Unique Aeolian Bedforms of Mars: Transverse Aeolian Ridges

Transverse Aeolian Ridges (TARs) are among the unique aeolian bedforms of Mars, which witnessed a series of investigation for the last two decades thanks to the high-resolution remote sensing data. This paper summarized the understanding with respect to distribution, morphology, sedimentology, formation hypotheses and formation time of TARs. It is suggested that TARs are a kind of aeolian bedforms with meter-scale height and decameter-scale wavelength. TARs are primarily distributed in the equator and low-latitude regions, being rare in high and mid-latitude regions, and more popular in the south hemisphere than in the north hemisphere. Higher albedo and symmetric cross-sections are the most outstanding features of TARs, being analogous to the megaripples and reversing dunes on the Earth. The grain-size distribution of TARs’ sediments is generally bimodal, with granule cover and low thermal inertia. Three formation hypotheses were proposed for TARs: Megaripple hypothesis, reversing dune hypothesis and dust induration hypothesis, with more evidences supporting the megaripple hypothesis. Similar to dunes, TARs are geologically recent morphology on Mars, but generally predate dunes, formed in the last few million years so that most TARs are indurated or lithified and are immobile. However, contemporary mobileTARs are also developed in some regions. The unique features of TARs make them the mostenigmatic aeolian bedforms of Mars. It is proposed that high-resolution information on TARs sedimentology and integrated regional surveying should be listed in the priorities of future Mars exploration with respect to TARs study.