Observing the Yardang unit at Gale crater on Mars with ChemCam’s RMI

The Remote Microscopic Imager (RMI) of the ChemCam instrument onboard Curiosity rover provides high-resolution imaging capabilities [1,2]. RMI was first designed to document the LIBS analysis on rocks and soils located at few meters from the rover. RMI progressively proved also to be a powerful long distance imaging reconnaissance tool, thanks to its 700mm focal length. In particular, a new software was uploaded in 2015 to automatically focus up to infinity, a capability which was not implemented in the original design [3].  

Since then, RMI has been regularly used to investigate distant various landscapes. Among these, the so-called « Light-toned Yardang unit » [4] was first observed beginning sol 1183 (Figure 1). Several RMI image mosaics acquired up to Sol 1998 helped to identify successive sequences of aeolian deposition-erosion. This is among the youngest sedimentary layers that can be observed in Gale crater with Curiosity cameras. It is interpreted as a succession of fossil aeolian dunes and deflation surfaces [4, 5]. The Yardang unit could result from cyclic changes from semi-arid to arid conditions, including wind regime changes. No hydrated mineral has been detected from orbital imaging spectroscopy. Still, there is interest in finding out the role that water may have played in the induration and diagenesis of the rocks that make up this Yardang unit[5].

Between Sols 3671 and 4389, several new long distance RMI mosaics have been acquired while pointing at the base of the Yardang unit. The closer vantage point helps to identify multiple morphologies such as fine-scale layering, wind erosion patterns, or scallops. These features were not accessible nor resolved from orbital imagery only. They could shed light on the formation process of this massive unit. Figure 2 shows an example of a 10800x3200 pixels mosaic corresponding to an assemblage of 60 individual RMI frames which were acquired during three 20x1 sequences between Sols 4384 and 4389.

Curiosity has already driven 34 km since the landing in 2012. If Curiosity ever reaches the base of the Yardang unit [6], it would provide the opportunity to sample it directly and reveal its bulk composition, in addition to deriving information from distant geomorphological investigations. 

Fig. 1: Imaging of the Yardang unit. The white line corresponds to Curiosity’s traverse. The first RMI observation toward the Yardangs occurred on Sol 1183. More systematic close-range observations were acquired later on, in particular between sols ~4000 and 4389, revealing fine-scale details on the morphologies. 

Fig. 2: RMI mosaic of sequences CCAM02386, CCAM02384 and CCAM02389 acquired between Sols 4384 and 4389, and showing fine-scale layering, wind erosion patterns, or scallops.

 

References:

[1] Maurice et al., Space Sci. Rev. 170, 95-166, 2012.

[2] Le Mouélic et al., Icarus 249, 93-107, 2015.

[3] Perret et al., 14th International Conference on Space Operations, 2016.

[4] Le Deit et al., J. Geophys. Res. Planets, 118, 2439-2473, 2013.

[5] Dromart et al., EPSL 554, 116681, 2021.

[6] Vasavada et al., 56^th LPSC, 2025.