TY - JOUR
T1 - Chlorine on the surface of Mercury
T2 - MESSENGER gamma-ray measurements and implications for the planet's formation and evolution
AU - Evans, Larry G.
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.
N1 - Funding Information:
This work was supported by the NASA Discovery Program under contracts NAS5-97271 to The Johns Hopkins University Applied Physics Laboratory and NASW-0002 to the Carnegie Institution of Washington. All of the data used in the present study are available in the Planetary Data System (PDS). Support was also provided to LGE, DJL, LRN, and RDS by the MESSENGER Participating Scientist Program. FMM and DSE acknowledge support from the NASA Cosmochemistry Program during this study (through grants NNX14AK43G and NNX10AI42G, respectively). We especially thank the dedicated MESSENGER operations team for their continued support of this mission.
Publisher Copyright:
© 2015 Elsevier Inc.
PY - 2015/9/1
Y1 - 2015/9/1
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.
KW - Gamma-ray spectroscopy
KW - Geological processes
KW - Mercury, surface
KW - Planetary formation
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U2 - 10.1016/j.icarus.2015.04.039
DO - 10.1016/j.icarus.2015.04.039
M3 - Article
AN - SCOPUS:84930943244
SN - 0019-1035
VL - 257
SP - 417
EP - 427
JO - Icarus
JF - Icarus
ER -