Temperatures of Marco Polo Mission Targets Marco Delbo, Patrick Michel June 5, 2008 Observatoire de la Côte d Azur; Laboratoire Cassiopée with contributions from: A. Barucci, D. Koschny Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 1 / 24
Table of contents Temperature of Marco Polo s targets: Outline 1 Parameters that influence surface temperatures 2 Thermophysical parameters geology of the surface 3 How do we derive/calculate temperatures: thermophysical models 4 Surface and sub surface (regolith) temperature (surface operations, sample extraction) 5 Thermal evolution (orbital evolution) 6 Discussion, future observations and instruments needs Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 2 / 24
Parameters that influence asteroid surface temperatures Parameters that influence asteroid surface temperature Heliocentric distance (r) Bolometric Albedo (A) Rotation period (T) Direction of rotation axis (λ P,β P ) Thermal inertia (Γ = ρκc) heat diffusion in the regolith Surface roughness (e.g. craters) small scale multiple scattering Gross shape (shadows) Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 3 / 24
Parameters that influence asteroid surface temperatures Asteroid surface temperature vs. heliocentric distance 1400 Low thermal inertia High thermal inertia 1200 1000 Temperature (K) 800 600 400 200 0 0.1 1 10 Heliocentric distance (AU) Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 4 / 24
Surface temperature of Marco Polo s targets Surface temperature of 1999 JU 3 for different values of Γ Effect of thermal inertia and asteroid rotation 400 350 TI=0 TI=50 TI=300 TI=2500 300 Surface Temperature (K) 250 200 150 100 Thermal Inertia 50: Moon soil 300: km-sized NEAs 2500: Basalt 50 0 0 0.2 0.4 0.6 0.8 1 Rotation phase Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 5 / 24
Thermal inertia and regolith Thermal inertia (Γ) and asteroid surface nature Thermal inertia gives information about the presence (or absence), depth and thickness of regolith, and the presence of exposed rocks on the surface of atmosphere less bodies (Γ in SI units: Jm 2 s 0.5 K 1 ). 25143 Itokawa 433 Eros The moon 1 Ceres Γ = 600 Γ = 150 Γ = 50 Γ = 10 Coarse regolith Finer and thicker Mature and Very fine and boulders regolith fine regolith regolith?? Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 6 / 24
Thermal inertia and regolith Close up of asteroids regolith: Itokawa Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 7 / 24
Thermal inertia and regolith Close up of asteroids regolith: Itokawa Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 8 / 24
Thermal inertia and regolith Close up of asteroids regolith: (433) Eros Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 9 / 24
Thermal inertia and regolith Close up of asteroids regolith: (433) Eros Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 10 / 24
Thermophysical Models Thermophysical Models 1 Thermophysical Model ( 96-07) Lagerros 1996; Delbo 2004; Mueller 2007 2 ρc T(r i,t) t k 2 T(r i,t) r 2 i = 0 3 Parameters: size, albedo, thermal inertia (Γ), surface roughness (θ). 4 Required: shape, spin state. Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 11 / 24
Thermophysical Models How thermal inertia is derived: thermophysical modeling Models parameters are: 1 object size 2 surface roughness 3 thermal inertia Chi squared 70 60 50 40 30 no roughness low roughness medium roughness high roughness They are adjusted to yield the best fit to the IR data. 20 10 10 100 1000 Thermal Inertia (SI units) Delbo and Tanga, 2008; Mueller, 2007 (Ph.D. thesis) Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 12 / 24
Thermophysical Models Surface temperature of 1989 UQ 500 (65679) 1989 UQ 400 Temperature (K) 300 200 Perihelion Aphelion 100 Midday 0 0.0 0.2 0.4 0.6 0.8 1.0 Rotational phase Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 13 / 24
Sub soil temperature Subsoil temperature (1999 JU 3 ): Γ = 300Jm 2 s 0.5 K 1 380 360 Regolith temperature of 1999JU3 (Gamma=300 S.I.; r=0.96 AU; T=7.5h) Midday Midnight 340 Temperature (K) 320 300 280 260 240 220 0 0.05 0.1 0.15 0.2 0.25 0.3 Regolith depth (m) Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 14 / 24
Orbital evolution of Marco Polo targets 2001 SG 286 Variation of the orbital elements with time (1 clone). 2.5 Semimajor axis (AU) 2.5 1 Semimajor axis (AU) 1 2 2 0.8 0.8 Semimajor axis (AU) 1.5 1.5 Orbital eccentricity (e) 0.6 0.4 0.6 0.4 1 1 0.2 0.2 0.5 0.5 0 1e+06 2e+06 3e+06 4e+06 5e+06 6e+06 Time (years) 0 0 0 1e+06 2e+06 3e+06 4e+06 5e+06 6e+06 Time (years) Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 15 / 24
Thermal evolution of Marco Polo targets 2001 SG 286 600 Temperature Perihelion distance 2.5 500 2 Max surface Temperature (K) 400 300 1.5 1 Perihelion distance (AU) 200 0.5 100 0 1e+06 2e+06 3e+06 4e+06 5e+06 6e+06 0 Time (years) Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 16 / 24
Thermal evolution of Marco Polo targets 2001 SK 162 600 Temperature Perihelion distance 1.3 1.2 500 1.1 Max surface Temperature (K) 400 300 1 0.9 0.8 0.7 0.6 Perihelion distance (AU) 200 0.5 0.4 100 0.3 0 2e+06 4e+06 6e+06 8e+06 1e+07 1.2e+07 1.4e+07 1.6e+07 1.8e+07 Time (years) Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 17 / 24
Thermal evolution of Marco Polo targets 2001 SK 162 600 Temperature Perihelion distance 5 500 4 Max surface Temperature (K) 400 300 3 2 Perihelion distance (AU) 200 1 100 0 0 100000 200000 300000 400000 500000 600000 700000 800000 900000 Time (years) Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 18 / 24
Conclusion Concluding remarks 1 Knowledge of target temperature is important for surface operation: landing, sample collection... 2 Information about physical (e.g. spin state) and thermophysical parameters (e.g. thermal inertia) are required for accurate thermophysical modeling. Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 19 / 24
Conclusion Concluding remarks 1 Knowledge of target temperature is important for surface operation: landing, sample collection... 2 Information about physical (e.g. spin state) and thermophysical parameters (e.g. thermal inertia) are required for accurate thermophysical modeling. Follow up observations important! Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 19 / 24
Conclusion Concluding remarks 1 Knowledge of target temperature is important for surface operation: landing, sample collection... 2 Information about physical (e.g. spin state) and thermophysical parameters (e.g. thermal inertia) are required for accurate thermophysical modeling. Follow up observations important! On board thermal IR photometer/spectrometer! see O. Groussin s tomorrow talk! Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 19 / 24
Conclusion Concluding remarks 1 Knowledge of target temperature is important for surface operation: landing, sample collection... 2 Information about physical (e.g. spin state) and thermophysical parameters (e.g. thermal inertia) are required for accurate thermophysical modeling. Follow up observations important! On board thermal IR photometer/spectrometer! see O. Groussin s tomorrow talk! Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 19 / 24
Back up slides Backup slides Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 20 / 24
Asteroids thermal inertia The thermal inertia of asteroids Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 21 / 24
Asteroids thermal inertia Subsoil temperature (1999 JU 3 ): Γ = 300, 1000Jm 2 s 0.5 K 1 380 360 Regolith temperature of 1999JU3 (Gamma=300 and 1000 S.I.; r=0.96 AU; T=7.5h) Midday (Gamma=300) Midnight (Gamma=300) Midday (Gamma=1000) Midnight (Gamma=1000) 340 Temperature (K) 320 300 280 260 240 220 0 0.1 0.2 0.3 0.4 0.5 Regolith depth (m) Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 22 / 24
Asteroids thermal inertia Subsoil temperature (1989 UQ): low thermal inertia 330 320 310 Low TI; Perihelion; 3.0cm Low TI; Perihelion; 5.0cm Low TI; Aphelion; 3.0cm Low TI; Aphelion; 5.0cm Sub-Soil Temperature (K) 300 290 280 270 260 250 240 0 5 10 15 20 25 Time (hours) Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 23 / 24
Asteroids thermal inertia Subsoil temperature (1989 UQ): high thermal inertia 400 380 High TI; Perihelion; 3.2cm High TI; Perihelion; 5.4cm High TI; Aphelion; 3.2cm High TI; Aphelion; 5.4cm Sub-Soil Temperature (K) 360 340 320 300 280 260 0 5 10 15 20 25 Time (hours) Marco Delbo, Patrick Michel () Temperatures of Marco Polo Mission Targets June 5, 2008 24 / 24