Mercury Exploration Assessment Group (MExAG) Annual Meeting 2023

February 1–3, 2023

 

Program

 

Times listed are Eastern Standard Time (EST).

Find your local time here.

 

Wednesday, February 1, 2023

11:00 a.m.

MExAG Agency and Mission Updates and Decadal Survey Discussion

12:45 p.m.

MExAG Community and Technology

 

Thursday, February 2, 2023

11:00 a.m.

Deep Insight from the Surface

11:40 a.m.

MExAG Posters

12:40 p.m.

MExAG Community Priorities

 

Friday, February 3, 2023

11:00 a.m.

Magnetospheric Fun

11:45 a.m.

Global Geology

12:15 p.m.

Searching for Mercury's Surface Secrets

12:55 p.m.

Bringing that Big Magnetospheric Energy

1:25 p.m.

Atoms Above and at the Surface

1:45 p.m.

MExAG Meeting Summary

 

 

Wednesday, February 1, 2023

MEXAG AGENCY AND MISSION UPDATES AND DECADAL SURVEY DISCUSSION

11:00 a.m.

Times

Authors (*Presenter)

Abstract Title and Summary

11:00 a.m.

 

Welcome, Logistics, Meeting Policies

11:10 a.m.

Glaze L. *

Planetary Science Division Overview

11:35 a.m.

Benkhoff J. *  Murakami G. *

BepiColombo Updates

BepiColombo - First Results from Mercury Flybys and Mission Update [#6006]
BepiColombo was launched on 20 October 2018 from the European spaceport in French Guyana and is now on route to Mercury to unveil Mercury’s secrets. BepiColombo, a two-orbiter mission, with its state of the art and very comprehensive payload will perform measurements to increase our knowledge on the fundamental questions about Mercury’s evolution, composition, interior, magnetosphere, and exosphere. On 23 June 2022 BepiColombo performed its 2nd flyby at Mercury, where about half of the science instruments could be operated. Results from measurements of this and other flybys will be shown. In addition, during cruise some of the instruments operated in a so called “background science mode” to monitor the environment. A summary of these measurement and a brief mission status update will be given.

12:05 p.m.

Christensen P.  Grove T. *

Decadal Survey Panel Discussion

12:35 p.m.

 

BREAK

 

Wednesday, February 1, 2023

MEXAG COMMUNITY AND TECHNOLOGY

12:45 p.m.

Times

Authors (*Presenter)

Abstract Title and Summary

12:45 p.m.

Rivera-Valentin E.  Lynch K. *

IDEA Workshop Overview and Outcomes

1:00 p.m.

Lennox A. R. *  Rothery D. A.

Naming Conventions and Underrepresentation: on Mercury and Across the Solar System [#6032]
The current naming conventions for astronomical discoveries exacerbate the underrepresentation of marginalised groups in space science. Conventions, as established by the IAU, dictate what new discoveries on planets and satellites can be named, adopting, for example the names of famous people or locations on Earth. In theory, the nomenclature should reflect a diverse array of people (representing different genders, cultures, races, etc.) and places. However, this expectation is not a reality; we found that for craters on Mercury women feature less than 12%. A gender imbalance is not unique to Mercury, with only 2% of craters named after a person on the Moon and Mars commemorating a woman. This is not just a gendered issue, and many modes of diversity are lacking across the solar system. One reason we suggest for this underrepresentation is that the conventions inherently disadvantage women and marginalised groups. It is important to be aware of this when naming features in the future.

1:08 p.m.

Montbach, E. N. *

PSD Technology Overview

1:28 p.m.

Parman S. W. *  Mustard J. F.  Pieters C. M.  Kremer C. H.  Bramble M. S.  Green R. O.  Johnson L.

Mercury Scout: Mineral Mapping and High-Resolution Imaging [#6030]
Mercury Scout is a low-cost orbiter concept that will 1) map the silicate mineralogy of the surface using diagnostic emissions in the 4-8 micron wavelength region and 2) provide meter-scale visible wavelength images. These two data sets fill fundamental science knowledge gaps, and provide key data for choosing sites for future landed missions. The spectrometer is based on Lunar Trailblazer’s HVM3, and uses a unique HOT BIRD detector developed at JPL to work at 4-8 micron wavelengths. This spectral region is uniquely suited to identifying Mercury’s low-Fe minerals. To minimize travel time (~4-5 years) and cost, and provide the longest possible orbit duration, the propulsion system will be a ~1500 square meter solar sail. Long orbiting duration will allow 1) repeated spectral mapping for high spatial resolution with the desired signal to noise ratio, 2) an increased number of targets for the high-resolution visible camera and 3) studies of surface evolution over extended time periods.

1:36 p.m.

Zender J. *  Maturilli A.  Dachwald B.  Mangano V.  Ulamec S.  Helbert J.  Besse S.  Hiesinger H.  Andre N.  Berezhnoy A.  Murakami G.  Byrne P.  Benkhoff J.  Alberti T.  Heyner D.  Lucchetti A.  Oliveira J.  Pajola M.  Chabot N.  De Angelis E.  Delcourt D.  Dirri F.  Hadid L.  Kohout T.  Lindsay S.  Longobardo A.  Martellato E.  Mura A.  Narita Y.  Palomba E.  Rispoli R.  Saito Y.  Scully J.  Yokota S.  Wright J.  Zambon F.

Mercury Impactor: A Mission to Study Mercury’s Subsurface [#6040]
The surfaces of airless bodies like Mercury undergo processes of gardening, due to the direct and continuous exposition of the regolith to the solar and cosmic radiation. The long exposure to the meteoritic and to the energetic ion bombardments causes deep changes in the surface features.  Eventually, to have a real knowledge of the body, it would be necessary to study the layers below the exposed surface, down to at least tens of meters.  The present mission idea consists in launching a massive and high velocity projectile, able to volatilize an adequate surface volume and generate a crater of up to a hundred meters. The projectile should be built of a special alloy that would be easily distinguishable from the one of the planet surface. This artificial impact would allow the investigations of the underlying surface layers and composition.Two mission scenarios will be presented, one of them allowing an arrival during BepiColombo’s nominal mission.

1:44 p.m.

Blake D. F. *  Rampe E. B.  McCubbin F. M.  Sarrazin P.  Bristow T. S.  Zacny K.

In Situ Mineralogical Analysis of Mercury’s Surface Using X-Ray Diffraction and X-Ray Fluorescence (XRD/XRF) [#6020]
The CheMin XRD instrument on MSL Curiosity revolutionized our understanding of the early geologic history of Mars. Improvements in X-ray technology coupled with lessons learned during a decade of CheMin operations on Mars by our team have guided the design of XRD/XRF instruments intended for future deployment on Mars, the Earth’s moon, Venus and Mercury. The new instruments are half the mass and have reduced power requirements, higher 2-theta resolution and vastly improved XRF capabilities. XRD/XRF analysis of Mercury regolith delivered by the HBR PlanetVac will: (1) Identify and quantify all minerals present at >1 wt. %, including their structure states and cation occupancies; (2) Determine abundance and valence state of all major elements present in each mineral (H and above) from their refined lattice parameters; (3) Quantify the amount and elemental composition of the amorphous component (if present); and (4) Detect and quantify all major and minor and some trace elements.

1:52 p.m.

 

DISCUSSION

 

BACK TO TOP

 

Thursday, February 2, 2023

DEEP INSIGHT FROM THE SURFACE

11:00 a.m.

Times

Authors (*Presenter)

Abstract Title and Summary

11:00 a.m.

 

Welcome

11:05 a.m.

Wang Y. *  Xiao Z.  Xu R.  Xiao Z.

Dark Spots on Mercury Show No Signs of Weathering During 30 Earth Months [#6014]
Dark spots are recently-formed thin and low-reflectance materials that are related with volatile activity and supposed to be much shorter-lived than their central hollows. Containing unique information about the possible building blocks of Mercury, dark spots have unresolved darkening phases, formation mechanism, and lifetime. Here we investigated reflectance spectra, sub-resolution roughness, and temporal changes of dark spots using the full-mission dataset of MESSENGER. We find that dark spots have the highest concentration of graphite and an intense outgassing origin. Temporal imaging reveals no detectable reflectance changes in 30 Earth months, and possibly over 40 Earth years. These observations show that thermally unstable sulfides such as MgS and CaS are not the major components in dark spots. Possible reflectance changes of dark spots may occur at much longer time scales, providing a reference for modeling the spectral behavior of graphite caused by space weathering on Mercury.

11:13 a.m.

Wright J. *  Caminiti E.  Rae A. S. P.  Besse S.

Mercury’s Hollow-Forming Materials: Insights from Impact Modeling and MASCS spectra of the Caloris Basin [#6037]
Caloris ejecta exposes on Mercury’s surface materials excavated from great depths. Hollows, landforms generated by volatile-loss, have been observed in the circum-Caloris knobs, which are interpreted as remnant Caloris ejecta blocks. This implies that at least these knobs were sourced from a volatile-bearing region within Mercury. Here, we aim to constrain the depth within Mercury that is enriched in hollow-forming materials, with implications for the planet’s formation and evolution. Building on earlier work that mapped the locations of the knobs, we are mapping the hummocky Odin Formation that hosts the knobs, while documenting where hollows are found. We are using iSALE numerical impact simulations to estimate the source depth of the mapped Odin Formation and knobs. We are using MASCS data to investigate if the Odin Formation and knobs have spectral characteristics of hollows in general, even where they are not visible. We present preliminary results.

11:21 a.m.

Lark L. H. *  Head J. W.  Huber C.

Carbon in Mercury’s Deep Interior; Insights from Low-Reflectance Material [#6019]
Low-reflectance material (LRM) observed on Mercury’s surface is thought to be darkened by graphite. Hypotheses as to its origin predict drastically different quantities of carbon available to darken LRM and carry different implications for the abundance and distribution of carbon in Mercury’s deep interior. We estimate a lower bound on the absolute quantity of carbon in Mercury’s global shallow interior from observations of LRM exposures in 5 large basins. We find that if LRM is darkened by 2-7 wt.% graphite, the amount required to match our observations exceeds the expected late delivery of cometary material by ~1000x and is likely also too much to have been sourced from the silicate melt of Mercury’s magma ocean. Planetary or core carbon saturation could easily have resulted in enough near-surface carbon. Our results support carbon as an abundant light element in Mercury’s core, with implications for interpretation of geophysical measurements and of Mercury’s thermal evolution.

11:29 a.m.

 

DISCUSSION

11:35 a.m.

 

BREAK

 

Thursday, February 2, 2023

MEXAG POSTERS

11:40 a.m.

Authors (*Denotes Presenter)

Abstract Title and Summary

Pisello A.  Poggiali G.  Bisolfati M.  Brucato J. R.  Perugini D.

Mid-IR Reflectance of Silicate Glasses as a Possible Analog for Mercury: Influence of Granulometry [#6029]
Volcanic products are widely present on Mercury both as lava flows and possible volcaniclastic material, and silicate glasses represent a major component in such products. Using experimental petrology, we have reproduced a Mercury-like silicate glass, from which we have obtained powdered samples having different granulometric characteristics. Reflectance of samples was investigated in the Mid-Infrared (MIR) region: we observe how reflectance intensity is increasing with grain size, and the presence of extremely fine material defines emergence of Transparency Feature (TF). We offer reference data with qualitative observations and quantitative parameterization of spectral characteristics, and in particular we observe how a small fraction of fine material can greatly influence spectral response of coarser powders. Results of this work will be pivotal for the interpretation of data collected by BepiColombo mission, but need to be integrated with other possible Mercurian compositions.

Kremer C. H.  Mustard J. F.  Pieters C. M.  Green R. O.  Parman S. W.  Bramble M. S.

Mercury Science Questions Addressed with Imaging Spectroscopy Observations Across the New Intermediate Infrared (IMIR) Spectral Range [#6035]
Silicate minerals such as olivine, low-Ca pyroxene, and high-Ca pyroxene exhibit unique and well-defined spectral bands in the Intermediate Infrared (IMIR) wavelength region (4–8 µm). These mineral spectral bands, which result from combinations and overtones of fundamental vibrations at longer wavelengths, are especially prominent in low-Fe and Fe-free olivine and pyroxene, offering unique potential for remotely detecting, measuring, and mapping silicate minerals on Mercury. The unique spectral bands of Mg olivine and pyroxene make IMIR spectroscopy a highly attractive tool for the direct detection of silicate minerals across the surface of Mercury. Strong, unique spectral bands of high-Mg olivine and pyroxene make IMIR spectroscopy a highly attractive tool for the direct detection of silicate minerals on the surface of Mercury. Applications to Mercury are discussed further by Parman et al. (this volume).

Schmude R. W. Jr.

J and H Filter Photometry of the Moon and Mercury [#6022]
The Moon is considered to be a close analogy to Mercury since it has almost no atmosphere and is close to the Sun.  The writer has carried out disk-integrated brightness measurements of the Moon using an SSP-4 photometer and filters that have been transformed to the J and H system. In this system, the J and H passbands correspond to respective wavelength ranges of 1150–1350 and 1500–1800 nm. The writer has reported his J- and H-filter results for Mercury. In this brief presentation, he reports that at a phase angle of 90 degrees, the J - H color index of the Moon is 0.64 magnitudes. This is close to the corresponding value for Mercury. The J - H color index of the Moon at a phase angle of 60 degrees drops to 054 magnitudes. This is lower than the corresponding value for Mercury (0.73 magnitudes).  Therefore, the Moon’s J - H color index is close to that for Mercury at a phase angle of 90 degrees but may differ a little at lower phase angles.

Killen R. M.  Burger M. H.  Vervack R. J. Jr.

Revised g_Values for Atoms and Ions in Mercury’s Exosphere [#6002]
The discrete photoemission properties of atomic and molecular species stimulated by solar radiation are an important tool for remote sensing. In an optically thin atmosphere, the total column amount of a given species is given in terms of a solar-forced g-value, defined as an emission probability per atom (photon /s/atom). For an optically thin gas and a measured emission brightness (4pi I), the column abundance, N, is given by 4pi I= gN. Of importance for Mercury is the dependence of the g-values on the heliocentric motion of the gas. Mercury’s orbit results in a variation of the heliocentric relative velocity of +/-10 km/s. The g-values published by Killen et al. (2009) were calculated for Doppler shifts of this magnitude. However, radiation pressure  can accelerate atoms to high velocity  antisunward of Mercury. We have extended g-values to +/-50 km/s relative to their at-rest value for sodium, potassium, calcium, hydrogen, helium, oxygen, sulfur, magnesium, carbon, Ca+ and Mg+.

Sun W. J.  Dewey R. M.  Slavin J. A.  Raines J. M.  Poh G.

MESSENGER Observations of Distribution of Planetary Ions Near Mercury’s Space: Their Dependence on True Anomaly Angle and Escape Rates [#6017]
This study presents MESSENGER observations of the distribution of Na+-group ions in the regions near Mercury’s space. The regions include the solar wind, magnetosheath, and magnetosphere. We have investigated the distributions of Na+-group ions in these regions separately and divided them into four true anomaly angles (TAAs) groups. We have shown their distributions in electric field coordinates. The intensity of Na+-group ions is the highest in the magnetosphere and the lowest in the solar wind. The Na+-group ions show clear dependencies on the TAAs. The escape rates of the Na+-group ions are estimated in different regions and different TAA intervals.

Romanelli N.  DiBraccio G. A.  Slavin J.  Bowers C.  Weber T.

Mercury’s Magnetotail Twisting: Comparing MESSENGER and Terrestrial Magnetometer Observations [#6003]
Studies have indicated that the magnetotails on Earth and Mars can twist due to solar wind-planetary interaction; however, the underlying physical processes in intrinsic and induced magnetospheres remain unclear. Particularly, spacecraft observations show the dawn-dusk component (By) of the Interplanetary Magnetic Field (IMF) plays a significant role in both environments, affecting the sense of the tail twist. A comprehensive analysis of all MESSENGER Magnetometer data is conducted to estimate the influence of the IMF By on Mercury’s magnetotail. We find that Mercury’s tail twist is very small (<~3 deg), for a median downtail distance of ~2 Mercury radii. A correlation is also found between the IMF By and the local By component around the magnetotail current sheet. These results suggest the small (or lack of) twist may be explained by the dipolar field strength in the near-magnetotail. These observations are compared to studies on the terrestrial magnetotail to test this hypothesis.

Smith K. D.  Jackman C. M.  Garton T. M.  Mangham S.  Sun W. J.  Griton L.  James M.  Smith A. W.

Machine Learning Classification of Mercury Magnetospheric Boundary Crossings [#6021]
In this work we employ supervised machine learning to classify the near-Mercury environment (magnetosphere, magnetosheath, solar wind) based on observations made using the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft’s magnetometer (MAG). We train on data spread over the first 3 years of the MESSENGER mission, taking a supervised learning approach, and utilising a previously published list of magnetopause and bow shock boundary crossing intervals. We tested several long short-term memory recurrent neural networks. These models performed particularly well, with a 1024 node, single layer LSTM performing the best with an overall accuracy of 95 reproducing manually created labels. This work has potential future utility for the upcoming BepiColombo mission to quickly characterise magnetospheric regions from magnetometer data only.

Morrissey L. S.  Schaible M. J.  Tucker O. J.  Szabo P. S.  Bacon G.  Killen R. M.  Savin D. W.

A Sensitivity Study to Develop a Best-Practice for SDTrimSP Simulations of Solar Wind Ion Induced Sputtering [#6010]
Surface sputtering by solar wind (SW) ion irradiation is an important process for understanding the surface and exosphere of airless celestial bodies such as Mercury. Theoretical sputtering models are often used to study the incoming ions, impacted surface, and sputtered atoms. Within SDTrimSP there are several user-specific inputs that have been applied differently in previous SW sputtering simulations. These parameters can influence the simulated behavior of both the target and sputtered atoms. It is therefore of great interest to understand how sensitive sputtering behavior is to these inputs and what parameter choices best approximate SW sputtering. We have conducted a detailed sensitivity study into SDTrimSP parameters to produce a best-practice for simulating SW impacts onto the lunar surface. These results can be used to establish a more consistent methodology for simulations of SW induced sputtering.

Szabo P. S.  Poppe A. R.  Biber H.  Mutzke A.  Pichler J.  Jäggi N.  Galli A.  Wurz P.  Aumayr F.

Simulating Energetic Neutral Atoms (ENAs) from Scattered Solar Wind Protons for Constraining Surface Properties of Mercury [#6009]
Emission of energetic neutral atoms (ENAs) resulting from solar wind protons that are reflected and neutralized at the surface has been observed at the Moon. This process is expected to occur similarly at Mercury, which will be investigated by BepiColombo. We have developed a model of the ion-surface interaction accounting for the granular structure of the lunar regolith that explains observations at the Moon. With this model, we have been able to show that the solar wind reflection is strongly influenced by the grain stacking, allowing to constrain the porosity of the lunar regolith at the surface to 85 ± 15 %. We now further discuss scattering energies as well as angles of the reflected particles. Based on these results, we can predict how the ENA emission process is expected to occur on Mercury. In doing so, we examine the possibility of using ENA studies for constraining the porosity of Mercury’s regolith as well as other surface properties that influence the solar wind scattering.

Glass A. N.  Raines J. M.  Jia X.  Dewey R. M.  Sun W.

Statistical Assessment of Mercury’s Northern Plasma Sheet Horn with MESSENGER Data [#6025]
In previous work, we have identified three geometries of MESSENGER’s orbit through Mercury’s magnetosphere in which Mercury’s northern plasma sheet horn can be observed by the Fast Imaging Plasma Spectrometer (FIPS). We have also shown case study orbits of each such geometry. Statistical analysis of the horn is motivated by the desire to constrain the typical conditions of precipitating plasma within the northern horn, the extent of the space on the nightside over which precipitation through the horn occurs, and knowledge about what effect the upstream conditions have on the horn conditions and precipitation footprint. Using a new database of over 300 more observations of Mercury’s plasma sheet horn by MESSENGER, we begin to gain insights into each of these unresolved areas.

Martellato E.  Luther R.  Benkhoff J.  Da Deppo V.  Casini C.  Palumbo P.  Rotundi A.  Slemer A.  Cremonese G.

MESSENGER: A Tool to Study Mercury Beyond Its Operative Life [#6024]
In this work, we model the crater produced by MESSENGER on Mercury with iSALE shock physics code. The spacecraft is approximated by an aluminum cylinder, impacting at about 4 km/s on Suisei Planitia, which is modeled as a two-layer target (basaltic crust overlaid by a regolith layer of variable thickness (T)). We find that craters forming in competent rock surfaces (T=0) are small (<10 m wide). In two-layer targets with a thin regolith layer (T=1-2 m), we obtain flat-floor craters, as much as 20 m wide, and 2 m deep. In the case of thick regolith layers (T>5 m), the crater develops entirely in the upper regolith layer, and it is about 20 m wide, and 4 m deep.The final goal is to verify if the MESSENGER crater might be observed by the BepiColombo SIMBIO-SYS camera. Given instrument performances and the numerical modeling results, the crater can be observed by the only SIMBIO-SYS high-resolution channel (HRIC), when the near-surface stratigraphy is made of a >5 m thick layer of regolith.

Dunnigan A. H.  Soderlund K. M.  Liu D.  Steinbrügge G.  Rivoldini A.  Dumberry M.  Schubert G.  Cao H.  Schroeder D. M.

Using Fe-S-Si Internal Structure Models to Study Mercury’s Interior [#6036]
The Mercury Surface, Space, Environment, Geochemistry, and Ranging (MESSENGER) mission provided new geodetic and magnetic measurements we can use to constrain the planet’s internal structure, as well as test hypotheses for how its magnetic field is generated and maintained. By better understanding Mercury’s interior, we can improve our understanding of how planetary interiors and magnetic fields function in general. Building upon theoretical models from Dumberry and Rivoldini (2015) and Steinbrügge et al. (2021), we create present-day internal structure models with Fe-S-Si core compositions set to match geodetic constraints. By working under the assumption that Mercury’s magnetic field is sustained by an iron-snow supported dynamo, we can constrain its interior properties, such as the mean mantle density, core-mantle boundary temperature, core mass, core light element concentrations, and inner core size.

Wohlfarth K.  Tenthoff M.  Wright J.  Galluzzi V.  Wöhler C.  Hiesinger H.  Helbert J.  Zender J.  Benkhoff J.

Computational Models for Mercury Surface Analysis [#6034]
We present two computational models that support Mercury surface science. 1) Shape (and Albedo) from Shading refines coarser laser altimeter or stereo DEMs [1,2]. The algorithm works on MDIS and BepiColombo’s MCAM imagery and is ready for future datasets. We reconstructed several targets on Mercury, such as scarps, hollows, pit craters, volcanic features, and large regions for geomorphologic analysis [3].2) We developed a fractal rough thermal model with self-heating, self-scattering, and shadowing that predicts the thermal emission of airless bodies. This model aids MERTIS calibration for mineralogical mapping and thermal modeling in polar regions. We validated it with lunar data from Gaofen-4 and the MERTIS flyby [4,5]. [1] Grumpe and Wöhler (2014) ISPRS J. Photogramm. Remote Sens, 94, 34-57[2] Grumpe et al. (2014) Adv. Space Res., 53(12), 1735-1767[3] Tenthoff et al. (2020) RS, 12(23), 3989[4] Wohlfarth et al. (2022) subm.[5] Wohlfarth et al. (2022) 53rd LPSC, #2431.

Shackelford A.  Donaldson Hanna K. L.  Klima R. L.  Thompson M. S.  Parman S.

Space Weathering on the Mercurian Surface: Shedding Light on the Darkening [#6023]
We see evidence for carbon present on the surface of Mercury today from excavations of low-reflectance materials (Klima et al. 2018), but how is this theorized carbon intermixed with the regolith? Could the harsh space weathering environment affect carbon in the regolith, producing nanophase carbon particles on grain rims? We aim to investigate these questions in a laboratory study featuring low- to Fe-free analogs, multiple opaque phases, and a new ultra-high vacuum, simulated environment system designed to mimic relevant surface conditions across the Solar System, including Mercury’s near-surface environment. To simulate the hermean regolith, we will use three analog minerals and three carbon opaques to create mixtures. The samples will be weathered with a UV lamp and reflectance spectra will be collected before, during, and after irradiation. We will also take TIR emissivity spectra and characterize any changes in mineral phase in the vapor and melt layers with TEM and SEM analyses.

Deutsch A. N.  Bickel V. T.  Blewett D. T.

The Mercury HORNET: Ongoing Progress to Automatically Map and Classify Hollows [#6001]
To date, three major degradation states of hollows have been observed on Mercury. Class 1 hollows have high reflectances and distinct morphologies (rounded, irregular outlines and flat, shallow floors) and are interpreted to be in an early active developmental stage. Class 2 hollows lack high reflectance interiors/halos, but retain distinct morphologies and are interpreted to be further along in development. Class 3 hollows lack high reflectance, have softened morphologies, and are interpreted to be late-stage, inactive/expired hollows. Questions remain regarding when or why hollows evolve through these stages. We present ongoing work to train a convolutional neural network, the Mercury HOllows Retrieval NETwork (HORNET), to automatically detect hollows in MESSENGER images and classify their degradation states. This will enable a better understanding of hollow evolutionary sequences by analyzing the environments and growth patterns of hollows in various degradation states.

Rothery D. A.

Smooth Crater Floor Material — Time to Reassess How Much is Lava? [#6007]
The floors of craters down to 20 km diameter on Mercury are conventionally mapped as either smooth or hummocky. The latter mostly represents the original floor with or without landslides/hollows. The former could be lavas or impact melt or ejecta from another crater. Folk have tended to shy away from a lava explanation except in large basins and equally old smaller craters, perhaps because of the narrative that the waning of plains volcanism accords with the closing of magma ascent pathways by establishment of global contraction, even though explosive volcanic vents and faculae on crater floors attest to volcanism continuing through the Mansurian and likely into the Kuiperian. On Mars, Perseverance study of the floor of the 45 km Jezero crater has now demonstrated emplacement of up to three lava units 100 Ma or more after the crater was formed. Unless these came over the rim (which is not ruled out) this example should increase our confidence in within-crater lava effusion on Mercury.

Giuri B.  Van der Bogert C.  Hiesinger H.

A New Map of Mercurian Smooth Plains [#6008]
Smooth plains (SP) are flat, smooth, sparsely cratered and have sharp boundaries. In this work, we used MDIS images to study SPs with particular focus on previously unmapped small-scale deposits and crater floor deposits down to 20 km in diameter. The mapping is based on the visual identification of sharp and smooth deposits with respect to adjacent terrains. We observe large-scale deposits to be consistent with previous maps and a higher density of small-scale deposits compared to previous work. This map supports the interpretation a volcanic origin for most SPs, but also provides a basis for alternative hypothesis. Consequently, we find the distribution of SPs in our new map to be 33.5% of the globe. We aimed at mapping all identifiable smooth and flat deposits, regardless origin. This will allow us and future work to have a global view of the true distribution of smooth deposits for a more complete assessment of their origin.

Blance A. J.  Rothery D. A.  Wright J.  Balme M. R.  Galluzzi V.

Mercury’s Chaos Terrain Revisited [#6039]
Mercury’s chaotic terrain, in the Discovery (H11) quadrangle, consists of numerous knobs, pits, and linear grooves. These cut across crater rims, drastically altering their surface expression. This terrain is the largest, and potentially sole example of its kind on Mercury, found at the antipode to the Caloris basin. Previous studies (Schultz and Gault, 1975) suggested the Caloris impact formed the terrain, where seismic shaking and impact ejecta deposition at the antipode resurfaced the area. Alternatively, Rodriguez et al. (2020) suggested the terrain may have been formed by later volatile loss. Our investigations have so far focused on dating the terrain relative to the Caloris impact event. Crater counts of the terrain and the Caloris crater rim (thought to best represent the age of impact) produce ages indistinguishable from each other. Work is ongoing in investigating the terrain’s morphology, with an emphasis on comparison to chaotic terrains on other planetary bodies.

Loveless S. R.  McCullough L. R.  Klimczak C.  Crane K. T.  Byrne P. K.

Geomorphology of Mercury’s Shortening Structures Shows No Grouping into Categories [#6028]
Shortening landforms on Mercury, thrust faults underlying displacement-gradient folds, have traditionally been grouped qualitatively into 3 distinct categories: “lobate scarps,” “wrinkle ridges,” and “high-relief ridges.” Here, we assess these categories by measuring morphological variables across 100 landforms at randomly selected locations. We conduct a multivariate statistical analysis to test which parameters govern the variability observed amongst landform shapes. Of the measured parameters, the relief, final length (i.e., breadth), and initial length (i.e., total transect length) of the shortening landforms have the most influence on the morphological variability we observe. Shortening strain and the slope of the forelimb also show a strong influence on observed variability. Our computed statistics indicate no distinct clustering of shortening landform parameters that would clearly allow a distinction of landform types.

 

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Thursday, February 2, 2023

MEXAG COMMUNITY PRIORITIES

12:40 p.m.

Times

Abstract Title and Summary

12:40 p.m.

Update on MExAG Science Goals Document

12:45 p.m.

MExAG Community Priorities Breakouts

1:30 p.m.

Report from Breakout Sessions

1:45 p.m.

Open Microphone Discussion Period

 

Friday, February 3, 2023

MAGNETOSPHERIC FUN

11:00 a.m.

Times

Authors (*Presenter)

Abstract Title and Summary

11:00 a.m.

 

Welcome and Presentation of Preliminary Findings

11:15 a.m.

Zomerdijk-Russell S. *  Masters A.  Korth H.  Heyner D.

Modelling the Time-Dependent Magnetic Fields that BepiColombo will use to Probe Down into Mercury’s Mantle [#6026]
Inductive processes, resulting from external solar wind forcing of a magnetosphere causing magnetopause motion and changes of this boundary’s current structure, can be exploited to determine the interior structure of magnetized planets. In preparation for BepiColombo’s arrival at Mercury, and through analysis of data acquired by the Helios spacecraft, we assess solar wind ram pressure forcing in this planet’s environment and the resulting impact on the magnetopause’s inducing field. These measurements suggest that BepiColombo will see highly unpredictable solar wind conditions and that the inducing field generated in response to variable solar wind ram pressure is non-uniform across the planet’s surface. Example inducing magnetic field spectra generated, with frequencies between approximately 5.5×10^-5-1.5×10^-2 Hz, suggest that transfer functions derived from the two BepiColombo spacecraft could allow us to obtain a profile of conductivity through Mercury’s crust and into the mantle.

11:23 a.m.

Chen Y. C. *  Dong C. D.

Studying the Distribution of Sodium Ions in Mercury’s Dynamic Magnetosphere with Multifluid MHD Simulations [#6027]
Mercury’s magnetosphere is smaller but more dynamic than that of Earth because of its weak intrinsic magnetic field and its proximity to the Sun. Although Mercury does not have an atmosphere like Earth, it has a tenuous exosphere, where sodium is the dominant species. The exospheric neutrals can be ionized. Those heavy ions are transported through Mercury’s magnetosphere and may have a significant influence on its dynamics. To quantify the role of the heavy ions, we include an exosphere and implement the associated photochemistry in a global multifluid MHD model. We perform numerical simulations to investigate the sodium ion density distributions with different exosphere configurations under different upstream solar wind conditions. Dawn-dusk asymmetries of the sodium ion distributions are identified from the simulation results. The asymmetric distributions are produced by the separation of sodium ion fluid velocity and solar-wind hydrogen velocity.

11:31 a.m.

Shi Z. *  Rong Z. J.  Fatemi S.  Slavin J. A.  Klinger L.  Dong C.  Wang L.  Zhong J.  Raines J. M.  Holmström M.  Yuan C. J.  Barabash S.  Wei Y.

An Eastward Current Encircling Mercury [#6004]
Mercury has a terrestrial-like magnetosphere which is usually taken as a scaled-down-version of Earth’s magnetosphere with a similar current system. We examine Mercury’s magnetospheric current system based on a survey of Mercury’s magnetic field measured by the Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) spacecraft as well as computer simulations. We show that there is no significant Earth-like ring current flowing westward around Mercury, instead, we find, for the first time, an eastward current encircling the planet near the night-side magnetic equator with an altitude of ~500–1000 km. The eastward current is closed with the dayside magnetopause current and could be driven by the gradient of plasma pressure as a diamagnetic current. Thus, Mercury’s magnetosphere is not a scaled-down Earth magnetosphere, but a unique natural space plasma laboratory. Our findings offer fresh insights to analyze data from the BepiColombo mission, which is expected to orbit Mercury in 2025.

11:39 a.m.

 

DISCUSSION

 

Friday, February 3, 2023

GLOBAL GEOLOGY

11:45 a.m.

Times

Authors (*Presenter)

Abstract Title and Summary

11:45 a.m.

Head J. W. *  Huber C.  Lark L.  Parman S.  Parmentier E. M.  Wilson L.

Mercury Magmatic, Tectonic and Geodynamic History: A Comparative Planetology Analysis [#6031]
Terrestrial planetary exploration has provided significant insight into volcanic-tectonic records, global lithospheric stress state/magnitude, and mantle convection patterns with increasing planetary radius. Differences in planetary core-mantle radius ratios (Moon ~0.023 to Mercury ~5.25) are clearly an important evolutionary factor.  We review the importance of Mercury’s core-mantle radius ratio/scale, heat transfer history and mantle convection patterns/scales: 1) Magma oceanography aftermath & predictions for mantle composition, fO2, volatile content parameter space; 2) How the magnitude and timing of global contraction can help constrain the nature of heat sources/timing for mantle melting (relative roles of mantle internal heating & core interior/core-mantle heat flux patterns in mantle bottom-heating with time); and 3) How the observed volcanic record of magma generation, ascent and eruption is related to Mercury’s thin mantle & heat generation/convection patterns and scale.

11:53 a.m.

Besse S. *  Munoz C.  Barraud O.  Doressoundiram A.  Cornet T.  Izenberg N.

Spectral Properties of Geological and Geochemical Units of Mercury [#6015]
The MESSENGER mission was able to retrieve resolved reflectance spectral parameters of most of the planet. Using the MASCS instrument, the MESSENGER science team was able to define the average spectral response of Mercury’s surface from 300nm to 1400nm (Izenberg et al. 2014).  In this work, we present a revisited analysis of the Mercury Mean Spectra (MMS) together with spectral characteristics of Mercury geological and geochemical units. Making use of the Mercury Surface Spectroscopy (MeSS) architecture we can select more accurately and in greater number MASCS footprints that provide the representative spectral properties of a given unit. This methodology, by greatly increases the number of spectra used, improves significantly the signal-to-noise of the resulting average spectra and help us better understand the properties of Mercury’s surface. The resulting average spectra highlight very well Mercury’s spectral differences previously identified and new ones.

12:01 p.m.

Bernhardt H. *  Clark J.  Preusker F.  Klimczak C.  Banks M. E.  Williams D. A.  Nelson D.  Watters T. R.

Global Map and Parameter Catalog of Shortening Structures on Mercury Using Novel High-Resolution Topography Data [#6012]
The distribution of shortening structures on Mercury as well as the geographic and temporal trends of their morphometric parameters are key to better understand the planet’s history of contraction, lithologic/rheologic variations in its crust, and the nature of stress fields that acted through time. Using the latest MDIS mosaics (166 m/pix) and novel terrain models (222 m/pix), we will significantly increase the number of mapped structures, minimize previous biases caused by difficult illumination conditions, and precisely measure the geographic distribution of several parameters (e.g., width, length, height, depth of faulting, lobateness, segmentation, spatial density, D/L). Combined with temporal assessments based on craters intersected by shortening structures, we will test a variety of predictions made by several hypotheses, e.g., regarding global contraction, tidal despinning, thermal weakening, mascon subsidence, and lithologic/rheologic variations.

12:09 p.m.

 

DISCUSSION

 

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Friday, February 3, 2023

SEARCHING FOR MERCURY’S SURFACE SECRETS

12:15 p.m.

Times

Authors (*Presenter)

Abstract Title and Summary

12:15 p.m.

Chabot N. L. *  Malaret E.

New Additions and Capabilities to Mercury QuickMap [#6005]
Mercury QuickMap is a public, easy to use, web-based tool, developed by Applied Coherent Technology (ACT): https://mercury.quickmap.io/ Mercury QuickMap was supported by and heavily used during NASA’s MESSENGER mission and is an important bridge between the MESSENGER and BepiColombo datasets. Through NASA’s support of a BepiColombo Interdisciplinary Scientist position, it has been possible to add new product layers and new capabilities to Mercury QuickMap. These additions benefit the BepiColombo team but are also publicly available to the entire Mercury community. In this presentation, we will introduce those new capabilities added to Mercury QuickMap supported by this effort.

12:23 p.m.

Glantzberg A. K. *  Chabot N. L.  Barker M. K.  Mazarico E.  Siegler M. A.  Martinez-Camacho J. M.  Hamill C. D.  Rivera-Valentin E. G.  Meyer H.  Bertone S.  Deutsch A. N.

Investigating the Distribution of Surface Ice in Mercury’s Northernmost Craters [#6011]
MESSENGER results indicated that permanently shadowed regions in the northernmost craters on Mercury have thermal environments conducive to the presence of exposed water ice at the surface. However, previous models were at an insufficient resolution for conducting detailed analyses. In this study, we constructed local high-resolution (125 m/pixel) digital elevation, illumination, and thermal models for four of the largest northernmost craters suspected of hosting water ice at the surface - Kandinsky, Chesterton, Tolkien, and Tryggvadottir. Arecibo S-band radar, MDIS, and MLA datasets were then compared to simulated stability models for water ice and other volatiles to search for evidence of surface deposits. Here we present our results, which have implications for understanding these ice-bearing deposits on Mercury and for exploring future opportunities with BepiColombo.

12:31 p.m.

Fischer E. L. *  Parman S. W.

Constraining Mercury’s Bulk Silicate Composition [#6033]
We use the average terrane compositions from [1], combined with 19 enstatite chondrite (EC) compositions, to estimate a bulk silicate composition for Mercury. The southern hemisphere, low-fast terrane, high-Mg region, and Caloris interior plains define a linear trend in Al/Si vs Mg/Si. This Mercury fractionation line (MFL) is consistent with forsterite + enstatite fractionation. Bulk silicate Mercury should fall on the MFL. The compositions of the 19 EC plot to the high Si side of (below) the MFL, suggesting Si was removed, likely to the core. We calculate the percent of Si fractionation required to bring each EC composition to the MFL. The average Si removed from EH is 27.3% and is 19.6% from EL. The Si-corrected EC compositions were averaged to produce new estimates of Mercury’s bulk silicate composition, that are consistent with both the igneous fractionation trends and EC bulk compositions.[1] McCoy et al. (2019) in Mercury: The view after MESSENGER.

12:39 p.m.

 

DISCUSSION

12:45 p.m.

 

BREAK

 

Friday, February 3, 2023

BRINGING THAT BIG MAGNETOSPHERIC ENERGY

12:55 p.m.

Times

Authors (*Presenter)

Abstract Title and Summary

12:55 p.m.

Exner W. *  Heyner D.

On the Influence of the IMF Direction to Mercury’s Nightside Current Sheet [#6041]
The size of Mercury’s global magnetosphere magnetosphere is primarily influenced by the upstream solar wind ram pressure.The contents of the inner magnetosphere as cusp locations, field-aligned currents, and nightside current sheet, however, seem to be heavily influenced by the IMF direction.In this study, we explore the effect of 6 distinctly different IMF directions onto the nightside magnetosphere via the global hybrid model AIKEF under otherwise nominal upstream pressure conditions.Our results indicate that the angle of the nightside current sheet to the equatorial plane depends mostly on the IMF-By component, while the IMF-Bx component governs its warping and flapping behavior.This will have significant influence on the determination of the magnetic equator from spacecraft neutral sheet crossings.

1:03 p.m.

Dewey R. M. *  Jasinski J. M.  Raines J. M.

Energy Dispersions in Mercury’s Northern Magnetospheric Cusp [#6038]
Dispersions in proton energy in Mercury’s northern magnetospheric cusp are common. These features were recorded by MESSENGER/FIPS as changes in average proton energy as the spacecraft passed latitudinally through the region, and were observed under a range of solar wind conditions and interplanetary field orientations. We find that these signatures are spatial rather than temporal in nature, and that they correspond to ions on newly-opened field lines streaming away from the reconnection site. The duration of these signatures and their common occurrence indicate that the dayside magnetopause reconnection rate often remains constant for longer than a Dungey timescale. We demonstrate how these dispersions can be used to estimate the local convective electric field strength and the dayside open-closed field boundary latitude, both of which provide new estimates of magnetospheric forcing and constraints for modeling comparison.

1:11 p.m.

Hadid L. Z. Dr. *  Delcourt D.  Saito Y.  Franz M.  Harada Y.  Aizawa S.  Leblanc F.  Modolo R.  Yokota S.  Fiethe B.  Verdeil C.  Katra B.  Fischer H.  Fontaine D.  Krupp N.  Michalik H.  Illiano J. M.  Berthelier J. J.  Kruger H.  Murukami G.  Matsuda S.

BepiColombo 2nd Mercury Flyby: Ion Composition Measurements from the Mass Spectrum Analyzer [#6016]
On June 23rd 2022, BepiColombo performed it’s second gravity assist maneuver (MFB2) at Mercury. Just like the first encounter which took place on October 1 2021, the spacecraft approached the planet from dusk-nightside to dawn-dayside to an extremely close distance within about 200 km altitude above the planet’s surface. This distance is closer than the two orbiters of BepiColombo will orbit the planet after the orbit insertion in 2025.In this work, we will present the first observations of the Mass Spectrum Analyzer (MSA, Delcourt et al. 2016) at Mercury during MFB2. MSA is part of the low energy sensors of the Mercury Plasma Particle Experiment (MPPE, PI: Y. Saito), which is a comprehensive instrument package for plasma, high-energy particle and energetic neutral atom measurements (Saito et al. 2021), onboard the Mercury Magnetospheric Orbiter (Mio). We will focus on the ion composition during 1) the closest approach and on the outbound orbit in the 2) foreshock region.

1:19 p.m.

 

DISCUSSION

 

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Friday, February 3, 2023

ATOMS ABOVE AND AT THE SURFACE

1:25 p.m.

Times

Authors (*Presenter)

Abstract Title and Summary

1:25 p.m.

Bu C. *  Morrissey L. S.  Bostick B. C.  Bowen K. P.  Chillrud S. N.  Domingue D. L.  Dukes C. A.  Ebel D. S.  Harlow G. E.  Ivanov D. A.  Killen R. M.  Ross J.  Schury D.  Tucker O. J.  Urbain X.  Zhang R.  Savin D. W.

A Novel Laboratory Apparatus to Simulate Solar Wind Ion Irradiation on the Surface of Mercury [#6013]
Models of the formation of Mercury’s exosphere are limited by our poor understanding of how solar wind ions interact with the regolith surface, due to the challenges of laboratory studies using regolith-like loose powders. We have built a novel apparatus to measure the doubly differential angular sputtering yields for various impactors and target materials. Sputtered particles are collected by catcher foils surrounding the sample. The foils are analyzed ex-situ using a high precision, automated quartz-crystal microbalance to derive the sputter yield and its angular distribution. We will present our proof-of-principle measurements, using 20-keV Kr+ ions impacting a polycrystalline Cu slab, and discuss their implications for the SDTrimSP simulation tool that is commonly used for modeling ion sputtering. We will also discuss future measurements using loose powders of plagioclase feldspar, expected to be abundant on Mercury’s surface.

1:33 p.m.

Lierle P. *  Schmidt C.  Baumgardner J.  Moore L.  Bida T.  Swindle R.

Characterizing Mercury’s Potassium Exosphere with Ground-Based Observations [#6018]
Aside from sodium, the potassium D lines are the only optical emissions in Mercury’s exosphere bright enough to image above the dayside disk. We map the K brightness over Mercury’s evening hemisphere, which shows an enhancement at low to midlatitudes, well equatorward of the Na emission structure. Both species are brighter in Mercury’s southern hemisphere, but K lacks the strong polar enhancements of Na and shows less north/south symmetry. The disk-averaged Na/K ratio is between 70 and 130. High resolution line width measurements of Na D1 and D2 produce temperatures of 1114 K and 1211 K, respectively, broadly consistent with the 1200 K MESSENGER estimate based on atmospheric scale height. The K line width shows it to be the coldest metal in Mercury’s exosphere, constrained between the surface temperature and 1000 K. Although Na and K are chemical analogs that are often assumed to have similar properties, these results highlight how their exosphere characteristics are quite different.

1:41 p.m.

 

DISCUSSION

 

Friday, February 3, 2023

MEXAG MEETING SUMMARY

1:45 p.m.

Times

Abstract Title and Summary

1:45 p.m.

Meeting Wrap Up Discussion Including Preliminary Findings

 

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