Modification of the composition and density of Mercury from late accretion
Ryuki Hyodo, Hidenori Genda, Ramon Brasser
Late accretion is a process that strongly modulated surface geomorphic and geochemical features of Mercury. Yet, the fate of the impactors and their effects on Mercury’s surface through the bombardment epoch are not clear. Using Monte-Carlo and analytical approaches of cratering impacts, we investigate the physical and thermodynamical outcomes of late accretion on Mercury. Considering the uncertainties in late accretion, we develop scaling laws for the following parameters as a function of impact velocity and total mass of late accretion: (1) depth of crustal erosion, (2) the degree of resurfacing, and (3) mass accreted from impactor material. Existing dynamical models indicate that Mercury experienced an intense impact bombardment (a total mass of ∼8×1018−8×1020 kg with a typical impact velocity of 30−40 km s−1) after 4.5 Ga. With this, we find that late accretion could remove 50 m to 10 km of the early crust of Mercury, but the change to its core-to-mantle ratio is negligible. Alternatively, the mantles of putative differentiated planetesimals in the early solar system could be more easily removed and their respective core fraction increased, if Mercury ultimately accreted from such objects. Although the cratering is notable for erasing the older geological surface records on Mercury, we show that ∼40−50 wt% of the impactor’s exogenic materials, including the volatile-bearing materials, can be heterogeneously implanted on Mercury’s surface as a late veneer (>3×1018−1.6×1019 kg in total). About half of the accreted impactor’s materials are vaporized, and the rest is completely melted upon the impact. We expect that the further interplay between our theoretical results and forthcoming surface observations of Mercury, including the BepiColombo mission, will lead us to a better understanding of Mercury’s origin and evolution.
Comments: 19 pages, 7 figures. Accepted for publication in Icarus
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2008.08490 [astro-ph.EP] (or arXiv:2008.08490v1 [astro-ph.EP] for this version)
Submission history
From: Ryuki Hyodo
[v1] Wed, 19 Aug 2020 15:06:10 UTC (11,806 KB)
