Re‐Evaluation of Large Martian Ripples in Gale Crater: Granulometric Evidence for an Impact Mechanism and Terrestrial Analogues

Abstract

Aeolian ripples and dunes are ubiquitous and familiar surface features across the solar system. Importantly, these bedforms provide a natural test environment for theories of fluid-sediment interactions. Extraterrestrial environments, most commonly Mars, have been studied for several decades to validate theories of bedform formation and sediment transport in multiple environments (e.g.,

The Aeolian Environment in Glen Torridon, Gale Crater, Mars

“…The largest dark sand ripples have coarser grains concentrated at crests but lack continuous mantles of very coarse, creep‐only grains covering crests, so are different from terrestrial megaripples. They are similar to other martian large ripples in dark sand deposits investigated by rovers at Gusev crater and elsewhere at Gale (Ehlmann et al., 2017; Ewing et al., 2017; Gough et al., 2021; Lapotre et al., 2016, 2018; Sullivan et al., 2008, 2020; Weitz et al., 2018), as well as large ripples observed from orbit in many other dark sand deposits across Mars (e.g., Bridges et al., 2007, Bridges, Ayoub, et al., 2012, Bridges, Bourke et al., 2012; Chojnacki et al., 2011, 2014, 2015; Silvestro et al., 2010; Vaz et al., 2017; among many other contributions). These large ripples have no terrestrial analogue and their origins have been debated.…”

Planetary Aeolian Landforms: An Introduction to the Fifth Planetary Dunes Workshop Special Issue

“…A better knowledge of where and when coarse sediment is displaced will be helpful to correctly understand atmospheric model output and interpret the sedimentary record of Mars (and of Titan in the future) Barnes et al, 2021). In particular, as previously reported, the knowledge of bedform grain size distributions is key to correctly scale sediment transport models to the Martian and Titan environments (Burr et al, 2014;Gough et al, 2021). The ∼5 m ripples that were observed to migrate on Mars are located in between dunes, which are preferentially occupied by megaripples (Silvestro et al, 2020).…”

“…The authors of this work concluded that an Earth‐like impact mechanism is likely responsible for their formation without the necessity to invoke other explanations (e.g., fluid‐drag) (Sullivan et al., 2020). This article is key to continuing discussions concerning ripple formation processes within the aeolian scientific community and highlights the need for future work (Gough et al., 2021; Lapôtre et al., 2021; Lorenz, 2020). Terrestrial aeolian fluid‐drag ripples are not well understood and most of the knowledge of these features relies on the Bagnold (1954) wind tunnel seminal work.…”

“…As recently reported, more detailed grain size analysis from Martian bedforms must be performed in order to have statistically significant measurements to derive formation mechanisms (Gough et al., 2021). Nevertheless, the results reported in this collection show that even dedicated fluid‐dynamic modeling can be used to understand the effects of different atmospheric environments on ripple morphologies (Siminovich et al., 2019; Yizhaq, Siminovich, et al., 2021).…”

Granule Ripples in the Kumtagh Desert, China: Morphological and Sedimentary Characteristics, and Development Processes

“…The Martian granule ripples were measured and found to have a wavelength of 38 m and a height of 5.7 m (Yizhaq, 2005), giving a ripple index of 6.7, which is much lower than the value for terrestrial granule ripples, which averages about 15. These huge Martian granule ripples may result from a combination of the lower Martian gravity and the higher overall wind speeds required for saltation in the planet's low‐density atmosphere, which leads to a greatly increased saltation length (Chojnacki et al., 2021; Gough et al., 2021; Silvestro et al., 2020; Sullivan et al., 2020; Yizhaq, 2005).…”