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Experimental evidence that potassium is a substantial radioactive heat source in planetary cores

Abstract

The hypothesis that 40K may be a significant radioactive heat source in the Earth's core was proposed on theoretical grounds1,2 over three decades ago, but experiments3,4,5,6,7,8 have provided only ambiguous and contradictory evidence for the solubility of potassium in iron-rich alloys. The existence of such radioactive heat in the core would have important implications for our understanding of the thermal evolution of the Earth and global processes such as the generation of the geomagnetic field, the core–mantle boundary heat flux and the time of formation of the inner core9,10,11,12. Here we provide experimental evidence to show that the ambiguous results obtained from earlier experiments are probably due to previously unrecognized experimental and analytical difficulties. The high-pressure, high-temperature data presented here show conclusively that potassium enters iron sulphide melts in a strongly temperature-dependent fashion and that 40K can serve as a substantial heat source in the cores of the Earth and Mars.

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Acknowledgements

We thank M. Drake and D. Draper for comments and suggestions, N. Irvine for providing the K-silicate glass, B. Mysen for advice on silicate melt properties, C. Hadidiacos for assistance in electron microprobe analyses and C. Alexander, R. Carlson, E. Hauri, J. Li, F. Nimmo, D. Stevenson and J. Van Orman for discussions. This work was supported by a Grant-in-aid from the University of Minnesota (V.R.M.), the NASA (Y.F.), a Carnegie Institution Postdoctoral Fellowship and the Swiss National Science Foundation (W.v.W.).

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Correspondence to V. Rama Murthy.

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The authors declare that they have no competing financial interests.

Supplementary information

Supplementary Information: In this supplementary section we provide further analytical details and high resolution images of a typical run product. (PDF 131 kb)

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Further reading

Figure 1: Potassium loss from oil polished sample compared to dry polished sample.
Figure 2: Effect of temperature on DK.
Figure 3: Effect of silicate depolymerization on DK.
Figure 4: Effect of pressure on DK.

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