Sedna and the Oort Cloud Around a Migrating Sun (1108.1570v1)

Abstract: Recent numerical simulations have demonstrated that the Sun's dynamical history within the Milky Way may be much more complex than that suggested by its current low peculiar velocity. In particular, the Sun may have radially migrated through the galactic disk by up to 5-6 kpc. This has important ramifications for the structure of the Oort Cloud, as it means that the solar system may have experienced tidal and stellar perturbations that were significantly different from its current local galactic environment. To characterize the effects of solar migration within the Milky Way, we use direct numerical simulations to model the formation of an Oort Cloud around stars that end up on solar-type orbits in a galactic-scale simulation of a Milky Way-like disk formation. Surprisingly, our simulations indicate that Sedna's orbit may belong to the classical Oort Cloud. Contrary to previous understanding, we show that field star encounters play a pivotal role in setting the Oort Cloud's extreme inner edge, and due to their stochastic nature this inner edge sometimes extends to Sedna's orbit. The Sun's galactic migration heightens the chance of powerful stellar passages, and Sedna production occurs around ~20-30% of the solar-like stars we study. Considering the entire Oort Cloud, we find its median distance depends on the minimum galactocentric distance attained during the Sun's orbital history. The inner edge also shows a similar dependence but with increased scatter due to the effects of powerful stellar encounters. Both of these Oort Cloud parameters can vary by an order of magnitude and are usually overestimated by an Oort Cloud formation model that assumes a fixed galactic environment. In addition, the amount of material trapped in outer Oort Cloud orbits can be extremely low and may present difficulties for models of Oort Cloud formation and long-period comet production.

Evaluating the Oort Cloud and Sedna in the Context of Solar Migration

The paper "Sedna and the Oort Cloud Around a Migrating Sun" investigates the implications of the Sun's potential migration within the Milky Way on the formation and structure of the Oort Cloud, focusing specifically on the unusual orbit of the trans-Neptunian object, Sedna. This paper utilizes advanced numerical simulations to reassess conventional notions about the Solar System's outskirts, considering the dynamic galactic environment the Sun might have traversed.

The central premise challenges traditional models that assume a static solar galactic environment, suggesting instead that the Sun may have migrated several kiloparsecs from its birth location. This radial migration implies that both the strength and frequency of gravitational perturbations from passing stars, as well as the Galactic tide, could have been significantly different at various points in the solar system's history. Such migration potentially influenced the architecture of the Oort Cloud, particularly in potentially incorporating Sedna within its bounds.

The authors employ simulations to analyze the formation of an Oort Cloud around stars on solar-type orbits in a dynamically evolving galactic disk. The results indicate a considerably variable Oort Cloud inner edge, influenced heavily by stochastic stellar encounters rather than the continuous Galactic tide, which had previously been considered the dominant factor. Remarkably, the paper finds that Sedna's orbit might indeed belong to the Oort Cloud, contradicting earlier beliefs driven by models assuming a stable galactic environment.

Key numerical results underline that powerful stellar passages are instrumental in defining the innermost edge of the Oort Cloud. Such encounters increase in likelihood due to the proposed solar migration, leading to Sedna-like bodies being part of about 20-30% of the solar analog hypotheses tested. The simulations reveal that the median semimajor axis of the Oort Cloud and its inner edge can vary by an order of magnitude, demonstrating the substantial impact of solar migration and further suggesting that traditional models might overestimate Oort Cloud dimensions without accounting for migration.

The implications for our understanding of the Oort Cloud extend beyond merely accommodating Sedna. The paper suggests that increasing the inner concentration of the Oort Cloud through migration could have significant ramifications for the long-period comet (LPC) flux and broader cometary dynamics. Furthermore, these insights could potentially integrate into models considering the capture of non-native bodies during the dissolution of a solar birth cluster, a hypothesis that has implications for explaining the current LPC population without an unreasonably massive primordial disk.

Looking forward, future investigations in the field will benefit from this paper's findings, particularly in refining simulations that encapsulate not just the static galactic tides but also incorporate the non-axisymmetric components of the Milky Way. Understanding the specific migration trajectory of the Sun will remain a fundamental question, influencing models of the solar system's primordial environment and the dynamical pathways available for outer solar system bodies. As astronomers and planetary scientists continue to assimilate new observational data, notably from surveys such as LSST and Pan-STARRS, the models and insights from this paper offer a robust framework for reinterpreting distant solar system constituents and their evolutionary histories.