Formation of Venus, Earth and Mars : Constrained by Isotopes

Abstract

Here we discuss the current state of knowledge of terrestrial planet formation from the aspects of different planet formation models and isotopic data from ¹⁸²Hf-¹⁸²W, U-Pb, lithophile-siderophile elements, ⁴⁸Ca/⁴⁴Ca isotope samples from planetary building blocks, recent reproduction attempts from ³⁶Ar/³⁸Ar, ²⁰Ne/²²Ne, ³⁶Ar/²²Ne isotope ratios in Venus’ and Earth’s atmospheres, the expected solar ³He abundance in Earth’s deep mantle and Earth’s D/H sea water ratios that shed light on the accretion time of the early protoplanets. Accretion scenarios that can explain the different isotope ratios, including a Moon-forming event ca. 50 Myr after the formation of the Solar System, support the theory that the bulk of Earth’s mass (≥80%) most likely accreted within 10–30 Myr. From a combined analysis of the before mentioned isotopes, one finds that proto-Earth accreted most likely a mass of 0.5–0.6 M_Earth within the first ≈3–4.5 Myr, the approximate lifetime of the protoplanetary disk. For Venus, the available atmospheric noble gas data are too uncertain for constraining the planet’s accretion scenario accurately. However, from the available imprecise Ar and Ne isotope measurements, one finds that proto-Venus could have grown to a mass of up to 0.85–1.0 M_Venus before the disk dissipated. Classical terrestrial planet formation models have struggled to grow large planetary embryos, or even cores of giant planets, quickly from the tiniest materials within the typical lifetime of protoplanetary disks. Pebble accretion could solve this long-standing time scale controversy. Pebble accretion and streaming instabilities produce large planetesimals that grow into Mars-sized and larger planetary embryos during this early accretion phase. The later stage of accretion can be explained well with the Grand-Tack model as well as the annulus and depleted disk models. The relative roles of pebble accretion and planetesimal accretion/giant impacts are poorly understood and should be investigated with N-body simulations that include pebbles and multiple protoplanets. To summarise, different isotopic dating methods and the latest terrestrial planet formation models indicate that the accretion process from dust settling, planetesimal formation, and growth to large planetary embryos and protoplanets is a fast process that occurred to a great extent in the Solar System within the lifetime of the protoplanetary disk.

• author: Lammer, Helmut ; Brasser, Ramon ; Johansen, Anders ; Scherf, Manuel and Leitzinger, Martin
• organization: eSSENCE: The e-Science Collaboration; Lund Observatory - Has been reorganised
• publishing date: 2021-02
• type: Contribution to journal
• publication status: published
• subject: Astronomy, Astrophysics and Cosmology
• keywords: Isotopes, Noble gases, Pebble accretion, Terrestrial planet formation
• in: Space Science Reviews
• volume: 217
• issue: 1
• article number: 7
• publisher: Springer
• external identifiers: scopus:85098453914
• ISSN: 0038-6308
• DOI: 10.1007/s11214-020-00778-4
• language: English
• LU publication?: yes
• additional info: Funding Information: R. B. acknowledges financial assistance from the Japan Society for the Promotion of Science (JSPS) Shingakujutsu Kobo (JP19H05071). A.J. acknowledges funding from the European Research Foundation (ERC Consolidator Grant 724687-PLANETESYS), the Knut and Alice Wallenberg Foundation (Wallenberg Academy Fellow Grant 2017.0287) and the Swedish Research Council (Project Grant 2018-04867). H.L. and M.S. acknowledge the support of Europlanet 2020 RI. Europlanet 2020 RI has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 654208. We thank Nathan Kaib and Matt Clement for information regarding their ‘Early instability’ model. H. L. and M. S. acknowledge support from the FWF NFN subproject S11607-N16. M. L. acknowledge support of the Austrian FWF projects P27256-N27 and P30949-N36. The authors also thank the International Space Science Institute (ISSI) in Bern, Switzerland for the support. Finally, we thank the referee S. B. Jacobsen and an anonymous referee for their very helpful comments and suggestions that helped to improve this review article. Funding Information: R. B. acknowledges financial assistance from the Japan Society for the Promotion of Science (JSPS) Shingakujutsu Kobo (JP19H05071). A.J. acknowledges funding from the European Research Foundation (ERC Consolidator Grant 724687-PLANETESYS), the Knut and Alice Wallenberg Foundation (Wallenberg Academy Fellow Grant 2017.0287) and the Swedish Research Council (Project Grant 2018-04867). H.L. and M.S. acknowledge the support of Europlanet 2020 RI. Europlanet 2020 RI has received funding from the European Union?s Horizon 2020 research and innovation programme under grant agreement No 654208. We thank Nathan Kaib and Matt Clement for information regarding their ?Early instability? model. H. L. and M. S. acknowledge support from the FWF NFN subproject S11607-N16. M. L. acknowledge support of the Austrian FWF projects P27256-N27 and P30949-N36. The authors also thank the International Space Science Institute (ISSI) in Bern, Switzerland for the support. Finally, we thank the referee S. B. Jacobsen and an anonymous referee for their very helpful comments and suggestions that helped to improve this review article. Publisher Copyright: © 2020, Springer Nature B.V. Copyright: Copyright 2020 Elsevier B.V., All rights reserved.
• id: 0ac13ad9-26f1-41fa-9cf9-bfb993ed934e
• date added to LUP: 2021-09-16 08:41:25
• date last changed: 2024-04-20 11:17:36