Size-dependent modification of asteroid family Yarkovsky V-shapes

摘要

The thermal properties of the surfaces of asteroids determine the magnitudeof the drift rate cause by the Yarkovsky force. In the general case of MainBelt asteroids, the Yarkovsky force is indirectly proportional to the thermalinertia, $\Gamma$. Following the proposed relationship between $\Gamma$ andasteroid diameter $D$, we find that asteroids' Yarkovsky drift rates might havea more complex size dependence than previous thought, leading to a curvedfamily V-shape boundary in semi-major axis, a, vs. 1/$D$ space. This impliesthat asteroids are drifting faster at larger sizes than previously considereddecreasing on average the known ages of asteroid families. The V-Shapecurvature is determined for $>$25 families located throughout the Main Belt toquantify the Yarkovsky size-dependent drift rate. We find that there is nocorrelation between family age and V-shape curvature. In addition, the V-shapecurvature decreases for asteroid families with larger heliocentric distancessuggesting that the relationship between $\Gamma$ and $D$ is weaker in theouter MB possibly due to homogenous surface roughness among family members.