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

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

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, 188-191, 2008] 3/16

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]

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

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

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

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

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]

(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 = 140 +140/-100 J m-2 K-1 s-1/2 f = 60 ± 30 %

(1862) Apollo Yarkovsky/YORP Measured Yarkovsky: da/dt = -32.1 ± 3.4 m yr-1 Measured YORP: dω/dt = (7.3 ± 1.6) ×10-3 rad yr-2 ATPM Yarkovsky/YORP modelling determines: ρ = 2850 +480/-680 kg m-3 pv = 14 +21/-14 % dω/dt = (6.1 +3.2/-1.2) ×10-3 rad yr-2 dξ/dt = 1.5 +0.3/-0.5 °/105 yr

(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!

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

New Binary NEAs Studied

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