Astronomy and Astrophysics for June (vol. 699) is shorter than usual. Still, consider the following:
Smirnov, E. A. Chaotic diffusion and transient resonance captures of the near-Earth asteroid 2024 YR4 A26 202554489
Zhang, Y. Xu, Y-B. Qi, Z. et al. Shape index of Yarkovsky effect on irregularly shaped asteroids A28 202453612
Now that the hype has died down, we can discuss asteroid 2024 YR4 a bit more seriously. That, and it takes time to do a proper study, worthy of scientific publication. Planets are big, and dominating. Asteroids and comets are small, and can be perturbed from one orbit to another (at least, on sufficient timescales). NEOs, for one, cannot hold their orbits forever and must have come from somewhere else. Considering perturbations from the planets, the Yarkovsky effect, and sometimes others, Smirnov has back-calculated the history of 2024 YR4. It looks, to him at least, like the asteroid has had an interesting history. It arrived at its current orbit by drifting about one or more resonant orbits- orbits constrained by relationships with the planets.
Now, about that Yarkovsky effect. When a body rotates, it has one “dawn” side and “dusk” side. The thermal difference from dawn to dusk means the body radiates heat unevenly. This uneven radiation acts as a gentle push on the body. Over long enough time, even a gentle push can mean a slight orbital drift. If an asteroid is a perfect sphere, finding its Yarkovsky push is straightforward. But asteroids aren’t perfect spheres- certainly, ones small enough for the Yarkovsky effect to be relevant. Yang-Bo Xu (the second author here) had postulated a parameter, “shape index”, to account for nonspherical bodies. This paper is now a refinement of that paper.