Footprints of the YORP effect in asteroid families

Abstract

The YORP effect affects not only the rotation rate, but also the spin orientation of asteroids. For this reason, due to Yarkovsky effect, it influences also the evolution of the semimajor axis with time. In asteroid dynamical families, the combined outcome can be a depletion of objects in the central part of the family, shown by the absolute magnitude vs. semimajor axis so-called V-plot. A reclassification of asteroid families, extended to a very large database of proper elements, has recently been performed by Milani et al. [2014] (Icarus, 239, 46-73). Only some of the related V-plots, used to estimate the age of several families, exhibit the depletion predicted above. In this paper we discuss the problem, introducing the concept of the YORP-eye and a general method of analysis. We show that the effect may sometimes be located in the low H tail, and thus difficult to detect. Moreover, it may be hindered by several anomalous physical properties of the family (asymmetry, cratering origin, multiple collisions history and so on). With a new method of analysis, we identify the footprints of the effect for most of the analysed families, obtaining also an independent estimate of the age of the family. In spite of the uncertainties, we obtain a very good agreement between these ages and those estimated on the basis of the slope of the V-plot: a result which supports both methods and the underlying physics

The Maria asteroid family

“…11, we report the time behaviour of the values of A S for our simulated family as a function of time. Our results showed good agreement with the age estimated by Spoto et al (2015), Paolicchi & Knežević (2016) and Carruba & Nesvorný (2016). The figure shows two different peaks: one after 1750 −231 +537 Myr and the other after 2100 −254 +590 Myr of the parent body's break-up, which could be related to some numerical artefact in the SWIFT package.…”

Asteroid cratering families: recognition and collisional interpretation

“…The problem which is not solved by the model above is that the number density as a function of proper a is highly variable, with two peaks around a = 3.12 and 3.16 au. The gap around a = 3.145 is due to the g − g 6 resonance, not to the YORP eye, which would be located in a nearly empty region of comparatively large bodies (Paolicchi & Knežević 2016).…”

“…Please note that we cannot use the information from the distribution for the proper a of the family members because these are affected by nongravitational Yarkovsky (Spoto et al 2015) and YORP (Paolicchi & Knežević 2016) effects acting over the age of the family. Therefore the distribution of proper a does not at all represent the original distribution of relative velocities in the direction along track (apart for the case of recent families, with age < 10 Myr), but mostly contains information which can be used to compute the ages.…”

Solar system science with the Wide-Field Infrared Survey Telescope

“…The study of asteroid families within the main asteroid belt, which represent disrupted parent bodies or swarms of fragments ejected from a parent asteroid's surface, informs compositional, taxonomic, and dynamical questions concerning asteroid family origin and evolution [166][167][168]. In particular, questions concerning actually genetic family membership, the presence of interlopers (i.e., non-genetic family members) among a family population, family space weathering trends, and the ability of asteroid taxonomies to correctly identify family members are issues that must be addressed to accurately determine the distribution and abundance of genetic asteroid family members [169][170][171][172][173][174][175]. Only through accurate identification of family members that originated from their respective parent asteroids can rigorous compositional and dynamical studies of individual families be conducted.…”