recurring slope lineae in equatorial regions of mars...1 supplementary information for recurring...

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Supplementary Information for Recurring Slope Lineae in Equatorial Regions of Mars

Alfred S. McEwen, Colin M. Dundas, Sarah S. Mattson, Anthony D. Toigo, Lujendra Ojha, James J. Wray, Matthew Chojnacki, Shane Byrne, Scott L. Murchie, Nicolas Thomas This supplementary material includes a large table of information about confirmed and partially confirmed RSL in places other than the southern mid-latitudes (Table S1). Tables S2 and S3 list THEMIS brightness temperatures for two craters on the floor of VM. Figures S1 to S4 illustrate features discussed in the main paper. Table S4 provides CRISM column abundances of H2O at representative RSL sites; data from two sites are plotted in Figures S5 and S6. In addition, a set of animated GIFs are available at http://www.uahirise.org/sim/ to illustrate the motion of some of the well-monitored RSL sites where we have produced DTMs and orthorectified images. See http://www.uahirise.org/sim/science-2011-aug-4.php for similar animated GIFs of mid-latitude RSL from reference 3. We also include a GIF of active dune slopes in Nili Patera to show how these streaks differ in behavior from RSL—each streak appears suddenly with no evidence for incremental growth over time periods of weeks. Supplementary Discussion A rigorous definition of RSL is necessary because many different processes create dark lines on steep slopes. Our three categories and some discussion follow: Fully confirmed RSL: We have observed the full temporal sequence: Incremental growth of many (≥10) flows on a slope, fading when inactive, and recurrence in multiple Mars years. The fading may not lead to complete disappearance. This category includes seeing the full sequence in one year, and a single image showing RSL candidates on the same slope in another year, that are different from the other year (demonstrating that they are not just due to incomplete fading). On some east- and west-facing slopes in VM the RSL may be intermittently active year-round, in which case we consider >1 year observation of activity to be the equivalent of recurrence. Partially confirmed RSL: We have seen many (≥10) flows on a slope plus either incremental growth or recurrence. Apparent fading may be deceptive so only this observation is not sufficient for partial confirmation. There are some cases where either recurrence or incremental growth may have occurred, and we cannot tell which is the case. There are some sites in this category in Table S1 where slope lineae grow incrementally but rarely fade or recur, such as in Aram Chaos, which may need a different classification. Candidate RSL: Any place with many (≥10) relatively dark lines on a slope that resemble RSL but with insufficient temporal observation for even partial confirmation to be possible (until we get more data). True RSL fading can be difficult to confirm because it may be incomplete, or difficult to observe due to topographic shading and because RSL follow channels, or because they may appear faded when the atmospheric dust opacity is high. Also, we now realize that some active RSL actually

Recurring slope lineae in equatorial regions of Mars

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have a very low contrast with the background in HiRISE images (they look faded, but are growing from image to image). There are also partially confirmed RSL in equatorial regions that do not appear to fade at all, such as in Aram Chaos, or only their tips fade and regrow, as in Hydrae Chasma. The RSL fans sometimes exhibit rapid changes in brightness. Figure S2 illustrates fans darkening for at most a few weeks in Coprates Chasma, and Figure S3 shows more extensive darkened fans in the Eos/Capri Chasma site. Elorza crater (see animations in http://www.uahirise.org/sim/) shows additional examples of fans darkening. We can resolve that the darkening is due to many lineae in some fans in Elorza crater, so unresolved lineae may explain the darkening of other fans. As with RSL, the darkening might be due to a small degree of water in the soil or to changes in surface grain size or texture19. The darkening illustrated in Figure S2 was associated with a period of time in which dust storm activity was especially high in VM, as discussed in the main text. Atmospheric dust will lower daytime temperatures, thus keeping relative humidities higher, conceivably prolonging the early morning conditions that allow metastability of deliquescent liquids28. However, the darkening in Figure S3 was not associated with dusty air, and may have persisted longer. Future monitoring will improve our understanding of fans that sometimes darken. RSL appear to interact with 3 basic types of surfaces:

(1) Bedrock, where the RSL may temporarily darken the surface or where the darkening may be difficult to see under some lighting conditions (perhaps hidden in cracks and shadows). RSL often appear to emanate from just below such bedrock, but they could flow over or through the bedrock from higher levels, yet not be clearly detected in HiRISE images.

(2) Slopes with fine-grained soils that are slowly permeable, where RSL flow may gradually erode small gullies. Some gully floors have the same relative IRB color as the fans. RSL might not fade away completely in such locations, if the gullies have exposed a darker substrate or the RSL have deposited material with a distinctive color.

(3) Slopes covered by permeable materials such as windblown sand, where water might infiltrate and wick to the surface in discontinuous lines. The fans where RSL terminate often have distinctive grooves that are elongated down the slope (Figure S4), similar to the avalanche slopes of active Martian dunes. The groove spacing is a few meters, similar to the ubiquitous ripples in sand deposits, and sometimes they transition into what are clearly aeolian ripples. These are also the locations where we often see discontinuous RSL (Figure S4). Further analysis is needed to understand the relations between RSL and saltating sand.

Several RSL attributes are not yet understood: (1) the relation between apparent RSL activity and dustiness of the atmosphere; (2) variability in RSL activity from year to year (perhaps related to dustiness of the air); (3) salt composition and concentration; (4) seasonal control of activity on north-facing equatorial slopes in spite of little change in temperature; and (5) temporal changes in the color properties of fans where RSL terminate. Continued orbital monitoring and data analysis, laboratory experiments, modeling, and future orbital and landed exploration with new measurement types are needed.


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Table S1. Observations and notes about confirmed and partially confirmed RSL north of 30S latitude. (SL = slope lineae, not necessarily RSL) Eos/Capri Chasma Lat

-15.4 Lon 309.5

Stereo: N

DTM: N

Elev. (km) -2.7

Notes

Image MY Ls (°) SL? Aspect Emis. Illum Phase Fully confirmed ESP_029331_1645 31 197 y NW, N 0 55 55 Many long narrow gullies, some with faint SL (bin2

image) ESP_030109_1645 31 234 n 14 50 36 Maybe very faded SL ESP_030610_1645 31 269 n 5 43 47 Maybe very faded SL ESP_032100_1645 31 329 y NW, NE 9 31 40 Huge numbers of new SL, large fan areas darkened

within and below SL ESP_032667_1645 31 352 y NW, NE 0 36 36 Significant growth, very active. Fans still dark. Slopes in E Coprates

Lat -14.7

Lon 304.6

Stereo: Y

DTM: Y

Elev. (km) -2.1

Notes

Image MY Ls SL? Aspect Emis. Illum Phase Partially confirmed (incremental growth + fading) ESP_025441_1650 31 50 y W, SW 10 54 62 Striated fan merges with wind-rippled deposits;

dashed SL—permeable? Faint SL on dunes S end. Can’t see SE-facing sites in shadows.

ESP_027973_1650 31 140 y W, SW, SE

17 61 48 Incremental growth. Some SL may be faded, extreme west edge. Faint SL on dunes S end.

ESP_029318_1650 31 196 y W, SW, SE

2 55 53 More incremental growth, new SL on dunes, all slope aspects

ESP_029674_1650 31 213 y W, SW 0 52 53 Mostly fading, some growth (W, SW –facing slopes) ESP_029885_1650 31 223 y W, SW 6 51 45 Hazy image, maybe fading ESP_030241_1650 31 241 y W, SW 5 48 43 Hazy image, but whole fans darkened and changed

color! See figure ESP_030452_1650 31 251 y W, SW 16 46 31 Fans re-brightened, similar to 29885 and prior images ESP_031019_1650 31 279 y W, SE,

SW, S 21 40 20 Subtle differences (new streaks + fading) N half dark

surfaces ESP_031876_1650 31 319 y W, SW,

S, SE 3 32 35 Some growth (W, S–facing slopes), new RSL on SW-

facing slope and SL on W-facing dunes ESP_032298_1650 31 337 y W, SW,

S, SE 5 33 28 Growth of RSL on SE, S, and SW-slopes. Very active

large SW-slope RSL. Lower elevation RSL appear faded. W-facing SL hard to identify in earlier images.

ESP_032865_1650 31 360 y W, SW, S, SE

9 39 31 Continued growth. (No significant N-facing slopes in scene.)

Eastern Coprates Lat

-14.6 Lon 302.4

Stereo: Y

DTM: Y

Elev. (km) -1.3

Notes

Image MY Ls SL? Aspect Emis. Illum Phase Fully confirmed PSP_010277_1650 29 137 y NW, N 9 63 56 Faint SL, large striated fans PSP_010699_1650 29 153 y NW, N 26 63 41 Faint SL, but clear incremental growth. Dunes to N

with faint SL ESP_032087_1650 31 328 y NW 31 30 61 Similar faint SL on NW slopes as in MY29 but with

new patterns (recurrence), SL in dunes ESP_032430_1650 31 342 y NW 29 36 11 Low-phase view, difficult to compare to 32087 with

opposite large rolls. RSL more prominent. ESP_032654_1650 31 352 y NW 25 34 58 Maybe low-contrast changes from 32087 (similar

geometry) N-facing slopes in Coprates ridge

Lat -14.4

Lon 304.6

Stereo: Y

DTM: N

Elev. (km) -3.8

Notes

Image MY Ls SL? Aspect Emis. Illum Phase Partially confirmed (incremental growth, maybe fading)

ESP_026786_1655 31 96 y N 20 61 75 Most fans S end of image (higher elevation) ESP_027063_1655 31 106 y N 6 63 58 Small changes between images—incremental growth ESP_030030_1655 31 230 n 11 49 60 SL faded, but somewhat hazy image Crater on Coprates floor

Lat -14.1

Lon 296.9

Stereo Y

DTM: Y

Elev. (km) -3.1

Notes

Image MY Ls SL? Aspect Emis. Illum Phase Fully confirmed ESP_018123_1660 30 102 y N,W 7 63 58 Crater with steep slopes on floor of Coprates, striated

fans on N,W,S slopes with rel. greenish IRB color, clear gullies on C, E-facing slopes. Slopes on S. Side: upper gullies 27-55°, SL 37° +/-5°, fans 23° (variable)


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ESP_026905_1660 31 101 y N, W 7 61 67 Smaller SL than prior image (recurrence), faint on W-face slope

ESP_027182_1660 31 110 y N,W 18 63 51 A little growth from previous image (incremental) ESP_027327_1655 31 115 y N.W 5 61 65 No obvious change (much less active than MY 30) ESP_027749_1655 31 131 y NW 10 60 68 Growth on W slope, not N. Slopes on W. Side: upper

gullies 22-60°, SL 32° +/-9°, fans 25° (variable) ESP_028382_1655 31 156 n 15 58 71 RSL faded N and W slopes, prob not haze (active Ls

101-131) ESP_028593_1655 31 164 n 15 57 71 Same as above ESP_029582_1655 31 209 y S,W 8 54 46 New RSL and growth on W and S-facing slopes; N-

facing RSL faded ESP_030294_1655 31 243 n 3 47 49 RSL faded (maybe dusty air hides them) ESP_031006_1655 31 278 y SW 11 38 49 Growth of RSL on SW-facing slope, but not as

extensive as 29582 ESP_031995_1660 31 324 n 8 32 24 Only covers E edge of the crater. Many SL on dune

slip faces. ESP_032351_1660 31 339 n 2 33 35 Covers center and western side of crater. Fading (?)

on SW-slopes from 31006. Dark upper (short) SL on N-facing slopes near sand sheet as earlier images but little or no growth.

ESP_032707_1655 31 354 n 6 36 41 Same as previous image ESP_032852_1660 31 359 n 24 36 58 More fading of RSL on SW wall. Coprates slope and Dunes

Lat -13.9

Lon 296.8

Stereo? Y

DTM? Y

Elev. (km) -1.8

Notes

Image MY Ls SL? Aspect Emis. Illum Phase Fully confirmed PSP_006480_1660 29 2 y NSEW 0 39 39 Big SL on S-facing slope, shorter ones on NW-facing

slopes. Many SL candidates all over dune slip faces ESP_028026_1660 31 142 n 7 60 54 All previous SL faded, on S and NW facing rocky

slopes; maybe some faint new SL rather than faded?; faded on dunes

ESP_028804_1660 31 173 n 5 57 61 Same as above. Why not active on NW-facing slopes? (hazy image)

ESP_029938_1660 31 225 y W, S 5 50 55 New small SL, recurrence, growth of dark SL over bright streak at 7500, 18263 or RED nomap.

ESP_030505_1660 31 254 y W, S 7 45 38 Growth in small RSL, not the big ones seen in early MY29, SL on dunes—new?

ESP_030861_1660 31 271 y W, S, N,E 1 41 40 More growth (NE corner), maybe some fading in places. Large-scale darkening uphill of RSL? (also lighting changes). Growth on dunes—all aspects

ESP_031217_1660 31 288 y NSEW 5 36 42 More growth on dunes, growth and fading on bedrock slopes

ESP_031929_1660 31 321 y NSEW 14 31 45 New RSL on dunes, possible growth of some dune RSL, fading. Bedrock RSL N end of image, S-facing slopes

ESP_031995_1660 31 324 y NSEW 8 32 24 Not great coverage of N Wall, few new SL on dunes, little evidence for incremental growth

ESP_032351_1660 31 339 y NSEW 2 33 35 Bedrock RSL NE corner, SW-facing slope—doesn’t overlap previous images; dune SL

Ridges in north Coprates

Lat -12.9

Lon 295.4

Stereo? Y

DTM? N

Elev. (km) -1.4

Notes

Image MY Ls SL? Aspect Emis. Illum Phase Partially confirmed (recurrence). Spurs with RSL extended down to striated fans with rel green (IRB) color

ESP_022303_1670 30 283 y NSEW 9 37 46 Major SL and slopes are NW and NE facing. ESP_032562_1670 31 348 y NSEW 7 41 348 Clear recurrence of RSL in same locations as 22303 Ridges in north Coprates

Lat -12.9

Lon 295.5

Stereo? Y

DTM? Y

Elev. (km) -1.4

Notes

Image MY Ls SL? Aspect Emis. Illum Phase Fully confirmed. Spurs with RSL extended down to striated fans with rel green (IRB) color

ESP_024993_1670 31 35 y N, W, E 4 48 51 More RSL on N end of image, not covered in subsequent images except 25340_1670, N-facing slopes

ESP_025349_1670 31 47 y N, W, E 15 52 64 No new growth; appears faded but poorer image ESP_027815_1670 31 134 y N, W, E 5 59 64 New growth (incremental) on NW-facing slopes (see

fig.)


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ESP_028303_1670 31 153 y N,W,E 15 59 47 Appears faded, but poorer image ESP_028659_1670 31 167 y N,W.E 5 57 62 Partial image, some new growth and apparent fading

(? Image quality) on NW, NE slope ESP_029226_1670 31 192 y N,W,E 6 54 60 Changes not obvious, fading confirmed on NE-, NW-

face slope ESP_032127_1670 31 329 y N, W, E 32 35 4 Numerous SL apparent at low phase, some new

(recurrence v. 24993), some lengthening from previous image. New (?) RSL on east-side of ridge resolvable with low phase angle, some darkening? Light-toned SL on sand.

Coprates landslide scarp

Lat -12.9

Lon 293.4

Stereo? Y

DTM? N

Elev. (km) +0.1

Notes

Image MY Ls SL? Aspect Emis. Illum Phase Partially confirmed (incremental growth) ESP_020879_1670 30 214 y SW 5 52 58 Big SL, can see in CTX, but changes difficult to

assess ESP_021657_1670 30 252 y SW 8 46 38 Some incremental growth, like tip of biggest SL (west

side) ESP_024347_1670 31 11 y SW 5 52 58 Some growth(?). Not fading. ESP_029503_1670 31 205 y W No change to big SL, but RSL growth on extreme

west middle outcrop. (moved target a bit) ESP_030070_1670 31 232 y W 5 50 45 No change to big SL, but growth on west middle

outcrop. Big SL not fading when inactive like RSL. ESP_032549_1670 31 347 y W 32 37 10 Minor tip growth of a few big SL. ESP_032694_1670 31 353 y W 18 37 21 No obvious changes from previous image ESP_032839_1670 31 359 y 0 37 37 No obvious changes, missed the most active site Melas Chasma slope

Lat -12.2

Lon 291.1

Stereo? N

DTM? N

Elev. (km) -3.0

Notes

Image MY Ls SL? Aspect Emis. Illum Phase Partially confirmed (recurrence, maybe fading) PSP_004054_1675 28 253 y NW, SW 7 47 40 A few tens of SL, sulfate bedrock erosion morphology,

BD1900 in CRISM 61F3 ESP_030703_1675 31 263 6 44 38 Some SL on both slopes faded. Probably new SL in

some of the same places but not as long as in 4054, or fading of distal ends. No distinct SL fans.

S of large impact in Coprates

Lat -12.6

Lon 294.7

Stereo? Y

DTM? N

Elev. (km) -3.1

Notes

Image MY Ls SL? Aspect Emis. Illum Phase Fully confirmed ESP_018189_1675 30 104 y N, W 6 62 58 Good candidate RSL, bin-2 image ESP_025982_1675 31 69 y N, W, S? 16 57 69 New RSL (recurrence) (overlaps SE corner)

25626_1675 (Ls 57) misses active area; other RSL seen again in 25982 (N-facing) not obviously changed

ESP_029292_1670 31 195 y W 9 55 47 RSL incremental growth, esp. NW corner. Moved target footprint.

ESP_029859_1675 31 222 y W 14 52 39 Mostly fading, but some growth from prior image ESP_030360_1675 31 246 y SW 3 47 49 Mostly fading, but appear to be a few new small SL on

SW-facing slopes ESP_030571_1675 31 257 y SW 6 45 39 Active RSL SW-facing. Also E-facing SL on dunes

(poor SNR) ESP_030927_1675 31 274 y S, SW,

W, NW? 3 41 38 Very active RSL on S and SW-facing slopes-middle

and SE corner. SL on SE, NE dune slopes. Maybe a bit on NW slope, mid bottom image.

ESP_031784_1675 31 315 ? 19 31 50 Hazy image, but RSL appear largely faded? ESP_031850_1675 31 318 y S, SW,

W, NW? 5 33 28 RSL distinct, but many shorter than in 30927—faded

or covered by dust then new formation? Nice high-contrast image—probably due to low phase angle. Dark SL on N-facing slope of 18189 and 25982 are bright, and IRB “greenish”. Dune SL

ESP_032061_1675 31 326 y S, SW, W 3 32 29 Lengthening of RSL on SW wall, few new SL, some no change, most activity on W-facing wall, new SL on dune (E and N facing) with some recurrence?

ESP_032206_1675 31 331 y S, SW, W, NW?

17 31 48 Fading on S wall, SL becomes relatively darker to the S but with no growth.

ESP_032272_1670 31 336 y S, SW, W, NW?

11 33 22 RSL on S- SW-slopes remain relatively dark, but no clear growth. Possible new SL on dark dune slip faces. Some growth of faint SL on SW-facing slope near bottom of image.


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Crater on Melas Chasm floor

Lat -11.5

Lon 290.3

Stereo? Y

DTM? Y

Elev. (km) -5.2

Notes

Image MY Ls SL? Aspect Emis. Illum Phase Fully confirmed CTX-7034_1676 28 23 n 0 46 46 No SL detected in CTX CTX-8181_1676 28 63 n 1 58 58 No SL detected in CTX ESP_027802_1685 31 133 y N, W, E 3 59 62 Large, extensive RSL on N-facing slope, can see in

simultaneous CTX (but not prior CTX images). Many small gullies. Slopes (all sides): upper gullies 35-50° (variable), RSL 30° +/-2°, fans 25° (variable)

ESP_028501_1685 31 161 y N, W, E 14 58 46 Significant RSL growth (incremental) from prior image ESP_029213_1685 31 192 y N, W, E,

S 5 54 59 RSL faded on N-facing slopes; new RSL on S-facing

slopes ESP_029780_1685 31 218 y S 1 52 51 Much RSL growth on S-facing slopes ESP_030136_1685 31 235 y S 5 49 54 No (or very little) new growth! Maybe fading, but

dusty air ESP_030347_1685 31 246 y s 9 48 40 fading ESP_030769_1685 31 267 y s 24 44 22 New growth, dark tips ESP_031059_1685 31 281 y s 1 39 40 More growth—large RSL ESP_031771_1685 31 314 n 8 32 40 RSL faded. Hazy image, but preferential fading of

formerly dark RSL is distinct compare to other features.

ESP_032048_1685 31 326 y N,W,S,E 16 33 18 A few new flows on SW-, E- N- and W-facing slopes, very small and few

ESP_032615_1685 31 350 y N 21 36 17 Faded on E slope, slight growth on N slope? ESP_032905_1685 32 1 y N 13 37 48 Minor growth N slope (recurrence) ESP_033116_1685 32 10 y N 2 40 38 Minor growth N slope Big little gullies in Coprates

Lat -11.5

Lon 291.6

Stereo? Y

DTM? N

Elev. (km) -4.1

Notes

Image MY Ls SL? Aspect Emis. Illum Phase Fully confirmed (but still weak incremental growth). Close match SL size to gullies. CRISM: BD530 and SH600 bright on SL slope

PSP_008616_1685 29 78 y N 3 61 59 Slope with many long gullies; a few dark SL. PSP_009051_1685 29 93 y N 16 61 73 A few changes—incremental growth ESP_028791_1685 31 173 y N 3 56 59 SL faded ESP_030281_1685 31 243 n 1 48 49 No change ESP_030426_1685 31 250 n 15 45 61 No change ESP_031204_1685 31 288 n 2 38 40 Nice clear image but no clear SL. Only active Ls 78-

93? ESP_032338_1685 31 339 y N 0 32 33 Incremental growth of small SL on N-slope, same

slope as in MY 29 (recurrence) W Melas Chasma Lat

-11.2 Lon 284.9

Stereo? Y

DTM? N

Elev. (km) -1.2

Notes

Image MY Ls SL? Aspect Emis. Illum Phase Fully confirmed PSP_007522_1685 29 40 y NW 1 51 52 Distinct SL ESP_025389_1690 31 49 y? NW 6 54 48 Bin2 RED; color-only strip ESP_025666_1685 31 58 y NW 30 57 38 Fewer SL, some new (recurrence), very oblique S2 ESP_030123_1685 31 235 ? 10 49 59 Faded RSL? (hazy image) ESP_031257_1685 31 290 y E, SE 1 37 36 Maybe new activity, or maybe a better image (lower

phase angle) ESP_032892_1685 32 1 y E, SE 18 36 52 A little growth on E-facing slopes Crater in Terra Sabaea

Lat -10.8

Lon 32.0

Stereo? Y

DTM? N

Elev. (km) +2.1

Notes

Image MY Ls SL? Aspect Emis. Illum Phase Partially confirmed (incremental growth). Highest elevation candidate RSL in equatorial region

ESP_025240_1690 31 43 y N, W 3 50 53 Bin2 image, SL on N-facing slope and N and W slopes of smaller crater to south

ESP_025728_1690 31 60 y N, W 26 57 40 Bin2, same as above ESP_027007_1690 31 104 y N, W 8 59 65 SL fans of southern crater brightened relative to

25240 and 25728, can’t tell if SL lengthened ESP_028339_1690 31 154 y N, W 7 58 52 Incremental growth, SL fans S crater darkened again? ESP_029618_1690 31 210 y N, W 15 52 67 Looks the same but hazy image ESP_030897_1690 31 273 y N, W 19 40 59 New RSL, fans on larger crater darkened in places ESP_032453_1690 31 343 y N, W 4 33 30 RSL prominent at low phase and maybe clear

atmosphere, probably some changes NE Melas Lat

-10.0 Lon 290.0

Stereo? Y

DTM? Y

Elev. (km) -3.6

Notes

Image MY Ls SL? Aspect Emis. Illum Phase Partially confirmed (incremental growth) ESP_028857_1700 31 176 y W 5 56 51 SL over small area, middle right. Small gullies and


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ESP_028857_1700 31 176 y W 5 56 51 SL over small area, middle right. Small gullies and IRB “green” fans are extensive. Slopes on W. side: upper gullies 32-55°, RSL 34° +/-8°, fans 30° (variable)

ESP_028923_1700 31 179 y w 29 58 31 Incremental growth of SL Elorza Crater central pit

Lat -8.8

Lon 304.8

Stereo? Y

DTM? Y

Elev. (km) -0.2

Notes

Image MY Ls SL? Aspect Emis. Illum Phase Fully confirmed PSP_005649_1710 28 305 y N,W,S,E 2 33 32 Small SL, all slope aspects, dust-storm year, more

RSL than any subsequent image ESP_012479_1710 29 234 n 20 54 35 Faded SL but subtle changes ESP_021551_1710 30 247 n 23 46 69 Faded SL, brightened fans ESP_021828_1710 30 261 n 15 46 32 Subtle changes ESP_021973_1710 30 268 ? 4 43 47 small SL ESP_023107_1710 30 321 n 7 32 39 Subtle changes ESP_024874_1710 31 31 y N 8 46 39 Small, new SL, darkened fans ESP_025652_1710 31 58 6 49 58 Same as previous image ESP_027907_1710 31 137 y N 9 58 51 Incremental growth on several slopes, whole fans

darkened ESP_029819_1710 31 220 y N, SW 6 52 57 A little more growth, maybe some fading, very small

features ESP_031098_1710 31 283 y W 7 40 47 RSL in previous image faded, some small ones still

present. See Elorza figure ESP_032509_1710 31 346 y W 30 36 8 RSL prominent at low phase, lots of small changes as

in previous images Central Ius Chasma Lat

-7.1 Lon 274.2

Stereo? N

DTM? N

Elev. (km) +0.1

Notes

Image MY Ls SL? Aspect Emis. Illum Phase Partially confirmed (incremental growth or recurrence). CRISM BD530 bright over RSL slopes

PSP_002103_1730 28 163 y N, W 0 57 57 A few SL in SW corner (or topo shading?) PSP_006639_1730 29 8 y N,W,NE 5 38 43 Many more RSL in overlap with 2103—probably either

incremental growth or recurrence. Much activity after dust-storm summer.

ESP_029741_1730 31 216 n 4 53 56 No obvious RSL, but worth monitoring ESP_030664_1730 31 261 n 7 45 52 No obvious changes ESP_032365_1730 31 340 n 4 33 29 No obvious changes Hydrae Chasma Lat

-6.85 Lon 298.0

Stereo? Y

DTM? N

Elev. (km) -1.6

Notes

Image MY Ls SL? Aspect Emis. Illum Phase Partially confirmed (minor recurrence and incremental growth, minor fading)

ESP_013033_1730 29 262 y W, S 0 48 48 SL on west edge (Science Fig S6); N wall (bin2) ESP_013745_1730 29 296 Y W,S 16 38 53 Slight extension of a few SL (bin2) ESP_019336_1730 30 147 Y W 9 56 65 Only covers the W-facing slope (bin2), no obvious

changes ESP_019969_1730 30 172 y W 7 56 50 Slight growth (bin2) ESP_021815_1730 30 260 y W 5 46 50 A few changes from previous—new and “retreated”

SL (bin2). Definite changes from 13033 (~same Ls and photometric angles)

ESP_022804_1730 30 307 y W,S 9 36 28 Some new growth? (bin1) changes not obvious W or S slopes

ESP_028738_1730 31 171 y W, S 4 55 59 RSL often different (recurrence), but some very similar in whole set (bin1)

ESP_029516_1730 31 206 y W, S 9 54 46 Some growth compared to 28738, but also a sharper image. In general SL are very stable here compared to typical RSL.


8

Juventae Chasma Lat -4.7

Lon 298.6

Stereo? Y

DTM? N

Elev. (km) -4.2

Notes

Image MY Ls SL? Aspect Emis. Illum Phase Fully confirmed PSP_006203_1750 28 352 y NESW 0 35 35 Large SL on all slope aspects ESP_030373_1755 31 247 y SW 5 49 54 New RSL N hill ESP_030795_1755 31 268 y SW 12 46 35 Some new/growing RSL on N hill, and some fading ESP_030940_1755 31 275 y SW 0 44 44 Big, new RSL on SW-facing slope of N hill, and some

fading, very active ESP_031863_1755 31 318 y ESW 2 34 33 New long RSL on SW-, S-, and SE-facing slope of N

hill, new RSL on W-face of S hill ESP_032074_1755 31 327 y ESW 0 33 33 New growth, especially SE-facing on N hill. Also

some fading ESP_032219_1755 31 334 y NESW 19 31 50 New growth, especially SE-facing on N hill. Also

fading. New activity NE-facing slopes N hill, and 1 flow on N side of S hill. Overall activity comparable to MY28 image.

ESP_032496_1755 31 345 y NESW 22 35 13 Minor growth, mostly fading (?—low phase angle), including NE-facing slopes of N hill and N side of S hill.

ESP_032997_1755 32 5 y NESW 2 37 35 Fading on all slopes Aram Chaos Lat

3.3 Lon 339

Stereo? Y

DTM? N

Elev. (km) -3.3

Notes

Image MY Ls SL? Aspect Emis. Illum Phase Partially confirmed (minor incremental growth, minor fading). Nearby CRISM with strong BD530 and SINDEX along scarp to the SE (7FA4)

ESP_025954_1835 31 68 y SW 9 49 42 Big SL all along scarp. Color like sand; distinct from background

ESP_029343_1835 31 197 y SW 8 55 62 Growth in a few SL, stunted like Hydrae Chasma? ESP_030121_1835 31 235 y SW 7 55 48 No changes are obvious (bin-2 image), but broad

darkening of a slope region (3467, 10317) ESP_031756_1835 31 313 y SW 5 39 34 Mostly fading of thin RSL, some minor growth ESP_031967_1835 31 323 y SW 8 38 30 No change or minor fading Crater in S Acidalia Planitia

Lat 35.2

Lon 327.9

Stereo? N

DTM? N

Elev. (km) -4.4

Notes

Image MY Ls SL? Aspect Emis. Illum Phase Fully confirmed Low-albedo and rocky crater so temperatures high for this latitude

ESP_027840_2155 31 135 y W 5 48 42 Prominent SL on W-facing slope, faded SL on S-facing slope?

ESP_028684_2155 31 168 y W 7 57 51 Largely unchanged, but slight incremental growth on a few flows. Did we catch the very end of the active season?

ESP_028829_2155 31 175 y W 5 58 63 unchanged ESP_029607_2155 31 210 y W 4 69 65 Fading SL (but hazy image) ESP_030319_2155 31 244 y W 3 72 75 More fading ESP_030530_2155 31 255 y W 4 73 70 Mostly faded ESP_032020_2155 31 325 y W 4 58 55 Mostly faded ESP_033088_2155 32 8 y W 8 45 52 New RSL (recurrence)


9

Table S2. THEMIS brightness temperatures for crater on Melas Chasma floor. Ls THEMIS # TOD MY Peak T (K) on sun-facing slope 3 I01601002 15.35 26 268 (W-facing) 129 I38341002 16.2 30 248 (NW-facing) 160 I05708001 17.2 26 238 (W-facing) 230 I07180014 17.3 26 257 (SW-facing) 307 I08679001 16.2 26 281 (SW-facing) 323 I34048001 14.7 29 >287 (WSW-facing) Table S3. THEMIS brightness temperatures for crater on floor of Coprates Chasma. Ls THEMIS # TOD MY Peak T (K) on sun-facing slope 24 I35508003 15.3 30 259 (WNW-facing) 58 I36419001 15.8 30 252 (WNW-facing) 168 I05895001 17.3 26 242 (W-facing) 201 I14956001 17.6 27 244 (W-facing) 221 I07006001 17.4 26 259 (WSW-facing) 240 I07368002 17.1 26 265 (SW-facing) 279 I08116018 16.6 26 277 (SW-facing) 289 I33349002 15.1 29 289.5 (SW-facing) 319 I42309002 14.9 30 281 (WSW-facing) 339 I17713027 16.2 27 265 (W-facing)


10

Table S4. CRISM column abundances of H2O at representative RSL sites. Data are precipitable microns normalized to a reference 6.1 mbar pressure surface, binned by 5 degrees in longitude, 2 degrees in latitude, and 30 degrees in Ls, and come from the first full Martian year of MRO observations26. Blanks indicate no data were available in the spatial and temporal bins. Ls (degrees) Lat Lon 0-30 30-60 60-90 90-120 120-150 150-180 180-210 210-240 240-270 270-300 300-330 330-360 -52.4 157.8 1.7 4.6 5.9 12.5 16.0 13.6 3.6 3.6 -48.1 242.4 5.6 5.9 13.4 19.0 9.1 5.2 5.2 -47.7 4.6 2.3 3.4 9.5 9.8 13.7 13.4 -46.9 5.1 2.4 3.7 9.2 11.6 12.0 12.2 -46.0 9.5 3.3 3.7 10.2 13.4 11.8 5.3 4.8 -43.8 34.3 1.8 2.4 3.6 5.7 9.9 14.1 8.2 7.1 -43.3 343.2 2.7 5.8 4.6 9.3 13.5 8.1 6.3 -41.6 202.3 1.9 9.6 12.8 10.8 7.8 4.5 4.4 -39.7 88.1 1.8 16.6 15.4 14.2 5.7 4.2 -39.0 223.7 1.5 2.7 5.8 7.1 10.4 12.6 8.2 4.3 7.6 -38.8 159.5 1.3 3.1 4.6 6.1 11.5 11.0 4.2 4.5 -38.2 224.0 1.5 2.7 5.8 7.1 10.4 12.6 8.2 4.3 7.6 -38.2 188.9 2.0 3.8 10.0 14.0 11.7 8.7 -37.4 229.0 2.3 5.1 8.4 11.5 14.0 7.0 5.4 4.5 -37.3 176.4 6.5 5.7 9.0 11.7 11.6 4.0 -37.2 192.0 2.0 3.8 10.0 14.0 11.7 8.7 -32.7 120.1 2.4 3.0 5.4 9.3 12.6 14.2 7.7 4.2 -32.0 140.8 3.8 6.6 10.8 11.4 11.5 7.0 6.6 5.3 -14.1 296.9 2.8 11.6 6.0 9.0 10.9 12.7 8.6 -14.7 304.6 5.0 3.3 7.1 11.6 11.4 5.7 4.0 3.8 -14.4 304.6 5.0 3.3 7.1 11.6 11.4 5.7 4.0 3.8 -12.9 295.5 2.0 5.8 4.7 8.5 10.1 12.2 7.5 -12.9 293.5 2.0 5.8 4.7 8.5 10.1 12.2 7.5 -12.6 294.7 2.0 5.8 4.7 8.5 10.1 12.2 7.5 -11.5 290.3 7.2 9.4 10.7 11.6 5.4 -11.5 291.6 7.2 9.4 10.7 11.6 5.4

-9.3 281.6 5.6 8.6 7.5 13.2 16.4 7.3 7.3 -7.0 274.2 6.0 7.9 7.2 8.1 12.6 9.8 6.4 5.0

-14.6 301.4 4.1 4.4 7.8 8.2 10.9 6.5 15.6 -13.9 296.8 2.8 6.1 8.0 10.9 12.7 8.6 -12.9 291.1 7.2 9.4 10.7 11.6 5.4 -11.2 284.9 8.4 6.3 13.1 10.7 7.2 6.7 -10.8 32.0 5.1 8.8 6.3 11.0 10.9 11.9 7.3 9.1 -10.0 290.0 4.1 7.0 10.3 10.2 13.6 5.5

-8.8 304.8 5.6 7.4 9.7 9.8 8.0 4.0 -7.1 274.2 6.3 6.9 10.2 10.1 13.6 8.9 6.5 5.5 -6.9 298.0 5.9 8.1 8.6 10.9 7.2 4.5 -4.7 298.6 6.4 6.6 8.1 9.0 7.8 7.3 3.8 3.3 339.0 3.6 4.7 8.9 7.8 9.2 7.5 6.1 3.8

35.2 327.9 3.4 14.7 11.9 21.1 7.7 3.0 3.7 2.5 2.0 2.5 2.1


11

Figure S1. Comparison of albedo/color and size of streaks on dusty slopes of Olympus Mons (left), likely dust avalanches, to RSL in Palikir crater (middle and right). Surface and atmospheric photometric corrections were applied, but without using DTMs to correct for slopes. Instead, since the areas of interest in both images are about 30° sun-facing slopes, we normalized brightnesses to an incidence angle of 30° (~0° on these slopes). Resulting normalized albedo values at the 5 lettered locations (IR, RED, and BG bandpasses, respectively), are A: 0.38, 0.23, 0.09; B: 0.52, 0.30, 0.11; C: 0.29, 0.16, 0.07; D (RSL): 0.059, 0.059, 0.027; E (bright fan): 0.079, 0.073, 0.034. This illustrates that RSL are ~3x darker and ~2x less red than slope streaks.


12

Figure S2. Set of three images in west Coprates Chasma (14.7°S, 304.6°E) showing transient darkening of the IRB “greenish” fans where RSL terminate. Photometric angles are similar in each image (Table S1) but the middle image was acquired through dustier air. Red arrows point to some of these fans. Geometry is that of the raw images; north is ~7° to the right of up. Larger fans darkened and rebrightened in the larger region covered by simultaneous CTX images. Image widths ~300 meters. Figure S3 (below). Extensive darkening of fans observed in Eos/Capri Chasma site (15.4°S, 309.5°E). The first 2 images (Ls=234° and 269° of MY 31) show no RSL and bright fans, while the last 3 images (Ls=329° and 352° of MY 31) show extensive RSL ending on darkened fans (white arrows). The white box marks a location that is enlarged at bottom. This site includes some of the longest RSL seen to date, up to 1.2 km in length. Scene width ~1.1 km, raw image geometry with north approximately up.


13


14

Figure S4. Part of ESP_025441_1650 in Coprates Chasma illustrating the lineated fans that RSL frequent. North is up and downhill is to the west (left). Arrows at A point to typical RSL, B points to discontinuous RSL, and C shows where the lineated fan transitions into wind ripples.


15

Figure S5. Plot of CRISM column abundance of atmospheric water vapor over a typical mid-latitude RSL site. Data are from Ls=120° of MY 28 to Ls=120° of MY 29 (Table S4). Empty regions here and in Figure S6 indicate lack of data.

Lon = 9.537, Lat = -45.951

0 90 180 270 360LS

0

5

10

15

20h w

ater

6.1_

mba

r (pr. µ

m)


16

Figure S6. Plot of CRISM column abundance of atmospheric water vapor over a typical RSL site in Valles Marineris. Data are from Ls=120° of MY 28 to Ls=120° of MY 29 (Table S4). The error bars are larger than in the middle latitudes (Figure S5) due to fewer observations.

Lon = 295.500, Lat = -12.900

0 90 180 270 360LS

0

5

10

15

20h w

ater

6.1_

mba

r (pr. µ

m)


recurring slope lineae in equatorial regions of mars...1 supplementary information for recurring...

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