Three Decades of Martian Surface Changes

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Plates & Figure 1

Time-series of MGS global monitoring images. This montage of red filter MOC WAC mosaics shows the appearance of Mars at various times during each of two martian years from 4/1999 to 1/2003. The mosaics are shown in equal-area cylindrical map projections and are labeled with the MGS mission phase and the solar longitude (Ls). Seasonal phenomena that can be seen in these snapshots include the annual appearance of polar hoods and surface frosts, brightening within the great basins of Hellas and Argyre, and the occurrence of equatorial clouds adjacent to the volcanoes of Tharsis and Elysium. The global dust storm of 2001 obscured surface albedo contrast (especially during phase E09) and produced many minor surface changes.

Plate 1A Viking color DIM (top) vs. MGS cloud-free mosaic (bottom) in equal area cylindrical map projections. (170 KB)
Plate 1B Viking (left) and MGS (right) views of the northern hemisphere of Mars in polar orthographic map projections. (130 KB)	Plate 1C Viking (left) and MGS (right) views of the southern hemisphere of Mars in polar orthographic map projections. (140 KB)
Figure 1 (1.7 MB)	Figure 1 color (1.4 MB)

Figure 2

Differences between Viking and MGS albedos of Mars. These images map the albedo changes that took place between Viking and MGS as seen by two types of sensors. The upper image shows albedo changes computed by subtracting the Viking red filter image mosaic of McEwen et al. (1994) from the cloud-free red filter mosaic from MGS MOC. The image is scaled so that black tones represent a decrease in albedo of -0.06 (I/F) and white represents an increase of +0.03. The lower image shows a similar result, produced by subtracting the Viking IRTM broadband albedo from the MGS TES broadband albedo, stretched to portray a range of albedo changes from -0.09 to +0.09. The images are presented in equal area map projections from 60 S to 60 N, the limits of reliable IRTM coverage. Both of the data products indicate darkening at higher latitudes, particularly in the southern hemisphere, and brightening at tropical latitudes.

Figure 2
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Figure 3

Locations of large-scale surface changes. Boxes outlining the major surface changes described in the text are overlain on an MGS MOC red filter mosaic (top), a gray-scale rendition of MOLA topography (middle) and a map of thermal inertia from MGS TES (bottom). Note that all of the major surface changes took place in areas of moderate to high thermal inertia. The individual albedo features discussed in Section 4 are as follows: 1. Syrtis Major. 2. Nilosyrtis and Alcyonius. 3. Hyblaeus. 4. Cerberus. 5. Propontis. 6. Southern Tropical Dark Band (Mare Cimmerium - Mare Sirenum). 7. Southern High-Latitude Band (Mare Chronium - Mare Australis) at Phaethontis Quadrangle. 8. Aonis Sinus. 9. Solis Lacus. 10. Acidalia.

Figure 3
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Figure 4

Surface changes at Nilosyrtis and Alcyonius. Nilosyrtis is the name given to the dark terrain in the northern part of this region. Alcyonius is the isolated dark patch to the southeast of Nilosyrtis. Both of these low albedo zones enlarged between the time of the Viking images (top) and the MGS observations (bottom). Note the complex and sharply defined albedo boundaries dividing bright and dark terrain. These images span an east-west distance of 2440 km at 40°N latitude. The MGS mosaic shown is from Caplinger (2002).

Figure 4
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Figure 5

Surface changes at Nilosyrtis and Alcyonius during the Viking era. Two Viking Orbiter views taken on orbits 605A and 347S show changes in albedo patterns already underway. Earlier Mariner 9 observations showed Alcyonius buried, indicating that the surface changes in this region have been going on for at least three decades.

Figure 5
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Figure 6

Dust-devil tracks in Nilosyrtis. A portion of a MOC NAC image (left) shows a close-up view of recently darkened terrain in western Nilosyrtis at 54.28°N, 292.69°W. The surface in the darkest parts of the picture (near the middle of the footprint plot on the MOC WAC context image, at right) is crisscrossed with filamentary linear streaks that are diagnostic of dust-devil tracks. The width of the NAC image is 3.4 km, and the context image is 133 km across. These images were processed by Malin Space Science Systems.

Figure 6
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Figure 7

Nilosyrtis dust-devil track locations. A survey of MOC NAC images from mission phases AB1 to E06 identified dust devil tracks in 107 NAC images (solid black rectangles). Ambiguous cases, including vague or partially erased tracks, are shown as open rectangles. Definitive nondetections were made in another 180 NAC images (white rectangles). The dust devil tracks are strongly zoned during all seasons, confined to latitudes ~45°N to ~65°N. In areas such as Alcyonius that darkened outside of this latitude band, dust devil tracks are absent and the surface is pervaded instead by linear wind streaks indicative of persistent winds.

Figure 7
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Figure 8

Surface changes at Cerberus. This classical albedo feature largely disappeared during the interval between the Viking (top) and MGS observations (bottom). The linear bright and dark wind streaks with diffuse albedo boundaries are indicative of erosion by persistent winds. These images span an east-west distance of 1700 km at 10°N latitude. The MGS mosaic shown is from Caplinger (2002).

Figure 8
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Figure 9

Cerberus close-up. This portion of a MOC NAC image centered at 13.96°N, 199.51°W (left) shows dark-floored craters and incipient erosional streaks that suggest a thin dust cover. The dust within the largest crater is organized into dune-like ripples; elsewhere in Cerberus, such dust-filled craters serve as sources for bright streaks. The context image (right) shows dark erosional streaks that originate at topographic irregularities such as craters and knobs. The width of the NAC image is 3.0 km, and it is excerpted from a point 1/3 of the way from the top of the footprint plot shown in the context image. These images were processed by Malin Space Science Systems.

Figure 9
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Figure 10

Surface changes in Phaethontis Quadrangle. A broad region with indistinct boundaries south of 50°S darkened between the imaging observations of Viking (top) and MGS (bottom). This area is part of a large, newly formed dark ring that encircles the south pole. Farther north, both darkening and brightening have taken place at subtropical latitudes from 30°S to 40°S. The images span an east-west distance of 2230 km at 50°S latitude.

Figure 10
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Figure 11

Phaethontis dust-devil track locations. The distribution of dust-devil tracks in Phaethontis Quadrangle sampled during southern summer is shown superimposed on the Viking image mosaic. Black rectangles indicate the locations of NAC images in which dust-devil tracks were observed, whereas white rectangles show the locations of definite nondetections. The size of each rectangle indicates the uncertainty in its location rather than the density of dust-devil tracks. This cursory survey suggests that dust-devil tracks are concentrated in the mid- to high-latitudes from 45°S to 65°S.

Figure 11
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Figure 12

Phaethontis close-up. Many of the dark-floored craters in Phaethontis Quadrangle are occupied by fields of dark dunes that dwarf the bright ripples made by dust. This example is at 52.87°S, 144.42°W. The dune field is huddled to the northwest side of a small crater within a larger crater. Tendrils of sand make their way up gullies on the northwest side of the small crater. The northwest side of the larger exterior crater is blackened, and an outlying dune appears on the exterior crater wall. The MOC NAC image is 3.0 km across. These images were processed by Malin Space Science Systems.

Figure 12
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Figure 13

Phaethontis dune locations. The locations of dark dune fields in Phaethontis Quadrangle identified in MOC NAC images up to phase R09 are shown superimposed on the Viking image background. Dark dunes are scattered throughout the area that darkened between Viking and MGS imaging observations. Many of the splotch craters that currently lack high-resolution coverage are likely to contain dunes as well.

Figure 13
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Figure 14

Surface changes in southern Acidalia. The albedo boundary dividing bright and dark surfaces advanced towards the southwest during the interval between Viking (top) and MGS (bottom) imaging observations. Linear wind streaks and diffuse albedo boundaries indicate erosion by persistent southwesterly winds. These images span an east-west distance of 2700 km at 30°N latitude. The MGS mosaic shown is from Caplinger (2002).

Figure 14
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Figure 15

Acidalia dust-devil track locations. A cursory survey of northern summertime high resolution MOC NAC images detected no dust-devil tracks along the recently darkened southern margin of Acidalia. In common with the Nilosyrtis region, dust-devil tracks in Acidalia were found only in higher latitudes ranging from ~50°N to ~65°N. At lower latitudes, where most of the darkening took place, the albedo is controlled by bright and dark linear streaks that taper towards the southwest.

Figure 15
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Figure 16

Acidalia close-up. A close-up view of the newly darkened terrain at 26.10°N, 42.91°W shows that most of the bright dust has been removed from the region already. The little dust that remains is concentrated in the sheltered floors of impact craters, where it forms small dune-like ripples. Bright streaks extend towards the southwest, downwind from the dust-filled craters. These images were processed by Malin Space Science Systems.

Figure 16
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