What long-period comets tell us about the Oort Cloud

Abstract

Context. The Oort Cloud is located in the farthest outskirts of the Solar System, extending to a heliocentric distance of several tens of thousands of au, and remains the last region of the Solar System where no object has been detected. Thus, all our knowledge of the Oort Cloud has been deduced from the observed long-period comets that are thought to originate from it. Aims. We aimed to retrieve valuable information that might be hidden in the orbital distributions of the observed long-period comets. Such information will allow us to impose constraints not only on the present shape of the Oort Cloud but also on its initial shape 4.5 Gyr ago. This has direct implications for the scenario proposed for its formation. Methods. We used two different databases of long-period comets. First, we calculated the distribution of orbital elements that might carry valuable information about the shape of the Oort Cloud. Then, we compared the distribution with that obtained from two synthetic samples of observable comets. These samples correspond to two considerably different initial configurations: one is a disk model, where we consider a swarm of comets with orbits aligned to the ecliptic plane and with a cometary perihelion close to the giant planets. The other is an isotropic model, where we consider a fully isotropic and thermalized initial distribution of comets. Results. The comparison revealed that the databases contained several features that were in better agreement with the disk model than with the isotropic model. The Oort Cloud contained an initial disk of objects with perihelia close to the planetary region of the Solar System and aphelia extending out to roughly 20 000 au. Some parts of this disk likely remain in the present Solar System. However, the fit to the disk model is poor. The discrepancy between the observational and synthetic results indicates that some dynamical processes in the current Oort Cloud were not included in either model. Conclusions. This initial shape of the Oort Cloud implies that planetary scattering was crucial during its formation. In addition, the fact that some dynamical features are still detec table 4.5 Gyr after the cloud formation imposes constraints on the role of exosolar effects, such as giant molecular clouds, Galactic tides, and the stellar cluster surrounding the Solar System at the time of its formation.

Solar Sail Optimal Performance in Heliocentric Nodal Flyby Missions

“…Long-period comets, on the other hand, are not contaminated by these natural effects because they have ideally never previously entered the inner region of the Solar System and, therefore, are likely to retain internally unaltered information about the formation and evolution of our planetary system [7]. This is a peculiarity important because some cosmological issues are still not completely clear and require further investigation and experimental measurements [8,9]. For example, what is the origin and evolution of planetesimals and the environment of the early Solar System?…”

Classification of Subgroups of Solar and Heliospheric Observatory (SOHO) Sungrazing Kreutz Comet Group by the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) Clustering Algorithm

“…In addition, these comets serve as indispensable markers of the Sun's behavior, offering critical perspectives on solar flares and occasional encounters among themselves (Iseli et al 2002;Jia et al 2014). In light of their potential ramifications for Earth, the examination of interactions between these comets and the Sun stands as a matter of paramount consequence (Bzowski & Krolikowska 2005;Brown et al 2011;Rasca et al 2014;Hou et al 2021;Fouchard et al 2023).…”