Dust deposition and lifting at the Zhurong landing site

Introduction

Dust deposition poses the challenges to the survival of instruments and solar-powered missions on Mars [1, 2]. Zhurong in-situ observations provide an opportunity to study dust dynamics. Here, we present the dust evolution at the Zhurong landing site by means of the deposited optical depth on the Multispectral Camera (MSCam) calibration target and dust factor measured by the solar panels.

In-situ observation

MSCam calibration target observation: the deposited dust would modify the reflectance properties of the MSCam calibration target. A dust correction model based on the two-layer radiative transfer model [3, 4] is applied to estimate the dust deposited optical depth on the MSCam calibration targets.

Solar panel observation: the progressive deposition of dust can also decline the solar panel current output. We calculate the dust factor, indicating the ratio of the measured power output to that of an array without any dust [5], to measure the dust accumulation on the rover.

Results and discussion

The dust deposited optical depths on the MSCam calibration target are very low for the first 110 sols (Fig. 1a), suggesting that there is almost no dust deposited on the calibration target or the deposited dust is too thin to modify the reflectance of the calibration targets. After the solar conjunction, dust starts to accumulate on the calibration target with a deposition rate of 0.12%-0.19% per sol. The dust factor derived from the solar panel exhibits a similar trend with the observation from the MSCam calibration target (Fig. 1b). The dust factor shows a relatively slow decrease for the first 200 sols with an exponential decay of 0.07% per sol but a severe decline after Sol 200 with a rate of 0.46% per sol .

The two separate observations reveal two distinct dust deposition stages at the Zhurong landing site: very slow dust deposition for the initial 200 sols, then followed by a significant acceleration in dust deposition rate after Sol 200. The increasing deposited optical depth and declining dust factor also suggest the lack of dust cleaning events during the 300 sols’ traverse.

Fig. 1 (a) The deposited optical depth on the MSCam calibration target as a function of time [6]. (b) dust factor derived from solar panels as a function of time [7]. The two vertical gray dashed lines represent the last MSCam observation before the solar conjunction and first observation after the solar conjunction, respectively. The black lines are dust factor exponential decline of two different stages, and the black dashed line shows a 0.18% per sol exponential decline of the first 300 sols observations.

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