Available online at www.sciencedirect.com Geomorphology 94 (2008) 247–255 www.elsevier.com/locate/geomorph Recent aeolian dune change on Mars ⁎ M.C. Bourke a,b, , K.S. Edgett c, B.A. Cantor c a Planetary Science Institute, Tucson, AZ 85719, USA b School of Geography and the Environment, University of Oxford, Oxford, OX1 3QY, UK c Malin Space Science Systems, PO Box 910148, San Diego, CA 92191-0148, USA Received 26 January 2007; received in revised form 24 May 2007; accepted 24 May 2007 Available online 8 June 2007 Abstract Previous comparisons of Martian aeolian dunes in satellite images have not detected any change in dune form or position. Here, we show dome dunes in the north polar region that shrank and then disappeared over a period of 3.04 Mars years (5.7 Earth years), while larger, neighboring dunes showed no erosion or movement. The removal of sand from these dunes indicates that not only is the threshold wind speed for saltation exceeded under present conditions on Mars, but that any sand that is available for transport is likely to be moved. Dunes that show no evidence of change could be crusted, indurated, or subject to infrequent episodes of movement. © 2007 Elsevier B.V. All rights reserved. Keywords: Mars; Aeolian; Dune; Sediment transport 1. Introduction dust is raised by wind somewhere on the planet nearly every Martian day (Cantor, 2003; Cantor et al., 2006; Aeolian bedforms are found at all latitudes on Mars Cantor, 2007). As sand is mobilized at a lower threshold (Thomas, 1982). Their presence requires that sand-sized friction speed than dust (Iverson and White, 1982), and material has been transported by saltation (Cutts and the impact of saltating grains will raise dust at threshold Smith, 1973). Saltation occurs on Mars under the current friction speeds lower than for dust alone (Greeley, 2002), low atmospheric pressures: a dust storm in June 1981 is sand must also be transported by these dust-raising events, believed to have caused the erosion of regolith piles at the provided that sand is available to be moved. Viking1landersite(Moore, 1985), and wind gusts, Many Martian sand dunes exhibit sharp brinks and perhaps during a March 2005 dust storm (Cantor et al., margins (Figs. 1 and 2) and do not appear to be peppered 2006), caused sand grains to be deposited on the 1 m high by small impact craters (Marchenko and Pronin, 1995; deck of the Mars Exploration Rover, Spirit, via saltation Malin and Edgett, 2001). This suggests that they are (Greeley et al., 2006). Daily global observations by the geologically young and may have been mobile at some Mars Global Surveyor (MGS) Mars Orbiter Camera time in the last 100,000 years (Hartmann, 2005; Malin (MOC) over a 4.04 Mars year period (1 Mars year is about et al., 2006). There are no published reports of dune 1.88 Earth years in duration) from March 1999, show that movement. Images of dunes acquired by the Mariner 9 (1972), Viking 1 (1976–1980), Viking 2 (1976–1978), and Mars Global Surveyor (MGS; 1997–2006) orbiters ⁎ Corresponding author. suggest that Martian dunes have not migrated during the E-mail address: [email protected] (M.C. Bourke). past 1–14 Martian years (Edgett and Malin, 2000; 0169-555X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2007.05.012 248 M.C. Bourke et al. / Geomorphology 94 (2008) 247–255 Fig. 1. Location of MGS MOC images on a subframe of Mars Odyssey THEMIS image V12629003. The swath placement and dimensions of each image differs slightly. MOC image numbers 1: FHA-00515 (March 1999), 2: E18-00494 (July 2002), 3: E23-00490 (December 2002), 4: S01-00007 (December 2004). Circles indicate the location of the small dome dunes (i, ii, iii) examined. Zimbelman, 2000; Malin and Edgett, 2001; Edgett, Several ideas have been put forward as to why 2002; Fenton et al., 2003; Williams, 2004; Schatz et al., Martian sand dunes do not appear to be moving today. 2006). Further, only a small number of images docu- The threshold friction wind speed required to move ment changes that occurred on dune slip-faces—8MOC sediment on Mars is higher than on Earth, and data from pictures studied by Fenton (2006) show new slip-face the Viking and Mars Pathfinder Lander missions indi- avalanches on a dune in Rabe Crater, and 2 MOC cated that these speeds were rarely met (Greeley et al., pictures described by Malin and Edgett (2005) show the 1982; Schofield et al., 1997). Under such conditions, formation of new steep-walled gullies on the slip-face of dunes might be moving so slowly that they are indeed a dune in an unnamed Martian crater. active today, but the rate is immeasurable given the M.C. Bourke et al. / Geomorphology 94 (2008) 247–255 249 Fig. 2. Subframes of MOC images in Fig. 1. Panels 1–3 show changes in the dome dunes that occurred between March 1999 and December 2004. limited, repeated spacecraft observations. Alternatively, southward toward the informally-named Victoria Crater some or all of the dunes may be crusted or indurated. (Richter et al., 2006). Evidence for crusting or induration Crusts were common in the regolith at the Viking lander of dunes comes from MOC images showing the presence sites (Arvidson et al., 1989); and the Mars Exploration of erosional steps on the windward slopes of barchan Rover, Opportunity, routinely encountered crusted sand- dunes (Bourke, 2004), and the steep walls of avalanche and granule-sized windblown sediment during its trek scars on some dune slip-faces (Malin and Edgett, 2001; Table 1 Migration rates of small terrestrial dunes in unidirectional wind settings Location Dune type Time interval Movement rate (per year) Reference Pampa de la Joya, Peru Barchan 1955–1958 9–23 m Hastenrath (1967) 1958–1964 17–56 m Pampa de la Joya, Peru Barchan 1955–1958 9–30 m Finkel (1959) Imperial Valley, California, USA Barchan 1941–1956 7–24 m Long and Sharp (1964) 1956–1963 14–40 m Taklimakan Desert, China Dome ‘6’ 1991–1993 75 m Dong et al. (2000) Dome ‘8’ 1991–1993 6 m Namib Sand Sea, Namibia Dome 1976–1999 ~4 m (Bristow and Lancaster, 2004) 250 M.C. Bourke et al. / Geomorphology 94 (2008) 247–255 Table 2 Mars dune sites repeatedly monitored for movement by MGS MOC Location Lat. Lon. First image Last image Interval (Mars years) Picture no. Date Ls Picture no. Date Ls Unnamed crater 1.7°N 351.7°W Viking 709A42 27-May-1978 92° S19-01867 24-Jun-2006 71° 13.9 Near Briault 8.8°S 271.1°W Viking 755A19 12-Jul-1978 113° R14-01173 10-Feb-2004 348° 13.7 Unnamed crater 20.1°N 280.7°W SP1-23008 10-Apr-1998 308° S18-02048 25-May-2006 57° 4.3 Kaiser crater 47.1°S 341.3°W AB1-10004 21-Jan-1998 260° S12-02197 23-Nov-2005 329° 4.2 North polar 76.4°N 264.8°W FHA-00515 10-Mar-1999 108° S22-00197 4-Sep-2006 102° 4.0 Kaiser crater 46.9°S 340.9°W M02-04432 28-Jun-1999 162° S02-01242 31-Jan-2006 153° 4.0 Herschel crater 14.3°S 231.8°W SP2-36507 14-Jun-1998 345° S12-02169 22-Nov-2005 329° 4.0 North polar 81.1°N 188.0°W M00-00545 5-Apr-1999 120° S21-02221 21-Aug-2006 96° 3.9 Gale crater 4.7°S 222.7°W M03-01521 9-Jul-1999 168° S19-00049 1-Jun-2006 60° 3.7 North polar 76.8°N 105.4°W M02-03150 22-Jun-1999 159° S13-02421 25-Dec-2005 346° 3.5 Dawes crater 9.5°S 323.1°W M09-03471 14-Nov-1999 244° S12-02647 28-Nov-2005 331° 3.2 North polar 79.1°N 251.2°W M14-00429 6-Apr-2000 331° S17-02242 27-Apr-2006 45° 3.2 Unnamed crater 4.1°S 348.0°W M12-01178 11-Feb-2000 300° S14-02432 23-Jan-2006 1° 3.2 Herschel crater 15.1°S 232.3°W M02-02819 10-Jun-1999 158° S06-01757 18-May-2005 214° 3.2 Herschel crater 14.4°S 231.6°W FHA-01381 23-Mar-1999 114° S04-00076 2-Mar-2005 169° 3.2 Unnamed crater 19.9°N 280.6°W M14-00676 10-Apr-2000 334° S14-01565 15-Jan-2006 357° 3.1 Proctor crater 47.5°S 329.8°W M03-03088 16-Jul-1999 172° S05-00330 6-Apr-2005 189° 3.0 Trouvelot crater 16.3°N 13.5°W SP2-53203 3-Sep-1998 24° R17-02141 25-May-2004 38° 3.0 Green crater 53.0°S 8.8°W E01-02009 2-Feb-2001 123° S23-00204 4-Oct-2006 116° 3.0 Unnamed crater 7.3°N 353.4°W M21-00827 13-Nov-2000 76° S20-01013 16-Jul-2006 80° 3.0 Unnamed crater 10.9°N 2.9°W M07-01793 10-Sep-1999 204° S05-01727 27-Apr-2005 201° 3.0 Proctor crater 47.7°S 330.0°W M10-01334 11-Dec-1999 261° S08-03035 28-Jul-2005 258° 3.0 Proctor crater 47.5°S 329.7°W M02-02711 20-Jun-1999 157° S02-01021 25-Jan-2005 150° 3.0 North polar 76.7°N 239.4°W M02-04193 27-Jun-1999 161° S03-00289 5-Feb-2005 156° 3.0 North polar 84.8°N 26.7°W M02-00783 8-Jun-1999 151° S02-00302 7-Jan-2005 141° 3.0 North polar 75.9°N 84.3°W E02-00183 3-Mar-2001 125° S23-00440 8-Oct-2006 118° 3.0 Kaiser crater 46.8°S 340.8°W M02-04432 28-Jun-1999 162° S02-01242 31-Jan-2005 153° 3.0 Unnamed crater 10.8°N 351.0°W SP1-26004 24-Apr-1998 317° R10-05174 30-Oct-2003 290° 2.9 Unnamed crater 6.3°N 345.9°W M11-01425 10-Jan-2000 280° S08-00832 8-Jul-2005 245° 2.9 North polar 82.7°N 45.0°W E01-01325 19-Feb-2001 120° S17-00850 19-Apr-2006 41° 2.8 North polar 76.5°N 264.7°W M02-03026 21-Jun-1999 158° R19-01239 17-Jul-2004 62° 2.7 North polar 74.9°N 50.9°W M23-01695 26-Jan-2001 108° S13-00388 30-Dec-2005 349° 2.7 North polar 76.6°N 268.4°W E01-01881 25-Feb-2001 122° S13-02134 22-Dec-2005 345° 2.6 Unnamed crater 8.4°N 55.2°W E02-00082 2-Mar-2001 124° S13-02634 27-Dec-2005 347° 2.6 Unnamed crater 8.5°N 15.8°W E05-03231 29-Jun-2001 186° S16-01017 12-Mar-2006 24° 2.6 Unnamed crater 11.0°N 14.5°W E05-01993 21-Jun-2001 182° S13-02485 25-Dec-2005 346° 2.5 North polar 76.7°N 256.1°W E14-01084 16-Mar-2002 343° S23-00067 2-Oct-2006 115° 2.4 Rabe crater 43.9°S 325.6°W M17-01061 28-Jul-2000 28° S01-00886 20-Dec-2004 132° 2.3 Unnamed crater 8.9°N 1.2°W