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

    17 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

    Fingerprint

    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 - Peplowski, Patrick N.

    AU - McCubbin, Francis M.

    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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