Evidence of Exposed Dusty Water Ice within Martian Gullies

Khuller, A. R.; Christensen, P. R.

doi:10.1029/2020je006539

Cited by 15 publications

(15 citation statements)

References 151 publications

(307 reference statements)

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“…Many gullies are incised into mantling materials (e.g., Christensen, 2003), which in many cases likely have a high H 2 O ice content because the total apron volumes are smaller than the eroded alcoves (Conway & Balme, 2014; Gulick et al., 2019). Khuller and Christensen (2021) documented exposure of bright material interpreted as water ice by slumping in several alcoves.…”

Section: Mass Wasting and Slope Processesmentioning

confidence: 99%

“…In aggregate, it appears that the morphology of gullies is currently being shaped by modern CO 2 frost processes, although a few studies still explore whether brines may be involved in the present‐day activity of linear dune gullies (e.g., Jouannic et al., 2019) and Khuller and Christensen (2021) suggested that melting in alcoves could occur in association with bright exposures. Dune gullies are so active that they must entirely form on timescales much less than obliquity cycles, and indeed a few new or completely redeveloped gullies are observed to form on sand dunes within a few Mars years (Dundas et al., 2012; Dundas, McEwen, et al., 2019).…”

Section: Mass Wasting and Slope Processesmentioning

confidence: 99%

“…On less‐mobile nonsand substrates, formation proceeds more slowly. The present‐day activity appears capable of forming the observed nondune gullies when integrated over ∼ Myr timescales (Dundas, McEwen, et al., 2019), but it is still debated whether other processes such as aqueous debris flows or snowmelt also contributed to their formation under past climate conditions (e.g., Conway et al., 2019; Khuller & Christensen, 2021).…”

Section: Mass Wasting and Slope Processesmentioning

confidence: 99%

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Active Mars: A Dynamic World

et al. 2021

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An axiom of geology is that the present is the key to the past. Knowledge of current processes and their consequences is an essential tool for understanding history, including the ancient rock record and the associated climate. Modern Mars is cold, with a thin atmosphere, and has previously been thought to have little ongoing geomorphic activity-especially when compared with ancient Mars, which had apparent largescale, Earth-like processes, as inferred from ancient landforms. This interpretation has led much research to focus not on the present Martian environment, but rather on Mars' early conditions and climate change over time. However, in recent years, observations of ongoing surface changes have proliferated, demonstrating that Mars' landscape is actively evolving and likely has been throughout the Amazonian epoch. These observed geomorphic changes shed light on a variety of active processes, some with no terrestrial analog, and reveal present-day Mars to be a dynamic world. This in turn may mean that more of the ancient and recent Martian geologic record can be explained without dramatic climate change.This work presents a comprehensive summary and categorization of the many types of observed changes on the Martian surface. Aeolian and frost-related surface activity are discussed in more detail in a parallel review by Diniega et al. (2021), which focuses on connecting specific landforms to their formative processes; the focus herein is to provide a broad overview of known types of changes in surface morphology and albedo. Weather and seasonal frost and ice are not discussed in detail here, except where necessary to describe their effects on the surface; observations of the atmosphere were reviewed by M. D. Smith (2008) and Martínez et al. (2017), and seasonal frost is discussed in Piqueux, Kleinböhl, et al. (2015) and references therein. Weathering and other microscale or chemical processes are not discussed. Even with these exclusions, the scope of the subject is broad and we have focused on the key discoveries and constraints.Studying surface changes on Mars yields a unique look at processes within an un-Earthly environment.

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Section: Mass Wasting and Slope Processesmentioning

confidence: 99%

Section: Mass Wasting and Slope Processesmentioning

confidence: 99%

Section: Mass Wasting and Slope Processesmentioning

confidence: 99%

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Active Mars: A Dynamic World

et al. 2021

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“…The presence, stability, and physical nature of H 2 O ice on Mars has major implications for understanding martian history, evolution, and future robotic and manned exploration. However, the pervasive presence of dust on Mars causes the ice to contain typically <∼1% dust, especially when exposed at the mid‐latitudes (Dundas et al., 2018; Khuller & Christensen, 2021). The ice is thought to have been deposited as snow during periods of high obliquity that occurred numerous times over the last few million years (Christensen, 2003; Jakosky & Carr, 1985; Madeleine et al., 2014).…”

Section: Introductionmentioning

confidence: 99%

“…Recent observations have indicated that dusty H 2 O ice is currently being exposed at martian mid‐latitudes (e.g., Byrne et al., 2009; Dundas et al., 2018; Khuller & Christensen, 2021). The precise nature (grain size and dust content) of this exposed ice is currently uncertain, and estimates of the time scale of martian snow metamorphism range from decades/centuries (Clow, 1987; Kieffer, 1990) to millions of years (Bramson et al., 2017).…”

Section: Introductionmentioning

confidence: 99%

Spectral Albedo of Dusty Martian H₂O Snow and Ice

2021

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The presence, stability, and physical nature of H 2 O ice on Mars has major implications for understanding martian history, evolution, and future robotic and manned exploration. However, the pervasive presence of dust on Mars causes the ice to contain typically <∼1% dust, especially when exposed at the mid-latitudes (Dundas et al., 2018;. The ice is thought to have been deposited as snow during periods of high obliquity that occurred numerous times over the last few million years (Christensen, 2003;Jakosky & Carr, 1985;Madeleine et al., 2014). At visible wavelengths, dust is far more absorbing than H 2 O ice (Figure 1; Wolff et al., 2009), so small amounts of dust can lower the albedo at these wavelengths (e.g., Dozier et al., 2009;Painter et al., 2013). Lower albedos lead to enhanced radiative heating, which affects the ice's energy balance and its stability and evolution over time.Radiative heating is also enhanced by snow metamorphism. On Earth, fresh snow (with grain radius 50-100 μm) quickly metamorphoses due to vapor diffusion and and grain-boundary diffusion (Kaempfer & Schneebeli, 2007); surface snow grains can grow to radii of several hundred μm. The density also increases, in three stages by three different mechanisms (grain-boundary sliding, mechanical deformation, and bubble shrinkage): (a) In snow, densification proceeds by grain-boundary sliding, up to 550 kg/m 3 . This is the maximum density obtainable for snow at the surface. (b) In subsurface firn, density can increase by mechanical deformation up to 830 kg/m 3 ; at this density, the air becomes closed off into bubbles, becoming "glacier ice." (c) Overburden pressure in glacier ice causes the air bubbles to shrink, further increasing the density to approach that of pure ice, 917 kg/m 3 (Cuffey & Paterson, 2010). Density per se has no effect on the albedo of opaque media, but in snow and ice the density does often correlate with grain size, which is the dominant Abstract Recent evidence of exposed H 2 O ice on Mars suggests that this ice was deposited as dusty (<∼1% dust) snow. This dusty snow is thought to have been deposited and subsequently buried over the last few million years. On Earth, freshly fallen snow metamorphoses with time into firn and, if deep enough, into glacier ice. While spectral measurements of martian ice have been made, no model of the spectral albedo of dusty martian firn or glacier ice exists at present. Accounting for dust and snow metamorphism is important because both factors reduce the albedo of snow and ice by large amounts. However, the dust content and physical properties of martian H 2 O ice are poorly constrained. Here, we present a model of the spectral albedo of H 2 O snow and ice on Mars, which is based on validated terrestrial models. We find that small amounts (<1%) of martian dust can lower the albedo of H 2 O ice at visible wavelengths from ∼1.0 to ∼0.1. Additionally, our model indicates that dusty (>0.01% dust) firn and glacier ice have a lower albedo than pure dust, making them difficult to distinguish in ...

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