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

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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 Paras Angell, Hema Werner, and Phil Christensen School of Earth and Space Exploration Mars 9 Abstract #6168 Arizona State University [email protected] 260 Introduction Year/31 Year/32 Year/33 Year/30 Exposed Water Ice Region 240 Surficial water ice on Mars is invaluable to 220 Figure 6: future human and robotic exploration. The (a) Mars Year 25 Region with 200 Martian polar regions are mostly covered with H2O ice CO2 ice, 10 km capped with a seasonal layer of CO2 ice [1-4]. Every 180 exposed H2O southern spring and summer dramatic changes transpire in the (K) Temperature Average 160 ice, and south polar region as the CO2 ice sublimates. regolith near A A 140 4 6 the southern 210 230 250 270 290 310 330 A5 In the 'cryptic terrain' [5-7], dark spots and streaks form on the Solar Longitude, Ls (°) polar cap surface due to basal sublimation of the CO2 ice [5,8,9]. Near the (85°S, 10°E). Figure 3: Average surface temperatures vs. Ls for cryptic False color edge of the perennial southern polar cap an exposed H2O ice terrain area A1 for MY 30, 31, 32, and 33 illustrating the thermal IR unit [10-11] is revealed after the seasonal CO ice layer 2 sharp rise in temperature for multiple Mars years. (b) Mars Year 33 images. sublimates. This project investigates the seasonal and (a) MY 25, interannual temperature variations and albedo Ls 334° Figure 9. False color composite thermal infrared images at Ls 337° variations in these two regions with the goal of Results: Cryptic Terrain (b) MY 33, and Ls 339° for Mars Year 33 showing an extended water ice region. Colors represent temperature. H O ice unit (green) extends understanding differences between A 2 • At Ls 188°, surface is mostly covered with CO2 ice; 4 A6 Ls 337°. more than 100 km. regions covered with CO2 ice dark spots have yet to form in A1 (Fig. 2(a)). A5 and H2O ice. • At Ls 224° CO2 sublimation is in full swing. A1 has 10 km dark streaks oriented NW (Fig. 2(b)). 160K 180K 200K 220K H2O ice regolith covered Ls 0° • Surface temperature increases slowly in Spring. 0.60 0.49 Exposed H2O Ice • Sharp temperature rise starts at Ls 250°. 240 Manhattan A4#(CO2#ice) 0.422 • Sharp rise onset repeatable year-to-year (Fig. 3). 0.67 0.36 220 A5#(H2O#ice) 7 km 0.8 200 Ls 180° A6#(regolith) Figure 10: Visible albedo image in false color at Ls 337 showing A1 A2 A3 0.7 differences in albedo for CO2 ice, H2O ice, and regolith for MY 33. Figure 1 (b): Schematic of 180 Colors represent albedo values. Martian seasons and solar 0.6 longitude, Ls. 160 Image Credit: NASA/JPL-Caltech 0.5 Table 1: Albedo Variations Near 85°S, 10°E as a function of Solar Longitude (Ls) for MY 32, 33, 34 0.4 140 Average Albedo Average Before CO2 Sublimation After CO2 Sublimation Figure 1 (a): MOLA map [12] of the Martian South Pole, the Average SurfaceTemperature (K) 0.3 Manhattan region (86° S, 99° E) in the cryptic terrain, and Exposed 120 Ls (°) 204.9° 242.1° 264.3° 324.0° 326.0° 337.4° H2O ice region (85° S, 10° E). Colors represent elevation. 180 200 220 240 260 280 300 320 340 360 0.2 Solar Longitude, Ls (°) A4 210 230 250 270 290 310 330 0.775 0.846 0.837 0.528 - 0.664 CO ice Solar Longitude, Ls (°) 2 Figure 7: Surface Temperature vs. Ls for CO2 ice, H2O ice, and Remote Sensing Techniques A5 Figure 4: Plot of average albedos as a function of solar regolith for a region near 85° S, 10° E for MY 32. 0.755 0.893 0.823 0.40 0.416 0.4335 • Regions studied (Figure 1): H2O ice longitude for A1, A2, A3 in the cryptic terrain for MY 32. A6 • Cryptic Terrain (86° S, 99° E) : Areas A1, A2, A3 A4 (CO2 ice) 240 regolith 0.763 0.88 - 0.339 0.333 0.356 • Exposed H2O Ice (85° S, 10° E) : A4, A5, A6 A5' 220 cover • Progression of CO2 sublimation in spring /summer Albedo Variations: Cryptic Terrain A5 (H2O ice) 200 studied using THEMIS visible images [13]. A6 (Regolith) • THEMIS visible albedos vary with solar longitude. 180 • Average albedos calculated from visible images [13]. • Albedo of the scene initially decreases as Spring A4' Highlights: 160 • Average surface temperature calculated from progresses due to regolith deposition (Fig. 4). Sharp rise in temperature starts earlier in cryptic 140 ♂ THEMIS infrared (band 9) images. • Albedo values increase again, peak at ~ Ls 245°. (K) Temperature Surface terrain (Ls 250°) compared with exposed H2O 120 • Surface temperatures studied as a function of solar • Albedo histograms shift to higher values 180 200 220 240 260 280 300 320 340 360 region (Ls 280°) due to basal sublimation of Solar Longitude, Ls (°) longitude (Ls) for Mars Years (MY) 30, 31, 32, & 33. corresponding to the peak in albedo (Fig. 5). translucent CO2 ice slab. Figure 8: Surface Temperature vs. Ls for CO2 ice, H2O ice, and • THEMIS images analyzed with JMARS [14]. regolith for a region near 85° S, 10° E for MY 33. ♂ Albedo peak corresponds to onset of sharp temp. rise, suggests water-ice frost formation [15]. ♂ Area A5 identified as H2O ice based on (b) Ls 186.6° Ls 247.7° Results: Exposed Water Ice Region (a) temperature (190 ± 3 K) and higher albedo (0.42) • In Spring, A4, A5, A6 have the same surface than regolith (0.33) [10]. temperature (Fig. 7 & 8). ♂ CO2, H2O, and regolith units thermally distinct. • After Ls 280°, CO2 ice sublimation reveals H2O ice Boundaries stable over many Mars years. and regolith. Frequency ♂ H2O ice widespread around southern perennial • H2O ice-regolith boundary stable within 200 m over 8 Mars years (Fig. 6). polar cap [22]. 2 km Albedo • After Ls 280° albedos differentiate (Table 1). ♂ Continuing work: SHARAD and HiRISE image • Albedos: regolith < Exposed H2O ice < CO2 ice. analysis. Figure 2: Progression of CO2 sublimation and regolith Figure 5: Albedo histograms showing how albedo changes deposition. Visible THEMIS images at Ls 188.2° and Ls with Ls for Area A1 for Mars Year 32. 224.0° for Area A1 in cryptic terrain for Mars Year 31. References: [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., [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). 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. [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. 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. 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] [22] Brown, et al. (2014). Earth and Planetary Science Letters, 406, 102-109. 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. 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. .
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