Determining surface characteristics at candidate MSL landing sites using
THEMIS high-resolution orbital thermal inertia data
Robin Fergason
Philip Christensen
MSL Landing Site Selection Workshop
May 31, 2006
Thermal Inertia Background
• Used to infer a particle size of the surface layer
• Helps to identify features, their location and extent on the surface, and their particle size
• Detect exposed bedrock and dust
Exposed Bedrock
800260
67.6 E
Nili Patera
66.9 E8.7 N
9.5 N
Ares Valles
Rog
ers
et a
l., 2
005
Chr
iste
nsen
et a
l., 2
003a
; 200
5
950190
341.6 E341.3 E5.9 N
6.4 N
3.4 km 3.5 km
THEMIS-derived thermal inertia overlain onto THEMIS visible
Hebes Chasma Interior Layered Deposits
V10052001
800 m
TI: 190-245
TI: 275-360
TI: 290-420
TI: 125-145
125 615
Fergason et al., submitted
Thermal Inertia Background
• I = (ρkc)1/2
ρ – bulk density
k – conductivity
c – specific heat
• Thermal inertia measures a material’s resistance to change in temperature
THEMIS-derived thermal inertia
• Use thermal model developed by H. H. Kieffer– Ls, latitude, local time from spacecraft
ephemeris– TES-derived albedo (8ppd)– MOLA-derived elevations (128 epd)– TES-derived dust opacity (2 ppd) every 30° Ls
• Radiance at 12.57 μm (Band 9) is converted to brightness temperature, correcting for drift and wobble of the spacecraft
• Interpolate upon a 7-D look-up table
THEMIS-derived Thermal Inertia Uncertainties
• Uncertainties are primarily due to:
(1) instrument calibration
(2) uncertainties in model input parameters
(3) thermal model uncertainties
• Variations in thermal inertia within a single image are accurate and represent differences in the physical properties of the surface
Comparison with TES
25 600
180 E40 S
40 N
180 E180 E40 S
40 N
180 E
THEMIS
TES
Fergason et al., submitted
Comparison of Mini-TES and
THEMISThermal Inertia
Fergason et al., 2006
250 430
THEMIS and Mini-TES Thermal Inertia
0
500
1000
1500
0 10 20 30 40 50 60 70 80
Spirit - Gusev Landing Site Number
Th
erm
al In
erti
a
Mini-TES Thermal Inertia THEMIS Thermal Inertia
Landing Site Characterization
• Identify regions of very high or very low thermal inertia– TI > 400 likely has rocky surface [Nowicki, 2006]– TI < 100 is likely dusty and not drivable
• Evaluate surface properties of the candidate landing sites
• Predicted surface temperature for the primary mission– Rover design temperature limits: 145 - 310 K– Maximum diurnal temperature range: 145 K
Opportunity THEMIS Temperature Mosaic - 2003
Opportunity THEMIS Temperature Mosaic - 2006
63.2 E
570175
26.8 N
26.3 N62.6 E
Fergason et al., submitted
THEMIS Day and Night IR
Predicting Surface Temperature
1. Thermal inertia is derived from THEMIS image
2. The derived thermal inertia value is then used to calculate the surface temperature for a given local time and season
Can predict the minimum surface kinetic temperature during the primary mission
ASU Will Provide
• Interpretations of THEMIS and TES thermal inertia data for all candidate landing sites
• Thermal inertia mosaics of candidate landing site regions (100 m)
– Relative thermal inertia values
ASU Will Provide
• Individual thermal inertia images of specific areas of interest (100 m)
– Thermal inertia values of specific morphologies
• Predicted temperature maps of candidate landing site regions (100 m)
– Predict range of temperatures– Derive maximum diurnal temperature range
