Science and Exploration

Mercury’s Formation Within The Early Instability Scenario

By Keith Cowing
Status Report
February 5, 2023
Filed under ,
Mercury’s Formation Within The Early Instability Scenario
Cartoon representation of the various initial conditions tested here, and in our past investigations of the early instability scenario in Paper 1, Paper 2 and Paper 3. The cartoon images of the outer planets are from

The inner solar system’s modern orbital architecture provides inferences into the epoch of terrestrial planet formation; a ~100 Myr time period of planet growth via collisions with planetesimals and other proto-planets.

While classic numerical simulations of this scenario adequately reproduced the correct number of terrestrial worlds, their semi-major axes and approximate formation timescales, they struggled to replicate the Earth-Mars and Venus-Mercury mass ratios. In a series of past independent investigations, we demonstrated that Mars’ mass is possibly the result of Jupiter and Saturn’s early orbital evolution, while Mercury’s diminutive size might be the consequence of a primordial mass deficit in the region.

Here, we combine these ideas in a single modeled scenario designed to simultaneously reproduce the formation of all four terrestrial planets and the modern orbits of the giant planets in broad strokes. By evaluating our Mercury analogs’ core mass fractions, masses, and orbital offsets from Venus, we favor a scenario where Mercury forms through a series of violent erosive collisions between a number of ~Mercury-mass embryos in the inner part of the terrestrial disk.

We also compare cases where the gas giants begin the simulation locked in a compact 3:2 resonant configuration to a more relaxed 2:1 orientation and find the former to be more successful. In 2:1 cases, the entire Mercury-forming region is often depleted due to strong sweeping secular resonances that also tend to overly excite the orbits of Earth and Venus as they grow.

While our model is quite successful at replicating Mercury’s massive core and dynamically isolated orbit, the planets’ low mass remains extremely challenging to match. Finally, we discuss the merits and drawbacks of alternative evolutionary scenarios and initial disk conditions.

Matthew S. Clement, John E. Chambers, Nathan A. Kaib, Sean N. Raymond, Alan P. Jackson

Comments: 23 pages, 9 figures, 3 tables, accepted for publication in Icarus
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2301.09646 [astro-ph.EP] (or arXiv:2301.09646v1 [astro-ph.EP] for this version)
Submission history
From: Matthew Clement
[v1] Mon, 23 Jan 2023 19:00:00 UTC (2,381 KB)

SpaceRef co-founder, Explorers Club Fellow, ex-NASA, Away Teams, Journalist, Space & Astrobiology, Lapsed climber.