Abstract
AbstractWe report the aeolian changes observed in situ by NASA's InSight lander during the first 400 sols of operations: Granule creep, saltation, dust removal, and the formation of dark surface tracks. Aeolian changes are infrequent and sporadic. However, on sols, when they do occur, they consistently appear between noon to 3 p.m., and are associated with the passage of convective vortices during periods of high vortex activity. Aeolian changes are more frequent at elevated locations, such as the top surfaces of rocks and lander footpads. InSight observed these changes using, for the first time, simultaneous in‐situ and orbital imaging and high‐frequency meteorological, seismological, and magnetic measurements. Seismometer measurements of ground acceleration constrain the timing and trajectory of convective vortex encounters, linking surface changes to source vortices. Magnetometer measurements show perturbations in magnetic field strength during the passage of convective vortices consistent with charged‐particle motion. Detachment of sand‐scale particles occurs when high background winds and vortex‐induced turbulence provide a peak surface friction wind speed above the classic saltation fluid threshold. However, detachment of dust‐ and granule‐scale particles also occurred when the surface friction wind speed remained below this threshold. This may be explained by local enhancement of the surface roughness and other effects described here and further studied in Part 2 (Baker et al., 2021). The lack of saltation and bright dust‐coated surfaces at the InSight landing site implies surface stability and the onset of particle motion may be suppressed by dust “cushioning.” This differentiates the InSight landing site from other areas on Mars that exhibit more aeolian activity.
Highlights
Wind is one of the most important geomorphological agents on present-day Mars (Bridges & Ehlmann, 2018; Bridges, Ayoub et al, 2012; Bridges, Bourke et al, 2012; Lapotre & Rampe, 2018)
We have identified consistent wind data gaps up to 5 s during near-lander vortex encounters, during the main episodic aeolian changes on sols 19, 26, 65, and 385
Around the time that these dark spots appeared, the ambient wind speed was 10 m s−1, with a corresponding surface friction wind speed of 0.63 m s−1, between the impact and fluid thresholds. This suggests that the putative saltating particles could have been sourced from an upwind region, perhaps from a distant vortex not detected by APSS measurements, with saltation sustained above the impact threshold
Summary
Wind is one of the most important geomorphological agents on present-day Mars (Bridges & Ehlmann, 2018; Bridges, Ayoub et al, 2012; Bridges, Bourke et al, 2012; Lapotre & Rampe, 2018). The surface friction wind speed predicted by atmospheric models and measured on the surface rarely exceeds this higher fluid threshold (Bridges et al, 2017; Kok et al, 2012; Newman et al, 2017), yet aeolian features and dust suspension are observed under present-day Martian atmospheric conditions (Bridges, Ayoub et al, 2012; Bridges, Bourke et al, 2012; Ewing et al, 2017; Greeley, Balme, et al, 2003; Greeley, Kuzmin, et al, 2003; Lapotre et al, 2016, 2018; Silvestro et al, 2010; Sullivan et al, 2008, 2005). Color lines are relative height contours with elevation intervals of 2 cm, showing a gentle slope of ∼2° to the SE
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