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The 0.7-5.3 mum IR spectra of Mercury and the Moon:: Evidence for high-Ca clinopyroxene on Mercury
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
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2005 (English)In: IcarusArticle in journal (Refereed) Published
Abstract [en]

We present infrared spectra of Mercury and the Moon in the wavelength range 0.7--

5.3 $\mu$m obtained with the SpeX spectrograph at the NASA Infrared Telescope Fac

ility. The spectra were acquired from pole and terminator locations of Mercury's

surface and of Mersenius C and the Copernicus central peak on the Moon. Spectra o

f both bodies were measured in close temporal succession and were reduced in the

same manner with identical calibration stars to minimize differences in the reduc

tion process. The Copernicus spectra display the expected absorption features due

to mafic minerals in the near infrared and show spectral features in the SiO com

bination/overtone vibrational band region above 4 $\mu$m. The spectra of Mercury

from longitude 170$^\circ$ and north and south midlatitudes display a 1-$\mu$m ab

sorption band indicative of high-Ca clinopyroxene, while a spectrum from longitud

e 260$^\circ$ and northern midlatitudes does not. The Mercury spectra show a broa

d feature of low emittance over the full 3--5 $\mu$m thermal infrared region, but

no narrow features in this spectral range. The longitude 260$^\circ$ spectrum sh

ows excess thermal emission around 5 $\mu$m attributable to the existence of a th

ermal gradient in the insolated dayside regolith. The thermal-IR spectra suggest

a significant difference in the compositional and/or structural properties of Mer

cury and the Moon that may be due to grain size, absorption coefficient, or the m

agnitude of near-surface thermal gradients. The results indicate that the composi

tion of Mercury's surface is heterogeneous on regional scales, and that the near

infrared wavelength range provides more discriminative information on the surface

composition than the 2--4 $\mu$m region, where the solar reflected and thermally

emitted radiation contribute approximately equally to the observed flux of these


Place, publisher, year, edition, pages
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Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:uu:diva-71432OAI: oai:DiVA.org:uu-71432DiVA: diva2:99343
SubmittedAvailable from: 2005-05-09 Created: 2005-05-09 Last updated: 2011-01-12

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Warell, Johan
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