- Issue
Journal of Geophysical Research: Planets: Volume 126, Issue 4
April 2021
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Research Article
Pyrolysis of Oxalate, Acetate, and Perchlorate Mixtures and the Implications for Organic Salts on Mars
- First Published: 30 March 2021
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Flight-like thermal analyses of organic salts suggest such phases may have been present in many of the samples analyzed by Mars missions
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Perchlorates greatly impacted the thermal decomposition of organic salts and enhanced CO2 production at the expense of other products
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The most compelling hints of organic salts occurred in pyrolysis data from altered Martian sedimentary rocks and modern eolian deposits
Issue Information
Editorial
Thank You to Our 2020 Peer Reviewers
- First Published: 19 April 2021
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Peer review is a crucial component of the high-quality planetary science published in JGR: Planets
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In 2020, 705 individuals provided 1,168 reviews of papers submitted
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Peer reviewers: thank you for your service to the planetary community
Research Article
Autocorrelation of the Ground Vibrations Recorded by the SEIS-InSight Seismometer on Mars
- First Published: 09 March 2021
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Autocorrelation functions (ACFs) of SEIS ambient vibrations and seismic events are computed and validated by intercomparison
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The stability of autocorrelations at 2.4 Hz resonance favor an excitation by a diffuse seismic wavefield
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Various arrivals are observed in ACFs and interpreted as seismic reflections on internal discontinuities
Mars: Abundant Recurring Slope Lineae (RSL) Following the Planet-Encircling Dust Event (PEDE) of 2018
- First Published: 12 January 2021
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The origin of recurring slope lineae (RSL) on present-day Mars has been controversial, including hypotheses with seeping water or dry granular flows
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Recurring slope line were substantially more abundant following the planet-encircling dust event in 2018
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Dust-lifting processes present multiple possible mechanisms that can trigger downslope movement of dust and sand
The Thermo-Chemical Evolution of Mars With a Strongly Stratified Mantle
- First Published: 26 January 2021
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Mars' mantle early differentiation likely created an enriched layer at the core-mantle boundary
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A basal mantle layer delays planetary cooling and promotes deep melting through the present-day
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Massive deep mantle melting yields strong tradeoffs between core size and layer thickness when interpreting geodetic and seismic data
The Aeolian Environment of the Landing Site for the ExoMars Rosalind Franklin Rover in Oxia Planum, Mars
- First Published: 01 February 2021
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Multiple wind regimes have influenced the surficial expression of Oxia Planum
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Transverse aeolian ridges (TARs), periodic bedrock ridges, dust devils, and windstreaks were used to determine formative wind directions
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Landscape evidence and climate modeling suggest contemporary winds lack the necessary strength to mobilize TAR-forming materials
A Comodulation Analysis of Atmospheric Energy Injection Into the Ground Motion at InSight, Mars
- First Published: 08 February 2021
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A comodulation analysis is implemented to describe and interpret the sensitivity of InSight's seismometers to atmospheric energy injection
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The seismic response of InSight to the wind and pressure is observed to vary diurnally and seasonally depending on atmospheric conditions
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The power from the wind and pressure signals injected into seismic events is quantified to assess marsquake discrimination
A Two-Phase Model for the Evolution of Planetary Embryos With Implications for the Formation of Mars
- First Published: 09 February 2021
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The mantle of a growing planetary embryo stays mostly solid during accretion
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A planetary embryo's mantle is expected to exhibit isotopic heterogeneity and undergo early silicate differentiation
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A comparison with Martian meteorites suggests that Mars is not a stranded planetary embryo that escaped giant impact with other embryos
First Focal Mechanisms of Marsquakes
- First Published: 13 February 2021
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We infer the tectonic setting in Cerberus Fossae on Mars by seismic source inversion
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We present a robust inversion strategy for single-station moment tensor inversion
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Three Marsquakes recorded by InSight reveal a predominantly normal faulting regime
Temperature and Density on the Forsterite Liquid-Vapor Phase Boundary
- First Published: April 2021
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We performed reverse impact experiments and shock-and-release experiments to probe the density and temperature of the liquid-vapor phase boundary
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The experimentally determined liquid-vapor dome does not agree with commonly used equation of state models
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Supercritical post-impact states are easier to achieve than previously modeled
Deriving Mercury Geodetic Parameters With Altimetric Crossovers From the Mercury Laser Altimeter (MLA)
- First Published: 12 March 2021
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We provide an independent solution for Mercury's orientation parameters based on the analysis of the Mercury Laser Altimeter crossovers
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Our solution places Mercury in a Cassini state with an obliquity ε = 2.03 ± 0.03, larger than the recent gravity-based estimate
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We provide a first estimate of Mercury's tidal Love number h2 to be in the range from 0.9 to 2.2
The Growth of Europa's Icy Shell: Convection and Crystallization
- First Published: 09 March 2021
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Crystallization of a tidally heated planetary ice shell in a stagnant lid regime controls the equilibrium thickness of the Europan shell
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Despite a wide range of possible ice shell thicknesses, the Europan shell lithosphere thickness is likely globally homogeneous
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Ice convection leads to much faster crystallization rates when compared to conduction-only ice shell growth
Jupiter’s Great Red Spot: Strong Interactions With Incoming Anticyclones in 2019
- First Published: 17 March 2021
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In 2018–2020, Jupiter’s Great Red Spot interacted with series of anticyclones, losing part of its visible red area and distorting its shape
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The Great Red Spot (GRS) increased its tangential velocity; it did not change its vorticity, but did temporarily change its 90-day oscillation in longitude
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Dynamical and radiative transfer modeling shows that the interactions affected the upper cloud of the GRS with no risk for its survival
A Rock Record of Complex Aeolian Bedforms in a Hesperian Desert Landscape: The Stimson Formation as Exposed in the Murray Buttes, Gale Crater, Mars
- First Published: 30 March 2021
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Compound cross-bedding at the Murray buttes record the migration of oblique aeolian dunes.
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Large dunes (draas) migrated to the NNW, while superimposed dunes migrated NE. The bulk sediment transport direction was broadly toward the north
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The Stimson formation observed at the Murray buttes shares a common depositional architecture seen in other Stimson formation outcrop observed elsewhere on the traverse
History and Future of the Martian Dynamo and Implications of a Hypothetical Solid Inner Core
- First Published: 09 March 2021
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We develop a new internal structure and thermal evolution model to study dynamo regimes on rocky planets, using Mars as a first example
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An early, thermally driven Martian dynamo could be followed by a later, compositionally driven dynamo, either in the past or the future
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Detection of a solid inner core on Mars could imply that the Martian dynamo will reactivate at some point in the future
The Physics of Falling Raindrops in Diverse Planetary Atmospheres
- First Published: 15 March 2021
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We present general methods to calculate raindrop shape, speed, and evaporation rate in diverse planetary atmospheres
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We define a dimensionless number that we show can closely capture the behavior of raindrop evaporation
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Maximum stable raindrop size is relatively insensitive to condensible species and atmospheric properties (including air density)
Analyzing Low Frequency Seismic Events at Cerberus Fossae as Long Period Volcanic Quakes
- First Published: 12 March 2021
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Low Frequency (LF) events that share attributes of volcanic quakes are traced to a young volcanic region on Mars
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LF events are modeled as deep volcanic quakes caused by pressure-driven flow across a channel at Cerberus Fossae
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LF attributes are matched by fluids less viscous and of higher fluxes than terrestrial flood basalts
The Conductive Cooling of Planetesimals With Temperature-Dependent Properties
- First Published: 15 March 2021
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Conductivity, heat capacity, and density are temperature dependent and control the cooling of planetesimals
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The estimated depth and timing of meteorite origin changes, if temperature-dependent properties are used to model the parent body
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Temperature-dependent properties in a model of the pallasite parent body delay the onset of core solidification by 40 million years
Felsic Tesserae on Venus Permitted by Lithospheric Deformation Models
- First Published: 30 March 2021
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Tessera terrain in southwest Tellus Regio, Venus, exhibits regularly spaced, low-amplitude folds with wavelengths of 6–19 km
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The folds in Venus tessera terrain may form due to buckling within dry crust of mafic to felsic composition
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The folds in Venus tessera terrain require an elevated geotherm and strain rate relative to present for all modeled compositions
A Volcanic Ash Layer in the Nördlinger Ries Impact Structure (Miocene, Germany): Indication of Crater Fill Geometry and Origins of Long-Term Crater Floor Sagging
- First Published: 17 March 2021
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A critical question in the evolution of impact-crater-hosted lakes is the origin and timing of post-impact floor subsidence
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We describe a volcanic ash layer from the Ries impact crater that demonstrates a deeply bowl-shaped geometry of its lacustrine crater fill
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This geometry, leading to a concentric outcrop pattern, requires significant crater floor sagging, in addition to sediment compaction
Carbonate-Phyllosilicate Parageneses and Environments of Aqueous Alteration in Nili Fossae and Mars
- First Published: 29 March 2021
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Carbonation affected serpentine deposits in the Nili Fossae Region, leading to magnesite/talc assemblages
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Methane and hydrogen were formed by hydrothermal oxidation or iron but at low pressures
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Carbonates can also result from evaporation of standing bodies of liquid but are different from hydrothermal assemblages
Modeling Lunar Pyroclasts to Probe the Volatile Content of the Lunar Interior
- First Published: 29 March 2021
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Parts of the lunar interior sampled by the source material of the DMDs investigated in this study range in water content from 400 to 800 ppm
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Remote sensing, modeling, and petrology can be used to determine the composition of the source material for remote lunar volcanic deposits
Impact of the 2018 Mars Global Dust Storm on the Ionospheric Peak: A Study Using a Photochemical Model
- First Published: 04 April 2021
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Ionospheric electron densities are calculated in the southern hemisphere (SH) during the onset and growth phases of the 2018 global dust storm
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The dust storm caused an uplift of the ionospheric peak altitude by ∼10 km in the SH
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The uplift of the ionosphere near equatorial and southern mid-latitudes lagged 22–26 days from the storm’s onset in the northern hemisphere
Estimate of the D/H Ratio in the Martian Upper Atmosphere from the Low Spectral Resolution Mode of MAVEN/IUVS
- First Published: 03 April 2021
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New method to derive D/H from Lyman-alpha vertical profile without spectrally resolve H and D
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Estimate D/H at 200 km during southern summer for three different Martian years at different local times
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Explain the variations of D/H between 80 and 200 km
First-Principles Diffusivity Ratios for Atmospheric Isotope Fractionation on Mars and Titan
- First Published: 02 April 2021
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Kinetic isotope fractionation depends on diffusivity ratios that have not been measured for conditions corresponding to Mars or Titan
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The relative diffusivity of isotopologues can be calculated as a function of temperature from high-accuracy intermolecular potentials
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Rigorous results agree well with simpler kinetic theory for water on Mars, but less well for methane on Titan
Aerosols and Tides in the Martian Tropics During Southern Hemisphere Spring Equinox From Mars Climate Sounder Data
- First Published: 07 April 2021
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Mars year (MY) 29 has large amplitude thermal tides in the tropics during southern hemisphere spring equinox that are not seen in other years
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Data in other years suggests there was a shift in the phase of the diurnal tide to an earlier local time in MY29, due to early dust activity
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Radiative cooling from water ice clouds at night causes increased downwelling and stronger temperature inversions due to adiabatic warming
Global Distribution of Electrostatic Electron Cyclotron Harmonic Waves in Saturn's Magnetosphere: A Survey of Over-13-Year Cassini RPWS Observations
- First Published: 07 April 2021
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The averaged amplitudes of Saturnian electron cyclotron harmonic (ECH) waves have a pronounced magnetic local time asymmetry, and they are larger on the nightside than the dayside
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The ECH wave occurrence rates are higher at high latitudes than those near the equator, but high-latitude averaged amplitudes are weaker
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The ECH wave averaged peak frequencies are generally below (n + 1/2) fce, with the smallest deviation from (n + 1/2) fce near the equator
Abnormal Phase Structure of Thermal Tides During Major Dust Storms on Mars: Implications for the Excitation Source of High-altitude Water Ice Clouds
- First Published: 07 April 2021
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The entire phase structure of migrating diurnal tide rises and falls with the dust height throughout a Mars year
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An abnormal upward phase progression is found during major regional dust storms indicating downward propagating tidal modes
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Downward propagating tidal modes may be excited by increased higher-altitude water ice clouds during dust storms
Relationship Between the Ozone and Water Vapor Columns on Mars as Observed by SPICAM and Calculated by a Global Climate Model
- First Published: 08 April 2021
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The relationship between the O3 and H2O columns on Mars is quantified from 4 Martian years of simultaneous measurements
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The O3 and H2O columns are distinctly anti-correlated at high latitudes but are uncorrelated at low latitudes
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Model simulations using the observed amount of H2O and the currently recommended kinetics underpredict O3 by about a factor of 2
Vortex-Dominated Aeolian Activity at InSight's Landing Site, Part 2: Local Meteorology, Transport Dynamics, and Model Analysis
- First Published: 17 December 2020
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NASA's InSight mission provides a chance to study aeolian transport through concurrent imaging and high-frequency atmospheric monitoring
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The surface at InSight's landing site is generally stable besides intermittent surface activity caused by convective vortex passage
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The vertical pressure gradient within the vortex core and increased drag caused by rotational winds help facilitate surface erosion
Review Article
Aerosols in Exoplanet Atmospheres
- First Published: 23 February 2021
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Aerosols are common in the atmospheres of exoplanets of all temperatures, masses, and compositions
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Observations and models are painting a coherent picture of the nature of exoplanet aerosols
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Advances in laboratory work are essential for unveiling how exoplanet aerosols form and evolve
Commentary
The Challenging Depths of Titan's Seas
- First Published: 09 April 2021
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Moray Sinus is deep, and a little “brackish”
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Kraken Mare is very deep, or absorbing (ethane-rich), or both
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Future exploration of Titan's seas must recognize a possible diversity of composition