Matching asteroid population characteristics with a model constructed from the YORP-induced rotational fission hypothesis

Abstract

From the results of a comprehensive asteroid population evolution model, we conclude that the YORP-induced rotational fission hypothesis can be consistent with the observed population statistics of small asteroids in the main belt including binaries and contact binaries. The foundation of this model is the asteroid rotation model of Marzari et al. (2011), which incorporates both the YORP effect and collisional evolution. This work adds to that model the rotational fission hypothesis, described in detail within, and the binary evolution model of Jacobson and Scheeres (2011a,b). The asteroid population evolution model is highly constrained by these and other previous works, and therefore it has only two significant free parameters: the ratio of low to high mass ratio binaries formed after rotational fission events and the mean strength of the binary YORP (BYORP) effect.We successfully reproduce characteristic statistics of the small asteroid population: the binary fraction, the fast binary fraction, steady-state mass ratio fraction and the contact binary fraction. We find that in order for the model to best match observations, rotational fission produces high mass ratio (> 0.2) binary components with four to eight times the frequency as low mass ratio (< 0.2) components, where the mass ratio is the mass of the secondary component divided by the mass of the primary component. This is consistent with post-rotational fission binary system mass ratio being drawn from either a flat or a positive and shallow distribution, since the high mass ratio bin is four times the size of the low mass ratio bin; this is in contrast to the observed steady-state binary mass ratio, which has a negative and steep distribution. This can be understood in the context of the BYORP-tidal equilibrium hypothesis, which predicts that low mass ratio binaries survive for a significantly longer period of time than high mass ratio systems. We also find that the mean of the log-normal BYORP coefficient distribution µ B 10 −2 , which is consistent with estimates from shape modeling (McMahon and Scheeres, 2012a).

The solar nebula origin of (486958) Arrokoth, a primordial contact binary in the Kuiper Belt

“…Alternately, these apparent facets may have been caused by higher-velocity impacts and mass loss, such as have affected the asteroids (115), although a heliocentric impact explanation is not consistent with the dearth of large craters on the visible faces of LL and SL, save perhaps for the largest, "Maryland" (8). .=DE F @ A, where w, r, and R are the spin rate, density, and equivalent radius of the asteroid in question, L☉ is the solar luminosity, c is the speed of light, and F = ⨀ 01 − ⨀ ' K is the solar-flux-weighted mean heliocentric distance (77). In the table P is the rotation period, w/(dw/dt) is the spin-rate doubling time, and data sources are indicated.…”

“…Asteroid (1862) Apollo, at 1.5 km across and orbiting at 1.5 au, exhibits the largest, measured YORP coefficient (Y), with an estimated YORP spin doubling time scale of ~5 × 10 5 years for an assumed density of 2500 kg m -3 (Table S1). Accounting for the larger size of Arrokoth, its greater distance from the Sun, and its much lower density (77) lengthens this time scale to 7.5 ×10 9 years. This exceeds the age of the Solar System, and adopting any of the other (lower) Y values in Table S1 would imply even longer time scales for Arrokoth, by up to two orders of magnitude.…”

Shape model and spin-state analysis of PHA contact binary (85990) 1999 JV6 from combined radar and optical observations

“…We have shown that JV6 is a bilobed body, a representative of a class of asteroids called contact binaries. The contact binaries are estimated to make up between 15 and 35% of the NEA population (Benner et al , 2015Jacobson et al 2016). The estimated sizes of the NEA contact-binary population are based on reported radar detections of such asteroids, and not on the results of detailed shape modelling.…”

“…We collected additional light-curve data with associated programmes at the 0.6 m Table Mountain Observatory (TMO) telescope in California (USA) in 2015, and at the 2.5 m Isaac Newton Telescope (INT) in La Palma (Spain) in 2007, and 2016. Close approaches to Earth in 2015, 2016, and 2017 offered an opportunity to observe JV6 with groundbased radar facilities. We observed JV6 as the target of a dedicated Arecibo planetary radar campaign in January 2015, 2016, and 2017.…”

YORP effect on the evolution of asteroid spin states

“…2000年Rubincam [2] 提出YORP效应是小行星自旋加速的最主要动 力, 给出了YORP力矩的理论公式并实现YORP曲线和 小行星自转状态演化曲线的计算, 在YORP效应的研 究历史中具有里程碑意义. 其后, 有关YORP效应的新 研究成果大量涌现, 包括力矩对地形和质心的高度敏 感性 [6,7] , 小行星碎石堆结构与自转状态耦合变化 [8] , 由YORP加速效应导致的结构演化类型(包括失效 [9] 、 表面滑坡 [10] 、变形 [11] 或分裂 [12] ), 以及双小行星系统 的YORP效应(Binary YORP Effect) [13] 等.…”