Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Forming the lunar farside highlands by accretion of a companion moon

Abstract

The most striking geological feature of the Moon is the terrain and elevation dichotomy1 between the hemispheres: the nearside is low and flat, dominated by volcanic maria, whereas the farside is mountainous and deeply cratered. Associated with this geological dichotomy is a compositional and thermal variation2,3, with the nearside Procellarum KREEP (potassium/rare-earth element/phosphorus) Terrane and environs interpreted as having thin, compositionally evolved crust in comparison with the massive feldspathic highlands. The lunar dichotomy may have been caused by internal effects (for example spatial variations in tidal heating4, asymmetric convective processes5 or asymmetric crystallization of the magma ocean6) or external effects (such as the event that formed the South Pole/Aitken basin1 or asymmetric cratering7). Here we consider its origin as a late carapace added by the accretion of a companion moon. Companion moons are a common outcome of simulations8 of Moon formation from a protolunar disk resulting from a giant impact, and although most coplanar configurations are unstable9, a 1,200-km-diameter moon located at one of the Trojan points could be dynamically stable for tens of millions of years after the giant impact10. Most of the Moon’s magma ocean would solidify on this timescale11,12, whereas the companion moon would evolve more quickly into a crust and a solid mantle derived from similar disk material, and would presumably have little or no core. Its likely fate would be to collide with the Moon at 2–3 km s−1, well below the speed of sound in silicates. According to our simulations, a large moon/Moon size ratio (0.3) and a subsonic impact velocity lead to an accretionary pile rather than a crater, contributing a hemispheric layer of extent and thickness consistent with the dimensions of the farside highlands1,13 and in agreement with the degree-two crustal thickness profile4. The collision furthermore displaces the KREEP-rich layer to the opposite hemisphere, explaining the observed concentration2,3.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Figure 1: Moon/companion moon collision.
Figure 2: Post-impact internal structure.
Figure 3: Post-impact spatial distribution of the impactor and thickness profile.

References

  1. 1

    Zuber, M. T., Smith, D. E., Lemoine, F. G. & Neumann, G. A. The shape and internal structure of the moon from the Clementine mission. Science 266, 1839–1843 (1994)

    ADS  CAS  Article  Google Scholar 

  2. 2

    Lawrence, D. J. Global elemental maps of the moon: the Lunar Prospector gamma-ray spectrometer. Science 281, 1484–1489 (1998)

    ADS  CAS  Article  Google Scholar 

  3. 3

    Jolliff, B. L., Gillis, J. J., Haskin, L. A., Korotev, R. L. & Wieczorek, M. A. Major lunar crustal terranes: surface expressions and crust-mantle origins. J. Geophys. Res. 105, 4197–4216 (2000)

    ADS  CAS  Article  Google Scholar 

  4. 4

    Garrick-Bethell, I., Nimmo, F. & Wieczorek, M. Structure and formation of the lunar farside highlands. Science 330, 949–951 (2010)

    ADS  CAS  Article  Google Scholar 

  5. 5

    Loper, D. E. & Werner, C. L. On lunar asymmetries 1. Tilted convection and crustal asymmetry. J. Geophys. Res. Planets 107, 131–137 (2002)

    Article  Google Scholar 

  6. 6

    Wasson, J. T. & Warren, P. H. Contribution of the mantle to the lunar asymmetry. Icarus 44, 752–771 (1980)

    ADS  Article  Google Scholar 

  7. 7

    Wood, J. A. Bombardment as a cause of the lunar asymmetry. Moon 8, 73–103 (1973)

    ADS  Article  Google Scholar 

  8. 8

    Ida, S., Canup, R. M. & Stewart, G. R. Lunar accretion from an impact-generated disk. Nature 389, 353–357 (1997)

    ADS  CAS  Article  Google Scholar 

  9. 9

    Canup, R. M., Levison, H. F. & Stewart, G. R. Evolution of a terrestrial multiple-moon system. Astron. J. 117, 603–620 (1999)

    ADS  Article  Google Scholar 

  10. 10

    Cuk, M. & Gladman, B. J. The fate of primordial lunar Trojans. Icarus 199, 237–244 (2009)

    ADS  Article  Google Scholar 

  11. 11

    Elkins-Tanton, L. T., Burgess, S. & Yin, Q.-Z. The lunar magma ocean: reconciling the solidification process with lunar petrology and geochronology. Earth Planet. Sci. Lett. 304, 326–336 (2011)

    ADS  CAS  Article  Google Scholar 

  12. 12

    Meyer, J., Elkins-Tanton, L. & Wisdom, J. Coupled thermal–orbital evolution of the early moon. Icarus 208, 1–10 (2010)

    ADS  Article  Google Scholar 

  13. 13

    Wieczorek, M. The constitution and structure of the lunar interior. Rev. Mineral. Geochem. 60, 221–364 (2006)

    CAS  Article  Google Scholar 

  14. 14

    Benz, W. & Asphaug, E. Simulations of brittle solids using smooth particle hydrodynamics. Comput. Phys. Commun. 87, 253–265 (1995)

    ADS  CAS  Article  Google Scholar 

  15. 15

    Jutzi, M., Benz, W. & Michel, P. Numerical simulations of impacts involving porous bodies. I. Implementing sub-resolution porosity in a 3D SPH hydrocode. Icarus 198, 242–255 (2008)

    ADS  Article  Google Scholar 

  16. 16

    Jutzi, M. & Asphaug, E. Mega-ejecta on asteroid Vesta. Geophys. Res. Lett. 38, L01102 (2011)

    ADS  Article  Google Scholar 

  17. 17

    Jop, P., Forterre, Y. & Pouliquen, O. A constitutive law for dense granular flows. Nature 441, 727–730 (2006)

    ADS  CAS  Article  Google Scholar 

  18. 18

    Benz, W. The origin of the moon and the single-impact hypothesis. I. Icarus 66, 515–535 (1986)

    ADS  Article  Google Scholar 

  19. 19

    Canup, R. M. & Asphaug, E. Origin of the Moon in a giant impact near the end of the Earth’s formation. Nature 412, 708–712 (2001)

    ADS  CAS  Article  Google Scholar 

  20. 20

    Melosh, H. J. Impact Cratering: A Geologic Process (Oxford Univ. Press, 1989)

    Google Scholar 

  21. 21

    Housen, K. R., Schmidt, R. M. & Holsapple, K. A. Crater ejecta scaling laws: fundamental forms based on dimensional analysis. J. Geophys. Res. 88, 2485–2499 (1983)

    ADS  Article  Google Scholar 

  22. 22

    Warren, P. H. The magma ocean concept and lunar evolution. Annu. Rev. Earth Planet. Sci. 13, 201–240 (1985)

    ADS  CAS  Article  Google Scholar 

  23. 23

    Parmentier, E. M., Zhong, S. & Zuber, M. T. Gravitational differentiation due to initial chemical stratification: origin of lunar asymmetry by the creep of dense KREEP? Earth Planet. Sci. Lett. 201, 473–480 (2002)

    ADS  CAS  Article  Google Scholar 

  24. 24

    Zuber, M. T. et al. in Proc. 39th Lunar Planet. Sci. Conf. abstr. 1074, 〈http://www.lpi.usra.edu/meetings/lpsc2008/pdf/1074.pdf〉 (Lunar and Planetary Institute, 2008)

Download references

Acknowledgements

Our work is sponsored by NASA’s Planetary Geology and Geophysics programme ‘Small Bodies and Planetary Collisions’. All simulations were run at the University of California, Santa Cruz, on the NSF-MRI-sponsored ‘pleiades’ cluster. We are grateful to M. Cuk, B. Gladman and R. Canup for guidance.

Author information

Affiliations

Authors

Contributions

Both authors contributed equally to this work.

Corresponding author

Correspondence to M. Jutzi.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Jutzi, M., Asphaug, E. Forming the lunar farside highlands by accretion of a companion moon. Nature 476, 69–72 (2011). https://doi.org/10.1038/nature10289

Download citation

Further reading

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Quick links