Program

MExAG (Mercury Exploration Assessment Group) 2021

February 3–5, 2021

 

Times listed in program are Eastern Standard Time (EST).  Time Zone Converter

8:00 a.m. PST

9:00 a.m. MST

10:00 a.m. CST

11:00 a.m. EST

5:00 p.m. CEST

1:00 a.m. (the following day) JST

 

Wednesday, February 3, 2021

11:00 a.m.

Oral Session

MExAG Overview I:  MExAG, BepiColombo, and NASA Planetary Science Division

12:45 p.m.

Oral Session

MExAG Overview II:  NASA Heliophysics, the Decadal Survey, and the Mercury Lander Study

 

Thursday, February 4, 2021

11:00 a.m.

Oral Session

Transient Events at Mercury and Their Consequences

12:05 p.m.

Poster Session:

Poster Session I: Heat -- It Does a Mercury Good

 

 

Poster Session II: That Curious Mercury Surface

 

 

Poster Session III: Exospheric Musings

 

 

Poster Session IV: Ions, Ions Everywhere

 

 

Poster Session V: Spotlight on the Magnetosphere

 

 

Poster Session VI: Volcanoes!

 

 

Poster Session VII: Putting the Pieces of the Surface Puzzle Together

 

 

Poster Session VIII: A Few Ideas About Exploring Mercury

12:50 p.m.

Oral Session

A (Geo)Physics Potpourri with a View to the Future

 

Friday, February 5, 2021

11:00 a.m.

Oral Session

Fun with Geochemistry:  Pits, Hollows, and Sulfur

11:45 a.m.

Oral Session

Post-Formation Evolution:  Geology Meets Space Weathering

12:35 p.m.

Oral Session

MExAG Goals Document Kickoff

1:45 p.m.

Oral Session

MExAG Preliminary Findings

 

Print Only

 

 

Wednesday, February 3, 2021

MEXAG OVERVIEW I:  MEXAG, BEPICOLOMBO, AND NASA PLANETARY SCIENCE DIVISION

11:00 a.m.

Chairs:  Carolyn Ernst and Steven Hauck

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Times

Authors (*Denotes Presenter)

Abstract Title and Summary

11:00 a.m.

Hauck S., Steering Committee *

Welcome, Introductions, Logistics, Meeting Policies, Agenda

11:15 a.m.

Benkhoff J. *   Murakami G.

BepiColombo — Comprehensive Investigations of Mercury [#6033]
BepiColombo was launched on 20 October 2018 the BepiColombo 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 its way to Mercury BepiColombo has several opportunities for scientific observations - during the cruise into the inner solar system and during nine flybys (one at Earth, two at Venus and six at Mercury). However, since the spacecraft is in a stacked configuration during the flybys only parts the instruments on both spacecraft are able to perform scientific observations. A summary of the mission and the status of instruments and results from measurements taken during the flybys will be given.

11:30 a.m.

Murakami G. *   Benkhoff J.   BepiColombo/Mio Science WG

Upcoming Exploration of Mercury’s Environment by BepiColombo/Mio:  Updated Status and Plans [#6040]
The next Mercury exploration mission is coming. BepiColombo is an ESA-JAXA joint mission to Mercury with the aim to understand the process of planetary formation and evolution as well as to understand Mercury’s extreme environment in the solar system by two orbiters. JAXA’s Mio spacecraft (Mercury Magnetospheric Orbiter:  MMO) is mainly designed for investigating Mercury’s environment by observing plasma particles, magnetic/electric fields, exosphere, and dusts. After the launch and commissioning activities, we have performed two observation campaigns during interplanetary cruise and Earth and Venus flyby observations in 2020. These observations showed the performance of each instrument and their capabilities. Here we will present the updated status, initial results from cruise and flyby observations, and future observation plans of the Mio spacecraft.

11:45 a.m.

 

BepiColombo Q&A/Discussion

11:50 a.m.

Glaze L. *

Planetary Science Division Overview

12:20 p.m.

Niebur C, *

New Frontiers 5 Status

12:35 p.m.

 

BREAK

 

Wednesday, February 3, 2021

MEXAG OVERVIEW II:  NASA HELIOPHYSICS, THE DECADAL SURVEY, AND THE MERCURY LANDER STUDY

12:45 p.m.

Chairs:  Steven Hauck and Gina DiBraccio

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Times

Authors (*Denotes Presenter)

Abstract Title and Summary

12:45 p.m.

Fox N. *

Heliophysics Division Overview

1:15 p.m.

Christensen P. *

Decadal Survey Update

1:35 p.m.

Ernst C. M. *   Mercury Lander Team

Mercury Lander:  A Planetary Mission Concept Study for the 2023–2032 Decadal Survey [#6007]
This Mercury Lander mission concept enables in situ surface measurements needed to understand Mercury’s unique mineralogy and geochemistry; characterize the proportionally massive core’s structure; measure the planet’s active and ancient magnetic fields at the surface; investigate the processes that alter the surface and produce the exosphere; and provide ground truth for current and future remote datasets. The concept achieves one full Mercury year (~88 Earth days) of surface operations with an 11-instrument, high-heritage, landed science payload. Landing occurs at dusk to meet thermal requirements, permitting ~30 hours of sunlight for initial observations. The RTG-powered Lander continues surface operations through the Mercury night. Thermal conditions exceed Lander operating temperatures shortly after sunrise, ending surface operations. The cost estimate demonstrates that a Mercury Lander mission is feasible and compelling as a New Frontiers-class mission in the coming decade.

1:45 p.m.

Steering Committee *

Poster Advertisements and Plans for the Next Two Days of MExAG

 

Thursday, February 4, 2021

TRANSIENT EVENTS AT MERCURY AND THEIR CONSEQUENCES

11:00 a.m.

Chairs:  Carolyn Ernst and Gang Kai Poh

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Times

Authors (*Denotes Presenter)

Abstract Title and Summary

11:00 a.m.

Steering Committee *

Welcome, Plans for the Day

11:10 a.m.

Rivera-Valentín E. G. *   Meyer H. M.   Bhiravarasu S. S.   Rodriguez Sanchez-Vahamonde C.   Taylor P. A.   Nolan M. C.   Chabot N. L.   Virkki A. K.

Arecibo S-Band Radar Observations of Mercury:  Now with MESSENGER data! [#6003]
The wealth of geological and compositional information provided by MESSENGER now provides excellent context that can help decipher radar products. For example, the most notable radar discovery about Mercury was the identification of radar-bright features at its poles suggestive of pure water ice. The MESSENGER spacecraft confirmed that typically radar-bright features are associated with locations persistently in shadow that are on average hydrogen-rich. However, MESSENGER also revealed that many permanently shadowed regions (PSR) lack radar-bright deposits and that some radar-bright features are not associated with PSRs. Using Arecibo observations from the 2019 and 2020 inferior conjunctions, the first since MESSENGER visited Mercury, we investigated the radar backscattering properties of the north pole at finer scales than ever before using machine learning algorithms. By comparing with MESSENGER-derived products, we can help resolve polar anomalies, including the ice burial depth.

11:18 a.m.

Hamill C. D. *   Chabot N. L.   Mazarico E.   Siegler M. A.   Barker M. K.   Martinez Camacho J. M.

New Illumination and Temperature Constraints of Mercury’s Volatile Polar Deposits [#6019]
Images from the MESSENGER mission reveal low-reflectance polar deposits that are interpreted to be lag deposits of organic-rich, volatile material. To better interpret these images, local, high-resolution (125 m/pixel) digital elevation models 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. The illumination and thermal models show that these low-reflectance polar deposits extend beyond the permanently shadowed region and correspond to a maximum surface temperature of 250 K to 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).

11:26 a.m.

Prem P. *   Ernst C. M.   Chabot N. L.   McFarland E. L.   Goldstein D. B.   Hurley D. M.

Simulating the Delivery of Water to Mercury’s Poles by a Hokusai-Like Impact [#6034]
Several lines of evidence suggest that Mercury’s polar water may have been delivered by a relatively recent, volatile-rich impact. Here, we test this hypothesis through numerical simulations of volatile transport following a Hokusai-like impact. Hokusai is one of the most prominent young craters on Mercury’s surface, and recent analysis suggests that an impact of this scale could have delivered enough water to polar cold traps to account for present-day observations (Ernst et al., 2018). However, the amount of vapor generated during such an impact may have transformed Mercury’s tenuous exosphere into a temporary atmosphere in which volatile transport may have occurred in a fundamentally different manner. We use the Direct Simulation Monte Carlo method to model (based on representative impact parameters) the fate of impact-delivered water over the course of minutes to days. We will report on initial simulation results and discuss implications for the origin of Mercury’s polar deposits.

11:34 a.m.

Deutsch A. N. *   Head J. W.   Parman S. W.   Wilson L.   Neumann G. A.   Lowden F.

Potential Contributions to Transient Atmospheres and Buried Polar Deposits from Volcanic Degassing on Mercury [#6045]
The emplacement of lavas on Mercury was accompanied by the release of magmatic volatiles, the bulk of which were lost to space. We consider the fate of erupted volatiles by quantifying the volumes of erupted volcanic plains and estimating the associated masses of erupted volatiles for a wide range of cases (IW-3 to -7) using existing experimental data and speciation models. We estimate the average duration of a transient volcanic atmosphere would be between ~250 and ~210,000 years, depending on the volume, degassed volatile content, and eruption rate of an individual eruption, and the fO2 conditions of Mercury. If a dense transient atmosphere was ever surface-bound long enough for erupted volatiles to migrate to the poles, those volatiles are predicted to exist as a diffuse layer at least 16 m beneath the surface given regolith gardening rates. Such volatiles would have a composition and age distinctly different from those of the H2O-ice deposits observed at the poles of Mercury today.

11:42 a.m.

Schmidt C. A. *   Cassidy T.   Merkel A.   Jasinski J.   Burger M.

Simulating Impulsive Events in the Mercury Exosphere as Observed by MESSENGER UVVS [#6025]
Each species in Mercury’s exosphere exhibits a different, but seasonally repeatable pattern. Episodic events that augment this behavior have been challenging to isolate with UVVS. We identify such events and simulate one with Na and Mg enhanced several times above nominal, but Ca showing no deviation from steady state. Simulations are consistent with a cm-size scale impactor releasing several kg of atomic Mg and Na in a ratio of 3, comparable to the ratio in the topmost soil. This non-response may reflect that Ca in impact ejecta condenses into a molecular form, e.g. CaO or CaS. The tail’s width indicates surprisingly hot Na ~10,000K and Mg ~15,000K. This impact occurred just 5–10° dawn-ward of the anti-solar point, making it favorable for detection in the tail. Its fast decay is poorly reproduced by simulations where atoms bounce across the surface, as expected for cold night-side interactions. Overall, it’s impressive that such strong signatures can be produced by only modest events.

11:50 a.m.

 

Q&A

12:00 p.m.

 

Directions to the Poster Sessions and Break

 

Thursday, February 4, 2021

POSTER SESSION I:  HEAT -- IT DOES A MERCURY GOOD

12:05 p.m.

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Authors (*Denotes Presenter)

Abstract Title and Summary

Parman S. W.   Anzures B. A.   Cukjati J. T.   Cooper R. F.   Dygert N.   Mouser M. D.   Ohldag H.

Silicon Bonding in Mercury’s Magmas [#6029]
XPS and Si K-edge XANES analyses indicate that Si-O bonding in experimentally produced basaltic melts changes at the very low oxygen fugacities relevant to Mercury lavas (<IW-3). Specifically, we see a decrease in the apparent mean valence of Si, suggesting the presence of suboxide Si (Si with valence less than +4). We speculate that this decrease is due to the high solubility of S, which substitutes for O [1], and reduces the overall ionic character of Si-O bonding. A change of Si-bonding would explain the experimentally observed decrease in melt viscosity at low fO2 [2]. Suboxide Si will act as a network modifier, lowering the overall polymerization of the melt. SiO2 activity in the melt would also be decreased (relative to fully oxidized Si), affecting the crystallization sequence of Mercury’s magma ocean, as well as its lavas. Reversal experiments and NMR analyses are being conducted to verify the result. [1] Anzures et al, 2020, GCA 286:1-8, [2] Mouser et al, 2020, LPSC 51: 2098.

Dumberry M.

The Influence of a Fluid Core and a Solid Inner Core on the Cassini Sate of Mercury [#6037]
In this work, I present a model of the Cassini state of Mercury that comprises an inner core, a fluid core and a mantle. The model includes inertial and gravitational torques between interior regions, and viscous and electromagnetic (EM) coupling at the boundaries of the fluid core. I show that the coupling between Mercury’s interior regions is sufficiently strong that the obliquity of the mantle spin axis deviates from that of a rigid planet by no more than 0.01 arcmin. I also show that the misalignment between the orientation of the gravity field (or, moment of inertia of the whole planet) and the mantle spin axis increases with inner core size, but that it is limited to 0.007 arcmin. Our results imply that the measured obliquities of the mantle spin axis and polar moment of inertia should coincide at the present-day level of measurement errors and cannot be distinguished from the obliquity of a rigid planet.

O’Neill C.

Geodynamic Evolution of Mercury-Type Planets [#6041]
Mercury is the most alien of the terrestrial planets in terms of its cosmochemistry and interior structure and serves as a unique analogue for end-members of terrestrial planet catalogue. Whilst details of geophysically important elements - including heat-producing elements in the mantle, and light elements in the core - are not constrained in detail, the thermal and volcanic evolution of Mercury provides important insight on its interior composition, and the geodynamics of Mercury-like exoplanets. Here we present simulations of the 3D evolution of Mercury’s interior, including melt-transport and volcanism, magnetic field evolution, and the effects of impacts. We extrapolate the simulations to the conditions of Earth-sized Mercury-type exoplanets and address their surface and volcanic evolution.

Lark L. H.   Head J. W.   Huber C.   Parmentier E. M.

Effect of Crustal Heating and Insulation on Processes Driven by Heat Transport in Mercury [#6053]
Heat loss is a major aspect of planetary thermal evolution, with the rate of heat loss driving volcanic and magnetic activity. On Mercury, heat is lost from the interior primarily by conduction through the crust. That crust is not vertically homogeneous; it likely has a low thermal conductivity megaregolith, as known to be present on the Moon. In addition, solidification of a low fO2 Mercurian magma ocean may have resulted in the upward segregation of buoyant sulfides enriched in heat-producing elements, resulting in high rates of radiogenic heating in the lower levels of the crust or uppermost mantle. We explore the relationship between layering of insulation/heating in the crust and planetary cooling using simple models based on heat conduction and convective heat transfer scaling laws. We find that the thickness of a megaregolith layer is a dominant factor controlling heat transfer through the crust, though volumetric heating may become important when heat flux is low.

 

Thursday, February 4, 2021

POSTER SESSION II:  THAT CURIOUS MERCURY SURFACE

12:05 p.m.

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Authors (*Denotes Presenter)

Abstract Title and Summary

Schmude R. W. Jr.

Temperature Effect on Mercury’s H-Filter Brightness [#6013]
Is it possible to measure a change in Mercury’s H-filter reduced magnitude value as a result of that planet’s changing temperature between aphelion and perihelion? In order to answer this question, I plotted 70 H-filter reduced magnitude values against the phase angle and determined the best fit cubic equation. I then computed the magnitude difference by subtracting each predicted (polynomial) value from the measured reduced magnitude value. Each magnitude difference value was then plotted against the Mercury-Sun distance. This graph shows Mercury’s reduced magnitude is 0.14 magnitudes brighter at perihelion than at aphelion. Base on a population correlation coefficient test, the correlation coefficient is statistically significant at the 95% confidence level. No significant correlation was found for a similar analysis of J-filter measurements. It is concluded that over ten percent of the H-filter light coming from Mercury, at perihelion, is from thermal emission.

Rodriguez A. P.   Domingue D.   Abramov O.   Travis B.   Weirich J.   Chuang F.   Palmer E.

The Devolatilized Landscapes of Mercury:  New Insights and Major Uncertainties [#6052]
There is emerging evidence of a current-day volatile-rich surface and subsurface materials on Mercury. We show evidence for Mercury’s chaotic terrain as the residue due to a devolatized crust. We show that volatile removal leading to hollows formation did not occur within the plains that they modify. Instead, the devolatilization likely occurred from within an extremely ancient, buried volatile-rich stratigraphy. We present evidence that the north circum-polar plains and adjoining cratered regions formed in a crustal layer originally composed of volatile-rich materials. Our scenarios explain the origin of a primordial volatile-rich layer, its connection to widespread chaotic terrain formation, the clustering of the north polar craters, and the formation of widespread younger volatile-rich plains, regionally modified by hollows.

Byrne P. K.

Geochemical Terranes on Mercury may Concentrate Shortening Strains at Their Boundaries [#6055]
Mercury is replete with thrust faults. Globally, these faults have a dominant north–south trend, but it is unclear if this trend is real or simply a function of lighting. Nonetheless, a dominant alignment is unexpected:  these faults are attributed to global contraction, and so their orientations and positions ought to be random. The superposition of stress from tidal spindown and/or longitudinal differences in lithospheric thickness have been proposed to account for deviations in thrust fault orientation from random. But such explanations treat the lithosphere as mechanically homogeneous. MESSENGER data revealed the presence of multiple geochemical terranes, including the “High-Mg Region” (HMR). The eastern margin of the HMR is bound by a north–south-oriented thrust belt. If these geochemically distinct terranes also differ in bulk mechanical properties, their boundaries may act as stress risers—localizing strain and helping to generate the global pattern of thrusts we see on Mercury.

 

Thursday, February 4, 2021

POSTER SESSION III:  EXOSPHERIC MUSINGS

12:05 p.m.

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Authors (*Denotes Presenter)

Abstract Title and Summary

Horanyi M.   Sternovsky Z.   Szalay J.

The Mercury Dust Experiment (MDEX) [#6001]
The bombardment of airless planetary bodies plays a significant role in shaping their surface properties and contributes to sustaining their tenuous atmospheres. The Lunar Dust Experiment (LDEX) onboard the LADEE mission highlighted the role of dust impacts as sources of several atmospheric species by correlating the simultaneous measurements of LDEX with the observations by UVS and NMS instruments. Similar measurements in orbit about Mercury will characterize the effects of dust impacts that are expected to be even more dramatic than at the Moon, due to the much larger impact speeds of the bombarding meteoroids. An updated version of LDEX, in addition to the size distribution of the ejected dust particles, could also measure their composition and map the surface composition of Mercury. This is an especially attractive opportunity to investigate the volatile content in permanently shadowed regions where optical remote sensing is not viable.

Milillo A.   Mangano V.   Massetti S.   Mura A.   Alberti T.   De Angelis E.   Kazakov A.   Ivanovski S. L.   Moroni M.   Orsini S.   Plainaki C.   Rispoli R.   Sordini R.

Mid-Latitudes Exospheric Na Distributions Along the Mercury Orbit [#6024]
The mid-latitudes peaks of the Na exosphere are frequently observed in emission lines from ground-based observations. They can vary in shape and intensity at (sub-)hourly time scales, accounting for about 10–20% of observed fluctuations in a full Mercury’s orbit. These peaks are generally interpreted as the planetary response to solar wind and Interplanetary Magnetic Field variability. Recently, an unexpected relationship between North or South peak emission and both TAA and local time has been found by means of THEMIS data set collected during the period between 2009 and 2013. In fact, a clear northern peak prevalence is seen in the orbit outbound leg, and a southern major peak in the inbound leg. These results seem to contradict those obtained from the analysis of the McMath-Pierce observations in the period 1997–2003. Some possible interpretations are suggested.

Orsini S.   Mangano V.   Mura A.   Milillo A.

The Exospheric Na Emission from Ground-Based Observation as a Tracer of Solar Wind Precipitation at Mercury [#6026]
Following previous studies from Orsini et al (2018), Mangano et al. (2015) and Massetti et al (2017), this presentation is based on the analysis of exospheric Na emission at Mercury as monitored during a long campaign of ground-based observations from THEMIS solar telescope in the Canary Islands, to investigate deeper the connection between the interplanetary magnetic field near Mercury and the morphology of the planetary Na exosphere. In particular, our work focuses on the possible relationship between the Na emission location at high latitudes on the day-side hemisphere of Mercury with the interplanetary magnetic field as measured in situ by the magnetometer onboard the MESSENGER spacecraft.

Both Na exospheric emission and magnetic field data are averaged over the same time periods, i. e. approximately one hour for each detection. The results that will be discussed are based on about 100 events extracted from THEMIS database in similar seeing conditions, performed during the MESSENGER mission lifetime.

Rognini E.   Mura A.   Capria M. T.   Milillo A.   Zinzi A.   Galluzzi V.

Possible Effects of Mercury Surface Temperatures on the Exosphere [#6042]
The BepiColombo mission will reach Mercury in December 2025, and will study in detail the surface, the exosphere and the magnetosphere of the planet. We have developed a thermophysical model that will help us to interpret the data provided by the instruments onboard the mission, and it is currently also used to study the sodium content in the planet’s exosphere. The temperature distribution calculated with the code is used as an input for an atmospheric circulation model that calculates the exospheric sodium content. We have studied the impact of different thermal models on the exospheric content, and the way it depends on the position of the planet along its orbit. Some features have been observed (MESSENGER mission, THEMIS telescope) and can be explained with a mix of source, loss and transport processes.

A version of the thermophysical code is almost ready to be available to the scientific community through MATISSE, the webtool developed at the SSDC in ASI.

 

Thursday, February 4, 2021

SESSION IV:  IONS, IONS EVERYWHERE

12:05 p.m.

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Authors (*Denotes Presenter)

Abstract Title and Summary

Jasinski J. M.   Cassidy T. A.   Raines J. M.   Regoli L. H.   Dewey R. M.   Slavin J. A.   Murphy N.

Photoionization Loss of Mercury’s Sodium Exosphere Measured by MESSENGER [#6050]
We present the first investigation and quantification of the photoionization loss process to Mercury’s sodium exosphere from spacecraft data. This is achieved by analyzing plasma and neutral sodium measurements from NASA’s MESSENGER spacecraft. We find that the sodium ion content and therefore the significance of photoionization varies with Mercury’s orbit around the Sun (i.e. true anomaly angle:  TAA). Na+ production is affected by the neutral sodium radiation acceleration loss process. We find that more Na+ was measured on the inbound leg of Mercury’s orbit at 180–360º TAA because less neutral sodium is lost downtail from radiation acceleration. Calculations using results from MESSENGER observations show that the photoionization loss process removes ~1024 atoms/s from the sodium exosphere, showing that previous modeling efforts have underestimated this loss process. This is an important result as it shows that photoionization is a significant loss process.

Bu C.   Bostick B. C.   Chillrud S. N.   Ebel D. S.   Harlow G. E.   Schury D.   Savin D. W.

Laboratory Simulation of Solar-Wind Ions Irradiation on the Surface of Mercury [#6054]
Characterization of the exosphere production and the surface spectrophotometry of Mercury is limited by our poor understanding of how solar wind ions interact with the regolith surface, due to the challenges of laboratory study using regolith-like loose powders. We have developed a novel apparatus to perform solar wind-like ion irradiation of loose powders and measure sputter yields and spectral changes. We will first study loose powders of plagioclase feldspar, expected to be common on Mercury. Sputtered particles will be collected by catcher foils surrounding the samples, with foils analyzed ex-situ using a high precision, automated quartz crystal microbalance system to derive the sputter yield and its angular distribution. Spectra spanning 350–2500 nm will be collected in vacuo and in situ as a function of ion fluence. The results will provide needed inputs for models of Mercury’s surface spectrophotometry and models of the production of the Hermean exosphere.

Sun W. J.   Slavin J. A.   Milillo A.   Raines J.   Orsini S.

The Sodium Ion Enhancement at Mercury’s High Latitude Magnetosphere During Flux Transfer Event Showers:  MESSENGER Observations [#6010]
This study presents MESSENGER observations of enhanced Na+ near Mercury’s northern cusp during the intervals of flux transfer event (FTE) showers. The result suggests that magnetopause reconnection can effectively modulate solar wind impact on the surface, which injects Na into Mercury’s surface bounded exosphere. The FTE shower contains frequent magnetic flux ropes (greater than 10 per minute), in which the magnetic field line has one end connecting to the interplanetary medium and the other to the planetary surface on the cusp. The FTE shower forms a solar wind entry layer, which converges toward the northern cusp and channels downward the solar wind particles. During the FTE shower intervals (in only tens of minutes), the Na+ is significantly enhanced in the solar wind entry layer compared to the intervals without FTE showers. This process is much faster than expected for exospheric temporal variations due to photon stimulated desorption and micrometeoroid impact vaporization.

Morrissey L. M.   Tucker O. J.   Killen R. M.   Domingue D.   Nakhla S.   Savin D. W.

Surface Sputtering by Ion Irradiation:  Benchmarking Binary Collision Approximation and Molecular Dynamics Models to Laboratory Measurements [#6011]
Surface sputtering by solar-wind ion irradiation is important for understanding Mercury’s exospheric composition. Due to the complexity of laboratory simulations, theoretical calculations are needed to provide the bulk of the data. The most common models use the binary collision approximation (BCA), such as SDTrimSP. While the BCA is often accurate at high impact (>1000eV) energies, error can be introduced below 1keV. In contrast, Molecular Dynamics (MD) models the entire collision cascade. Before either BCA or MD models can be used to reliably simulate planetary surface impacts, it is important to verify their accuracy by comparison to pre-existing experimental values. Here, we compare predicted sputtering yield and energy distributions from BCA and MD to experimental results for a Cu substrate impacted by Ar between 200–1000 eV.

 

Thursday, February 4, 2021

POSTER SESSION V: SPOTLIGHT ON THE MAGNETOSPHERE

12:05 p.m.

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Authors (*Denotes Presenter)

Abstract Title and Summary

Alberti T.   Milillo A.   Laurenza M.   Massetti S.   Ivanovski S. L.   Ippolito A.   Plainaki C.   De Angelis E.   Mangano V.   Mura A.   Orsini S.   Rispoli R.

Multiscale Features of the Near-Hermean Environment as Derived by the Hilbert-Huang Transform [#6016]
The interaction between the interplanetary medium and planetary environments gives rise to different phenomena on several temporal and spatial scales. Here we propose, for the first time, the application of the Hilbert-Huang Transform (HHT) to characterize both local and global properties of Mercury’s environment as seen during two MESSENGER flybys. Our findings support the ion kinetic nature of the Hermean plasma structures, with the magnetosheath being characterized by inhomogeneous ion-kinetic intermittent fluctuations, superimposed to both MHD fluctuations and large-scale field structure. We show that the HHT analysis allow to capture and reproduce some interesting features of the Hermean environment as flux transfer events, Kelvin-Helmholtz vortices, and ULF wave activity. Our approach demonstrates to be very promising for the characterization of the structure and dynamics of planetary magnetic field at different scales as well as for the identification of boundaries.

Yang W. Y.

The Variational Shape and Position of Mercury’s Bow Shock [#6039]
According to MESSENGER’s data, we studied the position and shape of Mercury’s bow shock. Firstly, we identified bow shock crossing events of all orbits. Then we studied the influence of the distance from the sun, the interplanetary magnetic field magnitude and direction on the shape of bow shock position.

Dargent J.   Lavorenti F.   Califano F.   Henri P.   Pucci F.   Cerri S. S.

Interplay Between Kelvin-Helmholtz and Kinetic Instabilities Along Mercury’s Magnetopause [#6046]
Boundary layers in space plasmas are always the locations of many phenomena allowing the mixing of plasma. But for a given boundary, different mechanisms can coexist and compete one with each other. In this work, we look with fully Particle-In-Cell simulations at velocity shear boundary layers with a gradient of density and magnetic field. We observe that in presence of a density gradient, kinetic instabilities (such as the lower hybrid drift instability) develops along the layer much quicker than the Kelvin-Helmholtz instability. In particular, we observe that one of those kinetic instabilities develops into forming large scale structures that compete (and even suppress) the Kelvin-Helmholtz instability, depending on the density gradient in the layer. Such a result can make us reconsider the main mixing mechanisms in plasma layers with strong density gradient, such as the magnetopause of Mercury.

Jia X.   Slavin J. A.   Li C.   Chen Y.   Toth G.

Global Simulations of Mercury’s Magnetospheric Interaction Under Nominal and Extreme Solar Wind Conditions [#6048]
Mercury’s comparatively weak intrinsic field, lack of an appreciable atmosphere and its close proximity to the Sun result in a magnetosphere that undergoes more direct space-weathering interactions than other planets. The shielding effect arising from the induction currents in the planetary core and erosion of the dayside magnetosphere by magnetopause reconnection compete against each other for dominance in controlling the global structure of the magnetosphere. We have developed a global MHD model for Mercury that electromagnetically couples the planet’s interior to the surrounding space environment, allowing us to self-consistently characterize Mercury’s dynamical response to time-varying external conditions (Jia et al., 2015). Here we present results from a set of simulations driven by nominal and extreme solar wind conditions as observed by MESSENGER (Jia et al., 2019; Slavin et al., 2019) to quantify the variability of Mercury’s magnetosphere in response to solar wind forcing.

 

Thursday, February 4, 2021

POSTER SESSION VI: VOLCANOES!

12:05 p.m.

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Authors (*Denotes Presenter)

Abstract Title and Summary

Head J. W.   Wilson L.   Parman S. W.   Jozwiak L. M.   Deutsch A. N.

Modeling Dike Emplacement and Pyroclastic Eruptions on Mercury:  Implications for Volatile Sources, Abundances and Fates [#6051]
Pyroclastic eruptions represent rapid transfer of magmatic volatiles from depth to the surface.  The nature, morphology, mineralogy and age of deposits and vent structures provide important evidence for assessing modes of eruption, volatile species and abundances, dispersal, transient atmosphere contributions and potential surface alteration processes. On Mercury, a large number of individual pyroclastic vents and deposits have been documented and many ages extend to post-extensive volcanic plains geologic history. We use deposit and vent characteristics and volumes, and their relatively young ages, to assess the nature of candidate dike-emplacement events and related periods of gas venting to the surface. We find that primary gas formation (propagating dike-tips) combined with significant secondary gas enrichment (stalled dikes) could result in rapid transient volatile venting to the surface in concentrations that do not necessarily represent the abundances in the primary magma.

Rothey D. A.   Man B.   Malliband C.   Pegg D. L.   Wright J.

Volcanology Targets for Future Exploration at Mercury [#6002]
Most plains units were emplaced as large volume lava flows. Regolith obscures many details, but we hope to see flow fronts and collapsed tubes in higher resolution images. Spatially-resolved elemental and mineralogic mapping should help to differentiate magmatic provenance. Higher resolution imaging may clarify the apparent continuity between plains interior and exterior to Caloris, and other examples. Similar clarity should emerge about smooth ponded patches, and on whether candidate volcanic cones are real.

Better imaging and topographic mapping of interiors of explosive vents should clarify cross-cutting and other age relationships in the majority that are compound vents, and reveal how they relate to faults. Element and mineral mapping of faculae, and comparison with ‘red pitted ground’, should cast light on the volatiles responsible for driving explosive eruptions, and may find exceptions to the apparent rule that explosive volcanism is never older than local effusive volcanism.

Crane K.   Bohanon A.   Branigan K.

Estimating Dike Propagation Distance During Global Contraction with Analogues and Frictional Faulting Theory [#6009]
Mercury’s geologic history is characterized by two contradictory processes within a stress framework:  global contraction and effusive volcanism. Global contraction produced horizontal compressional stresses and a global population of thrust faults, while effusive volcanism required opening mode fractures (dikes) to form smooth plains. Dikes can propagate in horizontally compressive stress regimes, but their propagation distance is limited by material properties and deviatoric stresses. Our group tested this relationship for dikes associated with the Columbia River Flood Basalts, which erupted in the same regime that produced the Earth analogue thrust structures of the Yakima Fold Province and calculated propagation distances of over 50 km. Applying the methodology to Mercury, and estimating deviatoric stresses with Frictional Faulting Theory, we estimate that dikes could have propagated 10 km even in a stress regime producing thrust fault-related landforms.

 

Thursday, February 4, 2021

POSTER SESSION VII: PUTTING THE PIECES OF THE SURFACE PUZZLE TOGETHER

12:05 p.m.

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Authors (*Denotes Presenter)

Abstract Title and Summary

Klima R. L.   Denevi B. W.   Ernst C. M.

Examining Localized Occurrences of Low-Reflectance Material on Mercury [#6032]
Low reflectance material (LRM) is found across the surface of Mercury and has been interpreted as being darkened by carbon. In global mapping efforts, LRM is associated with a broad, shallow ~600 nm absorption band, that correlates with carbon content in the regions that have been measured directly with the neutron spectrometer. However, because LRM is often associated with hollows, it is possible that the spectral signature of LRM that is observed on a global scale actually consists of a mixture of a dark, flat spectrum, characteristic of carbon, and an absorption in the hollows spectrum, perhaps due to sulfides or another phase. We examine high-resolution Mercury Dual Imaging System (MDIS) color images of prominent LRM deposits, with and without prominent hollows inside of them, to investigate the origin(s) of the 600-nm feature.

Deutsch A. N.   Bickel V. T.

The Mercury HORNET:  Deep Learning-Driven Mapping of Hermian Hollows [#6017]
Important questions remain about the origin and evolution of hollows on Mercury, such as the extent of a volatile-bearing layer, extent of a lag deposit proposed to limit volatile loss, and processes driving volatile loss. Mapping efforts can help address these questions by characterizing the global and local distribution of hollows (e.g., preferences for Sun-facing slopes).

We train a convolutional neural network, the Mercury HOllows Retrieval NET (HORNET), to detect hollows in MESSENGER NAC images. Promising preliminary results yield hollow detections at a range of spatial scales (~10–100 mpp) and illumination conditions. Future versions will include a segmentation capability for more accurate tracing and geometric measurements. We intend to infuse the Mercury HORNET with early BepiColombo data on the fly to allow for immediate and optimized progress in the global mapping of hollows, enabling efficient studies of surface change detection and possible hollow growth sequences.

Malliband C. C.   Rothery D. A.   Balme M. R.   Conway S. J.

Geological Mapping of the Derain (H-10) Quadrangle [#6021]
We have completed high resolution (1:3M) geological mapping of the Derain (H-10) quadrangle of Mercury. Linework was drawn at 1:300 000 scale. Mapping at the quadrangle scale shows considerable diversity within the plain’s units. To show this diversity, and best represent the visible stratigraphy, we have differentiated local intermediate plains units as well as the endmember intercrater and smooth plains units. To enable compatibility with all current map products, craters were classified in both the 3 and 5-class crater degradation classification systems. As mapping has been completed to the same definitions and standards as other recent European quadrangle maps, it currently being integrated into a coherent geological basemap to support BepiColombo mission planning and operations.

Yazici I. S.   Klimczak C.

Global Fracture Pattern on Mercury Revealed by Polygonal Impact Craters [#6036]
Global distributions of tectonic structures on Mercury show a systematic pattern of preferred orientations across the planet. During the formation of impact craters, fractures within bedrock are generally accepted to produce straight crater rims, paralleling or directly utilizing these fractures, resulting in polygonal plan-view shapes of the craters. To test if fracture sets governed the orientation impact crater rims, we rigorously mapped all 20 and 400 km-diameter impact craters. We then analyzed which crater rim segments are straight and thus contribute additional information about tectonic patterns of the innermost planet. Our results show a strong preferred east-west orientation of straight crater rims at the poles and weak north-south preferred orientations in the mid-latitude and equatorial regions. These findings indicate that fracture patterns revealed by polygonal impact craters on Mercury show a global pattern that compares well to previously observed tectonic patterns.

 

Thursday, February 4, 2021

POSTER SESSION VIII: A FEW IDEAS ABOUT EXPLORING MERCURY

12:05 p.m.

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Authors (*Denotes Presenter)

Abstract Title and Summary

D’Amore M.   Helbert J.   Maturilli A.   Knollenberg J.   Berlin R.   Peter G.   Säuberlich T.   Hiesinger H.

The Mercury Radiometer and Thermal Infrared Imaging Spectrometer (MERTIS) Onboard Bepi Colombo and Data Exploration Techinques Developed for Tthe Mercury Atmospheric and Surface Composition Spectrometer (MASCS) [#6043]
The MErcury Radiometer and Thermal Infrared Spectrometer (MERTIS) instrument will study the mineralogy and temperature distribution of Mercury’s surface in unprecedented detail. It will map the whole surface at 500m in the of 7-14µm and 7-40µm range. MERTIS observed the Moon in April 2020 and Venus in October 2020 in different condition from what it was originally planned for and returned several hundred thousands scientifically useful spectra from the two targets. Its main scientific objectives are: (1) Study of Mercury’s surface composition; (2) Identification of rock-forming minerals; (3) Mapping of surface mineralogy; (4). Study of surface temperature and thermal inertia.

We developed data exploration techniques on Mercury Atmospheric and Surface Composition Spectrometer (MASCS) data and data fusion with other instruments data from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft that will be applied on MERTIS data.

Morlok A.   Renggli C. J.   Reitze M. P.   Stojic A. N.   Weber I.   Wohlfarth K.   Schmedemann N.   Wöhler C.   Bauch K.   Klemme S.   Hiesinger H.   Helbert J.

Exploring the Surface Mineralogy of Mercury with MERTIS@BepiColombo:  FTIR Laboratory Work to Build a Database [#6047]
The MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer) on BepiColombo will map Mercury from 7–14 µm (resolution ~ 500 m) [1]. The Münster IRIS [2] and Berlin PSL [3] labs produce spectra for the interpretation. At the IRIS labs, we currently study: Impact Rocks as analog to regolith [4]. Synthetic Analogs based on remote sensing and modelling [5]. Studies of natural and synthetic feldspar [6]. Space Weathering simulated using an ArF UV laser and shock experiments [7, 8]. Gas/Mineral Interaction to synthesize sulfide-silicate mixtures [9]. Thermal surface modelling [10] and data deconvolution.[1] Hiesinger et al.(2020) SSR, 216,110 [2] Weber et al.(2020) 51st LPSC 1889 [3] Maturilli et al. (2018) EPSC2018-753 [4] Morlok et al.(2016) Icarus 264, 352 [5] Morlok et al.(2019) Icarus 324, 86 [6]Reitze et al.(2021) EPSL 554, 116697 [7] Weber et al.(2021) sub. [8] Stojic et al.(2020) Icarus In Pr.[9] Renggli et al.(2019) JGR Pl. 124:2563-2582 [10] Bauch et al.(2020) Icarus 354, 114083 .

Kremer C. H.   Anzures B. A.   Mustard J. F.   Pieters C. M.

Cross-Over (4-8 µm) Infrared Spectroscopy as a Tool to Identify Olivine and Determine Mg# on Mercury’s Surface [#6038]
Ongoing work has demonstrated that the “cross-over” range (4-8 µm) of the infrared is a promising tool for the remote sensing of silicate minerals. In the “cross-over” wavelength range, silicate minerals transition between volume scattering of photons in the VNIR and surface scattering in the MIR. Olivine shows strong, distinctive overtone-combination bands at ~5.6 and 6.0 µm that shift systematically with Mg#. Pyroxene and plagioclase also have distinctive spectral bands in the “cross-over” region. In addition to Mg#, our preliminary work suggests these minerals may be detected in cross-over spectra of mixtures and that space weathering has only a modest effect on spectra. Although current work focuses on the lunar applications, this technique could also complement mineralogical and compositional determination methodologies on BepiColombo and a proposed Mercury lander. Furthermore, “cross-over” detectors are in development and could have wide application.

Biswal M M K.   Annavarapu R N.

A Baseline Strategy for Mercury Exploration [#6005]
We discuss and provide some baseline strategy required for the robotic exploration missions to Mercury that includes the need to consider proper shielding of spacecraft to prevent damages from solar radiation, electrical-based maneuvering system against chemical propulsion and fuel exhaustion, enabling uninterrupted power supply for both electric maneuvering system and spacecraft power management via nuclear thermoelectric generators against solar array power production method, enabling laser-guided uninterrupted communication system against radio waves, and an approach to sustain thermal stability of the spacecraft required to manage fuel storage and onboard circuitry system. The results presented here are based on the experiences and challenges encountered by the past planetary probes. Finally, we discussed the prospect of spacecraft in exploring and gathering results of more scientific interest Mercury orbit.

Biswal M M K.   Das N B.   Annavarapu R N.

Potential Risks and Hazards of Scientific Exploration Missions to Mercury [#6018]
Space exploration is filled with hazards that need to be prepared for in advance and overcome for a safe and successful mission (manned or unmanned). These challenges arise due to galactic natural phenomena, cracks in artificial technologies and human error. This paper emphasizes on the hazards of an unmanned mission to Mercury. These hazards include the long distance from Earth to Mercury, high temperatures due to proximity to the Sun, scrambling of communication due to heavy electromagnetic interference, risk of solar flares and coronal mass ejection, execution of successful entry, descent, and landing, failure of solar panels, energy production, finding a scientific landing site, navigation and relay of information. The primary intent of this study is to present every prospective challenge and its recommendations impending a scientific exploration mission to Mercury.

 

Thursday, February 4, 2021

A (GEO)PHYSICS POTPOURRI WITH A VIEW TO THE FUTURE

12:50 p.m.

Chairs:  Catherine Johnson and Gina DiBraccio

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Times

Authors (*Denotes Presenter)

Abstract Title and Summary

12:50 p.m.

Romanelli N. *   DiBraccio G.   Gershman D.   Le G.   Mazelle C.   Meziane K.   Boardsen S.   Slavin J.   Raines J.   Glass A.   Espley J.

Upstream Ultra-Low Frequency Waves Observed by MESSENGER’s Magnetometer:  Implications for Particle Acceleration at Mercury’s Bow Shock [#6028]
We present the first statistical analysis of the main wave properties observed in the 0.05-0.41 Hz frequency range in the Hermean foreshock by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) Magnetometer. Although we find similar polarization properties to the 30 s waves observed at the Earth’s foreshock, the normalized wave amplitude and occurrence are much smaller. This suggests lower backstreaming proton fluxes, due to the relatively low solar wind Alfvenic Mach number around Mercury, smaller foreshock size, and/or more variable solar wind conditions. We also estimate the speed of resonant backstreaming protons in the solar wind reference frame (likely source for these waves) ranges between 0.95 and 2.6 times the solar wind speed. The closeness between this range and what is observed at other planetary foreshocks suggests that similar acceleration processes are responsible for this energetic population and might be present in the shocks of exoplanets.

12:58 p.m.

Plattner A. M. *   Johnson C. L.

Non-Axisymmetric Structure in Mercury’s Core Field [#6020]
Mercury’s internal magnetic field is weak, equatorially asymmetric, and axially symmetric, sometimes described as the field resulting from a dipole that is aligned with the planet’s rotation axis but offset toward the north. Magnetic fields caused by interaction of the solar wind with the planetary field dominate the residual magnetic field visible after subtraction of an offset axial dipolar magnetospheric model from MESSENGER data. Previous studies of these residuals have revealed short-wavelength (< ~500km) crustal fields, but internal fields at length scales of O(1000 km) remain uncharacterized. We estimate and subtract magnetic fields that are organized in Mercury’s solar reference frame, to demonstrate the presence of time-invariant regional-scale structure in the field spatially correlated with the Northern Rise topography. We invert for the source depth, using a recently developed method and show that the magnetic sources are likely close to Mercury’s core-mantle boundary.

1:06 p.m.

James P. B. *

The Role of Geophysics in Exploring Mercury’s Volcanic and Thermal Evolution [#6030]
Mercury’s gravity field exhibits a complex relationship with topography that distinguishes Mercury from the other terrestrial planets. This gravity field is a product of Mercury’s bombardment, volcanism, and thermal lithosphere rigidity. Lithospheres on Earth are commonly characterized with models of uncorrelated top loading and bottom loading, but the effusive nature of volcanism on Mercury requires a more customized analysis. The low-degree portion of the gravity field corresponds to gravity contributions from the crust and mantle, whereas the shortest wavelengths of the gravity field are almost exclusively dependent on Mercury’s crust. Since these high-degree data are facilitated by low-altitude spacecraft arcs, the extended mission of the MESSENGER spacecraft offers the best opportunity to comprehensively study loading on Mercury’s lithosphere.

1:14 p.m.

Steinbruegge G. *   Dumberry M.   Rivoldini A.   Schubert G.   Cao H.   Schroeder D. M.   Soderlund K. M.

Challenges on Mercury’s Interior Structure Posed by Recent Measurements of its Obliquity and Tides [#6004]
We calculated interior structure models based on recent measurements of Mercury’s obliquity and tides. Our models are consistent with the mean density, the moment of inertia (MoI), and the ratio of the mantle to whole planet MoI (Cm/C) of Mercury. We show that models that match a MoI=0.333, based on a recent obliquity measurement, pose a challenge to our current understanding of Mercury. Specifically, we confirm that a large inner core is required, which leads to lower mantle densities than previous models and implies the presence of light elements and/or convection in the mantle. The core radius is also lower than previous estimates, making it inconsistent with recent magnetic induction measurements. In addition, models that agree with the tidal Love number k2 require low viscosities in the lower mantle that are difficult to reconcile with possible thermal histories of Mercury. Hence, the structure of Mercury’s interior remains ambiguous and still leaves room for speculation.

1:22 p.m.

Mangano V. *   Leblanc F.   Killen R. M.   Schmidt C.   Milillo A.   Vervack R.   Bida T.   Kameda S.   Grava C.   Zender J.   Benkhoff J.

Coordinated Ground Based Observations of Mercury’s Na Exosphere and the Six BepiColombo Flybys in Years 2021–2025 [#6023]
For many decades, Earth-based observations have been the only way to study Mercury’s exosphere. They allowed the discovery of new species (Na, K, Ca), the morphological and dynamical studies of disk and tail, and their interaction with the surrounding environment.

Coordinated observations from different sites are still ongoing today, with facilities in New Mexico, Hawaii and Canaries.

The experience with MESSENGER demonstrated the important role of simultaneous exospheric Earth-based observations in complementing in-situ measurements made by spacecraft with global view images.

In 2021, BepiColombo will perform the first of 6 Mercury flybys. They will offer another important opportunity to perform coordinated observations between in-situ measurements of exosphere and magnetosphere and ground-based telescopes.

We review the BepiColombo flybys orbit trajectories and Mercury observability from Earth-based facilities and report on plans for coordinated exospheric studies in the next years.

1:30 p.m.

 

Q&A

1:40 p.m.

All *

Open-Mic Discussion

 

Friday, February 5, 2021

FUN WITH GEOCHEMISTRY:  PITS, HOLLOWS, AND SULFUR

11:00 a.m.

Chairs:  Kathleen Vander Kaaden and Ariel Deutsch

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11:00 a.m.

Steering Committee *

Welcome

Times

Authors (*Denotes Presenter)

Abstract Title and Summary

11:05 a.m.

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

Spectral Investigation of Mercury’s Pits Surroundings:  Pyroclastic Activity or Not? [#6022]
Hermean pyroclastic activity has been identified from MESSENGER flybys challenging the hypothesis that Mercury was depleted in volatile. Explosive volcanism is characterized by endogenic pits surrounded by spectrally bright and red deposits. Based on the spectral anomaly of the pyroclastic deposits a catalogue of 137 candidates have been published. From the identification of candidate endogenic pits, the number increases at 174 sites, 150 of which display a spectral anomaly. Reflectance spectra of the pyroclastic deposits from the near-ultraviolet (UV) to near-infrared (NIR) revealed a strong UV downturn. Moreover, various analyses highlighted the variations of spectral properties within and between the deposits. We now examine the reflectance spectra of the pits’ surroundings. The aim is to improve the classification and the understanding of the pyroclastic activity of Mercury. A related objective of this global analysis is to propose targets for the BepiColombo mission.

11:13 a.m.

Phillips M. S. *   Moersch J. E.   Viviano C. E.   Emery J. P.

Elemental Sulfur as the Hollow-Forming Volatile in a Novel Model for Hollow Formation [#6031]
One of the most intriguing results of the MESSENGER mission was the observation of “hollows” – mysterious geologic features that bear morphologic resemblance to sublimation-formed landscapes across the solar system. We present results from mass-loss rate calculations for 57 different candidate hollow-forming volatiles. Our model results, combined with an assessment of volatile species’ geological plausibility, indicate that elemental sulfur (S) is the most likely hollow-forming phase that we considered. We propose a new hollow formation model in which a subsurface heat source drives sulfur-rich fumarolic systems wherein S is emplaced in the near-surface at night and sublimates in the day to form hollows. Low nighttime temperatures on Mercury create a region where solid S is stable. We suggest the “sulfur permafrost zone” is analogous to terrestrial permafrost zones, but with respect to the thermal stability of S on a hermean diurnal basis instead of water on a terrestrial annual basis.

11:21 a.m.

Anzures B. A. *   Parman S. W.   Milliken R. E.   Namur O.   Cartier C.

An fO2-P-T-X Model of Sulfide Speciation in Mercurian Magmas [#6049]
MESSENGER revealed that lavas on Mercury are enriched in sulfur (1.5–4 wt.%) compared with other terrestrial planets (<0.1 wt.%) due to high S solubility under its very low oxygen fugacity (ƒO2). To understand S solubility and speciation in reduced magmas, S K-edge XANES spectra were collected in 60 experiments that span a range of P (177 bar to 5 GPa), T (1225 to 1850 °C), and ƒO2 (IW-0.8 to IW-8.6) using new XANES standards [1] and XANES unmixing technique [2]. We find that as ƒO2 decreases from IW-2 to IW-7, S speciation in silicate melt goes through two major changes. At IW-2, FeS and FeCr2S4 species are destabilized, and CaS becomes the dominant S species with minor Na2S and MnS. At IW-4, MgS is the dominant S species with minor CaS. The S speciation changes have substantial impacts on physicochemical properties such as viscosity, melting temperature, and mineral stability, which led to Mercury’s distinct evolution. [1] Anzures et al. (2020) Am. Min. [2] Anzures et al. (2020) GCA.

11:29 a.m.

Boujibar A. *   Goossens S.   Nittler L. R.   Righter K.

Evaluating Mercury’s Formation Scenarios Using MESSENGER Results, Experimental Data, and Differentiation Models [#6035]
One of Mercury’s most striking feature is its large iron-rich core. MESSENGER mission provided clues to our understanding of Mercury’s formation and the origin of its internal structure. Several scenarios were proposed to explain Mercury’s large core. These include “chaotic models” such as giant impacts, and “orderly models” such as aerodynamic sorting. We argue that Mercury’s core composition can be used as a constraint to test these two main models. In “orderly models”, metal-silicate separation occurs in small planetary embryos, at relatively low pressure and temperature. Conversely, “chaotic models” involve large planetary bodies with a specific signature of core segregation at high pressure-temperature. In these conditions and at low oxygen fugacity, Mercury’s core would be significantly enriched in Si. Here, we combine experimental data on Si partitioning, with models of Mercury core formation, and constraints from MESSENGER to better understand the origin of its large core.

11:37 a.m.

 

Q&A

 

Friday, February 5, 2021

POST-FORMATION EVOLUTION:  GEOLOGY MEETS SPACE WEATHERING

11:45 a.m.

Chairs:  Christian Klimczak and Suzie Imber

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Times

Authors (*Denotes Presenter)

Abstract Title and Summary

11:45 a.m.

Man B. *   Rothery D. A.   Balme M. R.   Conway S. J.   Wright J.

Extensional Landforms as Evidence for Recent Large-Scale Compressional Tectonism? [#6006]
A vast majority of tectonic landforms on Mercury have been formed by compression; extensional landforms do exist but are much rarer (Byrne, 2019; Crane and Klimczak, 2019). Pristine back-scarp grabens associated with small lobate scarps (tens of kms in length and tens of metres in relief) provide evidence for geologically recent tectonism (such features are not expected to survive for extended periods of time due to impact gardening; Byrne et al., 2018; Watters et al., 2016). These grabens form when thrusted material produces an anticline, causing local tensional stresses to form antithetic faults along the hinge zone. Calypso Rupes is the only large lobate scarp (381 km in length and ~1 km in relief) where such grabens have been identified to date (Banks et al., 2015). This work provides new evidence of graben formation along similarly large tectonic features and raises the question “has there been widespread recent tectonism and, if so, might it still be occurring to this day?”

11:53 a.m.

Orgel C. *   Fassett C. I.   Michael G.   Riedel C.   van der Bogert C. H.   Hiesinger H.

Mercury’s Early Impact History:  Population, Stratigraphy, and Sequence of Basins [#6015]
Mercury has one of the best preserved impact records in the inner solar system due to the absence of an atmosphere and relatively unmodified ancient surface. However, our knowledge of the early impact record and the nature of the impacting projectiles are far from complete. To get a better understanding of the early impact history, we examined large impact basins (D ≥ 300 km) on Mercury. We cataloged 94 basins, 80 of which we classify as certain or probable, 1.7 times more than previously recognized. We re-evaluate the crater densities of basins using the buffered nonsparseness correction technique, which we successfully applied for the Moon. Based on these results and comparison with the Moon, we infer that no more than half of the basin record remains observable and basins older than Borealis have generally been erased from the basin record.

12:01 p.m.

Raines J. M. *   Staudacher N. M.   Dewey R. M.   Tracy P. J.   Bert C. M.   Sarantos M.   Gershman D. J.   Jasinski J. M.   Slavin J. A.

Proton Precipitation in Mercury’s Northern Magnetospheric Cusp [#6027]
Ion precipitation onto Mercury’s surface through the planet’s magnetospheric cusps acts as a source of planetary atoms to both Mercury’s exosphere and magnetosphere. In this process, known as sputtering, solar wind ions impact the surface regolith and liberate material, mostly as neutral atoms. We have identified over 2800 northern magnetospheric cusp crossings throughout the MESSENGER mission, based on enhancements in proton flux observed by the Fast Imaging Plasma Spectrometer (FIPS). We find that the cusp centered in the range of 60–70° magnetic latitude and that cusp plasma can be found at latitudes ranging from 30° to 85° magnetic latitude (in separate crossings). 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 2 x 106 cm–2 s–1, ranging 103 –108 cm–2 s–1, and that this flux often varies on a 10 s time scale.

12:09 p.m.

Werner A. L. E. *   Leblanc F.   Chaufray J.-Y.   Modolo R.   Aizawa S.   Raines J. M.   Exner W.   Motschmann U.

Density, Energy and Phase Space Density Distribution of Planetary Ions He+, O+ and Na+ in Mercury’s Magnetosphere [#6008]
The Mercury plasma environment is enriched in planetary ions from the tenuous exosphere. We have developed a test-particle model which describes the full equation of motion for planetary ions produced from photo-ionization of the neutral exosphere. The new test-particle model is coupled to a Monte Carlo test-particle model of the neutral exosphere (Exospheric Global Model; EGM; Leblanc et al. 2017) and two hybrid-kinetic models:  LatHyS (Modolo et al. 2016) and AIKEF (Müller et al. 2011). This coupling will allow us to consider the impact of non-adiabatic energization on the ion density distribution as well as the connection to seasonal asymmetries in the neutral exosphere. We compare the density, energy and phase space density distribution of He+, O+ and Na+ from our model with observations from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) time-of-flight spectrometer Fast Imaging Plasma Spectrometer (FIPS; Raines et al. 2013).

12:17 p.m.

 

Q&A

12:25 p.m.

 

BREAK

 

Friday, February 5, 2021

MEXAG GOALS DOCUMENT KICKOFF

12:35 p.m.

Chairs:  Ron Vervack and Catherine Johnson

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Times

Authors (*Denotes Presenter)

Abstract Title and Summary

12:35 p.m.

 

MExAG Goals Document Introduction

12:45 p.m.

 

MExAG Goals Document Breakout Sessions

1:30 p.m.

 

Summary of Breakout Sessions and Discussion

 

Friday, February 5, 2021

MEXAG PRELIMINARY FINDINGS

1:45 p.m.

Chairs:  Steven Hauck and Carolyn Ernst

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Times

Authors (*Denotes Presenter)

Abstract Title and Summary

1:45 p.m.

 

Preliminary Findings and Meeting Wrap-up

 

PRINT ONLY

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Authors (*Denotes Presenter)

Abstract Title and Summary

Johnson P. A.   Johnson J. C.   Mardon A. A.

Ultraviolet Imaging Spectrometery and Spectroradiometry Techniques:  Applications for Remote Sensing on Mercury [#6012]
We identified three current NASA-funded remote sensor technology with the potential for implementation in Mercury missions, offering a range of UVISS data:  i) Solar Stellar Irradiance Comparison Experiment (SOLSTICE), ii) Ozone Monitoring Instrument (OMI), and iii) Ozone Mapping Profiler Suite (OMPS). While SOLSTICE is a hyperspectral instrument that measures solar spectral irradiance of the total solar disk at ultraviolet wavelengths between 115 to 430 nm, the latter two are sounding instruments that offer both ultraviolet profiles and other chemical species profiles. While OMI visualizes 740 wavelength bands in visible and ultraviolet, OMPS uses back-scattered ultraviolet radiation sensors for mapping of species, such as ozone. These technologies have a high potential for use for creating solar energy atlases, ozone mapping, geographical characterization of Mercury, among many uses.

Varatharajan I.   Tsang C.   Wohlfarth K.   Wöhler C.   Izemberg N.   Helbert J.

Near-Infrared Spectroscopy (0.7–2.5 µm) and Surface Mineralogy of Major Geochemical Terranes of Mercury Using Ground-Based NASA IRTF SpeX and MIRSI Facility [#6044]
Surface mineralogy of Mercury is poorly understood. On Dec. 16–18, 2018, we obtained global disk-resolved NIR spectra of Mercury of Mercury’s geochemical terranes to aid our preparations for BepiColombo data acquisition and science (MERTIS and SIMBIO-SYS/VIHI). We used both the SXD mode (0.7–2.55 µm) and LXD_short mode (1.67–4.2 µm) of SpeX at the Infrared Telescope Facility (IRTF) on Mauna Kea, HI at a spectral resolution of R~2000 and R~2500 respectively using a slit width of (0.3 x 15”). During the observation, Mercury was ~63–70% illuminated over the geochemical terranes including northern plains (NP), intermediate terrain (IT), and Low Reflectance Materials (LRM). In this spectral range, special attention has to be given to particular contributions of reflectance and thermal emission which depend on the local illumination conditions and the surface temperature. The results from the VNIR data and the first results of MIR observations will be presented at the meeting.