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.

Implications of an impact origin for the martian hemispheric dichotomy

Abstract

The observation that one hemisphere of Mars is lower and has a thinner crust than the other (the ‘martian hemispheric dichotomy’)1,2,3 has been a puzzle for 30 years. The dichotomy may have arisen as a result of internal mechanisms such as convection4,5. Alternatively, it may have been caused by one6 or several7 giant impacts, but quantitative tests of the impact hypothesis have not been published. Here we use a high-resolution, two-dimensional, axially symmetric hydrocode8,9 to model vertical impacts over a range of parameters appropriate to early Mars. We propose that the impact model, in addition to excavating a crustal cavity of the correct size, explains two other observations. First, crustal disruption10 at the impact antipode is probably responsible for the observed antipodal decline in magnetic field strength11. Second, the impact-generated melt forming the northern lowlands crust is predicted to derive from a deep, depleted mantle source. This prediction is consistent with characteristics of martian shergottite meteorites12,13 and suggests a dichotomy formation time 100 Myr after martian accretion13, comparable to that of the Moon-forming impact on Earth14.

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: Averaged crustal properties as a function of angular distance from impact centre (from ref.6) at 170° E, 50° N.
Figure 2: Results from typical axially symmetric impact simulation using Zeus hydrocode8,9.
Figure 3: Impact crustal excavation radius and melt production.

References

  1. 1

    Smith, D. E. et al. The global topography of Mars and implications for surface evolution. Science 284, 1495–1503 (1999)

    ADS  CAS  Article  Google Scholar 

  2. 2

    Neumann, G. A. et al. Crustal structure of Mars from gravity and topography. J. Geophys. Res. 109, E08002 (2004)

    ADS  Article  Google Scholar 

  3. 3

    Watters, T. R., McGovern, P. J. & Irwin, R. P. Hemispheres apart: The crustal dichotomy on Mars. Annu. Rev. Earth Planet. Sci. 35, 621–652 (2007)

    ADS  CAS  Article  Google Scholar 

  4. 4

    Wise, D. U., Golombek, M. P. & McGill, G. E. Tectonic evolution of Mars. J. Geophys. Res. 84, 7934–7939 (1979)

    ADS  Article  Google Scholar 

  5. 5

    Zhong, S. J. & Zuber, M. T. Degree-1 mantle convection and the crustal dichotomy on Mars. Earth Planet. Sci. Lett. 189, 75–84 (2001)

    ADS  CAS  Article  Google Scholar 

  6. 6

    Wilhelms, D. E. & Squyres, S. W. The Martian hemispheric dichotomy may be due to a giant impact. Nature 309, 138–140 (1984)

    ADS  Article  Google Scholar 

  7. 7

    Frey, H. & Schultz, R. A. Large impact basins and the mega-impact origin for the crustal dichotomy on Mars . Geophys. Res. Lett. 15, 229–232 (1988)

    ADS  Article  Google Scholar 

  8. 8

    Stone, J. M. & Norman, M. L. Zeus-2D – a radiation magnetohydrodynamics code for astrophysical flows in 2 space dimensions. 1. The hydrodynamic algorithms and tests. Astrophys. J. Suppl. Ser. 80, 753–790 (1992)

    ADS  Article  Google Scholar 

  9. 9

    Korycansky, D. G. & Zahnle, K. J. &. Mac Low, M. M. High-resolution calculations of asteroid impacts into the Venusian atmosphere. Icarus 146, 387–403 (2000)

    ADS  CAS  Article  PubMed  Google Scholar 

  10. 10

    Beals, C. S., Innes, M. J. S. & Rottenburg, J. A. in The Moon, Meteorites and Comets (ed. Middlehurst, B. M.) 235–284 (Univ. Chicago Press, Chicago, 1963)

    Google Scholar 

  11. 11

    Purucker, M. et al. An altitude-normalized magnetic map of Mars and its interpretation. Geophys. Res. Lett. 27, 2449–2452 (2000)

    ADS  CAS  Article  Google Scholar 

  12. 12

    Nyquist, L. E. et al. Ages and geologic histories of Martian meteorites. Space Sci. Rev. 96, 105–164 (2001)

    ADS  CAS  Article  Google Scholar 

  13. 13

    Debaille, V., Brandon, A. D., Yin, Q. Z. & Jacobsen, B. Coupled 142Nd–143Nd evidence for a protracted magma ocean in Mars. Nature 450, 525–528 (2007)

    ADS  CAS  Article  PubMed  PubMed Central  Google Scholar 

  14. 14

    Kleine, T., Palme, H., Mezger, M. & Halliday, A. N. Hf-W chronometry of lunar metals and the age and early differentiation of the Moon. Science 310, 1671–1674 (2005)

    ADS  CAS  Article  PubMed  Google Scholar 

  15. 15

    Frey, H. V. Impact constraints on the age and origin of the lowlands of Mars. Geophys. Res. Lett. 33, L08502 (2006)

    ADS  Article  Google Scholar 

  16. 16

    Marinova, M. M., Aharonson, O. & Asphaug, E. Mega-impact formation of the Mars hemispheric dichotomy. Nature 10.1038/nature07070 (this issue)

  17. 17

    McGill, G. E. & Squyres, S. W. Origin of the Martian crustal dichotomy – evaluating hypotheses. Icarus 93, 386–393 (1991)

    ADS  Article  Google Scholar 

  18. 18

    Hynek, B. M. & Phillips, R. J. Evidence for extensive denudation of the Martian highlands. Geology 29, 407–410 (2001)

    ADS  Article  Google Scholar 

  19. 19

    Tanaka, K. L. Sedimentary history and mass flow structures of Chryse and Acidalia Planitiae, Mars. J. Geophys. Res. 102, 4131–4149 (1997)

    ADS  Article  Google Scholar 

  20. 20

    Spudis, P. D. The Geology of Multi-Ring Impact Basins (Cambridge Univ. Press, Cambridge, UK, 2005)

    Google Scholar 

  21. 21

    Phillips, R. J. et al. Ancient geodynamics and global-scale hydrology on Mars. Science 291, 2587–2591 (2001)

    ADS  CAS  Article  PubMed  Google Scholar 

  22. 22

    Zuber, M. T. et al. Internal structure and early thermal evolution of Mars from Mars Global Surveyor topography and gravity. Science 287, 1788–1793 (2000)

    ADS  CAS  Article  PubMed  PubMed Central  Google Scholar 

  23. 23

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

    Google Scholar 

  24. 24

    Pierazzo, E. & Melosh, H. J. Melt production in oblique impacts. Icarus 145, 252–261 (2000)

    ADS  Article  Google Scholar 

  25. 25

    O’Keefe, J. D. & Ahrens, T. J. Impact-induced energy partitioning, melting and vaporization on terrestrial planets. Proc. Lunar Sci. Conf. 8th 3, 3357–3374 (1977)

    ADS  Google Scholar 

  26. 26

    Turner, S., Evans, P. & Hawkesworth, C. Ultrafast source-to-surface movement of melt at island arcs from Ra-226-Th-230 systematics. Science 292, 1363–1366 (2001)

    ADS  CAS  Article  PubMed  Google Scholar 

  27. 27

    Bruesch, L. S. & Asphaug, E. Modeling global impact effects on middle-sized icy bodies: applications to Saturn’s moons. Icarus 168, 457–466 (2004)

    ADS  Article  Google Scholar 

  28. 28

    Hood, L. L., Richmond, N. C., Pierazzo, E. & Rochette, P. Distribution of crustal magnetic fields on Mars: Shock effects of basin-forming impacts. Geophys. Res. Lett. 30 10.1029/2002GL016657 (2003)

  29. 29

    Acuna, M. H. et al. Global distribution of crustal magnetization discovered by the Mars Global Surveyor MAG/ER experiment. Science 284, 790–793 (1999)

    ADS  CAS  Article  PubMed  Google Scholar 

  30. 30

    Agee, C. B. & Draper, D. S. Experimental constraints on the origin of Martian meteorites and the composition of the Martian mantle. Earth Planet. Sci. Lett. 224, 415–429 (2004)

    ADS  CAS  Article  Google Scholar 

Download references

Acknowledgements

This work was funded by NASA’s MFR programme.

Author Contributions F.N. and S.D.H. carried out the two-dimensional runs and analysed the results, D.G.K. modified the two-dimensional code for the present application and C.B.A. carried out the SPH runs. F.N. conceived the project and wrote the first draft of the paper.

Author information

Affiliations

Authors

Corresponding author

Correspondence to F. Nimmo.

Supplementary information

Supplementary Information

The supplementary information contains three sections: 1) model results; 2) benchmarking and comparisons with smoothed-particle hydrodynamics (SPH) approach; 3) discussion of ejecta curtain velocity and behaviour. The file also contains Supplementary Figures S1-S7 with Legends. (PDF 650 kb)

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Nimmo, F., Hart, S., Korycansky, D. et al. Implications of an impact origin for the martian hemispheric dichotomy. Nature 453, 1220–1223 (2008). https://doi.org/10.1038/nature07025

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

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