Ferrovolcanism on metal worlds and the origin of pallasites


As differentiated planetesimals cool, their cores can solidify from the outside in1, as evidenced by palaeomagnetic measurements and cooling-rate estimates of iron meteorites2,3. The details of outside-in solidification and fate of residual core melt are poorly understood. For a core primarily composed of iron and nickel alloyed with lighter constituent elements such as sulfur, this inward core growth would probably be achieved by growth of solid iron–nickel dendrites4. Growth of iron–nickel dendrites results in interconnected pockets of residual melt that become progressively enriched in sulfur up to a eutectic composition of 31 wt% sulfur as iron–nickel continues to solidify4. Here, we show that regions of residual sulfur-enriched iron–nickel melt in the core attain sufficient excess pressures to propagate via dykes into the mantle. Thus, core material will intrude into the overlying rocky mantle or possibly even erupt onto the planetesimal’s surface. We refer to these processes collectively as ferrovolcanism. Our calculations show that ferrovolcanic surface eruptions are more likely on bodies with mantles less than 50 km thick. We show that intrusive ferromagmatism can produce pallasites, an enigmatic class of meteorites composed of olivine crystals entrained in a matrix of iron–nickel metal4. Ferrovolcanic eruptions may explain the observations that asteroid 16 Psyche has a bulk density inconsistent with iron meteorites5 yet shows evidence of a metallic surface composition6.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1: Structure of a differentiated planetesimal that may experience ferrovolcanic eruptions of sulfur-rich FeNi melt.
Fig. 2: Excess pressure associated with the buoyancy of sulfur-enriched iron melts surrounded by dense solid iron as a function of core radius.
Fig. 3: Mantle penetration height of ferromagmatic dykes as a function of sulfur content.
Fig. 4: Modelled density of Psyche, assuming a two-layer structure of a metal core and a rocky mantle compared with the observed density.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.


  1. 1.

    Williams, Q. Bottom-up versus top-down solidification of the cores of small Solar System bodies: constraints on paradoxical cores. Earth Planet. Sci. Lett. 284, 564–569 (2009).

    ADS  Article  Google Scholar 

  2. 2.

    Bryson, J. F. J. et al. Long-lived magnetism from solidification-driven convection on the pallasite parent body. Nature 517, 472–475 (2015).

    ADS  Article  Google Scholar 

  3. 3.

    Yang, J., Goldstein, J. I. & Scott, E. R. D. Iron meteorite evidence for early formation and catastrophic disruption of protoplanets. Nature 446, 888–891 (2007).

    ADS  Article  Google Scholar 

  4. 4.

    Scheinberg, A., Tanton, L. T. E., Schubert, G. & Bercovici, D. Core solidification and dynamo evolution in a mantle‐stripped planetesimal. J. Geophys. Res. Planets 121, 2–20 (2016).

    ADS  Article  Google Scholar 

  5. 5.

    Drummond, J. D. et al. The triaxial ellipsoid size, density, and rotational pole of asteroid (16) Psyche from Keck and Gemini AO observations 2004–2015. Icarus 305, 174–185 (2018).

    ADS  Article  Google Scholar 

  6. 6.

    Shepard, M. K. et al. Radar observations and shape model of asteroid 16 Psyche. Icarus 281, 388–403 (2017).

    ADS  Article  Google Scholar 

  7. 7.

    Wilson, L. & Head, J. W. Generation, ascent and eruption of magma on the Moon: new insights into source depths, magma supply, intrusions and effusive/explosive eruptions (part 1: theory). Icarus 283, 146–175 (2017).

    ADS  Article  Google Scholar 

  8. 8.

    Gudmundsson, A. Magma chambers: formation, local stresses, excess pressures, and compartments. J. Volcanol. Geotherm. Res. 237-238, 19–41 (2012).

    ADS  Article  Google Scholar 

  9. 9.

    Rubin, A. Propagation of magma-filled cracks. Annu. Rev. Earth Planet. Sci. 23, 287–336 (1995).

    ADS  Article  Google Scholar 

  10. 10.

    Kiefer, W. S., Macke, R. J., Britt, D. T., Irving, A. J. & Consolmagno, G. J. The density and porosity of lunar rocks. Geophys. Res. Lett. 39, L07201 (2012).

    ADS  Article  Google Scholar 

  11. 11.

    Keil, K. & Wilson, L. Explosive volcanism and the compositions of cores of differentiated asteroids. Earth Planet. Sci. Lett. 117, 111–124 (1993).

    ADS  Article  Google Scholar 

  12. 12.

    Boesenberg, J. S., Delaney, J. S. & Hewins, R. H. A petrological and chemical reexamination of main group pallasite formation. Geochim. Cosmochim. Acta 89, 134–158 (2012).

    ADS  Article  Google Scholar 

  13. 13.

    Scott, E. R. D. Impact origins for pallasites. In Proc. 38th Lunar and Planetary Science Conference 2284 (LPI, 2007).

  14. 14.

    Warren, P. H. Stable-isotopic anomalies and the accretionary assemblage of the Earth and Mars: a subordinate role for carbonaceous chondrites. Earth Planet. Sci. Lett. 311, 93–100 (2011).

    ADS  Article  Google Scholar 

  15. 15.

    Scott, E. R. D. Geochemical relationships between some pallasites and iron meteorites. Mineral. Mag. 41, 265–272 (1977).

    Article  Google Scholar 

  16. 16.

    Scott, E. R. D. Formation of olivine-metal textures in pallasite meteorites. Geochim. Cosmochim. Acta 41, 693–710 (1977).

    ADS  Article  Google Scholar 

  17. 17.

    Buseck, P. R. Pallasite meteorites—mineralogy, petrology and geochemistry. Geochim. Cosmochim. Acta 41, 711–721 (1977).

    ADS  Article  Google Scholar 

  18. 18.

    Ulff-Møller, F. U., Choi, B.-G., Rubin, A. E., Tran, J. & Wasson, J. T. Paucity of sulfide in a large slab of Esquel: new perspectives on pallasite formation. Meteorit. Planet. Sci. 33, 221–227 (1998).

    ADS  Article  Google Scholar 

  19. 19.

    Tarduno, J. A. et al. Evidence for a dynamo in the main group pallasite parent body. Science 338, 939–942 (2012).

    ADS  Article  Google Scholar 

  20. 20.

    Elkins-Tanton, L. T. et al. Asteroid (16) Psyche: the science of visiting a metal world. In Proc. 47th Lunar and Planetary Science Conference 1631 (LPI, 2016).

  21. 21.

    Asphaug, E., Agnor, C. B. & Williams, Q. Hit-and-run planetary collisions. Nature 439, 155–160 (2006).

    ADS  Article  Google Scholar 

  22. 22.

    Hardersen, P. S., Gaffey, M. J. & Abell, P. A. Near-IR spectral evidence for the presence of iron-poor orthopyroxenes on the surfaces of six M-type asteroids. Icarus 175, 141–158 (2005).

    ADS  Article  Google Scholar 

  23. 23.

    Assael, M. J. et al. Reference data for the density and viscosity of liquid aluminum and liquid iron. J. Phys. Chem. Ref. Data 35, 285–300 (2006).

    ADS  Article  Google Scholar 

  24. 24.

    Melosh, H. J. et al. South Pole–Aitken basin ejecta reveal the Moon’s upper mantle. Geology 45, 1063–1066 (2017).

    ADS  Article  Google Scholar 

  25. 25.

    Morard, G. et al. Liquid properties in the Fe–FeS system under moderate pressure: tool box to model small planetary cores. Am. Mineral. 103, 1770–1779 (2018).

    Google Scholar 

  26. 26.

    Melosh, H. J. Planetary Surface Processes (Cambridge Univ. Press, 2011).

  27. 27.

    Evans, B. & Kohlstedt, D. L. in Rock Physics & Phase Relations: A Handbook of Physical Constants Vol. 3 (ed. Ahrens, T. J.) 148–165 (AGU, 1995).

  28. 28.

    Freeman, J. R. & Quick, G. W. Tensile properties of rail and some other steels at elevated temperatures. Bur. Stand. J. Res. 4, 549–591 (1930).

    Article  Google Scholar 

  29. 29.

    Johnson, G. R. & Cook, W. H. A constitutive model and data for metals subjected to large strains, high strain rates and high temperatures. In Proc. 7th International Symposium on Ballistics 541–547 (International Ballistics Society, 1983).

  30. 30.

    Fagents, S. A. Considerations for effusive cryovolcanism on Europa: the post-Galileo perspective. J. Geophys. Res. 108, 5139 (2003).

  31. 31.

    Maccaferri, F., Bonafede, M. & Rivalta, E. A quantitative study of the mechanisms governing dike propagation, dike arrest and sill formation. J. Volcanol. Geotherm. Res. 208, 39–50 (2011).

    ADS  Article  Google Scholar 

  32. 32.

    Abrahams, J. N. H. & Nimmo, F. Ferrovolcanism: iron volcanism on metallic asteroids. Geophys. Res. Lett. 46, 5055–5064 (2019).

  33. 33.

    Byrne, P. K. et al. Widespread effusive volcanism on Mercury likely ended by about 3.5 Ga. Geophys. Res. Lett. 43, 7408–7416 (2016).

    ADS  Article  Google Scholar 

Download references


We thank H. J. Melosh, F. Nimmo, J. N. H. Abrahamson, E. R. D. Scott and M. Caffee for discussion and comments on this work.

Author information




B.C.J. conceived this study and the application of ferrovolcanism to pallasites and the Psyche observations, which M.M.S. had noted. B.C.J. produced the excess pressure and mantle penetration calculations, with input from all authors. M.M.S. produced the Psyche density calculations. All authors contributed to preparation of the manuscript and the conclusions presented in this work.

Corresponding author

Correspondence to Brandon C. Johnson.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Johnson, B.C., Sori, M.M. & Evans, A.J. Ferrovolcanism on metal worlds and the origin of pallasites. Nat Astron 4, 41–44 (2020). https://doi.org/10.1038/s41550-019-0885-x

Download citation

Further reading


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing