Yarkovsky-driven spreading of the Eureka family of Mars Trojans

Abstract

Out of nine known stable Mars Trojans, seven appear to be members of an orbital grouping including the largest Trojan, Eureka. In order to test if this could be a genetic family, we simulated the long term evolution of a tight orbital cluster centered on Eureka. We explored two cases: cluster dispersal through planetary gravity alone over 1 Gyr, and a 1 Gyr evolution due to both gravity and the Yarkovsky effect. We find that the dispersal of the cluster in eccentricity is primarily due to dynamical chaos, while the inclinations and libration amplitudes are primarily changed by the Yarkovsky effect. Current distribution of the cluster members orbits are indicative of an initially tight orbital grouping that was affected by a negative acceleration (i.e. one against the orbital motion) consistent with the thermal Yarkovsky effect. We conclude that the cluster is a genetic family formed either in a collision or through multiple rotational fissions. The cluster's age is on the order of 1 Gyr, and its long-term orbital evolution is likely dominated by the seasonal, rather than diurnal, Yarkovsky effect. If confirmed, Gyr-scale dominance of the seasonal Yarkovsky effect may indicate suppression of the diurnal Yarkovsky drift by the related YORP effect. Further study of Mars Trojans is essential for understanding the long-term orbital and rotational dynamics of small bodies in the absence of frequent collisions.

Asteroid (469219) 2016 HO3, the smallest and closest Earth quasi-satellite

“…Di Sisto, Ramos & Beaugé 2014;Wong, Brown & Emery 2014), Mars (see e.g. Marzari et al 2002;Connors et al 2005;Scholl, Marzari & Tricarico 2005;Ćuk, Christou & Hamilton 2015) or Neptune (see e.g. Parker 2015;Gerdes et al 2016).…”

Population control of Mars Trojans by the Yarkovsky & YORP effects

“…These amplitudes are relatively immune to change by the Yarkovsky effect ( Ćuk et al, 2015) and a good proxy for the original orbits of the family members. For the Eureka family, the spread in amplitudes translates into a velocity spread of < 3 m s −1 ( Ćuk et al, 2015;, comparable to the escape velocity from Eureka (∼ 1 m s −1 for a bulk density ρ = 1 − 3 g cm −3 ). This implies a gentle separation from the primary which is consistent with the YORP fission and escape scenario but more difficult to reconcile with an impact origin.…”

Is the Eureka cluster a collisional family of Mars Trojan asteroids?

“…The sample distribution moments are, however, very similar; the respective means and standard deviations are 2.95 ± 0.58 m s −1 and 2.79 ± 0.50 m s −1 . Therefore, this procedure may also be thought of as alternative method to calculate Trojan libration amplitudes (Milani, 1993;Ćuk et al, 2015) and we can use the new estimates to test the correlation found by Ćuk et al with the mean orbital inclinations. We find, as those authors did, that the two are negatively correlated but more weakly so (R 2 =0.17 vs 0.83 for that first set of libration amplitudes).…”