ALBEDO AND THERMAL INERTIA AT JEZERO CRATER DURING THE
FIRST 350 SOLS OF THE MARS 2020 MISSION
G.M. Martínez, Lunar and Planetary Institute/USRA, USA (gmartinez@lpi.usra.edu), E. Sebastián, Centro de
Astrobiología, Spain, A. Vicente-Retortillo, Centro de Astrobiología, Spain, E. Fischer, University of Michigan, USA, D. Toledo, Instituto Nacional de Técnica Aeroespacial, Spain, F. Gómez, Centro de Astrobiología,
Spain, M.D. Smith, NASA Goddard Space Flight Center, USA, L. Mora-Sotomayor, Centro de Astrobiología,
Spain, H. Savijärvi, University of Helsinki, Finland, J.R. Johnson, John Hopkins University/APL, USA, V.
Apéstigue, Instituto Nacional de Técnica Aeroespacial, Spain, I. Arruego, Instituto Nacional de Técnica
Aeroespacial, Spain, L. Mandon, LGLTPE, France, R. Hueso, University of the Basque Country, Spain, A.
Munguira, University of the Basque Country, Spain, M. Ramos, Universidad de Alcalá de Henares, Spain,
C.E. Newman, Aeolis Research, USA, M.T. Lemmon, Space Science Institute, USA, A. Sánchez-Lavega,
University of the Basque Country, Spain, L.K. Tamppari, Jet Propulsion Laboratory, USA, O. Prieto, Centro
de Astrobiología, Spain, A. Molina, Centro de Astrobiología, Spain, T.H. McConnochie, Space Science Institute, USA, P. Conrad, Carnegie Institution for Science, USA, F. Jordan, Centro de Astrobiología, Spain, A.M.
Harri, Finnish Meteorological Institute, Finland, M. Genzer, Finnish Meteorological Institute, Finland, M.
Hieta, Finnish Meteorological Institute, Finland, J. Poulko, Finnish Meteorological Institute, Finland, M.P.
Zorzano, Centro de Astrobiología, Spain, M. Hecht, Massachusetts Institute of Technology, USA, M. Siegler,
Planetary Science Institute, USA, M. Torre-Juárez, Jet Propulsion Laboratory, USA, and J.A. RodríguezManfredi, Centro de Astrobiología, Spain.

Figure 1. MEDA coverage during the first 350 sols
of the M2020 mission.

1
0.8
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Ground Temp (K)

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Sol #
30 72 116 161 205 248 288 326

c)

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Solar Longitude (deg)

e)

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30 72 116 161 205 248 288 326
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30 72 116 161 205 248 288 326

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30 72 116 161 205 248 288 326

b)

Air Density (kg/m3)

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Solar Longitude (deg)

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Pressure (Pa)

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Solar Flux (W/m2)

Aerosol Opacity

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30 72 116 161 205 248 288 326

a)

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Solar Longitude (deg)

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30 72 116 161 205 248 288 326

g)
RH (%)

Environmental Context: MEDA’s nominal
measuring strategy consists of 1 Hz measurements
taken during 1h-5min-long blocks starting at
even/odd full hour local mean solar times (LMST)
on even/odd sol numbers (Fig. 1).

1.4

VMR (ppm)

Introduction: We use measurements from the
Mars Environmental Dynamics Analyzer (MEDA)
instrument [1] to obtain albedo and thermal inertia
(TI) during the first 350 sols of the Mars 2020 mission. MEDA is one of the seven scientific instruments onboard M2020 [2]. It includes six sensors
measuring the environmental conditions at Jezero
Crater, Mars (77.5945°E, 18.3628°N, -2656m).
MEDA’s Thermal Infrared Sensor (TIRS) and
Radiation and Dust Sensor (RDS) are providing
novel measurements of radiative fluxes [3–4], allowing for the first in situ estimation of the net radiative
balance on Mars [5]. These measurements include
TIRS’ downwelling atmospheric IR flux (6.5–30
μm), upwelling IR flux emitted by the surface (6.5–
30 μm), surface-reflected solar flux (0.3–3 μm), and
RDS’ downwelling solar flux (0.2–1.2 μm).
Along with TIRS’ ground temperature, these
measurements allow the direct estimation of broadband albedo (0.3–3 μm) and TI at spatial scales of a
few m2 without the need for numerical models.

0 20 40 60 80 100 120 140 160 180
Solar Longitude (deg)

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Sol #
30 72 116 161 205 248 288 326

f)

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Solar Longitude (deg)
Sol #
30 72 116 161 205 248 288 326

h)

0 20 40 60 80 100 120 140 160 180
Solar Longitude (deg)

Figure 2. (a) Aerosol opacity at 880 nm; (b) Daily
max downwelling solar flux (0.2–5 μm); (c–d) Daily
max, mean and min atmospheric pressure and air
density at 1.4 m; (e–f) Daily max, mean and min
atmospheric air temperature at 1.4 m and ground
temperature; (g) Daily max atmospheric relative
humidity at 1.4 m; (h) Nighttime (04:00-06:00) water vapor VMR at 1.4 m. First 350 sols of the M2020
mission.

Fig. 2 shows the environmental conditions at
Jezero Crater during the first 350 sols of the M2020
mission. This period covers most of the northern
spring and summer, with solar longitudes (Ls) ranging from 5° to 175°.
Most notably, a regional dust storm hit Jezero
Crater on sol 313 (Ls ~153°) and lasted for a few
sols, strongly altering the environmental conditions.

c)

Reflected SW Flux (W/m2)

0 20 40 60 80 100 120 140 160 180
Solar Longitude (deg)
Sol #
30 72 116 161 205 248 288 326

e)

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Solar Longitude (deg)

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Solar Longitude (deg)
Sol #
30 72 116 161 205 248 288 326

d)

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Solar Longitude (deg)

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6

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Ground Temp (K)

LMST (h)

Figure 4. Ground temperature on sol 30 as measured
by TIRS (black) and as obtained by solving the heat
conduction equation for homogeneous terrains using
MEDA measurements of the surface energy budget
as the upper boundary condition (red curve). TI =
230 Jm-2K-1s-½ (tiu) provides the best match.
Shortwave and longwave radiative fluxes in Fig.
3 are measured by TIRS and RDS, while the turbulent heat flux is derived using wind speed, pressure,
and air and ground temperature measurements in
combination with similarity theory [5].
We note that the field of view (FoV) of the two
downward-looking TIRS channels, which measure
ground temperature and reflected solar radiative flux,
covers an area of a few m2, but most of its signal
comes from a smaller area corresponding to center of
the FoV. This results in ground temperatures that,
unlike for the Mars Science Laboratory Ground
Temperature Sensor [5], adjust very well to homogeneous terrains (Fig. 4).
Albedo: Fig. 5 shows 5min-averaged values of
broadband albedo (0.3-3 μm) for the first 350 sols of
the M2020 mission as a function of LMST and rover’s yaw (0° indicating North; 90° East; -90° West;
and ±180° South). Only values when the solar zenith
angle (SZA) is below 60° are included (SZA = 0°
indicates local zenith), resulting in local mean solar
times (LMST) between 07:00 and 17:00.

Sol #
30 72 116 161 205 248 288 326

0.22

f)

150
0.2
100
0.18
50

0 20 40 60 80 100 120 140 160 180
Solar Longitude (deg)

0.16
0
0.14
-50
0.12
-100

Figure 3. Surface energy budget across the first 350
sols of the Mars 2020 mission. (a–b) Daily max
downwelling and surface-reflected solar flux (0.2–5
μm); (c–d) Daily max, mean and min downwelling
atmospheric IR flux, and upwelling IR flux emitted
by the surface (6–80 μm); (e) Daily max, mean and
min turbulent heat flux; (f) Daily max mean and min
net heat flux into the ground.

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-150
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7

8

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LMST

Figure 5. Albedo values measured by MEDA for the
first 350 sols of the mission as a function of LMST
and rover’s yaw (color bar). We note that TIRS’ FoV
is pointed +75° with respect to the rover’s yaw.

Yaw

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Sol #
30 72 116 161 205 248 288 326

b)

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Solar Longitude (deg)

Sol #
30 72 116 161 205 248 288 326

75

TIRS
TI=230

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Albedo

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30 72 116 161 205 248 288 326

a)

Upwelling IR Flux (W/m2)

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Net Heat Flux (W/m2)

Turbulent Heat Flux (W/m2)

Downwelling IR Flux (W/m2)

Downwelling SW Flux (W/m2)

Methodology to Obtain Albedo and TI: We
obtain broadband albedo (0.3–3 μm) using TIRS’
measurements of reflected solar flux (0.3–3 μm) and
RDS’ measurements of downwelling solar flux
(0.2–1.2 μm). To convert RDS fluxes to TIRS’
range, we use the radiative transfer model
COMIMART [6]. Additionally, we correct for the
effects of dust deposition on the RDS’ upward looking channels, which on average decreased measured
fluxes by ~5% prior to the dust storm.
We obtain thermal inertia by solving the heat
conduction equation for homogeneous terrains using
MEDA measurements of the surface energy budget
as the upper boundary condition (Fig. 3). For each
sol when the rover was parked, we obtain TI by
minimizing the difference between measured and
numerically simulated values of the diurnal amplitude of ground temperature (Fig. 4).

Sols 30; t = 0.49; a = 0.12
290
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270
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Regardless of the rover pointing and type of terrain, the albedo shows a strong non-Lambertian
behavior, with lowest values around local noon.
Fig. 6 shows near-noon (i.e., daily minimum) albedo values as a function of Ls and sol number,
together with the TIRS’ FoV for the sols with highest and one of the lowest albedos (sols 125 and 282).
Interestingly, the regional dust storm which occurred
between sols 313 and 319 (Ls~155°) decreased the
albedo dramatically, producing the lowest measured
albedos up to sol 350 (the rover was parked on sols
287–328). Dust lifting and sand transport occurred
during the storm, and we are investigating the potential processes for such a decrease in albedo.

630 tiu range. Departures between both data sets are
likely caused by the different spatial resolution (104
m2/px for THEMIS, and a few m2 for MEDA).

Figure 6. (Left) Near-noon albedo values for the
first 350 sols of the M2020 mission. (Right) FoV of
MEDA measurements of reflected solar flux corresponding to the terrains with the highest (sol 125)
and one of the lowest (sol 282) albedo values. Note
that the lowest albedo values were achieved on sols
319-323, right after the peak of the regional dust
storm.
Comparison to satellite estimations: Lambertian
values at Jezero in the 0.3–2.9 μm range retrieved
from satellite by TES with a ~300 km2 spatial resolution are ~0.15. These retrievals are made at 14:00
LTST (MGS was on a polar orbit). For comparison,
MEDA-derived albedo values at 14:00 LMST are
typically lower than 0.15 (see Fig. 5). This discrepancy is likely explained by the different spatial resolution between both datasets and the Lambertian
assumption, and it is subject of ongoing investigations which also include OMEGA observations [7].
Thermal Inertia: Fig. 7 shows TI values across
Perseverance’s traverse only for sols when the rover
was parked. TI values range between 200 and 630
tiu, with the lowest and largest TI values on sols 106
(sand) and 125 (bedrock), respectively.
On sols when the rover was parked in the same
location (e.g., sols 138–152 or 211–237), MEDAderived TI values typically vary less than ~5%, indicating that the method to obtain TI is robust.
Comparison to satellite estimations: Fig. 8 shows
TI values derived from THEMIS (squares) and
MEDA (circles). While THEMIS values range between 200 and 450 tiu, MEDA values are in the 200–

Latitude (deg)

18.46

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200

18.45
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77.46

Thermal Inertia (TI Units)

Figure 7. (Left) Thermal inertia values for the first
350 sols of the M2020 mission when the rover was
parked for an entire sol. (Right) FoV of MEDA
measurements of ground temperature on sols 106
and 125, corresponding to the terrains with the lowest and highest TI values.

77.48

Longitude (deg)

Figure 8. Thermal inertia map retrieved from
THEMIS (squares) and MEDA (circles). The black
line represents the rover’s traverse for the first 350
sols.
Thermophysical Surface Units: Comparison of
thermal inertia and albedo can provide insight into
the characteristics of the surface materials, and it can
be used to delineate and characterize different surface units.
Fig. 9 shows combined values of TI and albedo
for the first 350 sols of the M2020 mission. In general, there is a positive correlation between both
quantities, although there are clusters of points that
deviate from this behavior (e.g., low albedo and
medium TI). Interesting relationships among the
values and surface materials are identified. These
analyses are subject of ongoing investigations.
Summary and Conclusions: MEDA’s novel
measurements of the net radiative balance at the
surface of Mars (Fig. 3) allow for the direct estimation of thermal inertia and broadband albedo across
Perseverance’s traverse.
Depending on the type of terrain, near-noon albedo values vary between 0.09 and 0.16 (Fig. 6),
while thermal inertia varies between 200 and 630 tiu
(Fig. 7).

Regardless of the type of terrain and rover geometry, the albedo shows a strong non-Lambertian
behavior, (Fig. 5) with lowest values near noon when
the solar zenith angle is lowest (sun closest to zenith).
Comparison of thermal inertia and albedo values
derived from MEDA and satellites indicate significant departures likely caused by the different spatial
resolution of both datasets (Fig. 8).
Analyses of correlations between thermal inertia
and albedo values can be used to delineate different
surface units (Fig. 9).

Thermal Inertia (TI units)

700
600
500
400
300
200
100
0.08 0.09 0.1 0.11 0.12 0.13 0.14 0.15 0.16 0.17
Albedo

Figure 9. Thermal inertia and albedo during the first
350 sols of the M2020 mission.
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