MErcury Surface, Space ENvironment, GEochemistry, And Ranging Research Articles

Estimating Interplanetary Magnetic Field Conditions at Mercury's Orbit From MESSENGER Magnetosheath Observations Using a Feedforward Neural Network

AbstractMercury's small magnetosphere is embedded in the dynamic and intense solar wind environment characteristic of the inner heliosphere. Both the magnitude and orientation of the interplanetary magnetic field (IMF) significantly influence the solar wind‐magnetospheric interaction at Mercury, driving phenomena such as magnetic reconnection. The MErcury Surface, Space Environment, Geochemistry and Ranging (MESSENGER) spacecraft provided in‐situ magnetic field measurements of the solar wind, the magnetosheath, and the magnetosphere along each orbit. However, it is a challenge to directly assess the IMF's impact on Mercury's plasma environment due to the temporal separation between observations within the solar wind and the magnetosphere, especially in the absence of an upstream monitor. Here, we present a feedforward neural network (FNN) trained on a subset of magnetosheath observations to estimate the strength and orientation of the IMF upstream of the bow shock. Utilizing magnetosheath magnetic field, cylindrical spatial coordinates, and heliocentric distance measurements, the FNN predicts upstream IMF conditions with an score of 0.70 and mean averaged error of 5.3 nT, thereby greatly decreasing the temporal separation between IMF estimates and magnetospheric measurements throughout the MESSENGER mission. This approach yields IMF estimates for all magnetosheath data measured by MESSENGER, providing a useful tool for future investigations of the IMF impact on Mercury's magnetosphere. This method will be integrable with the dual‐spacecraft BepiColombo magnetosheath measurements, providing useful estimates of upstream IMF conditions particularly during the extended periods in which neither spacecraft sample the solar wind. Our results demonstrate the utility of machine learning techniques on advancing space science research.

Mg Exosphere of Mercury Observed by PHEBUS Onboard BepiColombo During Its Second and Third Swing‐Bys

AbstractMercury's exosphere is an important target for understanding the dynamics of coupled systems in space environments, tenuous planetary atmospheres, and planetary surfaces. Magnesium (Mg) is especially crucial for establishing methods for estimating the surface chemical composition distribution through observations of the exosphere because its distribution in the exosphere and on the surface is strongly correlated. However, owing to its low radiance, the Hermean Mg exosphere has only been detected by the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) onboard the Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) spacecraft. Thus, we have few observation data for areas other than low latitude regions in addition to few detection cases of short‐term or sporadic fluctuations, resulting in a poor understanding of ejection and transportation mechanisms of the Mg exosphere. In this study, we analyzed the distribution of the Hermean Mg exosphere by the Probing of Hermean Exosphere by Ultraviolet Spectroscopy (PHEBUS) onboard the Mercury Planetary Orbiter of the BepiColombo mission during its second and third Mercury swing‐bys (MSBs). First, we constructed a calibration method including background subtraction and calibration using stellar observations. Mg light curves at two true anomaly angles were obtained, which were in agreement with the Chamberlain model and a three‐dimensional numerical calculation. Comparing the Mg and calcium (Ca) radiances obtained by PHEBUS during the MSBs, the exospheric Mg atoms have a lower energy than the exospheric Ca atoms. This is consistent with the lower energy necessary for producing the Mg atoms produced by molecular photodissociation than for Ca atoms.

Impact structures on Mercury from MESSENGER data: Implications on their formation processes and crustal structure

In this study high-resolution stereo images and Digital Terrain Models (DTMs) from MErcury Surface, Space ENvironment, Geochemistry and Ranging (MESSENGER) mission were utilized to detect impact structures in regions not covered by Mercury’s Laser Altimeter (MLA), while gravitational data was utilized as a supported data set. We have established an inventory of 314 impact structures ≥150 km, classified on their morphological and gravitational characteristics. 24 basins ≥300 km have been newly discovered. Additionally, we have identified significant surface modifications in impact structures of smooth material infill, which can be either impact-induced or volcanic in origin. The Bouguer anomaly and crustal thinning in the center are displaying an interplay of predominant change of crustal structure in impact basins. Further, this study reveals a common impact history of Mercury and the Moon. Nevertheless, cumulative density distributions suggest the possibility of either a divergence in impactor populations responsible for forming large basins on both celestial bodies or a significant shift in impactor rates. This work holds important implications not only for understanding impact structure formation and evolution processes but also for interpreting the crustal structure. It presents an updated and expanded catalog of impact structures on Mercury, encompassing buried basins, and identifies new areas of interest, potentially serving as target sites for the forthcoming BepiColombo mission.

Short large-amplitude magnetic structures (SLAMS) at Mercury observed by MESSENGER

Abstract. We present the first observations of short large-amplitude magnetic structures (denoted SLAMS) at Mercury. We have investigated approximately 4 years of MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) data to identify SLAMS in the Mercury foreshock. Defining SLAMS as magnetic field compressional structures, with an increase in magnetic field strength of at least twice the background magnetic field strength, when MESSENGER is located in the solar wind, we find 435 SLAMS. The SLAMS are found either in regions of a general ultra-low frequency (ULF) wave field, at the boundary of such a ULF wave field, or in a few cases isolated from the wave field. We present statistics on several properties of the SLAMS, such as temporal scale size, amplitude, and the presence of whistler-like wave emissions. We find that SLAMS are mostly found during periods of low interplanetary magnetic field strength, indicating that they are more common for higher solar wind Alfvénic Mach number (MA). We use the Tao solar wind model to estimate solar wind parameters to verify that MA is indeed larger during SLAMS observations than otherwise. Finally, we also investigate how SLAMS observations are related to foreshock geometry.

Dynamics of Sputtered Neutral Sodium Atoms in the Near‐Mercury Space

AbstractThe solar wind sputtering in the magnetospheric polar cusp is an important source of heavy atoms in Mercury’s exosphere and magnetosphere. However, the majority of ejected atoms are neutral, undergoing an extended period before photoionization occurs. In this study, we employ an ab initio simulation to investigate the behavior of sodium (Na) atoms prior to their photoionization. Our results reveal that overall only approximately 2.7% of the sputtered atoms contribute to magnetospheric ions, while the vast majority of these ions (∼82.9%) escape into interplanetary space. The remaining fraction (14.4%) eventually returns to the planetary surface. For Na atoms ionized inside the magnetosphere, a larger proportion of Na+ (53.5%) is supplied to the magnetotail compared to the polar cusp (39.4%), which is due to the tailward acceleration caused by solar radiation. Additionally, the remaining Na+ (7.1%) contributes to the dayside ring current region, as demonstrated by the observation of the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. Our research introduces a perspective on Na+ transport in the magnetosphere that complements and coexists with traditional mechanisms.

An Empirical Model for Mercury’s Field‐Aligned Currents Derived From MESSENGER Magnetometer Data

AbstractMercury is the only planetary magnetosphere which does not possess a significantly conducting ionosphere, yet magnetic field observations by the Mariner 10 and MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) missions revealed a stable presence of large‐scale field‐aligned currents (FACs). Several empirical magnetic field models have been developed to describe Mercury’s magnetospheric currents and their associated magnetic fields, but none attempted to include an explicit description of large‐scale FACs. Here, we describe a dynamic FAC magnetic field model for Mercury based on the analytical solution to conical currents, which are shielded by a dynamic magnetopause boundary. The model contains free parameters setting the FACs' latitudinal extent and amplitude as functions of magnetospheric activity. The parameters are fit by minimizing the root‐mean‐square (RMS) differences between the model and MESSENGER Magnetometer data. During magnetically quiet conditions, the modeled FACs have an intensity of ∼10 nA/m2 and extend in latitude from ∼83°N to ∼40°N. They intensify to ∼20 nA/m2 and expand equatorward to ∼28°N during the most active times. The inclusion of the FAC model reduces low‐altitude RMS residuals by 8.1% when compared to prior models. The model effectively captures the azimuthal component of the magnetic field present in the MESSENGER low‐altitude data, but largely misses the radial and co‐latitudinal components, indicating other large‐scale physics remain missing in the mathematical descriptions of Mercury's magnetosphere.

Statistical Analysis of Mercury's Magnetotail Lobe Field Using MESSENGER Observations

AbstractThe magnetotail lobe region at Mercury is characterized by low plasma density and low magnetic field variability compared to the nightside magnetosheath and central plasma sheet. At Mercury, as well as other planets, lobe magnetic fields play a crucial role in storing and releasing magnetic flux in response to changing upstream solar wind conditions such as interplanetary magnetic field (IMF) orientation and solar wind dynamic pressure (Pdyn). This makes the region significant for studying the magnetospheric interaction with the intense solar wind conditions at Mercury's orbit. Here, we identify and analyze magnetotail lobe observations made by the Mercury Surface, Space Environment, Geochemistry and Ranging (MESSENGER) spacecraft during its 4 years orbital phase. We empirically determined a set of criteria using magnetometer (MAG) and the Fast Imaging Plasma Spectrometer instruments onboard MESSENGER to identify lobe magnetic field intervals. From 3,332 MESSENGER orbits, we identify 1,242 lobe field intervals. We derive an expression for the average lobe magnetic field strength in nanotesla with respect to radial distance downtail: Blobe(r) = (135 ± 8) * r(−2.1±0.3) + (31 ± 8). The lobe magnetic field exhibits both small‐scale (∼3 min) and orbit‐to‐orbit (∼8–12 hr) variability in magnetic field strength compared to this averaged field strength expression. The orbit‐to‐orbit variability in lobe field strength is not significantly correlated with estimated IMF orientation, but is directly correlated with Pdyn. Thus, our findings provide evidence for the pressure balance between the inward facing Pdyn on the nightside magnetopause and the outward facing magnetic pressure supplied by the lobes.

Understanding the Dust Environment at Mercury: From Surface to Exosphere

We provide an overview of our understanding of the dust environment at Mercury and the role that dust plays in shaping the planet's surface and exosphere. Our understanding of the role that dust impacts play in the generation of Mercury's atmosphere has evolved considerably with continued analysis of results from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission. Recent models have provided evidence for the probable release of refractory species into Mercury's exosphere via impacts. However, there remain significant questions regarding the relative contributions of atoms released via impacts versus other mechanisms (e.g., photon-stimulated desorption) to the overall exospheric budget. We also discuss the state of observational and modeling efforts to constrain the dust environment at Mercury, including sources from the zodiacal cloud, cometary trails, and interstellar dust. We describe the advancements that will be made in our characterization of dust at Mercury with BepiColombo, providing observational constraints on the dust clouds themselves and the role that impacts play in exospheric generation. On Mercury's surface, there remain outstanding questions regarding the role that dust impacts play in the regolith cycling and development. We review how improved modeling efforts to understand grain lifetimes as a function of impactor flux will further our understanding of Mercury's regolith. Finally, there are few constraints on the role of dust impacts on the space weathering of Mercury's surface, particularly the expected chemical, physical, and spectral alterations to the regolith. Here we discuss the importance of laboratory experiments to simulate these processes for the interpretation of data from MESSENGER and BepiColombo.

The relation between the surface composition anomaly and distribution of the exosphere of Mercury

In celestial bodies with tenuous collisionless atmospheres, such as Mercury, the spatial distribution of the exosphere is expected to reflect the surface composition. In this study, we discuss whether the distributions of Mg, Ca, and Na, the primary exospheric components of Mercury, have a local exosphere–surface correlation by analyzing the observation data of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) and X-ray spectrometer (XRS) onboard the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. It was found that Mg has a strong local exosphere–surface correlation and Ca has a weak correlation. The Monte Carlo simulations of trajectories in the exosphere show that the weak correlation of Ca is due to the relatively large solar radiation acceleration. In addition, Na production rate in high-temperature regions is longitudinally dependent. This can be explained by considering that the weakly physisorbed Na layer on the surface is depleted under high temperature and that the distribution of strongly chemisorbed Na atoms is reflected in the exosphere. Based on these results, the conditions for components with a correlation in celestial bodies with thin atmospheres may include low volatility and low solar radiation acceleration.Graphical

Deep Learning Investigation of Mercury’s Explosive Volcanism

The remnants of explosive volcanism on Mercury have been observed in the form of vents and pyroclastic deposits, termed faculae, using data from the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) onboard the Mercury surface, space environment, geochemistry, and ranging (MESSENGER) spacecraft. Although these features present a wide variety of sizes, shapes, and spectral properties, the large number of observations and the lack of high-resolution hyperspectral images complicates their detailed characterisation. We investigate the application of unsupervised deep learning to explore the diversity and constrain the extent of the Hermean pyroclastic deposits. We use a three-dimensional convolutional autoencoder (3DCAE) to extract the spectral and spatial attributes that characterise these features and to create cluster maps constructing a unique framework to compare different deposits. From the cluster maps we define the boundaries of 55 irregular deposits covering 110 vents and compare the results with previous radius and surface estimates. We find that the network is capable of extracting spatial information such as the border of the faculae, and spectral information to altogether highlight the pyroclastic deposits from the background terrain. Overall, we find the 3DCAE an effective technique to analyse sparse observations in planetary sciences.

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.

Low sulfide concentration in Mercury’s smooth plains inhibits hollows

MESSENGER (Mercury, Surface, Space Environment, Geochemistry, and Ranging) mission to Mercury led to the discovery of hollows. These geological landforms have no close counterpart on other airless silicate bodies. Multispectral images and geochemical measurements by MESSENGER suggest that hollows are formed by the loss of volatile-bearing minerals. We investigated the mineralogical composition of the hollows using near-ultraviolet to near-infrared spectra obtained by MESSENGER. We compared reflectance spectra of hollows with laboratory spectra of Mercury's analogs: sulfides, chlorides, silicates, and graphite. The best candidates to reproduce the curvature of the hollow spectra are calcium sulfide, magnesium sulfide, and sodium sulfide. In addition, we performed spectral modeling with spectra obtained at the highest spectral and spatial resolution within the hollows. Our results show that the enrichment of sulfides in hollow material is up to two times higher than the sulfide concentration derived from chemical measurements of Mercury's high-reflectance smooth plains. This result explains the small percentage of hollows found within these plains.

Characterizing Interplanetary Coronal Mass Ejection-related Forbush Decreases at Mercury Using MESSENGER Observations: Identification of a One- or Two-step Structure

The large-scale magnetic structure of interplanetary coronal mass ejections (ICMEs) has been shown to cause decreases in the galactic cosmic ray (GCR) flux measured in situ by spacecraft, known as Forbush decreases (Fds). We use measurements of the GCR count rate obtained by NASA’s MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft during its orbital phase around Mercury to identify such Fds related to the passage of ICMEs and characterize their structure. Of the 42 ICMEs with corresponding high-quality GCR data, 79% are associated with a Fd. Thus, a total of 33 ICME-related Fds were identified, 24 of which (73%) have a two-step structure. We use a superposed epoch analysis to build an average Fd profile at MESSENGER and find that despite the variability of individual events, a two-step structure is produced and is directly linked with the magnetic boundaries of the ICME. By using results from previous studies at Earth and Mars, we also address whether two-step Fds are more commonly observed closer to the Sun; we found that, although likely, this is not conclusive when comparing to the wide range of results of previous studies conducted at Earth. Finally, we find that the percentage decrease in GCR flux of the Fd is greater at MESSENGER on average than at Earth and Mars, decreasing with increasing heliocentric distance. The relationship between the percentage decrease and maximum hourly decrease is also in agreement with previous studies, and follows trends relating to the expansion of ICMEs as they propagate through the heliosphere.

Observations of Mercury's Plasma Sheet Horn: Characterization and Contribution to Proton Precipitation

AbstractThe Mercury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) spacecraft was the first spacecraft to orbit the planet Mercury. Previous analysis of MESSENGER data has established that of all the planets in the solar system, Mercury's magnetosphere is the most like Earth's, dominated by the Dungey cycle in its dynamic response of the magnetosphere to solar wind forcing. In this work, we identify and describe for the first time Mercury's northern plasma sheet horn—a Dungey cycle feature key to plasma precipitation. We find three possible geometries for potential horn observation by MESSENGER and describe a case study of each. Two additional case studies are presented with geometries particularly favorable to estimating plasma precipitation within the horns. Estimates of proton precipitation flux are performed, which show precipitation levels on the order of 107 per cm2 per second, on the same order of magnitude as the estimated proton precipitation flux in the dayside cusp despite the higher average energy of the protons in the horn. Potential paths for future study of the horns are discussed.

Solar-wind-dependent streamline model for Mercury’s magnetosheath

Context.Mercury’s magnetosphere and magnetosheath are unique in the Solar System plasmas as they are highly time dependent, since the planet has only a small-scale magnetosphere originating from the weak intrinsic planetary magnetic field. Yet, it is believed that the plasma therein reaches a quasi-stationary state, that is, the ground state of magnetospheric dynamics, when the solar wind smoothly passes by the magnetosphere without energy or momentum exchange in quiet conditions.Aims.Here, we aim to construct a semi-analytical streamline model for Mercury’s magnetosheath to extend the modeling effort from the magnetospheric plasma to the magnetosheath plasma. The magnetosheath model should have the capability of determining the plasma density and the bulk velocity as a function of the radial distance from the planet, the zenith angle to the Sun, and the solar wind condition.Methods.Our magnetosheath model was constructed with (1) the steady-state continuity equation around a magnetospheric obstacle where the bow shock and magnetopause location may depend on the solar wind condition, (2) the jump conditions at the bow shock, and (3) the adiabatic behavior in the magneotsheath.Results.Our magnetosheath model reasonably explains and reproduces the in-situ measurements around Mercury by the MErcury Surface, Space Environment, GEochemistry and Ranging (MESSENGER) spacecraft as well as numerical simulations.Conclusions.The presented streamline model of Mercury’s magnetosheath serves as a useful tool for the on-going two spacecraft BepiColombo mission when analyzing the plasma data by tracing the plasma parcel along the streamline both forward from one spacecraft to another and backward, locating the shock crossing coordinate, or when estimating the elapsed time of plasma parcel after the shock crossing.

Proton Precipitation in Mercury's Northern Magnetospheric Cusp

AbstractIon precipitation onto Mercury's surface through its magnetospheric cusps acts as a source of planetary atoms to both Mercury's exosphere and magnetosphere. Through the process of ion sputtering, solar wind ions (∼95% protons) impact the surface regolith and liberate material, mostly as neutral atoms. We have identified 2760 northern magnetospheric cusp crossings throughout the MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) mission, based on enhancements in proton flux observed by the Fast Imaging Plasma Spectrometer (FIPS). We find cusp crossings spanning 50–85° in magnetic latitude with a geometric center typically at 60–70°. The cusp center is stable about its average but its latitudinal extent varies orbit‐to‐orbit. The mean latitude weakly depends on the magnitude of the interplanetary magnetic field (IMF), dropping by about 1.3° magnetic latitude for each increase of 10 nT in IMF strength. We have used these identified cusp boundaries to estimate the flux of protons which will precipitate onto Mercury's surface. We find an average proton precipitation flux of 1.0 × 107 cm−2 s−1, ranging 3.3 × 104–6.2 × 108 cm−2 s−1, and that this flux can vary substantially between subsequent 10‐s measurements. We also tabulated the peak precipitation fluxes for each cusp crossing. They range 9.8 × 104–1.4 × 109 cm−2 s−1, with a mean of 3.7 × 107 cm−2 s−1. We find strong dependencies on the local time of the cusp crossing as well as on Mercury's orbit around the Sun, which warrant further investigation.

ULF Modulations on Plasma Environment and Coherent Waves of Mercury's Magnetosphere: MESSENGER's Observation

AbstractUltra low frequency (ULF) waves are fundamental waves that can energize, transport, and scatter charged particles in planetary magnetospheres. With the measurements from MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER), we investigate the proton flux fluctuations and coherent waves associated with a series of ULF waves on the flanks of Mercury's magnetosphere. The ULF waves are mainly compressional with a frequency of ∼15 mHz and significantly modulate the intensity of proton flux. The coherent waves accompanied by the ULF waves correspond to a higher frequency (∼1 Hz). The wave power and compressibility of the coherent waves vary quasi‐periodically with the ∼15 mHz ULF waves. We conclude that the compressional ULF waves modulate the coherent waves with higher frequency. This modulation might result from the associated periodic proton flux changes and helps us understand the nature of the ∼1 Hz waves better.

Present Day Endogenic and Exogenic Activity on Mercury

AbstractExogenic and endogenic activities dictate how planetary surfaces evolve. However, the present‐day influence of each of these activities is not well constrained. MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) temporal imaging recorded surface changes associated with these activities between 2011 and 2015. Here we present the results of a temporal investigation that identified 20 reflectance changes. One change exhibited bright rays extending from the site, consistent with the aftermath of an impact event. If all changes result from impact events, the present flux rate is 1,000 times higher than models predict. Consequently, we also report changes on slopes in areas with concentrations of tectonic landforms and identify a subset of changes that are on or adjacent to hollows, consistent with present‐day endogenic activities. Therefore, we conclude that these observations captured endogenic and exogenic modifications to the surface.

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.

Estimation of Crust and Lithospheric Properties for Mercury from High-resolution Gravity and Topography

We have analyzed the entire set of radiometric tracking data from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission. This analysis employed a method where standard Doppler tracking data were transformed into line-of-sight accelerations. These accelerations have greater sensitivity to small-scale features than standard Doppler. We estimated a gravity model expressed in spherical harmonics to degree and order 180 and showed that this model is improved, as it has increased correlations with topography in areas where tracking data were collected when the spacecraft altitude was low. The new model was used in an analysis of the localized admittance between gravity and topography to determine properties of Mercury’s lithosphere. Four areas with high correlations between gravity and topography were selected. These areas represent different terrain types: the high-Mg region, the Strindberg crater plus some lobate scarps, heavily cratered terrain, and smooth plains. We employed a Markov Chain Monte Carlo method to estimate crustal density, load density, crustal thickness, elastic thickness, load depth, and a load parameter that describes the ratio between surface and depth loading. We find densities around 2600 kg m−3 for three of the areas, with the density for the fourth area, the northern rise, being higher. The elastic thickness is generally low, between 11 and 30 km.