1 research outputs found
Mercury: Midāinfrared (3ā13.5 Ī¼m) observations show heterogeneous composition, presence of intermediate and basic soil types, and pyroxene
Abstractā The Aerospace Corporation's broadband array spectrograph system (BASS) mounted on the NASA infrared telescope facility (IRTF) on Mauna Kea, Hawaii was used to obtain spectral measurements of Mercury's thermal emission on 1998 March 21 (45ā85Ā° longitude), and on 1998 May 12 (68ā108Ā° longitude). The spectra show heterogeneous composition on Mercury's surface between longitudes 45ā85Ā° and about 68ā108Ā°. These observations include measurements from 3 to 6 Ī¼m, a spectral region not previously covered by midāinfrared spectroscopy. Excellent quality data were obtained in the atmospheric windows between 3ā4.2 and 4.6ā5.5 Ī¼m. These wavelength regions exhibit high emissivity characteristic of a regolith with strong thermal gradients maintained in a vacuum environment with spectra dominated by grain sizes of Ė30 Ī¼m. Emission peaks are present at 3.5 and 5 Ī¼m in the 45ā85Ā° longitude data. The 5 Ī¼m peak has been tentatively attributed to clinopyroxene. Data were also obtained in the 7.5ā13.5 Ī¼m spectral region. Spectra obtained during both observing periods show wellādefined emissivity maxima (EM) in the spectral vicinity (between 7.7 and 9.2 Ī¼m) of the Christiansen frequency of silicate soils. The location of the EM for longitudes 45ā85Ā° (7.9 Ī¼m) is consistent with a surface composition of intermediate SiO2 content. The overall spectral shape is similar to that obtained previously at the same location with different instrumentation. In the region 68ā108Ā° longitude, three EM are observed at 7.8, 8.2, and 9.2 Ī¼m, indicating the presence of distinctly different surface composition from the other location. Comparisons of these data to other midāinfrared spectra of Mercury's surface and asteroids, and of the different instrumentation used in observations are included