Active Mars: A Dynamic World

Abstract

Mars exhibits diverse surface changes at all latitudes and all seasons. Active processes include impact cratering, aeolian sand and dust transport, a variety of slope processes, changes in polar ices, and diverse effects of seasonal CO₂ frost. The extent of surface change has been surprising and indicates that the present climate is capable of reshaping the surface. Activity has important implications for the Amazonian history of Mars: understanding processes is a necessary step before we can understand their implications and variations over time.

Keywords: Mars; aeolian processes; impact cratering; seasonal processes; surface changes.

Figure 1

Examples of new impact craters, including well‐defined blast pattern (a) and ice exposure (b) ((a): Subsection of High Resolution Imaging Science Experiment [HiRISE] image ESP_045270_1950. (b): Subsection of HiRISE image ESP_025840_2240. North is up and illumination from the left. All image figures have been stretched to optimize contrast and visibility; original data are available as described in the Data Availability statement).

Figure 2

(a) Spire streaks on Pavonis Mons. (b) Complex streak superposition on the North Polar Layered Deposits ((a): Subsection of Context Camera image P02_001893_1804_XN_00N113W. North is up and illumination from the left. (b): Subsection of High Resolution Imaging Science Experiment image PSP_009273_2610. North is to the upper right and illumination from lower left).

Figure 3

Active aeolian features on Mars. (a) Dust devil tracks in Gusev crater. (b and c) Advancing dune and changing ripples in Nili Patera. Note bedrock features indicated by arrows which are buried by sand in (c). (d) Dust devil tracks in Gusev crater confined to a region of thin dust cover ((a): Subsection of High Resolution Imaging Science Experiment [HiRISE] image PSP_005456_1650. (b): Subsection of HiRISE image ESP_017762_1890 [Mars Year, MY 30, L _S = 89°]. (c): Subsection of HiRISE image ESP_062069_1890 [MY 35, L _S = 97°]. (d): Colour and Stereo Surface Imaging System color image MY34_003860_344_1 [NIR, PAN, BLU filters]. North is up and illumination is from the left in (a–c). In (d), north is to the right and illumination is from the bottom right. In all comparison pairs such as (b and c), the panels are shown at the same resolution).

Figure 4

Examples of morphologic changes in nondune gullies. (a–c) Multi‐stage incision of a new channel section in Dunkassa crater via several flows. (d and e) Thick lobate deposit filling and partially burying a channel segment in Selevac crater ((a): Subsection of High Resolution Imaging Science Experiment [HiRISE] image ESP_013115_1420 [Mars Year, MY 29, L _S = 266°]. (b): Subsection of HiRISE image ESP_032011_1425 [MY 31, L _S = 325°]. (c): Subsection of HiRISE image ESP_055496_1420 [MY 34, L _S = 184°]. (d): Subsection of HiRISE image ESP_028622_1425 [MY 31, L _S = 166°]. (e): Subsection of HiRISE image ESP_055443_1425 [MY 34, L _S = 182°]. North is up and illumination is from the left in all panels).

Figure 5

Recurring slope lineae in Raga crater (a) and Coprates Chasma (b) ((a): Subsection of High Resolution Imaging Science Experiment [HiRISE] image ESP_014011_1315. (b): Subsection of HiRISE image ESP_059476_1670. North is up and illumination is from the left in both panels).

Figure 6

Example of a new slope streak (a and c) and various dark and bright streaks observed in Arabia Terra. (a) shows the full extent of the streak including the point source. (b and c) are before‐and‐after images showing the toe of the streak with identical resolution and very similar lighting. Many small topographic features within the streak are preserved, indicating minimal change in surface topography; arrow indicates a ridge, demonstrating topographic change. Similar features outside the streak are unchanged. (d) exhibits dark streaks (left), bright streaks (center), and a slope streak with dark and bright areas (right). Both dark and bright streaks are visible under the same illumination conditions, indicating that their brightness differences are independent of the viewing geometry ((a and c): Subsections of High Resolution Imaging Science Experiment [HiRISE] image ESP_028616_1920 [Mars Year, MY 31, L _S = 165°]. (b): Subsection of HiRISE image PSP_008441_1920 [MY 29, L _S = 72°]. (d): Subsection of Colour and Stereo Surface Imaging System image MY35_009504_159_0. North is up and illumination is from the left in all panels).

Figure 7

Examples of rockfalls that are brighter (a) and darker (b) than their surroundings. Note discontinuous nature indicating bouncing of the falling rocks, and division into multiple tracks ((a): Subsection of High Resolution Imaging Science Experiment [HiRISE] image ESP_026493_1690. (b): Subsection of HiRISE image ESP_036261_1705. North is up, illumination is from the left, and downhill is to the left in both panels).

Figure 8

Fan deposits (dark patches) and araneiform landforms near the south pole. The deposits appear dark because they are composed of lithic material which contrasts with surface frost, and exhibit no contrast after the frost sublimes (Subsection of High Resolution Imaging Science Experiment image ESP_055604_0930. North is to the lower right and illumination is from the upper right).

Figure 9

Changes in sand dunes in the north polar erg. (a and b) Formation of a decameter‐scale alcove on a dune slip face. (c and d) Formation of a furrow ((a): Subsection of High Resolution Imaging Science Experiment [HiRISE] image ESP_027394_2640 [Mars Year, MY 31, L _S = 118°]. (b): Subsection of HiRISE image ESP_036387_2640 [MY 32, L _S = 124°]. (c): Subsection of HiRISE image PSP_009439_2600 [MY 29, L _S = 106°]. (d): Subsection of HiRISE image ESP_18445_2600 [MY 30, L _S = 113°]. North is to the right and illumination is from the upper right in (a/b), and north is to the lower left and illumination is from the right in (c/d)).

Figure 10

(a and b) Evolution of pit fields via formation of pits on aeolian bedforms at 55.4°S. Arrows indicate the largest of many new pits ((a): Subsection of High Resolution Imaging Science Experiment [HiRISE] image ESP_040428_1245 [Mars Year, MY 32, L _S = 307°]. (b): Subsection of HiRISE image ESP_058019_1245 [MY 31, L _S = 305°]. The former image has a coarser pixel scale than the latter and has been enlarged 2× for easy comparison. North is up and illumination is from the left).

Figure 11

Expanding pit in the south polar residual cap. The upper panel shows a full‐resolution view of a pit; the lower sequence shows growth of the pit across seven Mars years. Arrow indicates common location in all panels (Top: Subsection of High Resolution Imaging Science Experiment [HiRISE] image ESP_058026_0930. Bottom: Subsections of HiRISE images PSP_005043_0930, ESP_013930_0930, ESP_022567_0930, ESP_031837_0930, ESP_041094_0930, ESP_049217_0930, and ESP_058026_0930. Images were acquired between L _S = 296–306° except for the Mars Year 32 image at L _S = 317°. North is up and illumination is from the left in all panels).

Figure 12

Avalanche cloud at the edge of the north polar layered deposits. Note color fringing near the avalanche toe due to motion of the cloud between acquisition of different colors (Subsection of High Resolution Imaging Science Experiment [HiRISE] image ESP_060176_2640. Color data are only acquired in the central swath of HiRISE images; lower part of the figure is red channel only. North is to the right and illumination is from the top).

Figure 13

Blockfalls on steep slopes in the north polar layered deposits indicating large morphological changes. (a and b) Blockfall in a small basal scarp, showing fall of a 5 × 22 m block and new rubble. (c and d) Socket left by fall of a 70 m slab of ice from the face of a steep scarp ((a): Subsection of High Resolution Imaging Science Experiment [HiRISE] image PSP_001628_2650 [Mars Year, MY 28, L _S = 144°]. (b): Subsection of HiRISE image ESP_054663_2650 [MY 29, L _S = 149°]. (c): Subsection of HiRISE image ESP_016292_2640 (MY 30, L _S = 39°). (d): Subsection of HiRISE image ESP_024639_2640 [MY 31, L _S = 22°]. North is to the lower right and illumination is from the upper left in all panels).

Figure 14

Distributions of surface changes from selected publications. Biases and incompleteness in the distribution of detections may exist due to the nature of the change detection methods and underlying data. Background is shaded relief from Mars Orbiter Laser Altimeter Digital Elevation Model.

Figure 15

Timing associated with different activity categories. Thick lines indicate primary activity periods; sinuous lines indicate activity that varies seasonally with slope aspect. Lines indicate the general interpreted timing of activity, not the full envelope of uncertainty for all observed events. Some constraints are based on a limited number of sites or examples and could be improved by expanded data. Aeolian sand transport occurs at most latitudes and the seasonality likely varies with latitude and regional wind pattern. Blue lines indicate activity that has been associated with seasonal frost with light blue indicating defrosting activity such as spots and fans; gold lines indicate processes not attributed to frost.