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  • Letter
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Darkening of Mercury's surface by cometary carbon

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Abstract

Mercury’s surface is darker than that of the Moon1,2. Iron-bearing minerals and submicroscopic metallic iron produced by space weathering are the primary known darkening materials on airless bodies. Yet Mercury’s iron abundance at the surface is lower than the Moon’s3,4; another material is therefore likely to be responsible for Mercury’s dark surface1,2,5,6,7,8. Enhanced darkening by submicroscopic metallic iron particles under intense space weathering at Mercury’s surface9,10,11,12 is insufficient to reconcile the planet’s low reflectance with its low iron abundance12. Here we show that the delivery of cometary carbon by micrometeorites provides a mechanism to darken Mercury’s surface without violating observational constraints on iron content. We calculate the micrometeorite flux at Mercury and numerically simulate the fraction of carbonaceous material retained by the planet following micrometeorite impacts. We estimate that 50 times as many carbon-rich micrometeorites per unit surface area are delivered to Mercury, compared with the Moon, resulting in approximately 3–6 wt% carbon at Mercury’s surface (in graphite, amorphous, or nanodiamond form). Spectroscopic analysis of products of hypervelocity impact experiments demonstrates that the incorporation of carbon effectively darkens and weakens spectral features, consistent with remote observations of Mercury1,2,5,6,7,8,12. Carbon delivery by micrometeorites provides an explanation for Mercury’s globally low reflectance and may contribute to the darkening of planetary surfaces elsewhere.

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Figure 1: Retention of micrometeorite impacts at Mercury.
Figure 2: Impact-generated agglutinates collected from crater floors.
Figure 3: Visible/near-infrared spectra of impact agglutinates and different terrain types at Mercury.

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Change history

  • 16 April 2015

    In the version of this Letter originally published online, the caption of Fig. 2 should have read 'Agglutinates generated in the presence of complex organics (right column) are visually darker than organics-free agglutinates (left column)'. This error has been corrected in all versions of the Letter.

References

  1. Denevi, B. W. & Robinson, M. S. Mercury’s albedo from Mariner 10: Implications for the presence of ferrous iron. Icarus 197, 239–246 (2008).

    Article  Google Scholar 

  2. Robinson, M. S. et al. Reflectance and color variations on Mercury: Regolith processes and compositional heterogeneity. Science 321, 66–69 (2008).

    Article  Google Scholar 

  3. Nittler, L. R. et al. The major-element composition of Mercury’s surface from MESSENGER X-ray spectrometry. Science 333, 1847–1850 (2011).

    Article  Google Scholar 

  4. Evans, L. G. et al. Major-element abundances on the surface of Mercury: Results from the MESSENGER Gamma-Ray Spectrometer. J. Geophys. Res. 117, E00L07 (2012).

    Article  Google Scholar 

  5. Rava, B. & Hapke, B. An analysis of the Mariner 10 color ratio map of Mercury. Icarus 71, 397–429 (1987).

    Article  Google Scholar 

  6. McClintock, W. E. et al. Spectroscopic observations of Mercury’s surface reflectance during MESSENGER’s first Mercury flyby. Science 321, 62–65 (2008).

    Article  Google Scholar 

  7. Denevi, B. W. et al. The evolution of Mercury’s crust: A global perspective from MESSENGER. Science 324, 613–618 (2009).

    Google Scholar 

  8. Blewett, D. T. et al. Multispectral images of Mercury from the first MESSENGER flyby: Analysis of global and regional color trends. Earth Planet. Sci. Lett. 285, 272–282 (2009).

    Article  Google Scholar 

  9. Cintala, M. J. Impact-induced thermal effects in the lunar and mercurian regoliths. J. Geophys. Res. 97, 947–973 (1992).

    Article  Google Scholar 

  10. Britt, D. T. & Pieters, C. M. Darkening in black and gas-rich ordinary chondrites: The spectral effects of opaque morphology and distribution. Geochim. Cosmochim. Acta 58, 3905–3919 (1994).

    Article  Google Scholar 

  11. Noble, S. K., Pieters, C. M. & Keller, L. P. An experimental approach to understanding the optical effects of space weathering. Icarus 192, 629–642 (2007).

    Article  Google Scholar 

  12. Riner, M. A. & Lucey, P. G. Spectral effects of space weathering on Mercury: The role of composition and environment. Geophys. Res. Lett. 39, L12201 (2012).

    Article  Google Scholar 

  13. Hartmann, W. K. et al. Basaltic Volcanism on the Terrestrial Planets 1049–1127 (Pergamon Press, 1981).

    Google Scholar 

  14. Delsemme, A. H. The chemistry of comets. Phil. Trans. R. Soc. Lond. A 325, 509–523 (1988).

    Article  Google Scholar 

  15. Moses, J. I., Rawlins, K., Zahnle, K. & Dones, L. External sources of water for Mercury’s putative ice deposits. Icarus 137, 197–221 (1999).

    Article  Google Scholar 

  16. Wiegert, P., Vaubaillon, J. & Campbell-Brown, M. A dynamical model of the sporadic meteoroid complex. Icarus 201, 295–310 (2009).

    Article  Google Scholar 

  17. Nesvorný, D. et al. Cometary origin of the zodiacal cloud and carbonaceous micrometeorites. Implications for hot debris disks. Astrophys. J. 713, 816–836 (2010).

    Article  Google Scholar 

  18. Duprat, J. et al. Extreme deuterium excesses in ultracarbonaceous micrometeorites from central Antarctic snow. Science 328, 742–745 (2010).

    Article  Google Scholar 

  19. Dobrică, E. et al. Connection between micrometeorites and Wild 2 particles: From Antarctic snow to cometary ices. Meteorit. Planet. Sci. 44, 1643–1661 (2009).

    Article  Google Scholar 

  20. Jessberger, E. K., Christoforidis, A. & Kissel, J. Aspects of the major element composition of Halley’s dust. Nature 332, 691–695 (1988).

    Article  Google Scholar 

  21. Brownlee, D. E. et al. Comet 81P/Wild 2 under a microscope. Science 314, 1711–1716 (2006).

    Article  Google Scholar 

  22. Gallien, J. P. et al. Characterization of carbon- and nitrogen-rich particle fragments captured from comet 81P/Wild 2. Meteorit. Planet. Sci. 43, 335–351 (2008).

    Article  Google Scholar 

  23. Borin, P., Cremonese, G., Marzari, F., Bruno, M. & Marchi, S. Statistical analysis of micrometeoroids flux on Mercury. Astron. Astrophys. 503, 259–264 (2009).

    Article  Google Scholar 

  24. Liou, J-C. & Zook, H. A. Comets as a source of low eccentricity and low inclination interplanetary dust particles. Icarus 123, 491–502 (1996).

    Article  Google Scholar 

  25. Thomas-Keprta, K. L. et al. Organic matter on the Earth’s moon. Geochim. Cosmochim. Acta 134, 1–15 (2014).

    Article  Google Scholar 

  26. McKay, D. S. et al. The Lunar Sourcebook 284–356 (Cambridge Univ. Press, 1991).

    Google Scholar 

  27. Ishii, H. A. et al. Comparison of Comet 81P/Wild 2 dust with interplanetary dust from comets. Science 319, 447–450 (2008).

    Article  Google Scholar 

  28. Clark, R. N. Spectral properties of mixtures of montmorillonite and dark carbon grains: Implications for remote sensing minerals containing chemically and physically adsorbed water. J. Geophys. Res. 88, 10635–10644 (1983).

    Article  Google Scholar 

  29. Neumann, G. A. et al. Bright and dark polar deposits on Mercury: Evidence for surface volatiles. Science 339, 296–300 (2013).

    Article  Google Scholar 

  30. Kenkmann, T., Hornemann, U. & Stöffler, D. Experimental shock synthesis of diamonds in a graphite gneiss. Meteorit. Planet. Sci. 40, 1299–1310 (2005).

    Article  Google Scholar 

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Acknowledgements

This research was supported by NASA’s Planetary Geology & Geophysics (NNX13AB75G) and NESSF (NNXC12AL79H) programs. The authors thank T. Daly and T. Hiroi for assistance with sample analysis and gratefully acknowledge the technical team at the Ames Vertical Gun Range for supporting the impact experiments.

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Authors

Contributions

M.B.S. wrote the manuscript and performed the calculations, impact experiments and sample analyses. P.H.S. assisted with impact experiments, development of ideas and manuscript edits. M.A.R. analysed remote sensing data for comparison with experimental results.

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Correspondence to Megan Bruck Syal.

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The authors declare no competing financial interests.

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Syal, M., Schultz, P. & Riner, M. Darkening of Mercury's surface by cometary carbon. Nature Geosci 8, 352–356 (2015). https://doi.org/10.1038/ngeo2397

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