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Astrophysics > Earth and Planetary Astrophysics

arXiv:2507.01826 (astro-ph)
[Submitted on 2 Jul 2025]

Title:Dynamical origin of Theia, the last giant impactor on Earth

Authors:Duarte Branco, Sean N. Raymond, Pedro Machado
View a PDF of the paper titled Dynamical origin of Theia, the last
giant impactor on Earth, by Duarte Branco and 2 other authors
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    Abstract:Cosmochemical studies have proposed that Earth accreted
    roughly 5-10% of its mass from carbonaceous (CC) material, with a
    large fraction delivered late via its final impactor, Theia (the
    Moon-forming impactor). Here, we evaluate this idea using
    dynamical simulations of terrestrial planet formation, starting
    from a standard setup with a population of planetary embryos and
    planetesimals laid out in a ring centered between Venus and
    Earth's orbits, and also including a population of CC
    planetesimals and planetary embryos scattered inward by Jupiter.
    We find that this scenario can match a large number of
    constraints, including i) the terrestrial planets' masses and
    orbits; ii) the CC mass fraction of Earth; iii) the much lower CC
    mass fraction of Mars, as long as Mars only accreted CC
    planetesimals (but no CC embryos); iv) the timing of the last
    giant (Moon-forming) impact; and v) a late accretion phase
    dominated by non-carbonaceous (NC) bodies. For this scenario to
    work, the total mass in scattered CC objects must have been ~ 0.2
    - 0.3 M$_{\oplus}$ , with an embryo-to-planetesimal mass ratio of
    at least 8, and CC embryos in the ~ 0.01 - 0.05 M$_{\oplus}$ mass
    range. In that case, our simulations show there are roughly 50-50
    odds of Earth's last giant impactor (Theia) having been a
    carbonaceous object - either a pure CC embryo or an NC embryo
    that previously accreted a CC embryo. Our simulations thus
    provide dynamical validation of cosmochemical studies.

Comments: 20 pages, 11 figures, to be published in Icarus
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as:  arXiv:2507.01826 [astro-ph.EP]
          (or arXiv:2507.01826v1 [astro-ph.EP] for this version)
          https://doi.org/10.48550/arXiv.2507.01826
          Focus to learn more
          arXiv-issued DOI via DataCite (pending registration)

Submission history

From: Duarte Branco [view email]
[v1] Wed, 2 Jul 2025 15:41:34 UTC (2,574 KB)
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