Chlorine on the surface of Mercury: MESSENGER gamma-ray measurements and implications for the planet's formation and evolution

Larry G. Evans, Patrick N. Peplowski, Francis M. McCubbin, Timothy J. McCoy, Larry R. Nittler, Mikhail Zolotov, Denton S. Ebel, David J. Lawrence, Richard D. Starr, Shoshana Z. Weider, Sean C. Solomon

Research output: Contribution to journalArticle

21 Citations (Scopus)

Abstract

Orbital measurements obtained by the MESSENGER Gamma-Ray Spectrometer have been analyzed to determine the surface abundance of chlorine in Mercury's northern hemisphere. The derived Cl/Si mass ratio is 0.0057±0.001, which for an assumed Si abundance of 24.6wt% corresponds to 0.14±0.03wt% Cl. The abundance of Cl is a factor of 2.9±1.3 higher in the north polar region (>80°N) than at latitudes 0-60°N, a latitudinal variation similar to that observed for Na. Our reported Cl abundances are consistent with measured bulk concentrations of neutron-absorbing elements on Mercury, particularly those observed at high northern latitudes. The Cl/K ratio on Mercury is chondritic, indicating a limited impact history akin to that of Mars, which accreted rapidly. Hypotheses for the origin of Mercury's high metal-to-silicate ratio must be able to reproduce Mercury's observed elemental abundances, including Cl. Chlorine is also an important magmatic volatile, and its elevated abundance in the northern polar region of Mercury indicates that it could have played a role in the production, ascent, and eruption of flood volcanic material in this region. We have identified several candidate primary mineralogical hosts for Cl on Mercury, including the halide minerals lawrencite (FeCl<inf>2</inf>), sylvite (KCl), and halite (NaCl), as well as Cl-bearing alkali sulfides. Amphiboles, micas, apatite, and aqueously deposited halides, in contrast, may be ruled out as mineralogical hosts of Cl on Mercury.

Original languageEnglish (US)
Pages (from-to)417-427
Number of pages11
JournalIcarus
Volume257
DOIs
StatePublished - Sep 1 2015

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MESSENGER (spacecraft)
chlorine
planets
planet
gamma rays
polar regions
halides
halide
polar region
gamma ray spectrometers
amphiboles
ascent
apatites
Northern Hemisphere
sylvite
mass ratios
volcanic eruptions
mars
mercury
sulfides

Keywords

  • Gamma-ray spectroscopy
  • Geological processes
  • Mercury, surface
  • Planetary formation

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Chlorine on the surface of Mercury : MESSENGER gamma-ray measurements and implications for the planet's formation and evolution. / Evans, Larry G.; Peplowski, Patrick N.; McCubbin, Francis M.; McCoy, Timothy J.; Nittler, Larry R.; Zolotov, Mikhail; Ebel, Denton S.; Lawrence, David J.; Starr, Richard D.; Weider, Shoshana Z.; Solomon, Sean C.

In: Icarus, Vol. 257, 01.09.2015, p. 417-427.

Research output: Contribution to journalArticle

Evans, LG, Peplowski, PN, McCubbin, FM, McCoy, TJ, Nittler, LR, Zolotov, M, Ebel, DS, Lawrence, DJ, Starr, RD, Weider, SZ & Solomon, SC 2015, 'Chlorine on the surface of Mercury: MESSENGER gamma-ray measurements and implications for the planet's formation and evolution', Icarus, vol. 257, pp. 417-427. https://doi.org/10.1016/j.icarus.2015.04.039
Evans, Larry G. ; Peplowski, Patrick N. ; McCubbin, Francis M. ; McCoy, Timothy J. ; Nittler, Larry R. ; Zolotov, Mikhail ; Ebel, Denton S. ; Lawrence, David J. ; Starr, Richard D. ; Weider, Shoshana Z. ; Solomon, Sean C. / Chlorine on the surface of Mercury : MESSENGER gamma-ray measurements and implications for the planet's formation and evolution. In: Icarus. 2015 ; Vol. 257. pp. 417-427.
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abstract = "Orbital measurements obtained by the MESSENGER Gamma-Ray Spectrometer have been analyzed to determine the surface abundance of chlorine in Mercury's northern hemisphere. The derived Cl/Si mass ratio is 0.0057±0.001, which for an assumed Si abundance of 24.6wt{\%} corresponds to 0.14±0.03wt{\%} Cl. The abundance of Cl is a factor of 2.9±1.3 higher in the north polar region (>80°N) than at latitudes 0-60°N, a latitudinal variation similar to that observed for Na. Our reported Cl abundances are consistent with measured bulk concentrations of neutron-absorbing elements on Mercury, particularly those observed at high northern latitudes. The Cl/K ratio on Mercury is chondritic, indicating a limited impact history akin to that of Mars, which accreted rapidly. Hypotheses for the origin of Mercury's high metal-to-silicate ratio must be able to reproduce Mercury's observed elemental abundances, including Cl. Chlorine is also an important magmatic volatile, and its elevated abundance in the northern polar region of Mercury indicates that it could have played a role in the production, ascent, and eruption of flood volcanic material in this region. We have identified several candidate primary mineralogical hosts for Cl on Mercury, including the halide minerals lawrencite (FeCl2), sylvite (KCl), and halite (NaCl), as well as Cl-bearing alkali sulfides. Amphiboles, micas, apatite, and aqueously deposited halides, in contrast, may be ruled out as mineralogical hosts of Cl on Mercury.",
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AU - McCoy, Timothy J.

AU - Nittler, Larry R.

AU - Zolotov, Mikhail

AU - Ebel, Denton S.

AU - Lawrence, David J.

AU - Starr, Richard D.

AU - Weider, Shoshana Z.

AU - Solomon, Sean C.

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N2 - Orbital measurements obtained by the MESSENGER Gamma-Ray Spectrometer have been analyzed to determine the surface abundance of chlorine in Mercury's northern hemisphere. The derived Cl/Si mass ratio is 0.0057±0.001, which for an assumed Si abundance of 24.6wt% corresponds to 0.14±0.03wt% Cl. The abundance of Cl is a factor of 2.9±1.3 higher in the north polar region (>80°N) than at latitudes 0-60°N, a latitudinal variation similar to that observed for Na. Our reported Cl abundances are consistent with measured bulk concentrations of neutron-absorbing elements on Mercury, particularly those observed at high northern latitudes. The Cl/K ratio on Mercury is chondritic, indicating a limited impact history akin to that of Mars, which accreted rapidly. Hypotheses for the origin of Mercury's high metal-to-silicate ratio must be able to reproduce Mercury's observed elemental abundances, including Cl. Chlorine is also an important magmatic volatile, and its elevated abundance in the northern polar region of Mercury indicates that it could have played a role in the production, ascent, and eruption of flood volcanic material in this region. We have identified several candidate primary mineralogical hosts for Cl on Mercury, including the halide minerals lawrencite (FeCl2), sylvite (KCl), and halite (NaCl), as well as Cl-bearing alkali sulfides. Amphiboles, micas, apatite, and aqueously deposited halides, in contrast, may be ruled out as mineralogical hosts of Cl on Mercury.

AB - Orbital measurements obtained by the MESSENGER Gamma-Ray Spectrometer have been analyzed to determine the surface abundance of chlorine in Mercury's northern hemisphere. The derived Cl/Si mass ratio is 0.0057±0.001, which for an assumed Si abundance of 24.6wt% corresponds to 0.14±0.03wt% Cl. The abundance of Cl is a factor of 2.9±1.3 higher in the north polar region (>80°N) than at latitudes 0-60°N, a latitudinal variation similar to that observed for Na. Our reported Cl abundances are consistent with measured bulk concentrations of neutron-absorbing elements on Mercury, particularly those observed at high northern latitudes. The Cl/K ratio on Mercury is chondritic, indicating a limited impact history akin to that of Mars, which accreted rapidly. Hypotheses for the origin of Mercury's high metal-to-silicate ratio must be able to reproduce Mercury's observed elemental abundances, including Cl. Chlorine is also an important magmatic volatile, and its elevated abundance in the northern polar region of Mercury indicates that it could have played a role in the production, ascent, and eruption of flood volcanic material in this region. We have identified several candidate primary mineralogical hosts for Cl on Mercury, including the halide minerals lawrencite (FeCl2), sylvite (KCl), and halite (NaCl), as well as Cl-bearing alkali sulfides. Amphiboles, micas, apatite, and aqueously deposited halides, in contrast, may be ruled out as mineralogical hosts of Cl on Mercury.

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KW - Planetary formation

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