Global Multivariate Spectral Analysis of Mercury and the Identification
of Geochemical Terrains: Derived from the MASCS Spectrometer onboard
NASA’s MESSENGER Mission
Abstract
The visible-infrared spectra of Mercury’s surface show little variation,
displaying no distinct spectral features except for the possible
spectral identification of sulfide within the hollows (Vilas et al.
2016). It is essential therefore to define and map any subtle spectral
heterogeneity across Mercury’s surface and to correlate these
differences where possible to geomorphological features, such as impact
craters, volcanic vents, and tectonic features. The Mercury Atmospheric
and Surface and Composition Spectrometer (MASCS) instrument onboard
MESSENGER spacecraft is the only hyperspectral reflectance spectrometer
to date that has mapped Mercury’s surface in the wavelength range 320 nm
- 1450 nm. The limitation of MASCS is that it’s a point spectrometer
that mapped Mercury’s surface at non-uniform spatial scale. In this
study, we resampled the global MASCS hyperspectral dataset to a uniform
spatial resolution of 1 pixel per degree. This enabled us to perform
global multivariate analyses, including standard spectral parameter
maps, k-means clustering, and principal component analysis (PCA) to
spectrally characterize Mercury’s surface. Among these techniques, PCA
significantly improved the identification of spectral heterogeneities
across Mercury correlated to both chemical and physical properties of
the surface, enabling us to identify units based on grain size, the
presence of amorphous materials, and space-weathering associated
alterations. The global MASCS PC color-composite map derived from
principal components 1, 2, and 6 effectively distinguishes varying
spectro-morphologies across Mercury’s surface, highlighting the spectral
properties of various geochemical terrains. We further demonstrate that
PCA spectrally differentiates between the two northern volcanic plains’
geochemical regions; the high-Mg and low-Mg terrains.