Aeolian Dust Deposits
KeywordsDust Storm Dust Devil Dust Deposit Mars Exploration Rover Surface Wind Velocity
A sedimentary deposit produced from the finest (silt-sized) fraction of planetary regolith that is carried in suspension and distributed by atmospheric activity.
The sizes of suspended particles were measured by the Mars Exploration Rovers and orbiters to be ~3 μm in diameter (Lemmon et al. 2004; Wolff and Clancy 2003). Particles accumulated on the Spirit rover were of sizes up to 300 μm in diameter, but these likely arrived via saltation (Landis et al. 2006).
Patterns (bedforms) of hypothesized dust deposits on Mars are described in reticulate ridges.
- (1)Unconsolidated to slightly consolidated aeolian dust deposits:
Loess (see under terrestrial analogs).
Loess-like sediments may be present on Mars in the polar layered deposits or in the latitude-dependent mantle. It is proposed that Martian “loess” is cemented together as a result of deposition of water-soluble minerals or from the sublimation of mineral-rich ice grains (Johnson and Lorenz 2000).
- (2)Consolidated aeolian dust deposits:
Duststone: Accumulation and compaction of dust, aided by aggregate growth and cementation, can become weakly lithified, forming duststones (Bridges and Muhs 2012). These proposed duststones may be similar to (a) terrestrial mudrocks except they lack clay minerals or (b) lithified loess (loessite) deposits. As loessites on Earth, duststones are proposed to have formed by prolonged settling of dust from the atmosphere, although regionally extensive volcanic ash deposits could have similar stratigraphic expression (Grotzinger and Milliken 2012). Duststones on Mars, similar to dust, would show bland spectral signatures lacking absorption features diagnostic of hydrous minerals. Such spectral signature may indicate either a thin, unconsolidated dust mantle or lithified rock (duststone) that is compositionally identical to dust. Prominent examples of such deposits are proposed to be at the top of Aeolis Mons in Gale Crater and in several places in Arabia Terra (Bridges and Muhs 2012; Grotzinger and Milliken 2012).
Loessite: consolidated loess.
Formation of aeolian dust deposits requires availability of dust-sized particles (e.g., from impacts, pyroclastic volcanism, aeolian abrasion, or chemical weathering (Garvin 1984)); an atmosphere, which is able to suspend particles; and surface wind velocities above the threshold friction speed, which can mobilize dust particles bound by interparticle cohesion forces (e.g., Greeley and Iversen 1987; Shao and Lu 2000; Pankine and Ingersoll 2004) and land regions characterized by surface wind velocities below the threshold speed where dust deposition can occur.
Although deposition may occur uniformly on a global scale, it may be more difficult to lift dust from rough terrains where non-erodible particles shelter dust from the wind (Zimbelman 1990).
On Mars, dust is redistributed by local-scale dust devils Sullivan et al. 2008, by small and large regional storms, and by global planet-encircling storms. During global dust storms on Mars, large quantity of dust is lifted into the atmosphere dramatically affecting its thermal and dynamic state (Zurek et al. 1992; Smith et al. 2002). Global dust storms occur during the southern summer and originate in the southern midlatitudes (Zurek and Martin 1993). The current distribution of aeolian dust deposits on the surface of Mars (Fig. 2) suggests that there is a net transport of dust from the southern to the northern midlatitudes. Global dust activity and net transport could undergo dramatic changes every few Ma, when insolation and atmospheric dynamics change due to variations in orbital parameters (Leovy 2001; Laskar et al. 2002). On shorter timescales (100 ka) the distribution of aeolian dust deposits may reflect self-organization (Pankine and Ingersoll 2004).
On slopes covered by aeolian dust deposits on Mars, mass wasting features form and produce slope streaks, although some of the models suggest that liquid brines may also contribute to their formation.
The mineralogy of Martian aeolian dust deposits has been investigated using spectroscopy. There is clear evidence for a ferric oxide component, plagioclase feldspar and possibly zeolite, and a few percent by volume carbonate (Bandfield et al. 2003; Bibring et al. 2006; Ruff 2004; Singer 1982). This fine-grained ferric oxide-bearing dust coats much of the surface of Mars in an optically thick, though possibly only several hundreds of micrometers thick layer, causing the red color of the surface of Mars (Grotzinger and Milliken 2012).
Aeolian dust deposits are well documented on Earth and Mars (e.g., Tharsis Montes, Amazonis Planitia, Elysium Mons, Arabia Terra). They are also evident on Venus and Titan.
Mars Exploration Rover solar panel power output analysis showed that at the beginning of a major dust storm, dust was initially removed from the panels, likely by increased winds. When winds started to dissipate, a large quantity of dust re-accumulated on the panels (Edmondson et al. 2007).
On Venus. Transient dust phenomena due to settling of dust were observed in landing site images following the landings of several Venera landers (Garvin 1984). Dust from impact processes may be suspended in the dense atmosphere and redistributed and deposited regionally or globally, blanketing the surface everywhere (Kreslavsky 2009). Wind streaks are proposed to represent ashfall deposits produced by limited pyroclastic activity (Guest et al. 1992).
On Titan, photochemical tholin aerosols may accrete into aggregates that sediment out from the atmosphere (Lorenz et al. 1995), which may form a fine tholin dust “snow” layer on the surface (Soderblom 2006).
The homogenous composition of dust on Mars implies that the finest fraction of the Martian regolith has been well mixed globally. It represents a mixture of the primary igneous and secondary alteration products of the Martian crust (Yen et al. 2005).
The invasive nature of dust on the Moon and Mars, especially electrostatically adhering dust, represents a challenging engineering problem for future human missions. Consideration is necessary in areas from space suit design to habitat dust control, due to its abrasive and toxic effects (Schmitt 2006: 124, Cain 2010).
Atmospheric dust may accumulate on the solar panels of landers or rovers resulting in power losses. The Mars Exploration Rovers temporarily lost up to 60 % of initial power, while dust removal events have removed dust leading to recoveries of approximately 90 % of initial power (Edmondson et al. 2007).
Deposits of clay and silt-sized aeolian particles. On Earth, persistent aeolian dust deposits are known as loess deposits derived from glaciogenic (alluvial/outwash plains) or desert-derived aerosolic (windblown) dust (e.g., Muhs and Budahn 2006). Loess is a homogenous, commonly nonstratified, porous, friable, slightly coherent, fine-grained (Bates and Jackson 1995), relatively well sorted, slightly diagenetized (Pécsi 1990), generally calcareous, blanket deposit. Loess sequences are usually divided with paleosoils or sand layers. Loess is composed of particles with a similar size range that of dust, but loess is not just accumulation of airborne dust: its particles on Earth are held together by calcareous cement, often forming relatively resistant cliff-forming units. Also calcite and allophane impregnations of clay bridges act as cementation bonds during loessification (Cilek 2001). Loess and loess-like deposits cover ~10 % of the surface of Earth (Pécsi 1990). On Earth, vegetation plays a great role in the stabilization of dust (Pécsi 1990). In the periglacial zones, patchy vegetation cover was characteristic, and during the accumulation of dust, soil development remained unbroken but inhibited by higher sedimentation rates. Through loessification biomineralization was inherited (Becze-Deák et al. 1997). Loess is often traversed by networks of small narrow vertical tubes (composing hypocoatings through calcite impregnation of the channels walls and/or they are characterized by calcium-carbonate coatings on the channel walls) left by successive generations of grass roots (Becze-Deák et al. 1997; Barta 2011). Dry loess can stand in steep or nearly vertical faces (Bates and Jackson 1995).
Martian counterparts of loess are termed “loess-like sediments,” because vegetation and soil-sedimentary processes that are absent on Mars play important roles in the diagenesis of (terrestrial) loess.
Origin of Term
Loess: from Löss, Lösch, “loose,” German. Duststone: Bridges and Muhs (2012).
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