Mercury Dual Imaging System Research Articles

Temperature-related Variations of 1064 nm Surface Reflectance on Mercury: Implications for Space Weathering

It has been predicted that high equatorial temperatures on Mercury could promote thermal annealing by Ostwald ripening, where nanophase metal particles (a product of space weathering) coalesce and grow into larger, microphase particles, resulting in lower albedo. Here, we test this prediction by studying the correlation between albedo and temperature in 1° spatial bins using newly recalibrated 1064 nm reflectance data acquired by the Mercury Laser Altimeter (MLA), low incidence angle data from the Mercury Dual Imaging System (MDIS), and newly modeled maximum surface temperatures (MSTs). Accounting for local geology and latitude, we compare the reflectance values of surfaces with MSTs >675 K (where Ostwald ripening is predicted to be most effective) to surfaces with MSTs <473 K (where ripening is predicted not to be effective). Smooth plain surfaces >675 K are 10% and 12% darker than surfaces <473 K in MLA and MDIS data, respectively, and nonsmooth plain surfaces >675 K are 8% and 7% darker than surfaces <473 K. However, open questions remain regarding the causation of this darkening; statistical tests cannot distinguish whether the reflectance differences are systematic or the result of compositional variations that happen to correlate with MST. Along Mercury’s thermal longitudes, we find that reflectance is typically lower along hot poles than along the 90°E cold pole in the low-to-midlatitudes, especially in the smooth plains, consistent with previous work identifying a decrease in optical maturity along the 90°E cold pole. Longitudinal reflectance variations correlate with temperature variations, rather than variations in micrometeoroid or solar wind fluxes.

A hybrid geological map of Sibelius Crater on Mercury, and its associated ejecta and impact melt deposits

Abstract Using MESSENGER Mercury Dual Imaging System data, we produced three new maps of Sibelius Crater, Mercury. Geomorphological and spectral maps were combined into a single hybrid map containing units associated with ejecta deposits, crater floor landforms and impact melt ponding. Spatial measurement of these units shows that ∼50% of the mapped melt pond area lies within a large, degraded impact crater (crater B), beyond the significantly lower northern Sibelius rim, with a potential melt flow to a smaller, degraded impact structure further north (crater C). Freshly processed spectral data from the eight-colour Map Projected Multispectral Reduced Data Record data highlight the emplacement of multiple uplifted ejecta units with distinct spectral properties. A new, high-resolution digital elevation model was created to help define and analyse crater floor uplift features and disrupted crater rims and to create detailed cross-sections. These illustrate a proposed location of B's central uplift structure exposed in the northern wall slopes of Sibelius. Small features at the limit of visibility, such as a groove possibly associated with a rolling or sliding mega-boulder and lobate melt flow on the crater floor with accompanying channel opening, are highlighted for future investigations by BepiColombo's instruments once it reaches orbit.

Investigating the Stability and Distribution of Surface Ice in Mercury’s Northernmost Craters

Observations made by Earth-based radar telescopes and the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft provided compelling evidence for water ice in Mercury's polar craters. In our investigation, we constructed higher-resolution (125 m pixel−1) digital elevation models (DEMs) for four of the largest northernmost craters, Kandinsky, Tolkien, Chesterton, and Tryggvadóttir. The DEMs were leveraged to model solar illumination and the thermal environment, products that were used to identify permanently shadowed regions and simulate surface temperatures. From these models, we predicted the regions of surface stability for ice and volatile organic compounds. These predictions were then compared against the Arecibo radar, Mercury Laser Altimeter (MLA), and Mercury Dual Imaging System (MDIS) data. Our radar analysis shows that areas of high radar backscatter are correlated with areas predicted to host surface ice. Additionally, we identify radar backscatter heterogeneities within the deposits that could be associated with variations in ice purity, mantling of the ice, or ice abundances. The MDIS analysis did not reveal conclusive evidence for ice or volatiles at the surface, while MLA results support the presence of water ice at the surface in these craters. However, evidence for boundaries between the surface ice and low-reflectance volatile organic compounds, as suggested could be present by our models, was inconclusive owing to the limited MESSENGER data in these regions. BepiColombo’s upcoming orbital mission at Mercury has the opportunity to obtain new measurements of these high-latitude craters and test our predictions for the distribution of surface volatiles in these environments.

Highly Resolved Topography and Illumination at Mercury’s South Pole from MESSENGER MDIS NAC

Mercury’s south polar region is of particular interest since Arecibo radar measurements show many high-reflectance regions consistent with ice deposits. However, current elevation information in Mercury’s southern hemisphere is not sufficient to perform detailed modeling of the illumination and thermal conditions at these radar-bright locations and to constrain properties of the volatiles potentially residing there. In this work, we leverage previously existing elevation maps of Mercury’s surface from stereo-photogrammetry at 665 m pix−1, Mercury Dual Imaging System Narrow Angle Camera images, and Shape-from-Shading tools from the Ames Stereo Pipeline, to provide the first high-resolution topographic maps of the south pole with a resolution of 250 m pix−1 poleward of 75°S. We show that the increased resolution and level of detail provided by our new elevation model allow for a more realistic recovery of illumination conditions in Mercury’s south polar region, thus opening the way to future thermal analyses and for the characterization of potential ice and volatile deposits. We compare both the old and new topographic models to the Mercury Dual Imaging System Narrow Angle Camera images to show the higher level of fidelity with our products, and we assess the improved consistency of derived permanently shadowed regions with reflectance measurements by Arecibo’s antennas.

High-Resolution Regional Digital Elevation Models and Derived Products from MESSENGER MDIS Images

The Mercury Dual Imaging System (MDIS) on the Mercury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft has provided global images of Mercury’s surface. A subset of off-nadir observations acquired at different times resulted in near-global stereo coverage and enabled the creation of local area digital elevation models (DEMs). We derived fifty-seven DEMs covering nine sites of scientific interest and tied each to a geodetic reference derived from Mercury Laser Altimeter (MLA) profiles. DEMs created as part of this study have pixel scales ranging from 78 m/px to 500 m/px, and have vertical precisions less than the DEM pixel scale. These DEMs allow detailed characterizations of key Mercurian features. We present a preliminary examination of small features called “hollows” in three DEM sites. Depth measurements from the new DEMs are consistent with previous shadow and stereo measurements.

Geology of the Kuiper quadrangle (H06), Mercury

ABSTRACT The Kuiper quadrangle (H06) is located at the equatorial zone of Mercury and encompasses the area between 288°E – 360°E and 22.5°N – 22.5°S. Using the NASA MESSENGER data, we compiled a geological map of the quadrangle at a 1:3,000,000 scale. The mapping was mainly based on photo-interpretation of an MDIS (Mercury Dual Imaging System) monochrome 166 m/pixel basemap. Additional datasets were also considered: stereo-DTM of the region, mosaics with high-incidence illumination, and the MDIS global color mosaic. The map shows that the quadrangle is characterized by the prevalence of crater materials which are distinguished into three classes based on their degradation degree. Different plain units were also identified and classified on the basis of their density of cratering. Several structures, mainly represented by contractional faults, were mapped in all quadrangle areas. The map represents the first complete geologic survey of H06 at this scale and provides a highly detailed analysis of the Kuiper quadrangle’s surface geology.

Near‐Ultraviolet to Near‐Infrared Spectral Properties of Hollows on Mercury: Implications for Origin and Formation Process

AbstractAmong the geological features revealed by the MESSENGER (MErcury Surface, Space ENvironment, GEochemistry and Ranging) mission on the surface of Mercury, hollows are the most surprising and least understood. Possibly related to volatile components, hollows are small depressions, surrounded by bright halos and are not observed on any other surfaces in our solar system. Previous analysis of multispectral data obtained by Mercury Dual Imaging System (MDIS) has shown that some hollows have weak spectral absorption features centered at around 600 nm. In this work, we analyzed four hollows with observations acquired by the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) on board MESSENGER with more than 230 spectral channels from the near‐ultraviolet to the near‐infrared. Unlike previous MDIS multispectral data, the MASCS reflectance spectra exhibit no absorption features in the MDIS wavelength range. However, we found that hollows have unique spectral properties in the near‐ultraviolet, with a spectral curvature between 300 and 600 nm that is distinctly different from other geological units. Moreover, we used MASCS observations with the best available spatial resolution (&lt;0.5 km/pixel) to analyze both parts of a hollow: the flat floor and the surrounding halo. Our results support the hypothesis that hollows form by a sublimation process and scarp retreat.

New Illumination and Temperature Constraints of Mercury's Volatile Polar Deposits.

Images from the Mercury Dual Imaging System (MDIS) aboard the MErcury Surface, Space ENvironment, GEochemistry, and Ranging mission reveal low-reflectance polar deposits that are interpreted to be lag deposits of organic-rich, volatile material. Interpretation of these highest-resolution images of Mercury’s polar deposits has been limited by the available topography models, so local high-resolution (125 m pixel−1) digital elevation models (DEMs) were made using a combination of data from the Mercury Laser Altimeter (MLA) and from shape-from-shading techniques using MDIS images. Local DEMs were made for eight of Mercury’s north polar craters; these DEMs were then used to create high-resolution simulated image, illumination, and thermal models. The simulated images reveal that the pixel brightness variations imaged within Mercury’s low-reflectance deposits are consistent with scattered light reflecting off of topography and do not need to be explained by volatile compositional differences as previously suggested. The illumination and thermal models show that these low-reflectance polar deposits extend beyond the permanently shadowed region, more than 1.0 km in some locations, and correspond to a maximum surface temperature of greater than 250 K but less than 350 K. The low-reflectance boundaries of all eight polar deposits studied here show a close correspondence with the surface stability boundary of coronene (C24H12). While coronene should only be viewed as a proxy for the myriad volatile compounds that may exist in Mercury’s polar deposits, coronene’s surface stability boundary supports the idea that Mercury’s low-reflectance polar deposits are composed of macromolecular organic compounds, consistent with the hypotheses of exogenous transport and in situ production.

Spectral properties of the surface reflectance of the northern polar region of Mercury

We analyze MESSENGER reflectance measurements covering the northern polar region of Mercury, the least studied region of the northern mercurian hemisphere. We use observations from the Mercury Dual Imaging System Wide-Angle Camera (MDIS/WAC) and the Mercury Atmospheric and Surface Composition Spectrometer (MASCS/VIRS) to study the spectral dependence of the surface reflectance. The results obtained from the observations made by both instruments are remarkably consistent. We find that a second degree polynomial description of the measured reflectance spectra gives very good fits to the data and that the information that they carry can best be characterized by two parameters, the mean reflectance and the mean relative spectral slope, averaged over the explored range of wavelengths. The properties of the four main types of terrains known to form Mercury’s regolith in the northern region, smooth plains (SPs), heavily cratered terrain (HCT), fresh ejecta/materials and red pitted ground (RPG), are examined in terms of these two parameters. The results are compared, and found consistent with those obtained by earlier studies in spite of difficulties met in obtaining accurate reflectance measurements under the large incidence angle condition characteristic of polar regions. These results will help with the preparation of the BepiColombo mission and with supporting its observational strategy.

Mercury Hollows as Remnants of Original Bedrock Materials and Devolatilization Processes: A Spectral Clustering and Geomorphological Analysis

AbstractWe perform a detailed geomorphological and compositional analysis on three craters hosting hollows located in the Victoria and Kuiper Quadrangles of Mercury. Based on Mercury Dual Imaging System data, high‐resolution detailed geomorphological mapping is provided in order to fully characterize the geological framework where hollows formed. In addition, we apply an unsupervised spectral clustering, based on a K‐mean algorithm, to separate in clusters our data sets. The comparison between the spectral and the well‐defined geomorphological units reveals a spatially coherent distribution. In particular, all hollows are uniquely identified by a well‐defined spectrum showing a wide absorption band between 0.558 and 0.828, with a possible hint of absorption toward 1 μm. Our analysis suggests that the composition of hollows may be characterized by a mixture of different minerals contributing to the absorptions found in our spectra. Indeed, sulfides alone (CaS, MnS, and MgS) cannot explain the spectrum behavior of hollows, even if the mechanism forming hollows likely involves the loss of volatiles from the surface. Hence, we have to consider bedrock‐forming material as partial responsible of the absorptions. For the studied hollows we suggest that the bedrock‐forming minerals are pyroxenes presenting transitional elements, like Cr, Ti, and Ni in substitution of Mg and/or Fe. Therefore, we suggest that the spectral characteristics of hollows are related to both remnant material produced by devolatilization process and to bedrock in which the hollows formed.

THERMAL EFFECTS ON CAMERA FOCAL LENGTH IN MESSENGER STAR CALIBRATION AND ORBITAL IMAGING

Abstract. We analyse images taken by the MErcury Surface, Space ENviorment, GEochemistry, and Ranging (MESSENGER) spacecraft for the camera’s thermal response in the harsh thermal environment near Mercury. Specifically, we study thermally induced variations in focal length of the Mercury Dual Imaging System (MDIS). Within the several hundreds of images of star fields, the Wide Angle Camera (WAC) typically captures up to 250 stars in one frame of the panchromatic channel. We measure star positions and relate these to the known star coordinates taken from the Tycho-2 catalogue. We solve for camera pointing, the focal length parameter and two non-symmetrical distortion parameters for each image. Using data from the temperature sensors on the camera focal plane we model a linear focal length function in the form of f(T) = A0 + A1 T. Next, we use images from MESSENGER’s orbital mapping mission. We deal with large image blocks, typically used for the production of a high-resolution digital terrain models (DTM). We analyzed images from the combined quadrangles H03 and H07, a selected region, covered by approx. 10,600 images, in which we identified about 83,900 tiepoints. Using bundle block adjustments, we solved for the unknown coordinates of the control points, the pointing of the camera – as well as the camera’s focal length. We then fit the above linear function with respect to the focal plane temperature. As a result, we find a complex response of the camera to thermal conditions of the spacecraft. To first order, we see a linear increase by approx. 0.0107 mm per degree temperature for the Narrow-Angle Camera (NAC). This is in agreement with the observed thermal response seen in images of the panchromatic channel of the WAC. Unfortunately, further comparisons of results from the two methods, both of which use different portions of the available image data, are limited. If leaving uncorrected, these effects may pose significant difficulties in the photogrammetric analysis, specifically these may be responsible for erroneous longwavelength trends in topographic models.

Calibration, Projection, and Final Image Products of MESSENGER’s Mercury Dual Imaging System

We present an overview of the operations, calibration, geodetic control, photometric standardization, and processing of images from the Mercury Dual Imaging System (MDIS) acquired during the orbital phase of the MESSENGER spacecraft’s mission at Mercury (18 March 2011–30 April 2015). We also provide a summary of all of the MDIS products that are available in NASA’s Planetary Data System (PDS). Updates to the radiometric calibration included slight modification of the frame-transfer smear correction, updates to the flat fields of some wide-angle camera (WAC) filters, a new model for the temperature dependence of narrow-angle camera (NAC) and WAC sensitivity, and an empirical correction for temporal changes in WAC responsivity. Further, efforts to characterize scattered light in the WAC system are described, along with a mosaic-dependent correction for scattered light that was derived for two regional mosaics. Updates to the geometric calibration focused on the focal lengths and distortions of the NAC and all WAC filters, NAC–WAC alignment, and calibration of the MDIS pivot angle and base. Additionally, two control networks were derived so that the majority of MDIS images can be co-registered with sub-pixel accuracy; the larger of the two control networks was also used to create a global digital elevation model. Finally, we describe the image processing and photometric standardization parameters used in the creation of the MDIS advanced products in the PDS, which include seven large-scale mosaics, numerous targeted local mosaics, and a set of digital elevation models ranging in scale from local to global.

Extending MESSENGER's Mercury dual imager's eight-color photometric standardization to cover all eleven filters

The photometric standardization model derived from the Mercury Dual Imaging System's (MDIS) eight-color photometric observations has been extrapolated to provide photometric parameters for the remaining three colors, such that images acquired through each of the eleven narrow-band filters can be photometrically standardized using a consistent model. The resulting photometric standardization parameters for the three filters not included in the original eight-color analysis display spectral variations commensurate with those observed within the original eight-color photometry. Some caution should be exercised on spectral interpretations based strongly on the behavior in the 698.8-nm filter.

Toward high-resolution global topography of Mercury from MESSENGER orbital stereo imaging: A prototype model for the H6 (Kuiper) quadrangle

We selected approximately 10,500 narrow-angle camera (NAC) and wide-angle camera (WAC) images of Mercury acquired from orbit by MESSENGER's Mercury Dual Imaging System (MDIS) with an average resolution of 150m/pixel to compute a digital terrain model (DTM) for the H6 (Kuiper) quadrangle, which extends from 22.5°S to 22.5°N and from 288.0°E to 360.0°E. From the images, we identified about 21,100 stereo image combinations consisting of at least three images each. We applied sparse multi-image matching to derive approximately 250,000 tie-points representing 50,000 ground points. We used the tie-points to carry out a photogrammetric block adjustment, which improves the image pointing and the accuracy of the ground point positions in three dimensions from about 850m to approximately 55m. We then applied high-density (pixel-by-pixel) multi-image matching to derive about 45 billion tie-points. Benefitting from improved image pointing data achieved through photogrammetric block adjustment, we computed about 6.3 billion surface points. By interpolation, we generated a DTM with a lateral spacing of 221.7m/pixel (192 pixels per degree) and a vertical accuracy of about 30m. The comparison of the DTM with Mercury Laser Altimeter (MLA) profiles obtained over four years of MESSENGER orbital operations reveals that the DTM is geometrically very rigid. It may be used as a reference to identify MLA outliers (e.g., when MLA operated at its ranging limit) or to map offsets of laser altimeter tracks, presumably caused by residual spacecraft orbit and attitude errors. After the relevant outlier removals and corrections, MLA profiles show excellent agreement with topographic profiles from H6, with a root mean square height difference of only 88m.

Geology of the Shakespeare quadrangle (H03), Mercury

ABSTRACTBy using images acquired by the Mercury dual imaging system (MDIS) on-board the MESSENGER spacecraft during 2008–2015 and available DTMs, a new 1:3,000,000-scale geological map of the Shakespeare quadrangle of Mercury has been compiled. The quadrangle is located between latitudes 22.5°–65.0°N and longitudes 270.0°–180.0°E and covers an area of about 5 million km2. The mapping was based on photo-interpretation performed on a reference monochromatic basemap of reflectance at 166 m/pixel resolution. The geological features were digitized within a geographic information system with a variable mapping scale between 1:300,000 and 1:600,000. This quadrangle is characterized by the occurrence of three main types of plains materials and four basin materials (pertaining to the Caloris basin), whose geologic boundaries have been here redefined compared to the previous map of the quadrangle. The stratigraphic relationships between the craters were based on three main degradation morphologies. Furthermore, previously unmapped tectonic landforms were detected and interpreted as thrusts or wrinkle ridges.

Ames stereo pipeline-derived digital terrain models of Mercury from MESSENGER stereo imaging

In this study, 96 digital terrain models (DTMs) of Mercury were created using the Ames Stereo Pipeline, using 1456 pairs of stereo images from the Mercury Dual Imaging System instrument on MESSENGER. Although these DTMs cover only ~1% of the surface of Mercury, they enable three-dimensional characterization of landforms at horizontal resolutions of ~50–250m/pixel and vertical accuracy of tens of meters. This is valuable in regions where the more precise measurements from the Mercury Laser Altimeter (MLA) are sparse. MLA measurements nonetheless provide an important geodetic framework for the derived stereo products. These DTMs, which are publicly released in conjunction with this paper, reveal topography of features at relatively small scales, including craters, graben, hollows, pits, scarps, and wrinkle ridges. Measurements from these data indicate that: (1) hollows have a median depth of ~32m, in basic agreement with earlier shadow measurement, (2) some of the deep pits (up to ~4km deep) that are interpreted to form via volcanic processes on Mercury have surrounding rims or rises, but others do not, and (3) some pits have two or more distinct, low-lying interior minima that could represent multiple vents.

Determining shape of a seasonally shadowed asteroid using stellar occultation imaging

A key objective in exploration of small, asteroidal bodies is to determine global shape and volume. The accuracy to which volume can be determined limits determination of bulk density, an important measurement for understanding internal structure. A special case for a rendezvous mission that uses stereo imaging to determine shape is a body with high obliquity encountered near solstice: half of the body is in shadow, and imaging of illuminated terrain alone under-constrains global shape. In this paper we demonstrate the use of stellar occultation imaging to place an upper bound on volume of such a shadowed hemisphere. Thirty-three sets of images of the night side limb of Mercury, acquired by the Mercury Dual Imaging System (MDIS) wide-angle camera (WAC) on MESSENGER, were used to bound the radius of that planet's night side. The maximum radius determined from this limited image set agrees with the actual radius to within ~0.1%. We show, by simulation, expected performance of a campaign of such night side limb images to bound the shape of an irregular, high-obliquity asteroid encountered at solstice. We assumed a body the size and shape of Deimos imaged from a 40-km radius orbit by an imager having specifications of the MDIS/WAC but an updated detector sensitive to mv~10 stars, and a day-side stereo imaging campaign by a well-calibrated camera system. From an equatorial orbit, with one hemisphere in shadow, a campaign of ≥150 night side limb images determines volume of the shadowed hemisphere to ~4 to 6% accuracy. Increasing orbital inclination to improve sampling of high latitudes decreases residuals for the dark hemisphere by 2 to 3%, for the same number of images. A ~2 to 3% uncertainty in global volume – from stereo imaging of illuminated terrain and stellar occultation imaging of shadowed terrain – compares favorably to uncertainty of up to ±25% in the absence of direct measurements of the radius of the shadowed hemisphere.

Comparison of areas in shadow from imaging and altimetry in the north polar region of Mercury and implications for polar ice deposits

Earth-based radar observations and results from the MESSENGER mission have provided strong evidence that permanently shadowed regions near Mercury's poles host deposits of water ice. MESSENGER's complete orbital image and topographic datasets enable Mercury's surface to be observed and modeled under an extensive range of illumination conditions. The shadowed regions of Mercury's north polar region from 65°N to 90°N were mapped by analyzing Mercury Dual Imaging System (MDIS) images and by modeling illumination with Mercury Laser Altimeter (MLA) topographic data. The two independent methods produced strong agreement in identifying shadowed areas. All large radar-bright deposits, those hosted within impact craters ≥6km in diameter, collocate with regions of shadow identified by both methods. However, only ∼46% of the persistently shadowed areas determined from images and ∼43% of the permanently shadowed areas derived from altimetry host radar-bright materials. Some sizable regions of shadow that do not host radar-bright deposits experience thermal conditions similar to those that do. The shadowed craters that lack radar-bright materials show a relation with longitude that is not related to the thermal environment, suggesting that the Earth-based radar observations of these locations may have been limited by viewing geometry, but it is also possible that water ice in these locations is insulated by anomalously thick lag deposits or that these shadowed regions do not host water ice.

Morphometry of impact craters on Mercury from MESSENGER altimetry and imaging

Data acquired by the Mercury Laser Altimeter and the Mercury Dual Imaging System on the MESSENGER spacecraft in orbit about Mercury provide a means to measure the geometry of many of the impact craters in Mercury's northern hemisphere in detail for the first time. The combination of topographic and imaging data permit a systematic evaluation of impact crater morphometry on Mercury, a new calculation of the diameter Dt at which craters transition with increasing diameter from simple to complex forms, and an exploration of the role of target properties and impact velocity on final crater size and shape. Measurements of impact crater depth on Mercury confirm results from previous studies, with the exception that the depths of large complex craters are typically shallower at a given diameter than reported from Mariner 10 data. Secondary craters on Mercury are generally shallower than primary craters of the same diameter. No significant differences are observed between the depths of craters within heavily cratered terrain and those of craters within smooth plains. The morphological attributes of craters that reflect the transition from simple to complex craters do not appear at the same diameter; instead flat floors first appear with increasing diameter in craters at the smallest diameters, followed with increasing diameter by reduced crater depth and rim height, and then collapse and terracing of crater walls. Differences reported by others in Dt between Mercury and Mars (despite the similar surface gravitational acceleration on the two bodies) are confirmed in this study. The variations in Dt between Mercury and Mars cannot be adequately attributed to differences in either surface properties or mean projectile velocity.

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 15km diameter Waters crater (106°W; 9°S) and the 62.3km 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, 350–450nm and 450–650nm, and the absolute reflectance in the 700–750nm 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 350–450nm window, while they display a bluer slope than the external reference area in the 450–650nm 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.