Formation, stratification, and mixing of the cores of Earth and Venus

Seth A. Jacobson*, David C. Rubie, John Hernlund, Alessandro Morbidelli, Miki Nakajima

*Corresponding author for this work

Research output: Contribution to journalArticle

25 Scopus citations

Abstract

Earth possesses a persistent, internally-generated magnetic field, whereas no trace of a dynamo has been detected on Venus, at present or in the past, although a high surface temperature and recent resurfacing events may have removed paleomagnetic evidence. Whether or not a terrestrial body can sustain an internally generated magnetic field by convection inside its metallic fluid core is determined in part by its initial thermodynamic state and its compositional structure, both of which are in turn set by the processes of accretion and differentiation. Here we show that the cores of Earth- and Venus-like planets should grow with stable compositional stratification unless disturbed by late energetic impacts. They do so because higher abundances of light elements are incorporated into the liquid metal that sinks to form the core as the temperatures and pressures of metal-silicate equilibration increase during accretion. We model this process and determine that this establishes a stable stratification that resists convection and inhibits the onset of a geodynamo. However, if a late energetic impact occurs, it could mechanically stir the core creating a single homogenous region within which a long-lasting geodynamo would operate. While Earth's accretion has been punctuated by a late giant impact with likely enough energy to mix the core (e.g. the impact that formed the Moon), we hypothesize that the accretion of Venus is characterized by the absence of such energetic giant impacts and the preservation of its primordial stratifications.

Original languageEnglish (US)
Pages (from-to)375-386
Number of pages12
JournalEarth and Planetary Science Letters
Volume474
DOIs
StatePublished - Sep 15 2017

Keywords

  • core formation
  • early Earth
  • early Venus
  • geodynamo
  • planet formation
  • planetary differentiation

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

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    Jacobson, S. A., Rubie, D. C., Hernlund, J., Morbidelli, A., & Nakajima, M. (2017). Formation, stratification, and mixing of the cores of Earth and Venus. Earth and Planetary Science Letters, 474, 375-386. https://doi.org/10.1016/j.epsl.2017.06.023