The birth and death of transverse aeolian ridges on Mars

Abstract

Transverse aeolian ridges (TARs) are small bright windblown deposits found throughout the Martian tropics that stand a few meters tall and are spaced a few tens of meters apart. The origin of these features remains mysterious more than 20 years after their discovery on Mars. This paper presents a new hypothesis, that some of the TARs could be indurated dust deposits emplaced millions of years ago during periods of higher axial obliquity. It suggests that these TARs are primary depositional bed forms that accumulated in place from dust carried by the winds in suspension, perhaps in a manner comparable to antidunes on Earth, and were subsequently indurated and eroded to their current states by eons of sandblasting. It points out examples of modern dust drifts and dune-like features that appear to have been recently formed by dust accumulating directly onto the surface from atmospheric suspension. It shows how these pristine dust deposits could evolve to explain the range of morphologies of the TARs. Finally, it explains how the known properties of many TARs are consistent with this hypothesis, including their composition, thermal behavior, and distribution.

Large wind ripples on Mars: A record of atmospheric evolution

“…2B) is the signature of TARs (48,51,52). TARs may form as a result of coarse-grain armoring, giant saltation trajectories, or deposition of dust transported in suspension (52)(53)(54)(55), and are distinct from the large ripples in activity and morphology: (i) activity of TARs has not been detected (46,56), (ii) their wavelengths are generally larger and more widely distributed (e.g., Table S2), (iii) they have symmetric topographic profiles (54), and (iv) they tend to have a much higher albedo than the dark, active, mafic sands. Thus, the large martian ripples are distinct from TARs.…”

Aeolian Ripple Migration and Associated Creep Transport Rates

“…This work was focused on typical aeolian ripples with heights and lengths of the orders of 0.01 and 0.1 m, respectively, with mean grain sizes (d) between about 0.1 and 0.5 mm that we believe to be in equilibrium or near equilibrium with the wind. We did not consider megaripples [20][21][22] or transverse aeolian ridges [23][24][25], although both of these bed forms have received considerable and appropriate attention in the literature.…”

Evidence for different episodes of aeolian construction and a new type of wind streak in the 2016 ExoMars landing ellipse in Meridiani Planum, Mars

“…Population 1 wavelengths (29 m on average, Table ) seem to be too small for a paleoerg formed by simple dunes (50–500 m) [ Lancaster, ]. Instead, the measured wavelengths are more consistent with Martian TAR and large terrestrial megaripple values [ Balme et al , ; Milana , ; de Silva et al , ; Geissler , ]. The high length variability might reflect the breakup of the crestlines that have been severely reworked while the inflection in the spacing distribution can indicate different subpopulations.…”

“…This suggests that population 1 may represents one of these two classes of bed forms. On Earth, ripples of similar size develop during extremely strong wind events [ Milana , ], suggesting that such strong winds should have been common on Mars, perhaps during a high‐obliquity axis period when winds were predicted to be stronger [ Haberle et al , ; Geissler , ]. Their widespread occurrence in the landing ellipse also suggests an extensive source area.…”

“…The higher complexity of the intracrater TARs can be explained by considering the influence of crater topography. This can probably explain their “ladderback” [ Reddering , ; Ramsay et al , ] appearance without involving a progressive build up from individual “deltoid” components [ Geissler , ]. The dominance of winds from the east implies a dramatic shift in the main wind direction (90° or 270°).…”