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1. An early giant planet instability recorded in asteroidal meteorites

   https://doi.org/10.1038/s41550-024-02340-6  

   Edwards, Graham_Harper; Keller, C_Brenhin; Newton, Elisabeth_R; Stewart, Cameron_W (August 2024, Nature Astronomy)

   Abstract Giant planet migration appears widespread among planetary systems in our Galaxy. However, the timescales of this process, which reflect the underlying dynamical mechanisms, are not well constrained, even within the Solar System. As planetary migration scatters smaller bodies onto intersecting orbits, it would have resulted in an epoch of enhanced bombardment in the Solar System’s asteroid belt. Here, to accurately and precisely quantify the timescales of migration, we interrogate thermochronologic data from asteroidal meteorites, which record the thermal imprint of energetic collisions. We present a database of⁴⁰K–⁴⁰Ar system ages from chondrite meteorites and evaluate it with an asteroid-scale thermal code coupled to a Markov chain Monte Carlo inversion. Simulations require bombardment to reproduce the observed age distribution and identify a bombardment event beginning$$11.{3}_{-6.6}^{+9.5}\, {\mathrm{Myr}}$$ $11.3_{-6.6}^{+9.5}\mathrm{Myr}$after the Sun formed (50% credible interval). Our results associate a giant planet instability in our Solar System with the dissipation of the gaseous protoplanetary disk. 

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2. Suprathermal Electron Transport in the Solar Wind: Effects of Coulomb Collisions and Whistler Turbulence

   https://doi.org/10.3847/1538-4357/ad28c3  

   Tang, Bofeng; Adhikari, Laxman; Zank, Gary P.; Che, Haihong (March 2024, The Astrophysical Journal)

   Abstract The nature and radial evolution of solar wind electrons in the suprathermal energy range are studied. A wave–particle interaction tensor and a Fokker–Planck Coulomb collision operator are introduced into the kinetic transport equation describing electron collisions and resonant interactions with whistler waves. The diffusion tensor includes diagonal and off-diagonal terms, and the Coulomb collision operator applies to arbitrary electron velocities describing collisions with both background protons and electrons. The background proton and electron densities and temperatures are based on previous turbulence models that mediate the supersonic solar wind. The electron velocity distribution functions and electron heat flux are calculated. Comparison and analysis of the numerical results with analytical solutions and observations in the near-Sun region are made. The numerical results reproduce well the creation of the sunward electron deficit observed in the near-Sun region. The deficit of the electron velocity distribution function below the core Maxwellian fit at low velocities results from Coulomb collisions, and the excess part above the core Maxwellian fit at high velocities is determined by strong wave–particle interactions. 

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3. A Collision Mechanism for the Removal of Earth's Trojan Asteroids

   https://doi.org/10.3847/PSJ/ac6958  

   Napier, Kevin J.; Markwardt, Larissa; Adams, Fred C.; Gerdes, David W.; Wen Lin 林, Hsing 省文 (May 2022, The Planetary Science Journal)

   Abstract Due to their strong resonances with their host planet, Trojan asteroids can remain in stable orbits for billions of years. As a result, they are powerful probes for constraining the dynamical and chemical history of the solar system. Although we have detected thousands of Jupiter Trojans and dozens of Neptune Trojans, there are currently no known long-term stable Earth Trojans (ETs). Dynamical simulations show that the parameter space for stable ETs is substantial, so their apparent absence poses a mystery. This work uses a large ensemble ofN-body simulations to explore how the Trojan population dynamically responds if Earth suffers large collisions, such as those thought to have occurred to form the Moon and/or to have given Earth its late veneer. We show that such collisions can be highly disruptive to the primordial Trojan population, and could have eliminated it altogether. More specifically, if Earth acquired the final 1% of its mass through $\mathit{}\left(10\right)$collisions, then only ∼1% of the previously bound Trojan population would remain. 

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4. Nucleation of transition waves via collisions of elastic vector solitons

   https://doi.org/10.1063/5.0156023  

   Yasuda, H; Shu, H; Jiao, W; Tournat, V; Raney, J R (July 2023, Applied Physics Letters)

   In this work, we show that collisions of one type of nonlinear wave can lead to generation of a different kind of nonlinear wave. Specifically, we demonstrate the formation of topological solitons (or transition waves) via collisions of elastic vector solitons, another type of nonlinear wave, in a multistable mechanical system with coupling between translational and rotational degrees of freedom. We experimentally observe the nucleation of a phase transformation arising from colliding waves, and we numerically investigate head-on and overtaking collisions of solitary waves with vectorial properties (i.e., elastic vector solitons). Unlike KdV-type solitons, which maintain their shape despite collisions, our system shows that collisions of two vector solitons can cause nucleation of a new phase via annihilation of the vector solitons, triggering the propagation of transition waves. The propagation of these depends both on the amount of energy carried by the vector solitons and on their respective rotational directions. The observation of the initiation of transition waves with collisions of vector solitons in multistable mechanical systems is an unexplored area of fundamental nonlinear wave interactions and could also prove useful in applications involving reconfigurable structures. 

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5. Modeling proton and electron heating in the fast solar wind

   https://doi.org/10.1051/0004-6361/202039297  

   Adhikari, L.; Zank, G. P.; Zhao, L.-L.; Nakanotani, M.; Tasnim, S. (June 2021, Astronomy & Astrophysics)

   null (Ed.)

   Context. The Parker Solar Probe (PSP) measures solar wind protons and electrons near the Sun. To study the thermodynamic properties of electrons and protons, we include electron effects, such as distributed turbulent heating between protons and electrons, Coulomb collisions between protons and electrons, and heat conduction of electrons. Aims. We develop a general theoretical model of nearly incompressible magnetohydrodynamic (NI MHD) turbulence coupled with a solar wind model that includes electron pressure and heat flux. Methods. It is important to note that 60% of the turbulence energy is assigned to proton heating and 40% to electron heating. We use an empirical expression for the electron heat flux. We derived a nonlinear dissipation term for the residual energy that includes both the Alfvén effect and the turbulent small-scale dynamo effect. Similarly, we obtained the NI/slab time-scale in an NI MHD phenomenology to use in the derivation of the nonlinear term that incorporates the Alfvén effect. Results. A detailed comparison between the theoretical model solutions and the fast solar wind measured by PSP and Helios 2 shows that they are consistent. The results show that the nearly incompressible NI/slab turbulence component describes observations of the fast solar wind periods when the solar wind flow is aligned or antialigned with the magnetic field. 

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