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Rocky Histories: The Effect of High Excitement on the Formation of Rocky Planets

Impact angle and ratio between collision and escape velocity of all collisions in the simulated runs. The size of the points corresponds to the total impact mass of the collision. The collisions in the simulations cover the entire parameter space of collision velocities and angles. Early in the formation process, when the embryos are small, large numbers of super catastrophic collisions occur. The distribution of collisions for larger embryos later in the formation process remains at lower velocities and other less destructive collision types. — astro-ph.EP

Rocky planets both inside and outside our solar system are observed to have a range of nuclear mass fractions (CMFs).

Imperfect collisions can preferentially remove mantle material from a planet, altering its CMF, and so it is believed to be the most likely cause of this observed CMF variation.

However, previous work implementing these collisions in N-body simulations of planet formation has struggled to reliably form high-CMF super-Earths. In this work, we specify our initial conditions and simulation parameters to maximize the prevalence of high-energy, CMF-altering collisions to form planets with highly diverse CMFs.

High energy collisions have a large vimp/vesc ratio, so we maximize this ratio by starting simulations with discs with high eccentricity and inclination to increase the difference in their orbital velocities, maximizing vimp. In addition, we minimize vesc by starting with small embryos. The latter planets undergo more high-energy, debris-producing collisions and experience significant CMF changes during their formation.

However, we find that a number of processes work together to average out a planet’s CMF over time, which is why we don’t consistently form high-CMF, high-mass planets. We form planets with high CMF below 0.5 M⊕. In addition, in these highly eccentric environments, we find that loss of debris mass due to impact grinding has a significant effect on final planet masses and CMFs, resulting in smaller planets and higher mean planet CMF. This work highlights the importance of improving measurements of high-density planets to better constrain their CMFs.

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Notes: 19 pages. This is the version of the article before peer review or editing, as submitted to ApJ. This article has been accepted by ApJ with some revisions
Topics: Earth and Planetary Astrophysics (astroph.EP)
Cite as: arXiv:2211.10491 [astro-ph.EP] (or arXiv:2211.10491v1 [astro-ph.EP] for this version)
Submission history
From: Jennifer Scora
[v1] Fri 18 Nov 2022 19:57:37 UTC (6,519 KB)



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