Late veneer and late accretion to the terrestrial planets

Abstract

It is generally accepted that silicate-metal (`rocky') planet formation relies on coagulation from a mixture of sub-Mars sized planetary embryos and (smaller) planetesimals that dynamically emerge from the evolving circum-solar disc in the first few million years of our Solar System. Once the planets have, for the most part, assembled after a giant impact phase, they continue to be bombarded by a multitude of planetesimals left over from accretion. Here we place limits on the mass and evolution of these planetesimals based on constraints from the highly siderophile element (HSE) budget of the Moon. Outcomes from a combination of N-body and Monte Carlo simulations of planet formation lead us to four key conclusions about the nature of this early epoch. First, matching the terrestrial to lunar HSE ratio requires either that the late veneer on Earth consisted of a single lunar-size impactor striking the Earth before 4.45 Ga, or that it originated from the impact that created the Moon. An added complication is that analysis of lunar samples indicates the Moon does not preserve convincing evidence for a late veneer like Earth. Second, the expected chondritic veneer component on Mars is 0.06 weight percent. Third, the flux of terrestrial impactors must have been low ( <=10^(-6) M_earth/Myr) to avoid wholesale melting of Earth's crust after 4.4~Ga, and to simultaneously match the number of observed lunar basins. This conclusion leads to an Hadean eon which is more clement than assumed previously. Last, after the terrestrial planets had fully formed, the mass in remnant planetesimals was ~10^(-3) M_earth, lower by at least an order of magnitude than most previous models suggest. Our dynamically and geochemically self-consistent scenario requires that future N-body simulations of rocky planet formation either directly incorporate collisional grinding or rely on pebble accretion.

Accepted for publication in Earth and Planetary Science Letters

References in corpus (2)

• Highly Siderophile Elements in the Earth's Mantle as a Clock for the Moon-forming Impact
• Re-examining the main asteroid belt as the primary source of ancient lunar craters

Cited by in corpus (25)

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• Reduced atmospheres of post-impact worlds: The early Earth
• A colossal impact enriched Mars' mantle with noble metals
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• Numerous chondritic impactors and oxidized magma ocean set Earth's volatile depletion
• The terrestrial planet formation paradox inferred from high-resolution N-body simulations
• Did Mars possess a dense atmosphere during the first ~400 million years?
• Evidence for Abiotic Dimethyl Sulfide in Cometary Matter
• Habitable planet formation around low-mass stars: Rapid accretion, rapid debris removal and the essential contribution of external giants
• Oort cloud asteroids: Collisional evolution, the Nice Model, and the Grand Tack
• Modification of the composition and density of Mercury from late accretion
• A Material-based Panspermia Hypothesis: The Potential of Polymer Gels and Membraneless Droplets
• Mars in the aftermath of a colossal impact
• The Abundance of Belatedly Habitable Planets and Ambiguities in Definitions of the Continuously Habitable Zone
• Can narrow disks in the inner solar system explain the four terrestrial planets?
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• Crash Chronicles: relative contribution from comets and carbonaceous asteroids to Earth's volatile budget in the context of an Early Instability
• A new estimate for the age of highly-siderophile element retention in the lunar mantle from late accretion
• Geoastronomy: Rocky planets as the Lavosier-Lomonosov Bridge from the non-living to the living world
• The distribution of impactor core material during large impacts on Earth-like planets
• Cosmic ray ionisation of a post-impact early Earth atmosphere: Solar cosmic ray ionisation must be considered in origin-of-life scenarios
• What the Solar System Can Teach Us About Rocky Exoplanets