On the ages of resonant, eroded and fossil asteroid families

Abstract

In this work we have estimated 10 collisional ages of 9 families for which for different reasons our previous attempts failed. In general, these are difficult cases that required dedicated effort, such as a new family classifications for asteroids in mean motion resonances, in particular the 1/1 and 2/1 with Jupiter, as well as a revision of the classification inside the 3/2 resonance.Of the families locked in mean motion resonances, by employing a numerical calibration to estimate the Yarkovsky effect in proper eccentricity, we succeeded in determining ages of the families of (1911) Schubart and of the "super-Hilda" family, assuming this is actually a severely eroded original family of (153) Hilda. In the Trojan region we found families with almost no Yarkovsky evolution, for which we could compute only physically implausible ages. Hence, we interpreted their modest dispersions of proper eccentricities and inclinations as implying that the Trojan asteroid families are fossil families, frozen at their proper elements determined by the original ejection velocity field. We have found a new family, among the Griquas locked in the 2/1 resonance with Jupiter, the family of (11097) 1994 UD1.We have estimated the ages of 6 families affected by secular resonances: families of (5) Astraea, (25) Phocaea, (283) Emma, (363) Padua, (686) Ger- suind, and (945) Barcelona. By using in all these cases a numerical calibration method, we have shown that the secular resonances do not affect significanly the secular change of proper a. For the family of (145) Adeona we could estimate the age only after removal of a number of assumed interlopers.With the present paper we have concluded the series dedicated to the determination of asteroid ages with a uniform method. We computed the age(s) for a total of 57 families with > 100 members. For the future work there remain families too small at present to provide reliable estimates, as well as some complex families (221, 135, 298) which may have more ages than we could currently estimate. Future improvement of some already determined family ages is also possible by increasing family membership, revising the calibrations, and using more reliable physical data.

Transit of asteroids across the 7/3 Kirkwood gap under the Yarkovsky effect

“…Similar phenomenon has been observed, e.g. in the 3/2 MMR with Jupiter (Milani et al 2017) and in the 1/1 MMR with the Earth . But the J7/3 MMR studied in this paper, as a 4th-order resonance and under the influences of complicated perturbations from other planets in the dynamical model, is relatively weak in term of dynamical effect.…”

Population control of Mars Trojans by the Yarkovsky & YORP effects

“…This will either confirm the lack of families of 101429 and 121514 or find their brightest members, if they exist. In addition, because the path in the space of libration amplitude vs inclination is deterministic (Ćuk et al, 2015), an approach similar to those used in Milani et al (2017) and Brož and Morbidelli (2019) to place bounds on ages of asteroid families in resonances will further constrain the Eureka family age and help remove one of the principal unknowns in the effort to understand the Martian Trojans. Farinella et al (1998).…”

The Sporadic Activity of (6478) Gault: A YORP-driven Event?

“…Gault is a dynamical member of the Phocaea family (Nesvorny 2015), which has been estimated to be (1.2 ± 0.3) Gyr old (Milani et al 2017). The Phocaea region is a high-eccentricity, high-inclination portion of the inner asteroid belt dominated by S-type asteroids (Carvano et al 2001) and is bounded by the 3:1 and 4:1 mean- Figure 3.…”