Asteroid families are valuable source of information to many asteroid-related researches, assuming a reliable list of their members could be obtained. However, as the number of known asteroids increases fast it becomes more and more difficult to obtain robust list of members of an asteroid family. Here we are proposing a new approach to deal with the problem, based on the well known Hierarchical Clustering Method (HCM). An additional step in the whole procedure is introduced in order to reduce a so-called chaining effect. The main idea is to prevent chaining through an already identified interloper. We show that in this way a number of potential interlopers among family members is significantly reduced. Moreover, we developed an automatic on-line based portal to apply this procedure, i.e to generate a list of family members as well as a list of potential interlopers. The Asteroid Families Portal (AFP) is freely available to all interested researchers.
Context. Asteroids smaller than about 100 m in diameter are observed to rotate very fast, with periods often much shorter than the critical spin limit of 2.2 h. Some of these super-fast rotators can also achieve a very large semimajor axis drift induced by the Yarkovsky effect, which, in turn, is determined by internal and surface physical properties. Aims. We consider here a small super-fast-rotating near-Earth asteroid, designated as 2016 GE1. This object rotates in just about 34 s, and a large Yarkovsky effect has been determined from astrometry. By using these results, we aim to constrain the thermal inertia of the surface of this extreme object. Methods. We used a recently developed statistical method to determine the thermal properties of near-Earth asteroids. The method is based on the comparison between the observed and the modeled Yarkovsky effect, and the thermal conductivity (inertia) is determined via a Monte Carlo approach. Parameters of the Yarkovsky effect model are fixed if their uncertainty is negligible, modeled with a Gaussian distribution of the errors if they are measured, or deduced from general properties of the population of near-Earth asteroids when they are unknown. Results. Using a well-established orbit determination procedure, we determined the Yarkovsky effect on 2016 GE1 and confirm a significant semimajor axis drift rate. Using a statistical method, we show that this semimajor axis drift rate can only be explained by low thermal inertia values below 100 J m−2 K−1 s−1/2. We benchmarked our statistical method using the well-characterized asteroid Bennu and find that only knowing the semimajor axis drift rate and the rotation period is generally insufficient for determining the thermal inertia. However, when the statistical method is applied to super-fast rotators, we find that the measured Yarkovsky effect can be achieved only for very low values of thermal inertia: namely, 90% of the probability density function of the model outcomes is contained at values smaller than 100 J m−2 K−1 s−1/2. Conclusions. We propose two possible interpretations for the extremely low thermal inertia of 2016 GE1: a high porosity or a cracked surface, or a thin layer of fine regolith on the surface. Though both possibilities seem somewhat unexpected, this opens up the possibility of a subclass of low-inertia, super-fast-rotating asteroids.
In this work we investigate the orbital distribution of interstellar objects (ISOs), observable by the future wide-field National Science Foundation Vera C. Rubin Observatory (VRO). We generate synthetic population of ISOs and simulate their ephemerides over a period of 10 years, in order to select those which may be observed by the VRO, based on the nominal characteristics of this survey. We find that the population of the observable ISOs should be significantly biased in favor of retrograde objects. The intensity of this bias is correlated with the slope of the size-frequency distribution (SFD) of the population, as well as with the perihelion distances. Steeper SFD slopes lead to an increased fraction of the retrograde orbits, and also of the median orbital inclination. On the other hand, larger perihelion distances result in more symmetric distribution of orbital inclinations. We believe that this is a result of Holetschek’s effects, which is already suggested to cause observational bias in orbital distribution of long period comets. The most important implication of our findings is that an excess of retrograde orbits depends on the sizes and the perihelion distances. Therefore, the prograde/retrograde orbits ratio and the median inclination of the discovered population could, in turn, be used to estimate the SFD of the underlying true population of ISOs.
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