11 research outputs found

    Speeding past planets? Asteroids radiatively propelled by giant branch Yarkovsky effects

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    Understanding the fate of planetary systems through white dwarfs which accrete debris crucially relies on tracing the orbital and physical properties of exo-asteroids during the giant branch phase of stellar evolution. Giant branch luminosities exceed the Sun‚Äôs by over three orders of magnitude, leading to significantly enhanced Yarkovsky and YORP effects on minor planets. Here, we place bounds on Yarkovsky-induced differential migration between asteroids and planets during giant branch mass loss by modelling gone exo-Neptune with inner and outer exo-Kuiper belts. In our bounding models, the asteroids move too quickly past the planet to be diverted from their eventual fate, which can range from: (i) populating the outer regions of systems out to 104‚ąí105au, (ii) being engulfed within the host star, or (iii) experiencing Yarkovsky-induced orbital inclination flipping without any Yarkovsky-induced semimajor axis drift. In these violent limiting cases, temporary resonant trapping of asteroids with radii of under about 10 km by the planet is insignificant, and capture within the planet‚Äôs Hill sphere requires fine-tuned dissipation. The wide variety of outcomes presented here demonstrates the need to employ sophisticated structure and radiative exo-asteroid models in future studies. Determining where metal-polluting asteroids reside a round a white dwarf depends on understanding extreme Yarkovsky physics

    What long-period comets tell us about the Oort Cloud

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    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

    The ‚Äúmemory‚ÄĚ of the Oort cloud

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    Aims. Our aim in this paper is to try to discover if we can find any record of the Oort cloud formation process in the orbital distribution of currently observable long-periodic comets. Methods. Long-term simulations of tens of millions of comets from two different kinds of proto-Oort clouds (isotropic and disk-like) were performed. In these simulations we considered the Galactic tides, stellar passage, and planetary perturbations. Results. In the case of an initially disk-like proto-Oort cloud, the final Oort cloud remains anisotroic inside of about 13 200 au. A record of the initial shape is preserved, here referred to as the ‚Äúmemory‚ÄĚ, even on the final distribution of observable comets. This memory is measurable in particular for observable comets for which the previous perihelion was beyond 10 au and that were significantly affected by Uranus or Neptune at that moment (the so-called Kaib-Quinn jumpers observable class). Indeed, these comets are strongly concentrated along an extended scattered disk that is the remnant of the initial population 1 Gyr before the comets are observable. In addition, for this class of comets, the distributions of ecliptic inclination and Galactic longitude of the ascending node at the previous perihelion preceding the observable perihelion highlight characteristics that are not present in the isotropic model. Furthermore, the disk-like model produces four times more observable comets than the isotropic one, and its flux is independent of the initial distribution of orbital energy. Also for the disk-like model, the region beyond Neptune up to ~40 au gives the major contribution to the final flux of observable comets. Conclusions. The disk-like model sustains a flux of observable comets that are more consistent with the actually observed flux than using the isotropic model. However, further investigations are needed to reveal whether a fingerprint of the initial proto-Oort cloud, such as those highlighted in the present article, is present in the sample of known long-period comets

    Observation of Vertically Ejected Plumes Generated by the Impact of Hollow Projectiles at Various Velocities

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    Recently, impact experiments in space have been conducted in planetary exploration using hollow or internally structured projectiles. In laboratory experiments using hollow projectiles to investigate the differences in crater and ejecta from the case of solid projectiles, a plume perpendicular to the target surface has been observed, which has not been seen in conventional cratering experiments using solid projectiles. In this study, we conducted crater-formation experiments using hollow resin projectiles to understand the mechanism through which vertical plumes form in the case of hollow projectiles. We examined the generation of a vertical plume as a function of the impact velocity, v _imp . We found that (i) no vertical plume occurs at v _imp < 200 m s ^‚ąí1 , (ii) the cases with or without a vertical plume are mixed at 200 < v _imp < 350 m s ^‚ąí1 , (iii) no vertical plume occurs at 350 < v _imp < 800 m s ^‚ąí1 , and (iv) a vertical plume occurs at 2 < v _imp < 3 km s ^‚ąí1 . We qualitatively discussed the generation mechanism of the vertical plume using the results of recovered projectiles. Depending on v _imp , an empty hole in which there is no projectile materials can be opened along the central axis, resulting in the generation of a vertical plume
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