`Oumuamua as a messenger from the Local Association

7 pages, one table, two figures, accepted for publication by ApJL. © 2018. The American Astronomical Society. All rights reserved.With a hyperbolic trajectory around the Sun, 'Oumuamua is the first confirmed interstellar object. However, its origin is poorly known. By simulating the orbits of 0.23 million local stars, we find 109 encounters with periastron less than 5 pc. 'Oumuamua's low peculiar velocity is suggestive of its origin from a young stellar association with similar velocity. In particular, we find that 'Oumuamua would have had slow encounters with at least five young stars belonging to the Local Association, thus suggesting these as plausible sites for formation and ejection. In addition to an extremely elongated shape, the available observational data for 'Oumuamua indicates a red color, suggestive of a potentially organic-rich and activity-free surface. These characteristics seem consistent with formation through energetic collisions between planets and debris objects in the middle part of a young stellar system. We estimate an abundance of at least 6.0 × 10 -3 au -3 for such interstellar objects with mean diameter larger than 100 m and find that it is likely that most of them will be ejected into the Galactic halo. Our Bayesian analysis of the available light curves indicates a rotation period of 6.96 +1.45 -0.39, which is consistent with the estimation by Meech et al. and shorter than those in other literature. The codes and results are available on GitHub (https://github.com/phillippro/Oumuamua).Peer reviewe

The Natural History of ‘Oumuamua

International audienceThe discovery of the first interstellar object passing through the Solar System, 1I/2017 U1 (`Oumuamua), provoked intense and continuing interest from the scientific community and the general public. The faintness of `Oumuamua, together with the limited time window within which observations were possible, constrained the information available on its dynamics and physical state. Here we review our knowledge and find that in all cases, the observations are consistent with a purely natural origin for `Oumuamua. We discuss how the observed characteristics of `Oumuamua are explained by our extensive knowledge of natural minor bodies in our Solar System and our current knowledge of the evolution of planetary systems. We highlight several areas requiring further investigation

On the asymmetry of the distribution of observable comets induced by a star passage through the Oort cloud

Single passage of a star through the Oort cloud yields anisotropic distribution of observable long period comets. This conclusion emerges from our extensive Monte Carlo simulations of the directional distribution of long-period comets induced by a stellar passage through the Oort cloud. For a broad range of simulation parameters we obtained the asymmetric distribution of comets as result of a single stellar passage. A direct result of our simulation is a guide-line for studies of the anisotropies in the observed long-period comet sample and searching for fingerprints of a recent stellar passage. We obtained an isotropic distribution, as simulated by Weissman ([CITE]) only for a very peculiar choice of input parameters. The accuracy of our calculations was verified by consistency of the impulse approximation and direct orbit integration results

Simulating observable comets

Context.This is the third of a series of papers on simulating the mechanisms acting currently on the Oort cloud and producing the observed long-period comets.Aims.In this paper we investigate the influence of current stellar perturbers on the Oort cloud of comets under the simultaneous galactic disk tide. We also analyse the past motion of the observed long-period comets under the same dynamical model to verify the widely used definition of dynamically new comets. Methods.The action of nearby stars and the galactic disk tide on the Oort cloud was simulated. The original orbital elements of all 386 long-period comets of quality classes 1 and 2 were calculated, and their motion was followed numerically for one orbital revolution into the past, down to the previous perihelion. We also simulated the output of the close future pass of GJ 710 through the Oort cloud. Results.The simulated flux of the observable comets resulting from the current stellar and galactic perturbations, as well as the distribution of perihelion direction, was obtained. The same data are presented for the future passage of GJ 710. A detailed description is given of the past evolution of aphelion and perihelion distances of the observed long-period comets. Conclusions. We obtained no fingerprints of the stellar perturbations in the simulated flux and its directional structure. The mechanisms producing observable comets are highly dominated by galactic disk tide because all current stellar perturbers are too weak. Also the effect of the close passage of the star GJ 710 is very difficult to recognise on the background of the Galactic-driven observable comets. For the observed comets we found only 45 to be really dynamically “new” according to our definition based on the previous perihelion distance value

Simulating observable comets

This is the first of a series of papers presenting an attempt to reproduce the mechanisms acting currently on the Oort cloud of comets and producing the observed long-period comets. In this first part we give a short review of papers on the stellar perturbations on the cometary cloud and on the observed long-period comet perihelia/aphelia directions distribution. We present in detail the effects of a single stellar passage through or near the cometary cloud by means of a Monte Carlo simulation based on the improved impulse approximation. The simulations are performed for two different steady-state numerical models of the Oort cloud and for different parameters of the stellar passage. Among others, we calculate the probabilities of producing an observable comet as well as ejecting it from the cloud, we characterize cometary shower resulting from the close stellar passage and discuss anisotropies in the observable sample of comets, produced by a simulated single stellar perturbation

The transparency of the Solar System to the Oort cloud comets

In long-term Monte Carlo simulations of the dynamics of the Oort cloud planetary perturbations cannot be taken directly into account. To do this we propose a simple approximation: estimating the Solar System transparency coefficient P measuring the probability for a comet to be removed from the cloud by planetary perturbations during a single perihelion passage. We estimated the value of this coefficient from the observed and artificial cometary samples. We excluded nongravitational forces fom our calculations. We obtained $P\cong0.25$ for inner cloud comets and $P\cong0.5$ for the outer and most active part of the cloud. The dependency of P on the comet observability limit ${\it OL}$ is also presented for various cometary samples

Dynamical history of the observed long-period comets

We present results of some numerical studies on the dynamical history of a large number of observed long-period comets. In our investigations we include all comets with good quality orbits. We calculated barycentric, original orbital elements for comets at a distance of 250 AU from the Sun and then followed the motion of each comet (elliptic orbits only) backwards to its aphelion and then to its previous perihelion passage, including the galactic perturbations. Several previously published statistics are compared with the current sample of long-period comets having well-defined orbits. A distinction between dynamically "new" and "old" comets is proposed on the basis of their previous perihelion distance instead of the inverse of the original semimajor axis. We also demonstrated the importance of stellar perturbations and made attempts to find a correlation between past dynamics and various physical parameters of comets

Simulating observable comets

This is the second in a series of papers presenting an attempt to reproduce the mechanisms acting currently on the Oort cloud of comets (Oort 1950, Bull. Astron. Inst. Nether., 11, 91) and producing the observed sample of long-period comets. We combine the effect of the close, recent stellar passage with the continuous action of the Galactic tidal perturbation, and concentrate on the dominant term of this effect, namely the tidal force induced by the galactic disk matter. The main results presented in the previous paper of this series are fully confirmed within a much more realistic model. The results we obtained is that the observable subpopulation of the Oort cometary cloud remained the same in number, even after the close stellar passage. The main output of such a passage is a short time variation in the observable influx of comets and strong asymmetries present in their perihelion direction distribution