Shallow crustal composition of Mercury as revealed by spectral properties and geological units of two impact craters

We have performed a combined geological and spectral analysis of two impact craters on Mercury: the 15 km diameter Waters crater (106°W; 9°S) and the 62.3 km diameter Kuiper crater (30°W; 11°S). Using the Mercury Dual Imaging System (MDIS) Narrow Angle Camera (NAC) dataset we defined and mapped several units for each crater and for an external reference area far from any impact related deposits. For each of these units we extracted all spectra from the MESSENGER Atmosphere and Surface Composition Spectrometer (MASCS) Visible-InfraRed Spectrograph (VIRS) applying a first order photometric correction. For all the mapped units, we analyzed the spectral slope in two wavelength ranges, 350-450 nm and 450-650 nm, and the absolute reflectance in the 700-750 nm range. Normalized spectra of Waters crater display a generally bluer spectral slope than the external reference area over both wavelength windows. Normalized spectra of Kuiper crater generally display a redder slope than the external reference area in the 350-450 nm window, while they display a bluer slope than the external reference area in the 450-650 nm wavelength range. The combined use of geological and spectral analyses enables reconstruction of the local scale stratigraphy beneath the two craters, providing insight into the properties of the shallower crust of Mercury. Kuiper crater, being ~4 times larger than Waters crater, exposes deeper layers with distinctive composition, while the result for Waters crater might indicate substantial compositional homogeneity with the surrounding intercrater plains, though we cannot exclude the occurrence of horizontal compositional heterogeneities in the shallow sub-surface

Making Sense of 2.5 Million Surface Reflectance Spectra of Mercury from MESSENGER

The Mercury Atmospheric and Surface and Composition Spectrometer (MASCS) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft has mapped the surface of Mercury on a global basis during its one-year primary orbital mission and the first third of its extended mission, producing ~2.5 million spectra from March 2011 to July 2012. The primary challenge to analyzing this dataset is to cope with its large size. In earlier studies of MASCS data, we combined several approaches, ranging from principal component analysis (PCA) to unsupervised cluster analysis and regridding to global and local fixed grids. Each of those techniques provided insight into spectral variations for different volumes of data, but each was quickly overcome by the growing dataset. The most recent version of our data analysis procedure uses PostgreSQL, a type of database management that controls the creation, integrity, maintenance, and use of a database. It embeds a high-level query language, which greatly simplifies database organization as well as retrieval and presentation of database information. We set up a data pipeline to update automatically the MASCS data, read them from the NASA Planetary Data System format, regrid the data to a common grid length, and store all information in the database. All data are then readily available to any authorized user in our network. We are working on a library to access the data directly from within our analysis software, and some preliminary functions have been implemented. As an example, the calculation of a parameter representing the database takes 2 s even for the full dataset of 2.5 million entries. It is thus straightforward to create and analyze rapidly the data, as for example the distribution of normalized radiance at a fixed wavelength. The new methodology provides facilities for controlling data access, enforcing data integrity, managing concurrency control, and recovering the database after a failure and restoring it from backup files, as well as maintaining database security. As an example, a simple query on the volume of data results in 2,476,048 spectra in 700 ms. Moreover, we use PostGIS to add support for geographic objects in a geographic information system (GIS) and to extend the database language with functions to create and manipulate geographic objects. A typical application is the definition of a large number of regions of interest (ROIs) and the search for all data points falling within each ROI. This facility may be used to extract spectral signatures specific to user-defined geological units in a few seconds and to explore the properties of the data from the different ROIs allowing quick analysis of the spectral characteristics of Mercury. We have successfully tested remote access to the database with a GIS visualization system, and we have created data visualization products that layer camera data and real-time-queried MASCS data

Combining High-Temperature Spectroscopy and Principal Component Analysis to Understand Mercury Surface Spectra from MESSENGER

For the first time we a PCA approach for the MESSENGER spectral data with new spectral data obtained in the Planetary Emissivity Laboratory (PEL) at the Deutsches Zentrum für Luft- und Raumfahrt (DLR) in Berlin

Exploiting the Mercury Surface Reflectance Spectroscopy Dataset from MESSENGER: Making Sense of Three Million Spectra

The Mercury Atmospheric and Surface and Composition Spectrometer (MASCS) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft has mapped the surface of Mercury on a global basis during its one-year primary orbital mission and the first third of its extended mission, producing more than three million spectra. To analyze this large dataset we make use of our recently developed advanced database management system. This system allows the extraction and simultaneous analysis of large amounts of data, transparent to the underlying data structure. As a test case we analyze here the statistical distribution of MASCS normalized reflectance at a few selected wavelengths. We obtain a separation of Mercury’s surface into spectral classes that are coherent with the results from unsupervised cluster analysis on the same data

Turn the heat up – A first look at MESSENGER's near-infrared spectra of Mercury using new high-temperature emissivity measurements

Analyzing the surface composition of Mercury's regolith from remote-sensing measurements is a challenging task. In support of the National Aeronautics and Space Agency's MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) mission and especially in preparation for the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) instrument on the BepiColombo mission of the European Space Agency and the Japan Aerospace Exploration Agency, we are developing a Planetary Emissivity Laboratory (PEL) at Deutsches Zentrum für Luft- und Rahmfahrt (DLR) in Berlin. The PEL allows measurement of the emissivity of Mercury-analogue materials at grain sizes smaller than 25 μm and at temperatures of more than 400°C, typical for Mercury's low-latitude dayside. The PEL development follows a multi-step approach. We have already obtained emissivity data at mid-infrared wavelengths that show significant changes in spectral behavior with temperature indicative of changes in the crystal structure of the samples. We are currently installing a new calibration target that will allow the acquisition of emissivity data over the full wavelength range from 1 to 50 micrometer with good signal-to-noise ratio. Here we present initial data in the range 1 to 1.4 micrometer, the near-infrared wavelength coverage of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) instrument on MESSENGER. Even these early PEL measurements have important implications for the analysis of the spectral observations obtained during MESSENGER's first Mercury flyby on 14 January 2008 as well as the data to be obtained during the probe's second Mercury flyby on 6 October

Unsupervised clustering analysis of spectral data for the Rudaki area on Mercury

We present a study of spectral reflectance data from Mercury focused on an area that encompasses the craters Kuiper-Murasaki, Rudaki, and Waters. The goal is to identify different spectral units and analyze potential relations among them. The study region is geologically and spectrally classified as heavily cratered intermediate terrain (IT) with mixed patches of high-reflectance red plains (HRP) and intermediate plains (IP), on the basis of multispectral images taken by the Mercury Dual Imaging System (MDIS) [1]. Recent analysis of observations by the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) instrument on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft with an unsupervised hierarchical clustering method shows a comparable number of units at global scales [2,3]. Analyses on the local scale reveal a larger number of spectral units with a substantially more complex relationship among units