The near-Earth carbonaceous asteroid 162173 Ryugu is thought to have been produced from a parent body that contained water ice and organic molecules. The Hayabusa2 spacecraft has obtained global multi-color images of Ryugu. Geomorphological features present include a circum-equatorial ridge, east/west dichotomy, high boulder abundances across the entire surface, and impact craters. Age estimates from the craters indicate a resurfacing age of ≲106 years for the top 1-meter layer. Ryugu is among the darkest known bodies in the Solar System. The high abundance and spectral properties of boulders are consistent with moderately dehydrated materials, analogous to thermally metamorphosed meteorites found on Earth. The general uniformity in color across Ryugu’s surface supports partial dehydration due to internal heating of the asteroid’s parent body.

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In this study we present the results from numerical simulations of the formation of the Oort comet cloud where we positioned the Sun in various parts of the disc of the Galaxy, starting at 2 kpc up to 20 kpc from the Galactic centre. All simulations were run for 4 Gyr. We report that the final trapping efficiency of comets in the Oort cloud is approximately 4% and is almost independent of the solar distance from the Galactic centre. This efficiency is not enough to explain the flux of long-period comets and be consistent with the mass of the protoplanetary disc. In addition, the population ratio between the Oort clouds and their corresponding scattered discs is at least two orders of magnitude lower than observed today. Solar migration from the inner regions of the Galaxy -where the initial trapping efficiency is higher -to farther regions -where the retention is higher -does not add enough of an effect to increase the efficiency to the necessary value of approximately 20%, so that other mechanisms for forming the Oort cloud need to be investigated.

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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's 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 one 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 10 4 − 10 5 au, (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's 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 around a white dwarf depends on understanding extreme Yarkovsky physics.