1. Thermal Inertia of Binary Near-Earth Asteroids
Ben Rozitis
with E.C. Brown, S.F. Green, S.C. Lowry, A. Fitzsimmons,
A. Rozek, C. Snodgrass, P. Weissman & T. Zegmott

2. Binary Formation by YORP
Fast
Slow
Produces fast and slow rotators in short timescales
Deforms the asteroid shape
Can cause asteroids to lose material and form a binary asteroid
2/16

3. N-Body Simulation Numerical simulation of binary asteroid formation
Spherical test particles under gravity with YORP spin-up
Top view
Side view
[Walsh et al. Nature 454, , 2008]
3/16

4. N-Body Simulation
Produces orbit and shape consistent with observed NEA binaries
1999 KW4 radar model, Ostro et al. 2005
[Ostro et al., Science 314, 1276, 2006]

5. Regolith Left Behind? YORP spin-up No cohesion – small grains lost
Large regolith grains
Cohesion – large grains lost
Initial body with small and large regolith grains
Small regolith grains
5/16

6. Thermal Inertia
Is a measure of a material’s resistance to temperature change
Can infer the presence or absence of loose material on a planetary surface
Thermal Inertia
Specific Heat Capacity
Density
Heat Conductivity
Lunar Regolith
Coarse Sand
Metal Rich Asteroidal Fragments
Pebbles
Solid Rock
Increasing Thermal Inertia

7. Temperatures and fluxes
Γ = 10
Γ = 200 80
160
240
320
400
Temperature (K)
Sun
Γ = 750
Γ = 2200

8. Delbo et al. NEATM Modelling
Solitary NEAs: 200 ± 40 J m-2 K-1 s-1/2 [Delbo et al. Icarus, 190, 238, 2007]
Binary NEAs: 480 ± 70 J m-2 K-1 s-1/2 [Delbo et al. Icarus, 212, 138, 2011]
Binary NEAs
Solitary NEAs

9. ATPM Thermal Modelling
Direct Sunlight
Scattered Sunlight
Re-absorbed Thermal Radiation
Conducted Heat
The Sun
Planetary Body
Thermal Radiation Lost To Space
Model geometry including scattered light and re-absorbed thermal radiation
Surface boundary condition
Total Incident Flux
Thermal Inertia
Heat Conducted
Radiated Energy
[Rozitis & Green, MNRAS, 415, 2042, 2011]

10. (1862) Apollo Thermal-IR
Strong detections of Yarkovsky orbital drift and YORP rotational acceleration, and has a diverse observational dataset
[Rozitis et al. A&A, 555, A20, 2013]
ATPM fitting determines:
D = 1.55 ± 0.07 km pv = 0.20 ± 0.07
Γ = /-100 J m-2 K-1 s-1/2 f = 60 ± 30 %

11. (1862) Apollo Yarkovsky/YORP
Measured Yarkovsky: da/dt = ± 3.4 m yr-1
Measured YORP: dω/dt = (7.3 ± 1.6) ×10-3 rad yr-2
ATPM Yarkovsky/YORP modelling determines:
ρ = /-680 kg m-3 pv = /-14 %
dω/dt = ( /-1.2) ×10-3 rad yr-2 dξ/dt = /-0.5 °/105 yr

12. (175706) 1996 FG3 Marco Polo-R target asteroid for sample return
Observed by Stephen Wolters in January 2011 using VLT
[Wolters et al. MNRAS, 418, 1246, 2011]
ATPM modelling derived a thermal inertia of 120 ± 50 J m-2 K-1 s-1/2
Likely to be a regolith for sampling!

13. Shape from Shepard et al. [Icarus 184, 198, 2006]
(276049) 2002 CE26
Shape from Shepard et al. [Icarus 184, 198, 2006]
C-type binary asteroid
D = 3.5 km, Prot = 3.29 hr
NEOWISE observations and ATPM modelling give:
Γ = 50 ± 30 at 2.98 AU
Γ = 100 ± 30 at 1.84 AU
Γ = 170 ± 30 at 1.32 AU
Rozitis et al. MNRAS, 477, 1782, 2018 13

14. New Binary NEAs Studied

15. Results and conclusions
Sorry – not for public consumption yet
See Rozitis et al. presentation at EPSC and published paper to follow