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
MEXAG
OVERVIEW I: MEXAG, BEPICOLOMBO, AND NASA
PLANETARY SCIENCE DIVISION
11:00
a.m.
Chairs: Carolyn Ernst and Steven Hauck
BACK TO TOP
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
BACK TO TOP
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
BACK TO TOP
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.
BACK TO TOP
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.
BACK TO TOP
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.
BACK TO TOP
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.
BACK TO TOP
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.
BACK TO TOP
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.
BACK TO TOP
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.
BACK TO TOP
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.
BACK TO TOP
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
BACK TO TOP
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
BACK TO TOP
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
BACK TO TOP
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.
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12:01 p.m.
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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.
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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.
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12:09
p.m.
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Werner A. L. E. * Leblanc F. Chaufray J.-Y. Modolo R. Aizawa S. Raines J. M. Exner W. Motschmann U.
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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).
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12:17 p.m.
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Q&A
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12:25
p.m.
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BREAK
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Friday,
February 5, 2021
MEXAG
GOALS DOCUMENT KICKOFF
12:35
p.m.
Chairs: Ron Vervack and
Catherine Johnson
BACK TO TOP
Times
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Authors (*Denotes Presenter)
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Abstract Title and Summary
|
12:35 p.m.
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MExAG Goals Document Introduction
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12:45
p.m.
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MExAG Goals
Document Breakout Sessions
|
1:30 p.m.
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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.
|
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Preliminary
Findings and Meeting Wrap-up
|
PRINT ONLY
BACK TO TOP
Authors (*Denotes
Presenter)
|
Abstract Title and Summary
|
Johnson P. A.
Johnson J. C. Mardon A. A.
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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.
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Varatharajan I. Tsang C. Wohlfarth K. Wöhler C. Izemberg N. Helbert J.
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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.
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