Twilight mesospheric clouds in Jezero as observed by MEDA Radiation and
Dust Sensor (RDS)
Abstract
The Mars Environmental Dynamics Analyzer (MEDA) instrument, on board
the NASA’s Mars 2020 Perseverance rover, includes a number of sensors to
characterize the Martian atmosphere. One of this sensors is the
Radiation and Dust Sensor (RDS) that measures the solar irradiance at
different wavelengths and geometries. We analyzed the RDS observations
made during twilight for the period between sol 71 and 492 of the
mission (Ls 39◦-262◦) to characterize the clouds over the
Perseverance rover site. Using the ratio between the irradiance at
zenith at 450 and 750 nm, we inferred that the main constituent of the
detected high-altitude aerosol layers was ice from Ls= 39◦ to 150◦
(cloudy period), an dust from Ls 150◦-262◦. A total of 161
twilights were analyzed in the cloudy period using a radiative transfer
code and we found: i) signatures of clouds/hazes in the signals in the
58 % of the twilights; ii) most of the clouds had altitudes between
40-50 km, suggesting water ice composition, and had particle sizes
between 0.6 and 2 μm; iii) the cloud activity at sunrise is
slightly higher that at sunset, likely due to the differences in
temperature; iv) the time period with more cloud detections and with the
greatest cloud opacities is during Ls 120◦-150◦; and v) a
notable decrease in the cloud activity around the aphelion, along with
lower cloud altitudes and opacities. This decrease in cloud activity
indicates lower concentrations of water vapor or cloud condensation
nuclei (dust) around this period in the Martian mesosphere.