INTRODUCTION
3.2 Introduction
Ejecta blankets surround craters on many planetary and satellite surfaces. Lunar and Mercurian deposits have ballistically emplaced ejecta blankets. They appear coarse and disordered near the rim, then gradually thin and smooth out with increasing distance from the crater. Eventually, they blend into fields of secondary craters, rays, and the surrounding terrain [Shoemaker, 1962]. On Mars, in contrast, most craters larger than about 4 km in diameter have lobate ejecta blankets with rampart or convex termini. Many craters smaller than 4 km and a small percentage larger than 4 km have lunarlike ballistic ejecta morphology with radial lineations and a thin, irregular boundary [Strom et al., 1992]. At diameters larger than about 50 km, radiallunarlike ejecta morphologies again
35 3.2 Introduction
dominate [Pike, 1980; Horner and Barlow, 1988]. A small percentage of craters have lobate blankets with superimposed radial striae. Many blankets are no longer visible due to erosion or blanketing by later deposits.
Formation of distinctive, relatively high relief, Martian lobate ejecta deposits with distinct tennini was originally attributed to aeolian modification of lunar like ejecta blankets [McCauley, 1973; Arvidson et al., 1976]. However, flow features evidenced more clearly in Viking images point toward formation by fluidized flow, such as shock-induced fluidization of volatiles in the surface materials [e.g., Carr et al., 1977; Mouginis-Mark, 1979; Barlow and Bradley, 1990]. Laboratory experiments involving impact into viscous targets have created ejecta blankets similar to those seen on Mars [Greeley et al., 1980;
Gault and Greeley, 1978]. Laboratory experiments that vary atmospheric pressure and particle size have also reproduced some lobate crater morphologies [Schultz and Gault, 1979, 1984]. One of my motivations in studying Martian thermally distinct ejecta blankets in detail is to discern any additional clues to the origin of fluidized ejecta blankets.
Lunar eclipse and lunar nighttime observations show that at least the inner regions of some younger ejecta blankets are thermally distinct (usually warmer than surroundings) [Shonhill, 1972]. This is attributed to a greater preponderance of blocks. Newly recognized thermal anomalies associated with Martian ejecta blankets extend further and appear to be more complex in origin.
I have used the high spatial resolution of the thermal infrared/visible Termoskan instrument to carry out the first thermal study of Martian ejecta blankets. Because of insufficient spatial resolution, studies of Viking IRTM data were unable to distinguish any Martian ejecta blankets as thermally distinct from their surroundings (P. R. Christensen, personal communication, 1991). Approximately 100 craters within the Termoskan data have an ejecta blanket distinct in the thermal infrared (EDITH) (e.g., see Figure 3.1). To better understand these features, I have undertaken a threefold analysis: (1) a systematic examination of all Termoskan image data using high-resolution image processing; (2) a
Thermally Distinct Ejecta Blankets 36
Figure 3.la. Image is from Tennoskan's visible channel. Time of day is near local noon. North is towards the left side of the page. Part of Valles Marineris can be seen in the northeast corner. Phase angle is approximately zero for all points. Image was obtained simultaneously with the thermal image shown in Figure 3.lb. The dark east-west band is the thermal signature of the passage of the shadow of Phobos. Black vertical lines represent missing lines of data.
37 3.2 Introduction
Figure 3.lb. Image is from Tennoskan's thennal infrared channel. The darker areas are cooler and lighter areas are wanner. Note the thermally distinct ejecta deposits which appear as bright or dark rings surrounding craters in the thermal image (examples denoted by arrows). These deposits are up to 5 K wanner or cooler than their surroundings. White lines indicate geologic map boundaries. Geologic units and boundaries are from Witbeck et al. [1991] and Scott and Tanaka [1986] with some interpolation between the two. Units shown, from oldest, are Nplr, Noachian plateau ridged unit; Nf, Noachian fractured unit; Hr. Hesperian ridged plains material; Hsl, Hesperian Syria Planum formation, Lower Member; and Hsu, Hesperian Syria Planum formation, Upper Member (see Table 3.2 for more detail).
Virtually all of the more than 100 EDITHs observed are situated on Hesperian age plains near Valles Marineris (e.g., Hr, Hsu, and Hf), but not on the older Noachian units (e.g., Nplr and Nf). EDITHs are almost exclusively associated with Hesverian al!e terrains throul!hout the data set.
Thennally Distinct Ejecta Blankets 38
formal study of the systematics of the data by compiling and analyzing a data base consisting of geographic, geologic, and morphologic parameters for a significant fraction
of the EDITHs and nearby non-EDITHs (total ejecta blankets 110); and (3) qualitative and quantitative analyses of localized regions of interest. These methods, results, and conclusions are presented in the remaining portions of this paper.
3.3 Properties Associated with Individual EDITHs
On the Hesperian units where EDITHs are present, intensity profiles across different ejecta blankets vary greatly in both the thermal and visible channels (see Figures 3.2 and 3.3). Some of the blankets appear warmer than their surroundings, some appear cooler, and some are not thermally distinct. Some thermally distinct ejecta blankets appear distinct in the visible channel; however, others do not
The boundaries of EDITHs often closely follow even very sinuous termini of lobate ejecta blankets (e.g., see Figures 3.4-3.7). Thus, the thermal anomalies are strongly associated with the blankets themselves. Those blankets that appear thermally distinct show no consistent pattern of radial thermal variation within each blanket. Many EDITHs are quite uniform in temperature across a given blanket
Crater interiors often appear warm relative to ejecta and surroundings, as exemplified by the thermal profiles in Figures 3.2 and 3.3 as well as in Figure 3.1. In some cases this is probably due to low inertia material within the craters. However, in all but the flat floors of the largest craters, one must consider the heating effects of slopes and of increased shadowing caused by crater topography. These effects are very difficult to separate from inertia and albedo effects without multiple observations. In this paper I will not comment further on the thermal signature of crater interiors. By contrast, slope and shadow history effects for ejecta blankets are much smaller due to the larger scales and smaller slopes involved.
39 3.3 Properties Associated with Individual EDfJHs
In order to search for correlations and better understand EDITHs, I compiled a data base of craters and their ejecta which includes quantitative and qualitative information (see Table 3.1). My data base includes 110 craters, most thennally distinct but some not.
This set covers all craters larger than 8 km in diameter and most craters larger than 5 km (smallest, 4.2 km; largest, 90.6 km) that are located in the northwest and southwest Coprates subquadrangles (MC-18NW and MC-18SW) and fall within the Termoskan panoramas. Local time of day within this region varies from approximately 1130 to 1330.
The craters selected are located between 23.0°S and 8.0°S in latitude and 67 .5°W to 90.0°W longitude. This area includes parts of Valles Marineris and several plains and ridged plains units of both Noachian and Hesperian age just south of Valles Marineris.
This region was chosen for its many thennally distinct ejecta craters and its variety of geologic units. Many lobate ejecta craters are seen in this region in Viking images even down to subkilometer scales [Clifford and Duxbury, 1988].
For each crater in the data base, I have cataloged representative average temperatures for both the ejecta (EJET in Table 3.1) and the area surrounding the ejecta (SURT). Because the relative precision of Termoskan is approximately 0.5 K and the absolute accuracy is better than 3 K [Murray et al., 1991], I have great confidence in relative Termoskan brightness temperatures. In Termoskan's less accurate visible channel, I similarly noted representative dn (signal) values for both ejecta (EVIS) and the area surrounding the ejecta (SVIS).
I developed three descriptive thermal parameters, each expressing a somewhat different aspect of the ejecta blankets. First, I assigned a subjective "thermal freshness"
parameter (TFR in Table 3.1) describing qualitatively how thennally distinct the ejecta appears relative to the surroundings. Second, I calculated temperature difference (DELT)
'between the ejecta blanket and the surrounding area using my representative average
temperature values. Third, I calculated an approximate time of day corrected temperature for the ejecta alone (ETDS), thus giving a thermal parameter that does not depend upon
Thermally Distinct Ejecta Blankets 40
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Figure 3.2. West to east Tennoskan infrared (curve A) and visible (cUive B) profiles across fluidized ejecta blanket and 11.4 km crater located at 18.4°S, 74.0°W (crater 25 in Table 3.1;
crater C in Figures 3.1 and 3.4). Note the three peaks in the temperature curve. The outer peaks correspond to the warm (relative to surroundings) ejecta blanket on either side of crater. The central peak corresponds to the warm crater interior. Note the inverse correlation between the temperature of the ejecta blanket and the visible signature, implying that in this case an albedo difference helps explain the wanner ejecta. This inverse correlation exists only in some crater profiles. The crater interior shows correlation between temperature and visible brightness, possibly indicating some degree of low inertia dust mantling in the crater interior.
41 3.3 Properties Associated with Individual EDITHs
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Figure 3.3. West to east Terrnoskan infrared (curve A) and visible (curve B) profiles across fluidized ejecta blanket and 12.6 km crater located at 18.5°S, 88.7°W (crater 1 in Table 3.1; just off the western edge of Figure 3.1). This crater has an ejecta blanket that is cooler than the surroWldings. Notice the two dips in the temperature curve that correspond to the fluidized ejecta blanket. Note that for this crater, the visible curve shows very little correlation to the temperature
in either the ejecta blanket or crater interior.
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IID LAT I ·18.53 2 ·18.28 3 -17.99 4 -18.36 5 -15.48 6 -17.93 7 -17.61 8 -16.05 9 -15.51 10 -18.73 II -18.5-4 12 -17.85 13 -16.38 14 -16.79 15 -17.06 16 -15.76 17 -IS.83 18 -18.38 19 -16.17 20 -19.12 21 -IS.7S 22 -16.71 23 -18.04 24 -17.68 25 -18.39 26 -17.99 27 -16.66 28 -16.2S 29 -16.06 30 ·IS.43 31 ·17.9S 32 -16.13 33 -17.70 3-4 ·19.21 35 -19.80 36 -18.79 37 -18.06 38 -17.50 39 -18.60 <40 -I 1.78 41 ·IO.SS 42 -10,02 43 -I 1.01 44 -9.3S 45 ·10.68
LOH 88.72 88.91 89.01 89.29 88.38 84.21 84.05 84.60 84.SI 83.43 81.98 82.07 82.07 81.20 79.58 79.78 78.49 77.94 71.55 76.21 76.33 15.99 74.49 74.36 73.95 73.84 73.66 73.71 73.67 73.01 72.03 7J.OS 70.64 70.69 68.98 69.13 68.52 68.23 61.56 90.01 89.92 89.78 89.62 88.83 88.67
DIA TYP 12.60 Rc 5.38 Sc 6.10 Sc 7.40 Rc 5.10 Rc 21.50 Sc 6.40 Sc 18.80 Rc 4.30 Rc 7.40 Rc 11.60 Rc 8.80 Rc 19.70 Rc 17.10 Rc 10.90 Rc II..SO Sc 20.40 Rc 10.60 Rc 15.70 Rc 11.60 Rc 35.50 Rc 8.20 Rc 9.10 Sc 13.90 Rc 11.40 Rc 9.10 Rc 7.00 Rc 4.30 Rc 4.30 Sc 10.60 Rc 16.90 Rc 16.90 Rc 12.60 Rc 5.20 Sc 12.70 Rc 24.10 Rc 8.60 Rc IO..SO Rc 6.20 Sc 90.60 De 4.70 Sc 4.50 Sc 7.60 Sc 3.90 Sc 6.00 Sc
E.1B INT SL Pk No No No No No No No No No No No No ML SY SL No SL PP SL PP SL Pk ML FP SL SY SL Pk No No ML SY SL Pk SL SY SL SY ML Pk Pn FP No No SL Pk SL FP SL FP SL Pk SL No No No SL Pk SL Pk ML pp SL Pk No No No No ML Pk No No No No No No No No No No No No No No No No No No
P'IDI UN1T TPR. 0.00 Hm -3 0.00 Hm -2 0.00 Hm -3 0.00 Hm -3 0.00 Hm -2 0.00 Hai/Hr/Hm 2 0.00 Hai/Hr/HJu 0 2.60 Hm -3 o.oo Hm 0 0.00 Hr -1 0.00 Hr -3 0.00 Hr 0 0.00 Hr I 1.20 Hr/Nf 1 0.00 Hr/Nf 2 0.00 Nf 0 3.70 Nplr 0 0.00 Hr -3 2.60 Nplr 0 2.30 Hr 3 0.00 Nplr 0 0.00 Nplr -2 0.00 Hr 0 0.00 Hr 3 0.00 Hr 3 0.00 Hr 3 0.00 Hr 2 0.00 Hr 2 0.00 Hr 2 0.00 Hr 0 0.00 Hr -1 0.00 Hr 0 0.00 Hr 2 0.00 Hr 2 0.00 Hr 0 0.00 Hr -1 0.00 Hr 0 0.00 Hr -1 0.00 Hr -1 0.00 Hm 0 0.00 Hm -1 0.00 Hm -2 0.00 Hsu -1 0.00 Hsu -1 0.00 Hm -2
E.1BT 256.50 2S6.00 2S6.00 256.00 2S1.50 260.56 260.56 2S8.00 2S8..SO m..so 256.50 2S9..SO 263.89 262.22 262.22 261.08 263.33 260.00 265.00 262.78 266.61 263.33 260.00 260.56 264.44 260.00 264.44 263.89 263.89 265.42 261.61 264.44 262.22 261.11 263.89 260.00 262.78 263.33 260.00 265.42 26!;.4: 265.00 264.44 264.44 264.44
SURT DELT I!TDS STDS 2S9.00 2S9.00 m..so 2S9.00 260.00 2S8.00 260.56 2S9.00 260.00 2S9.00 260.00 260.00 262.78 260.56 260.00 261.08 265.42 262.22 265.00 2S9.00 266.67 265.42 2S8.00 2S8.00 2S8.00 2S8.00 260.00 260.00 260.00 265.42 260.56 264.44 260.56 2S9..SO 263.89 262.22 262.78 265.42 263.33 265.42 266.61 266.25 266.67 265.42 265.83
-2.50 -3.00 -1.50 -3.00 -2.50 2.56 0.00 -1.00 -1.50 -1.50 -3.50 .0.50 1.11 1.66 2.22 0.00 -2.09 -2.22 0.00 3.78 0.00 -2.09 2.00 2.56 6.44 2.00 4.44 3.89 3.89 0.00 1.11 0.00 1.66 1.61 0.00 -2.22 0.00 -2.09 -3.33 0.00 -1.2S ·1.2S -2.23 .0.98 -1.39
.0.72 ·I. IS -1.43 .0.94 -1.86 0.94 o.ss -273 -2.60 -2.01 -3.52 .0.87 2.52 0.90 0.47 4.47 0.66 -I.IS 2.10 1.65 3.24 0.46 -2.14 -1.94 2.S9 -2.21 1.23 0.36 0.36 1.52 .0.69 0.68 -o.s8 .0.66 2.47 -2.13 0.31 0.52 -2.13 4.89 4.05 3.32 3.18 2.04 2.45
1.78 1.85 0,07 2.06 0.64 -1.62 0.55 -1.73 -1.10 .O.SI .0.02 -0.37 1.41 -0.76 -1.15 4.47 2.75 l.o? 2.10 -2.13 3.24 2.5S -4.14 -4.50 -3.85 -4.21 -3.21 -3.S3 -3.S3 1.52 ·1.80 0.68 -2.24 -2.27 2.47 0.09 0.31 2.61 1.20 4.89 5.30 4S1 S.41 3.02 3.84
EVJS 126.00 129.00 129.00 128.00 149.00 130.00 130.00 148.00 150.00 12S.OO 123.00 124.00 134.00 132.00 122.00 139.00 130.00 116.00 119.00 108.00 120.00 122.00 116.00 124.00 109.00 120.00 121.00 124.00 127.00 131.00 121.00 128.00 127.00 122.00 120.00 125.00 127.00 133.00 122.00 161.00 154.00 154.00 160.00 158.00 161.00
SVJS 121.00 121.00 120.00 121.00 149.00 130.00 130.00 150.00 ISO.OO 123.00 117.00 123.00 134.00 132.00 132.00 139.00 122.00 110.00 119.00 111.00 120.00 118.00 116.00 124.00 116.00 123.00 126.00 128.00 128.00 131.00 121.00 128.00 12S.OO 122.00 120.00 12S.OO 127.00 131.00 122.00 161.00 IS4.00 154.00 160.00 !S8.00 161.00
DELV s.oo 8.00 9.00 7.00 0.00 0.00 0.00 -2.00 0.00 2.00 6.00 1.00 0.00 0.00 -10.00 0.00 8.00 6.00 0.00 -3.00 0.00 4.00 0.00 0.00 -7.00 -3.00 -5.00 -4.00 -1.00 0.00 0.00 0.00 2.00 0.00 0.00 0.00 0.00 2.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
TOO 11.68 11.61 11.66 11.64 11.70 12.02 12.03 11.98 11.99 12.07 12.18 12.18 12.18 12.24 12.36 12.3S 12.44 12.48 12.51 12.61 12.60 12.63 12.74 12. 7S 12.78 12.79 12.80 12.80 12.80 12.85 12.92 13.00 13.03 13.02 13.1S 13.14 13.18 13.21 13.26 ll.S8 II.S9 11.60 11.61 11.61 11.68
AI.Ji 0.18 0.18 0.18 0.17 0.19 0.17 0.17 0.18 0.18 0.17 0.20 0.17 0.19 0.19 0.19 0.19 0.18 0.18 0.19 0.18 0.18 0.18 0.19 0.19 0.18 0.19 0.19 0.19 0.19 0.19 0.19 0.19 0.19 0.17 0.18 0.18 0.20 0.20 0.19 0.21 0.21 0.21 0.21 0.22 0.20
lNER TOPO RATIO 7.3 6597 2.08 7.3 6597 0.00 6.9 6176 0.00 7.3 6S32 2.50 6.3 S899 0.00 7.3 6106 0.00 7.3 6106 0.00 7.0 S591 3.61 7.0 SS91 0.00 1.5 6903 1.94 7.4 6210 2.80 7.2 SS78 2.17 7.2 5019 3.53 6.8 5000 2.60 7.2 sooo 2.20 6.2 5000 0.00 6.2 sooo 0.00 7.8 S626 2.20 7.3 sooo 3.14 7.8 S698 2.00 6.6 sooo 4.41 7.3 sooo 2.00 7.7 5163 0.00 7.7 5163 1.54 8.2 S473 2.00 8.0 5320 2.29 8.0 5002 2.00 8.0 SO<X2 0.00 8.0 SO<X2 0.00 6. 9 5000 2.50 8.0 S621 3.27 7.2 5206 2.80 7.2 5623 2.00 6.9 6142 1.67 6.5 6183 2.31 6.S 6017 4.19 6.6 587S 1.69 6.6 5815 2.06 6.5 628S 0.00 S.5 782S 0.00 5.4 8290 o.oo 5.4 8290 0.00 5.4 7607 0.00 5.1 8681 0.00 S.4 8271 0.00
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fir ~ N"":l ID LAT LON D!A TYP EJE INT PTDI UNIT TFR EJET SURT DELT ETDS STDS EVIS SVIS DELV TOO ALB INER TOPO RATIO ~ cr <46 -13.54 88.52 19.30 Rc No No 0.00 Htu 0 263.33 263.33 0.00 2.85 2.85 161.00 161.00 0.00 11.69 0.20 5.5 6290 1.60
-
(1) w 41 -13.29 88.45 6.10 De No No 0.00 Htu 0 263.33 263.33 0.00 2.78 2.78 162.00 162.00 0.00 11.70 0.20 5.5 6290 0.00-
48 -9.35 88.45 9.10 Rc No No 0.00 Hsu 0 265.00 265.00 0.00 2.40 2.40 159.00 159.00 0.00 11.70 0.22 5.1 8681 0.00 49 -13.47 88.38 7.00 Rc No No 0.00 Hsu 0 263.33 263.33 0.00 2.71 2.71 161.00 161.00 0.00 I 1.71 0.20 5.5 6290 0.00 (") 50 -9.76 88.29 I 1.30 Rc DL sP 1.20 Htu 0 264.44 264.44 0.00 2.00 2.00 161.00 161.00 0.00 I 1.71 0.22 5.1 8681 2.14 0 ::l 51 -14.02 87.88 5.70 Rc No No 0.00 Hsu 2 261.67 259.50 2.17 1.13 -1.04 160.00 158.00 2.00 11.74 0.18 6.5 5866 1.74s ·
52 -11.25 87.43 6.10 Sc No No 0.00 Hsu -2 262.22 265.00 -2.78 -0.18 2.60 163.00 161.00 2.00 11.78 0.19 5.7 7365 0.00 c: 53 -10.72 87.29 7.80 Rc No No 0.00 Hau 0 265.00 265.00 0.00 2.29 2.29 161.00 161.00 0.00 11.79 0.20 5.1 8071 0.00 (1) 54 -8.81 86.62 4.50 Sc No No 0.00 Hau 0 264.44 264.44 0.00 0.74 0.74 153.00 153.00 0.00 11.84 0.21 5.8 8365 0.00 p. 55 -9.04 86.33 13.40 Rc SL FP 0.00 Hau -1 263.33 264.44 -1.11 -0.48 0.63 155.00 154.00 1.00 11.86 0.20 5.8 8325 2.22 56 -12.82 86.13 4.50 Rc No No 0.00 Hau -2 257.50 259.50 -2.00 -4.38 -2.38 157.00 157.00 0.00 11.87 0.18 5.9 6462 2.20 57 -8.86 86.06 6.90 Rc No No 0.00 Hau 0 265.83 265.83 0.00 1.90 1.90 153.00 153.00 0.00 11.88 0.21 5.8 8365 0.00 58 -8.65 84.91 10.10 Sc No No 0.00 Hsu 0 267.92 267.92 0.00 3.31 3.31 147.00 147.00 0.00 11.96 0.19 6.3 8146 0.00 59 -14.13 84.10 7.50 Sc No No 0.00 Hr 0 260.00 260.00 0.00 -2.20 -2.20 160.00 160.00 0.00 12.03 0.18 7.0 5837 0.00 60 -11.79 84.10 6.00 Rc No No 0.00 Hr/Hau -I 262.78 263.89 -1.11 -0.53 0.58 160.00 160.00 0.00 12.03 0.20 6.0 7110 1.83 61 -9.60 84.10 5.80 Rc SL FP 0.00 Hau 0 266.25 266.25 0.00 1.71 1.71 155.00 151.00 4.00 12.~ 0.19 6.3 7982 2.47 62 -9.32 83.82 7.10 Rc SL FP 0.00 Hau 0 266.67 266.67 0.00 2.04 2.04 153.00 150.00 3.00 12.0S 0.21 6.1 7798 1.70 63 -11.96 83.72 4.20 Sc No No 0.00 Hr 0 265.00 265.00 0.00 1.60 1.60 160.00 160.00 0.00 12.0S 0.20 5.7 7066 0.00 64 -8.84 83.16 5.10 Rc No No 0.00 Htu 0 267.92 267.92 0.00 2.84 2.84 150.00 144.00 6.00 12.10 0.21 6.1 8085 2.37 65 -10.90 83.08 9.00 Rc No No 0.00 Hr 0 265.42 265.42 0.00 1.28 1.28 160.00 157.00 3.00 12.10 0.21 5.1 7434 1.96 66 -14.75 82.73 21.20 Rc SL Pic 0.00 Hr 0 262.78 262.78 0.00 -{).45 -0.45 155.00 155.00 0.00 12.13 0.18 6.7 5625 1.45 67 -9.n 82.35 8.30 Sc No No 0.00 Hau 0 267.50 267.50 0.00 2.60 2.60 152.00 152.00 0.00 12.16 0.23 6.1 7532 0.00 68 -11.29 82.27 5.00 Rc No No 0.00 Hr -2 265.42 266.67 -1.25 1.25 2.50 157.00 157.00 0..00 12.16 0.22 5.7 7154 0.00"""
69 -12.66 81.64 14.50 Sc No No 0.00 Hr 0 265.00 265.00 0.00 1.13 1.13 156.00 156.00 Q.OO 12.21 0.22 5.6 6920 0.00 \-.) 70 -11.30 81.41 15.50 Rc DL SY 3.10 Nplr/Hr 0 267.50 267.50 0.00 3.01 3.01 155.00 155.00 0.00 12.23 0.24 5.2 7179 3.12 l..o..> 71 -10.26 81.41 14.80 Rc SL FP 0.00 Hr -I 266.67 261.92 -1.25 1.69 2.9<4 156.00 156.00 0.00 12.23 0.24 5.2 7046 2.68 L... 72 -10.71 81.14 8.60 Rc SL FP 0.00 Hr -I 267.08 267.92 -0.84 2.01 2.85 157.00 157.00 0.00 12.25 0.24 5.2 7046 3.20., .,
73 -12.45 80.70 18.30 Rc SL FP 0.00 Nplr 0 267.50 267.50 0.00 3.34 3.34 160.00 160.00 0.00 12.28 0.23 5.6 7038 3.85 .g 74 -IO.ot 80.48 10.30 Rc SL FP 0.00 Hau -3 267.50 268.75 -1.25 2.02 3.27 157.00 157.00 0.00 12.30 0.24 5.2 7026 2.78"'
15 -10.59 80.34 6.00 Rc No No 0.00 Nplt 0 267.92 267.92 0.00 2.64 2.64 159.00 159.00 0.00 12.31 0.24 5.2 7026 1.83 ~ ;;;· 76 -12.25 80.27 18.30 Rc SL FP 0.00 Nplr 0 267.92 267.92 0.00 3.39 3.39 158.00 158.00 0.00 12.31 0.23 5.6 7038 2.16"'
n -10.08 80.09 5.40 Sc No No 0.00 Hau 0 270.00 270.00 0.00 4.-45 4.45 157.00 157.00 0.00 12.32 0.24 5.2 7026 0.00 ),... 80.02 Rc No Nplr 265.42 265.42 0.00 1.36 1.36 140.00 140.00 0.00 12.33 0.23 5.6 7038 0.00"'
78 -12.90 6.40 No 0.00 0"'
~ 79 -12.28 79.80 6.20 Sc No No 0.00 Nplr 0 267.50 267.50 0.00 3.10 3.10 159.00 159.00 0.00 12.35 0.22 5.1 7066 0.00,.,
80 -13.25 79.75 4.00 Rc No No 0.00 Nplr 0 265.00 265.00 0.00 0.87 0.87 135.00 135.00 0.00 12.35 0.20 5.1 6324 0.00 t;·"
81 -13.06 79.63 5.20 Rc No No 0.00 Nplr 0 265.00 265.00 0.00 0.84 0.84 134.00 134.00 0.00 12.36 0.20 5.7 6324 0.00 Q.. 82 -13.56 79.13 4.50 Rc No No 0.00 Nplr 0 266.25 266.25 0.00 2.22 2.22 141.00 141.00 0.00 12.40 0.20 5.7 6324 0.00 ~-83 -13.40 78.21 8.90 Sc No No 0.00 Nplr 0 267.08 267.08 0.00 2.81 2.81 140.00 140.00 0.00 12.47 0.20 5.7 5806 0.00
-
84 -12.40 78.19 4.70 Sc No No 0.00 Nplr 0 268.75 268.75 0.00 3.93 3.93 138.00 138.00 0.00 12.47 0.19 5.7 6733 0.00 ::r- ... 85 -13.10 78.05 10.70 Rc SL Pic 0.00 Nplr 0 267.08 267.08 0.00 2.50 2.50 134.00 134.00 0.00 12.48 0.20 5.7 5806 1.85 :: Q.. 86 -11.33 77.97 6.50 Sc No No 0.00 Nlllt/Hr 0 268.75 268.75 0.00 3.38 3.38 141.00 141.00 0.00 12.48 0.21 6.6 69n 0.00 ~· 87 -10.29 77.82 9.90 Sc No No 0.00 Hru 0 268.75 268.75 0.00 2.85 2.85 128.00 128.00 0.00 12.49 0.21 6.6 7449 0.00 iS.: 88 -13.07 77.28 11.10 Rc SL Pic 0.00 Nplr 0 265.83 265.83 0.00 1.11 1.11 134.00 134.00 0.00 12.53 0.18 6.1 5629 1.78§.
89 -12.11 76.76 11.60 Rc SL Pic 0.00 Nplr/Hr 2 267.50 266.67 0.83 2.16 1.33 142.00 142.00 0.00 12.57 0.19 6.1 6325 2.28tj
90 -10.95 76.72 10.30 Rc SL Pic 0.00 Hr 0 267.50 267.50 0.00 !.63 1.63 144.00 144.00 0.00 12.58 0.22 6.6 7313 1.92 91 -13.71 76.55 5.20 Sc No No 0.00 Nplr 0 266.67 266.67 0.00 2.09 2.09 137.00 137.00 0.00 12.59 0.19 6.1 5690 0.00 ... 5:1"'
~
10 LAT LON DlA TYP EJ1! INT P'IDI UNIT TFR EJ1!T SURT DBLT ETDS SIDS EVlS SVlS DELV TOO ALB INER TOPO RATIO;
0 92 -14.06 76.50 30.00 Rc SL sP 5.40 Nplr 0 266.25 266.25 0.00 1.95 1.95 136.00 136.00 0.00 12.59 0.18 6.6 5001 0.00~
w 93 -12.78 75.88 8.60 Rc No No 0.00 Nplr/Hr 0 266.67 266.67 0.00 1.70 1.70 138.00 138.00 0.00 12.64 0.18 7.2 6223 2.05 ~ ... 94 -10.87 75.88 7.60 Rc SL pp 0.00 Hr 0 266.67 266.67 0.00 0.67 0.67 136.00 136.00 0.00 12.64 0.19 8.0 7181 2.03 '<8
95 -13.26 75.75 17.50 Rc SL SY 3.10 Nplr/Hr 0 264.44 264.44 0.00 -0.27 -0.27 136.00 136.00 0.00 12.65 0.18 7.2 5415 3.52 ~ 96 -9.50 75.50 9.10 De No No 0.00 Hvl 0 269.17 269.17 0.00 2.39 2.39 111.00 111.00 0.00 12.67 0.21 7.6 6652 0.00g.
97 ·12.24 75.30 4.20 Sc No No 0.00 Hr 0 267.08 267.08 0.00 1.49 1.49 120.00 120.00 0.00 12.68 0.18 7.2 6223 0.00 §· 98 -13.86 75.1 I 4.70 Rc No No 0.00 Hr 0 26~ ()(, 265.00 0.00 0.45 0.45 131.00 131.00 0.00 12.70 0.18 7.2 5415 1.64 ~ c: 99 -12.81 74.90 9.30 Rc No No 0.00 Hf 0 267.08 267.08 0.00 1.95 1.95 121.00 121.00 0.00 12.71 0.16 7.2 6085 2.01 ~p.
100 -9.62 74.66 5.70 Rc No No 0.00 Avm -1 268.75 270.91 ·2.16 1.83 3.99 106.00 106.00 0.00 12.73 0.23 7.6 3308 1.93 ~ 101 -13.48 74.39 7.20 Rc No No 0.00 Hf 2 266.67 265.00 1.67 1.73 0.06 124.00 124.00 0.00 12.75 0.19 7.2 5246 1.99s
102 -13.61 73.11 4.80 Sc No No 0.00 Hf 0 266.25 266.25 0.00 1.19 1.19 123.00 123.00 0.00 12.85 0.19 7.4 5179 0.00 tl1 103 -14.44 69.96 17.20 Rc ML pp 0.00 Hf/Hr I 267.08 265.83 1.25 1.57 0.32 113.00 113.00 0.00 13.08 0.17 6.7 5344 4.22~
104 -8.30 69.96 9.60 Sc No No 0.00 Hf 0 269.58 269.58 0.00 1.91 1.91 m.oo 175.00 0.00 13.08 0.26 7.6 1295 0.00 105 -14.23 69.60 6.50 Rc No No 0.00 Hf/Hr 0 267.92 267.92 0.00 2.97 2.97 114.00 114.00 0.00 13.11 0.17 6.7 5344 0.00 0 106 -14.94 69.42 8.40 Rc SL pp 0.00 Hf/Hr -1 266.25 267.08 -0.83 1.88 2. 71 128.00 125.00 3.00 13.12 0.17 6.7 5344 2.10 fji 107 -8.68 68.61 6.40 Rc SL Pit 0.00 Hf 0 268.33 268.33 0.00 0.67 0.67 166.00 166.00 0.00 13.18 0.26 7.6 4480 0.00 108 ·14.98 68.23 12.00 Rc DL Pit 0.00 Hr 0 266.67 266.67 0.00 2.29 2.29 135.00 135.00 0.00 13.21 0.19 6.7 5572 2.02 109 -9.19 67.63 6.00 Sc No No 0.00 Hf 0 268.33 268.33 0.00 0.89 0.89 170.00 170.00 0.00 13.26 0.25 7.4 -195 0.00 110 -9.03 67.53 4.40 Sc No No 0.00 Hf 0 268.33 268.33 0.00 0.89 0.89 165.00 165.00 0.00 13.26 0.25 7.4 -195 0.00 Parameters ate dd'med u foUowa: ID, arbitary identification number; LAT. laticude; LON, weotlqitude; DlA, craler diameter (km); TYP, pre$ervational awe and general type or ejecta (Rc, lobate ejecta morphology; Sc, no discernible ejecta blanlr.e~ De, DO discernible ejecta and aaler almost oompleuoly obli~ rim bt.tely visible); EJE, ejecta morphology (SL, sln&)e lobe; DL, double lobe; ML. multiple lobe; No, no dusification); !NT, inu:rior rnorpbology (Pk. c:colral peak; FP, flat floor pristine; SY, f)'UIIIlWic caw.! pi~ aP, caunJ peak topped by small pit; No, DO clusification); PTDI, central pit diameter (bn), 0.00 l( no t pit; UNIT, geologic map unit. from Witbeck 11 al. [1991) and Scott and Tanaka [1986) with tome interpolation bet<vem the two; multiple unils ate listed forcrau:n occurring on or near unit boiDldaries; unit names and descriptions ate list<:d in Table 2; TFR. "thermal f~eu·, qualitative thermal distindiveoeu compared to rurroundi:tgs (0, not thermally distinct; 3, very distinctive and warmer; -3, very distinctive and cooler); EJET, representative average brightness temperature (I<) for ejecta; SURT, same but for •urroundinas; DEL T, EJET -SURT; ETDS, approximate time of day corrected temperscure for ejecta = EIET -model t<:mperature (see text); STDS, same but for surroundings; EVIS, repre~cnw.ive average visible si~ (dnyor ejecta; SVIS, same but for surroundings; DEL V, EVIS -SVIS; TOO, local time of day; ALB, I' x I' binned albedo from Plukat and Minor [1981); INER. 2' x 2' binned thermal inertia (10'3 cal em· K"1 s·1 ) from Palluconi and Kiefftr [1981); TOPO, elevation (m) from U.S. Gtolcgical Survey [1976); RA 110, rstio of ejecta diameu:r to crau:r diarneu:r. Parameters ID, LAT. LON, DIA, TYP, EJE,INT, and PTDI ate from N. G. Barlow, submitted repon, 1987.45 33 Properties Associated with Individual EDITHs
---...
~-.... ._
- - -
Figure 3.4. Region 1 (seen also in lower right of Figure 3.1): Temwskan thermal image (bottom) and Viking visible photomosaic (top) of an interesting local region of study with four craters near the south rim of an old filled crater, and three craters to the northeast of the old crater. The craters seen outside the old filled crater exhibit ejecta blankets that are significantly warmer than the surroundings. These all are from the group of craters observed which have darlcer albedo than the surroundings. The craters inside the old filled crater have ejecta blankets which are much cooler than ejecta blankets outside the old filled crater, but still warmer than their surroundings. The only
"ejecta blanket" that shows no temperature difference with the surroundings (the southwest crater) is the only crater for which no ejecta blanket can be seen in Viking images. Surviving portions of the old crater rim are also darker in the visible channel and warmer than the surnnmding terrain.
Also note that the southeast portion of the Noachian plateau ridged unit (Nplr), which appears to the northwest of the old filled crater, is also darker in the visible channel and warmer than surrounding areas. Crater C is an excellent example of thermal boundaries matching ejecta boundaries. The wide thermal anomaly associated with the crater just NE of the large filled crater is a counterexample.
Thermally Distinct Ejecta Blankets
".. ....__,. : ·'
,r
~ .~
A;' .,._
46
. • I
; : -
... _ '
JO k"'
Fig. 3.5. Region 2 (seen also in lower middle of Figure 3.1): Tennoskan thennal image (bottom) and Viking visible photomosaic (top) of several nearby craters, one with a thennally distinct ejecta blanket and the others without In particular, notice the two largest craters, crater A and crater B.
Crater A is thennally distinct; crater B is not. They have similar fresh appearing single lobe fluidized ejecta blankets (N. G. Barlow, submitted report, 1987). Both craters are on the Hesperian ridged plains unit (Hr). Crater A (18.54°S, 81.98°W; #11 in Table 3.1) has a very thennally distinct ejecta blanket which is approximately 3.5 K wanner than its surroundings. It has a diameter of 11.6 km and a flat floor pristine interior (N. G. Barlow, submitted report, 1987).
It is also distinct in the visible channel, being brighter than its surroundings. Crater B (17 .85°S, 82.07°W; 12 in Table 3.1) does not have a thennally distinct ejecta blanket It has a diameter of 8.6 km and a central peak (Pk) interior morphology. In the visible channel its ejecta blanket is not very distinct, if at all, from the surroundings. There are many smaller craters nearby and none of them appear thennally distinct
47 33 Properties Associated with Individual EDITHs
. .
.
(:)~.' ,_
-.... -
'
.
Fig. 3.6. Region 3: Terrnoskan thermal image (bottom) and Viking visible photomosaic (top) of three nearby almost aligned craters near the north rim of Valles Marineris (diameters 5.8 km, 10.5 km, and 9.8 km). They are centered approximately on 12.5°S, 59.3°W. All three craters have single lobe ejecta morphologies. All occur on the Hpl3 unit near a boundary with the Hr (Hesperian ridged plains) unit as determined by Witbeck eta/. [1991]. The largest (middle) crater is the only one of the three that does not have an EDITH. It also has the least fresh ejecta blanket based upon Viking images.
Thermally Distinct Ejecta Blankets 48
.. ; :.
.
• ... lf..
. '.._.~" ..
..: _ ...
...
Fig. 3.7. Region 4: Tennoskan thennal image (bottom) and Viking visible photomosaic (top) that include the four clearly distinct EDITHs (designated by arrows) of panorama 4. The four EDITHs are approximately centered upon 11.5°S, 197.0°W and are spaced over approximately 150 km.
Older highland materials appear to the south (bottom), and younger lowland material to the north.
EDITHs all lie near the boundary on lowland terrains (1 and 2 on Hpl3, 3 on either Hpl3 or Apk, 4 on Apk, using Greeley and Guest [1987]). Notice also the exposed crater rim of a buried crater near EDITH 2 (see text).
49 33 Properties Associated with Individual EDITHs
the surroundings. To remove the time of day effects to first order, I used a one- dimensional, homogeneous, thermal model of the Mars surface adapted from Clifford et a/. [ 1987]. From each ejecta blanket temperature, I subtracted model-derived temperatures for average Mars conditions (inertia 6.5 x
w-3
cal cm-2 K-1 s-112 and albedo 0.25) for the same time of day, season, and latitude. For comparison, I similarly subtracted model temperatures from surrounding temperatures (STDS). I looked for correlations between each of the three thermal ejecta parameters (TFR, DEL T, and ETDS) and the other parameters in my data base.My three descriptive thermal ejecta parameters showed no correlation with most of the parameters tested. Within the data base as a whole, there are no correlations between temperature difference, time of day corrected ejecta temperature, or thermal freshness with any of the following: crater diameter, ejecta morphology, interior morphology, existence of central pits, longitude, ratio of ejecta diameter to crater diameter, or time of day. The 1° x 1° binned albedo, 2° x 2° binned inertia, and 1° x 1° binned elevation roughly correlate with time of day corrected ejecta temperature on the higher elevation Hsu (Syria Planum Formation, Upper Member) areas but not elsewhere (see Table 3.2 for unit descriptions). These relationships unique to Hsu are discussed below under section 4.
I present the following conclusions and observations based upon my systematic examination of individual EDITHs in the Termoskan data set
1. On the plains where EDITHs occur, there cannot be uniform blanketing of depth greater than a very few centimeters (the diurnal skin depth) by material younger than the craters. Otherwise, ejecta blankets would not be thermally distinct
2. In regions with EDITHs there are varying degrees of ejecta blanket degradation at Viking Orbiter camera resolutions. Because there has not been significant blanketing in these regions (based upon conclusion #1), this degradation is probably due to erosion, not deposition.