as the satellite made one complete roll every 100 minutes. Therefore, the data was irregularly sampled in both space and time. Also, because of the changes in the spacecraft orbit, the spatial resolution of the data is variable, ranging from 25 to 125 kilometers. 

We have constructed a map of the south polar region that contains the date when the last CO2 sublimates, hereafter called the crocus date. The crocus date is based on sliding a representative temperature - versus - time curve along the observations for each location in the polar region and selecting the season of maximum temperature change.

Recessions in the classic area “ Mountains of Mitchell ” are delayed significantly, disappearing approximately at Ls 260. High resolution (26 Km) brightness temperature data at Ls 244 confirms that solid CO2 is the dominant cold component. 

One region (approx. 72-80 S, 180-250 W) within the annual polar cap became dark long before the temperatures begin to rise; in comparison with most areas that showed a gradual increase in brightness until a rapid darkening as the temperature rose well above CO2 frost value. This dark region, here after called the Cryptic region, appears to be a major contributor to the asymmetric polar recession. The cause of the Cyrptic region's unexpected behavior is currently under study.

South Pole Cryptic Region

The early part of the Mars Global Surveyor mission provided good TES coverage of the Mars south polar region. These data allow mapping of the polar cap recession, surface and atmospheric temperatures, and albedo features found within the seasonal cap itself (Kieffer et al, 1998, Titus et al, 1998). 

During the period observed, the seasonal south polar cap retreated continuously and asymmetrically around the geographic pole, much the way Viking observed in 1976-1977 (Kieffer et al., 1977). One of the most dominant albedo features on the seasonal cap is a region that appears almost as dark as bare ground, but yet remains cold. (See Figure 1.) We refer to this region, generally located between latitudes 85° S and 75° S and longitudes 150° W and 310° W, as the Cryptic region. 

A re-examination of the IRTM data revealed that the Cryptic region was not unique to the TES era, but also was quite appearant during the Viking era. (See Figure 2.) Interesting enough, Antoniadi (Blunck, 1977) observed dark regions forming on the season cap that loosely correlates to the Cryptic region: Depressio Magna (1909) and Depressio Parva (1929). These depressios were located at 270° W, 78° S and 166° W, 76° S, respectively. 

Analysis of both the TES and IRTM data indicate that the Cryptic region is unique in its thermophysical properties relative to the rest of the cap. The region is a repeatable event that occupies the same general area from year to year. It is darker and slightly warmer than the rest of the south polar cap. Even though the Cryptic region is slightly warmer, it must still be CO2 buffered since it remains “ cold ” for several days.

Spectral analysis of the TES longward of the 15 micron atmospheric band shows that the Cryptic region shows less spectral than the rest of the polar cap. This suggests that the region may be composed of “ ice ”, as opposed to snow or frost (Hansen, 1998). Further spectral analysis is on going.

References

  • 2005-03: Tracking Retreat of the North Seasonal Ice Cap on Mars: Results from the THEMIS Investigation (on the web) Lunar and Planetary Science Conference 36: A. B. Ivanov, K. L. Wagstaff, T. N. Titus
  • 2005-03: Thermal Inertia of the Arsia Mons Caldera: A Site for Nightly CO2 Condensation (on the web) Lunar and Planetary Science Conference 36: G. C. Cushing, T. N. Titus
  • 2005-03: Spatial Deconvolution of Mars Odyssey Neutron Spectroscopy Data: Analysis of Mars Southern Seasonal Cap (on the web) Lunar and Planetary Science Conference 36: T. H. Prettyman, R. C. Elphic, W. C. Feldman, J. R. Murphy, S. Nelli, T. N. Titus, R. L. Tokar
  • 2005-03: Nature of the South Pole on Mars Determined by Topographic Forcing of Atmosphere Dynamics (on the web) Lunar and Planetary Science Conference 36: A. Colaprete, J. R. Barnes, R. M. Haberle, J. L. Hollingsworth, H. H. Kieffer, T. N. Titus
  • 2005-03: Towards Onboard Orbital Tracking of Seasonal Polar Volatiles on Mars (on the web) Lunar and Planetary Science Conference 36: K. L. Wagstaff, R. Castano, S. Chien, A. B. Ivanov
  • 2005-03: Mars Polar Cap Edges Tracked Over 3 Full Mars Years (on the web) Lunar and Planetary Science Conference 36: T. N. Titus
  • 2005-03: Model Development and Testing for THEMIS Controlled Mars Mosiacs (on the web) Lunar and Planetary Science Conference 36: B. A. Archinal, S. Sides, L. Weller, G. C. Cushing, T. N. Titus, R. L. Kirk, L. A. Solderblom, T. C. Duxbury
  • 2005-02: A Microphysically-based Approach to Modeling Emissivity and Albedo of the Martian Seasonal Caps (on the web) Icarus V174 12: J. Eluszkiewicz, J. Moncet, T. N. Titus, G. B. Hansen
  • 2005-02: Evidence for Subsurface Water Ice in Korolev Crater, Mars (on the web) Icarus V174 12: J. C. Armstrong, T. N. Titus, H. H. Kieffer
  • 2004-12: Some Mars South Polar Swiss CheeseTerrain has Warm Walls (on the web) American Geophysical Union Fall Meeting 2004: T. N. Titus, G. C. Cushing, A. V. Pathare, P. R. Christensen
  • 2004-10: Exploring Martian Polar Atmospheric Circulation and Surface Interactions (on the web) EOS Transactions AGU V85 141: T. H. Prettyman, T. N. Titus
  • 2004-04: Mars: Water, Water Everywhere (on the web) Nature V428 16983: T. N. Titus
  • 2004-03: Intra-Annual Variations of the Martian Swiss Cheese Terrain (on the web) Lunar and Planetary Science Conference 35: T. N. Titus, G. C. Cushing, A. V. Pathare, P. R. Christensen, S. Byrne, A. B. Ivanov, A. Ingersoll, M. I. Richardson, R. L. Kirk, L. A. Solderblom
  • 2004-03: Seasonal Variations within Korolev Crater, Mars (on the web) Lunar and Planetary Science Conference 35: J. C. Armstrong, T. N. Titus, H. H. Kieffer
  • 2004-03: Summer Season Variability of the North Residual Cap of Mars from MGS-TES (on the web) Lunar and Planetary Science Conference 35: W. M. Calvin, T. N. Titus
  • 2004-03: Reconciling Different Observations of the CO2 Ice Mass Loading of the Martian North Polar Cap (on the web) Geophysical Research Letters V31 15: R. M. Haberle, B. Mattingly, T. N. Titus
  • 2003-12: Seasonal Variations of Albedo and Temperature of the North Polar Cap of Mars (on the web) American Geophysical Union Fall Meeting 2003: S. A. Mahoney, W. M. Calvin, T. N. Titus
  • 2003-12: Seasonal Variations of Thermophysical Units Within Korolev Crater, Mars (on the web) American Astronomical Society Meeting 203: J. C. Armstrong, T. N. Titus, H. H. Kieffer
  • 2003-10: THEMIS Visible Imaging of the South Polar Layered Deposits, Martian Southern Spring, 2003 (on the web) Mars Polar Science Conference 3: J. J. Plaut, P. R. Christensen, K. Bender, J. F. Bell, L. Cherednik, A. B. Ivanov, H. H. Kieffer, T. McConnochie, M. I. Richardson, T. N. Titus
  • 2003-10: South Polar Cryptic Region Revisited: THEMIS Observations (on the web) Mars Polar Science Conference 36: T. N. Titus, H. H. Kieffer, J. J. Plaut, P. R. Christensen, A. B. Ivanov
  • 2003-10: A Microphysically-based Approach to Inferring Porosity, Grain Sice, and Dust Abundance in the Seasonal Caps from Atmospherically-corrected TES Spectra (on the web) Mars Polar Science Conference 3: J. Eluszkiewicz, T. N. Titus
  • 2003-10: Constracing on the Within Season and Between Year Variability of the North Residual Cap from MGS-TES (on the web) Mars Polar Science Conference 3: W. M. Calvin, T. N. Titus, S. A. Mahoney
  • 2003-10: Reconciling the MOLA, TES, and Neutron Observations of the North Polar CO2 Mass Budget on Mars (on the web) Mars Polar Science Conference 35: R. M. Haberle, B. Mattingly, T. N. Titus
  • 2003-07: Temporal and Spatial Distribution of Seasonal CO2 Snow and Ice (on the web) Sixth International Conference on Mars: T. N. Titus, H. H. Kieffer
  • 2003-07: Analysis of Properties of the North Polar Layered Deposits: THEMIS Data in Context of MGS Data (on the web) Sixth International Conference on Mars: A. B. Ivanov, S. Byrne, M. I. Richardson, A. R. Vasavada, T. N. Titus, J. F. Bell, T. McConnochie, P. R. Christensen
  • 2003-07: A Novel Approach to Modeling Emissivity and Albedo of the Martian Seasonal Caps (on the web) Sixth International Conference on Mars: J. Eluszkiewicz, T. N. Titus
  • 2003-06 Morphology and Composition of the Surface of Mars: Mars Odyssey THEMIS Results (on the web) Science V300 15628: P. R. Christensen, J. L. Bandfield, J. F. Bell, N. Gorelick, V. E. Hamilton, A. B. Ivanov, B. M. Jakosky, H. H. Kieffer, M. D. Lane, et. al.
  • 2003-03: Martian South Polar Deformation and Sublimation Processes (on the web) Lunar and Planetary Science Conference 34: S. N. Brightwell, J. S. Kargel, T. N. Titus
  • 2003-03: Early Results from the Odyssey THEMIS Investigation (on the web) Lunar and Planetary Science Conference 34: P. R. Christensen, J. L. Bandfield, J. F. Bell, V. E. Hamilton, A. B. Ivanov, B. M. Jakosky, H. H. Kieffer, M. D. Lane, M. C. Malin, et. al.
  • 2003-02: Exposed Water Ice Discovered near the South Pole of Mars (on the web) Science V299 15609: T. N. Titus, H. H. Kieffer, P. R. Christensen
  • 2003-01: CO2 Cycle: Two Martian Years of Polar IR Observations (on the web) Mars Atmosphere Modelling and Observations Workshop 2003: T. N. Titus
  • 2002-12: Exposed Water ice Discovered Near the South Pole of Mars (on the web) American Geophysical Union Fall Meeting 2002: T. N. Titus, H. H. Kieffer, P. R. Christensen
  • 2002-12: Morphological analysis of the Mars polar terrains based on the THEMIS data (on the web) American Geophysical Union Fall Meeting 2002: A. B. Ivanov, H. H. Kieffer, T. N. Titus, J. J. Plaut, M. I. Richardson, S. Byrne, P. R. Christensen, G. L. Mehall
  • 2002-10: The carbon dioxide cycle on Mars (on the web) 34th COSPAR Scientific Assembly, The Second World Space Congress: P. James, G. B. Hansen, T. N. Titus
  • 2002-09: Application of a Sintering Model to the Analysis of TES Spectra of the Seasonal Caps (on the web) American Astronomical Society Meeting DPS #34 #15.22, Bulletin Vol 34: J. Eluszkiewicz, T. N. Titus
  • 2002-03: A Comparison of the Mars South Polar Recession Rates Between 1999 and 2001 (on the web) Lunar and Planetary Science Conference 33: T. N. Titus, H. H. Kieffer
  • 2001-11: IR Spectral Properties of Dust and Ice at the Mars South Polar Cap (on the web) American Astronomical Society Meeting DPS #33 #19.15, Bulletin Vol 33: T. N. Titus, H. H. Kieffer
  • 2001-11: Analysis of Multi-Angle Infrared Observations of the Mars South Polar Cap Abstract for TES Workshop: T. N. Titus, H. H. Kieffer
  • 2001-11: Application of a Sintering Model TES Workshop: J. Eluszkiewicz, T. N. Titus
  • 2001-10: Mars Global Surveyor Thermal Emission Spectrometer Experiment: Investigation Description and Surface Science Results (on the web) Journal of Geophysical Research V106 IE10: P. R. Christensen, J. L. Bandfield, V. E. Hamilton, S. W. Ruff, H. H. Kieffer, T. N. Titus, M. C. Malin, R. V. Morris, M. D. Lane, et. al.
  • 2001-10: TES Premapping Data: Slab Ice and Snow Flurries in the Martian North Polar Night (on the web) Journal of Geophysical Research V106 IE10: T. N. Titus, H. H. Kieffer, K. Mullins, P. R. Christensen
  • 2000-10: TES Mapping Data: Recession of the Mars Polar Caps (on the web) American Astronomical Society Meeting DPS #32 #59.01, Bulletin V32: T. N. Titus, H. H. Kieffer, P. R. Christensen
  • 2000-08: An Overview of TES Polar Observations to Date (on the web) International Conference on Mars Polar Science and Exploration: H. H. Kieffer, T. N. Titus, K. Mullins
  • 2000-04: Mars South Polar Spring and Summer Behavior Observed by TES: Seasonal Cap Evolution Controlled by Frost Grain Size (on the web) Journal of Geophysical Research V105 IE4: H. H. Kieffer, T. N. Titus, K. Mullins, P. R. Christensen
  • 1999-11: Slab Ice and Snow Flurries in the Martian Polar Night (on the web) EOS Transactions AGU V80: T. N. Titus, H. H. Kieffer, K. Mullins, P. R. Christensen
  • 1999-11: TES and IRTM Observations of the Martian Seasonal Cap Behavior Around the M98 Landing Site (on the web) EOS Transactions AGU V80: H. H. Kieffer, K. Mullins, T. N. Titus
  • 1998-11: TES Pre-Mapping-Phase Polar Observations (on the web) EOS Transactions AGU V79: H. H. Kieffer, K. Mullins, T. N. Titus
  • 1998-11: The Martian Surface As Investigated by the Mars Global Surveyor Thermal Emission Spectrometer Experiment (on the web) EOS Transactions AGU V79: P. R. Christensen, et. al.
  • 1998-09: TES Observations of the South Pole (on the web) American Astronomical Society Meeting DPS #30 #20.05, Bulletin V30: T. N. Titus, H. H. Kieffer, K. Mullins
  • 1998-03: Early TES Observations of the South Polar Region (on the web) Lunar and Planetary Science Conference 29: H. H. Kieffer, T. N. Titus, K. Mullins
  • 1998-01: Thermal Emission Spectrometer Observations of the South and North Polar Regions During the First Phase of Aerobraking Orbits (on the web) International Conference on Mars Polar Science and Exploration 1: H. H. Kieffer, T. N. Titus, K. Mullins