First Mars year of observations with the InSight solar arrays: Winds, dust devil shadows, and dust accumulation

Abstract

Solar array currents recorded on the InSight lander indicate a handful of faint (<1%) transient (<8 s) current drops, interpreted as shadows of passing dust devils, suggesting that a small fraction of the abundant convective vortices are visibly dust-laden. An area fraction of visible dust devils of 7E-7 to 1.4E-5 during the active part of the day is derived, consistent with the nondetection of dust devils in camera images (which suggest 1E-5 as an upper limit). This density of visible vortices is an order of magnitude lower than that observed at Gusev crater by the Spirit rover. Other variations in array currents (0.5–2%) and temperatures (up to 5 K) occur near mid-day with a period of 100–1000s, likely related to boundary layer convection modifying dust opacity and wind speed respectively. Daily peak currents evolve over the Martian year due to solar geometry, atmospheric dust opacity, and the accumulation of dust on the arrays. The latter effect (on average a 0.2% per Sol loss, consistent with previous missions) leading to visible dustiness of the arrays, has led to a fourfold drop in array currents after one Mars year, with no prominent cleaning events.