Introduction

Surficial water ice on Mars is invaluable to future human and robotic exploration. The

Martian polar regions are mostly covered with H2O ice capped with a seasonal layer of CO2 ice [1-4]. Every

southern spring and summer dramatic changes transpire in the south polar region as the CO2 ice sublimates.

In the 'cryptic terrain' [5-7], dark spots and streaks form on the surface due to basal sublimation of the CO2 ice [5,8,9]. Near the edge of the perennial southern polar cap an exposed H2O ice unit [10-11] is revealed after the seasonal CO2 ice layer

sublimates. This project investigates the seasonal and interannual temperature variations and albedo

variations in these two regions with the goal of understanding differences between

regions covered with CO2 ice and H2O ice.

References: [1] Kieffer, H.H. et al. (1976) Science 194, 1341-1344. [2] Titus, T.N. (2004). Nature 428, 610-611. [3] H. H. Kieffer, J. Geophys. Res. 84, 8263 (1979). [4] Christensen, P.R. (2006) GeoScienceWorld Elements. 3 (2): 151–155 [5] Kieffer, H.H., Christensen, P.R., Titus, T.N., 2006. Nature 442, 793–796. [6] Hansen, C.J. et al. Icarus 205 (2010) 283–295. [7] Piqueux, S., et al. (2003), J. Geophys. Res., 108(E8), 5084. [8] Piqueux, S., and Christensen, P.R., 2008. J. Geophys. Res.113, E06005. [9] Christensen, P.R., Kieffer, H.H., Titus, T.N., 2005. EOS Trans. AGU 86 (52) (P23c-04). [10] Titus, T. N., et al., 2003. Science 299 1048-1051. [11] Byrne and Ingersoll, 2003. Science 299 1051-1053. [12] NASA image credit, MOLA Science Team. [13] Christensen et al., 2004, Space Science. Reviews. 110, 85-130.

[14] Christensen et al., 2009, AGU Fall Meeting Abstracts. [15] Forget, François. Solar System Ices, 477-507 Revised, 1998. [16] Vincendon et al, 2010. J. Geophys. Res., 115 [17] Mount, C.P. and Titus, T.N., 2015. J. Geophys. Res.1252-1266. [18] Mount, C.P. and Christensen, P.R., 2016. Sixth Mars Polar Science Conf. 6061. [19] McEwen A.S. et al. (2007), J. Geophys. Res., 112 (E5), E05S02. [20] Piqueux S. et al. (2015) Icarus, 251, 164-180. [21] Portyankina, G., ed. (2006), Sixth Mars Polar Science Conf. 8040. [22] Brown, et al. (2014). Earth and Planetary Science Letters, 406, 102-109.

Acknowledgments: We would like to thank Jon Hill, Paul Wren, Meg Burris, Kim Murray, and Scott Dickenshied for help with image processing. This project was partially funded by the ASU/NASA Space Grant program.

Paras Angell, Hema Werner, and Phil Christensen School of Earth and Space Exploration

Arizona State University

Comparison of Seasonal Temperature Variations, Albedo Variations, and Sublimation Activity for CO2 ice and H2O ice Near the Martian South Pole

Mars 9 Abstract #6168Paras.Angell@asu.edu

Figure 4: Plot of average albedos as a function of solar longitude for A1, A2, A3 in the cryptic terrain for MY 32.

0.2

0.3

0.4

0.5

0.6

0.7

0.8

210 230 250 270 290 310 330

Ave

rage

Alb

edo

Solar Longitude, Ls (°)

A1 A2 A3

Albedo Variations: Cryptic Terrain• THEMIS visible albedos vary with solar longitude. • Albedo of the scene initially decreases as Spring

progresses due to regolith deposition (Fig. 4). • Albedo values increase again, peak at ~ Ls 245°. • Albedo histograms shift to higher values

corresponding to the peak in albedo (Fig. 5).

Results: Cryptic Terrain• At Ls 188°, surface is mostly covered with CO2 ice;

dark spots have yet to form in A1 (Fig. 2(a)). • At Ls 224° CO2 sublimation is in full swing. A1 has

dark streaks oriented NW (Fig. 2(b)). • Surface temperature increases slowly in Spring. • Sharp temperature rise starts at Ls 250°. • Sharp rise onset repeatable year-to-year (Fig. 3).

Exposed Water Ice Region

Highlights:♂ Sharp rise in temperature starts earlier in cryptic

terrain (Ls 250°) compared with exposed H2O region (Ls 280°) due to basal sublimation of translucent CO2 ice slab.

♂ Albedo peak corresponds to onset of sharp temp. rise, suggests water-ice frost formation [15].

♂ Area A5 identified as H2O ice based on temperature (190 ± 3 K) and higher albedo (0.42) than regolith (0.33) [10].

♂ CO2, H2O, and regolith units thermally distinct. Boundaries stable over many Mars years.

♂ H2O ice widespread around southern perennial polar cap [22].

♂ Continuing work: SHARAD and HiRISE image analysis.

Figure 6: Region with CO2 ice, exposed H2O ice, and regolith near the southern polar cap (85°S, 10°E). False color thermal IR images. 
(a) MY 25, 
Ls 334° (b) MY 33, 
Ls 337°.

160K 180K 200K 220K

Table 1: Albedo Variations Near 85°S, 10°E as a function of Solar Longitude (Ls) for MY 32, 33, 34Before CO2 Sublimation After CO2 Sublimation

Ls (°) 204.9° 242.1° 264.3° 324.0° 326.0° 337.4°

A4 CO2 ice

0.775 0.846 0.837 0.528 - 0.664

A5 H2O ice

0.755 0.893 0.823 0.40 0.416 0.4335

A6 regolith cover

0.763 0.88 - 0.339 0.333 0.356

Figure 3: Average surface temperatures vs. Ls for cryptic terrain area A1 for MY 30, 31, 32, and 33 illustrating the sharp rise in temperature for multiple Mars years.

140

160

180

200

220

240

260

210 230 250 270 290 310 330A

vera

ge T

empe

ratu

re (

K)

Solar Longitude, Ls (°)

Year/31 Year/32 Year/33 Year/30

Figure 2: Progression of CO2 sublimation and regolith deposition. Visible THEMIS images at Ls 188.2° and Ls 224.0° for Area A1 in cryptic terrain for Mars Year 31.

Remote Sensing Techniques • Regions studied (Figure 1):

• Cryptic Terrain (86° S, 99° E) : Areas A1, A2, A3 • Exposed H2O Ice (85° S, 10° E) : A4, A5, A6

• Progression of CO2 sublimation in spring /summer studied using THEMIS visible images [13].

• Average albedos calculated from visible images [13]. • Average surface temperature calculated from

THEMIS infrared (band 9) images. • Surface temperatures studied as a function of solar

longitude (Ls) for Mars Years (MY) 30, 31, 32, & 33. • THEMIS images analyzed with JMARS [14].

Results: Exposed Water Ice Region• In Spring, A4, A5, A6 have the same surface

temperature (Fig. 7 & 8). • After Ls 280°, CO2 ice sublimation reveals H2O ice

and regolith. • H2O ice-regolith boundary stable within 200 m over

8 Mars years (Fig. 6). • After Ls 280° albedos differentiate (Table 1). • Albedos: regolith < Exposed H2O ice < CO2 ice.

Figure 8: Surface Temperature vs. Ls for CO2 ice, H2O ice, and regolith for a region near 85° S, 10° E for MY 33.

120

140

160

180

200

220

240

180 200 220 240 260 280 300 320 340 360

Surf

ace

Tem

pera

ture

(K

)

Solar Longitude, Ls (°)

A4 (CO2 ice)

A5'

A5 (H2O ice)

A6 (Regolith)

A4'

Figure 7: Surface Temperature vs. Ls for CO2 ice, H2O ice, and regolith for a region near 85° S, 10° E for MY 32.

120

140

160

180

200

220

240

180 200 220 240 260 280 300 320 340 360

Ave

rage

Sur

face

Tem

pera

ture

(K

)

Solar Longitude, Ls (°)

A4#(CO2#ice)

A5#(H2O#ice)

A6#(regolith)

Figure 9. False color composite thermal infrared images at Ls 337° and Ls 339° for Mars Year 33 showing an extended water ice region. Colors represent temperature. H2O ice unit (green) extends more than 100 km.

Figure 1 (a): MOLA map [12] of the Martian South Pole, the Manhattan region (86° S, 99° E) in the cryptic terrain, and Exposed H2O ice region (85° S, 10° E). Colors represent elevation.

Manhattan

ExposedH2O Ice

Ls 0°

Ls 180°

Figure 1 (b): Schematic of Martian seasons and solar longitude, Ls. Image Credit: NASA/JPL-Caltech

0.4220.67

0.60 0.49

0.36

H2O ice regolith covered

Figure 10: Visible albedo image in false color at Ls 337 showing differences in albedo for CO2 ice, H2O ice, and regolith for MY 33. Colors represent albedo values.

A4 A6A5

(a) Mars Year 25

A4 A6A5

(b) Mars Year 33

10 km

Figure 5: Albedo histograms showing how albedo changes with Ls for Area A1 for Mars Year 32.

Ls 186.6° Ls 247.7°

Albedo

Freq

uenc

y

2 km

10 km

7 km

(a)(b)