Journal of Geophysical Research: Planets最新文献

CM (Mighei-type) carbonaceous chondrites host abundant OH/H₂O-bearing phyllosilicates formed from water-rock reactions in primitive planetesimals. Their infrared (IR) spectral features resemble those of C-type asteroids, making laboratory analyses of CMs essential for interpreting asteroid observations. However, CM chondrites are often breccias composed of lithologies with variable degrees of aqueous alteration, complicating their interpretation. Here we use in situ analytical techniques to characterize spectral-compositional relationships for phyllosilicates in 8 CM lithologies across two meteorite samples. Micro-Fourier Transform Infrared (μ-FTIR) spectra collected from phyllosilicate-rich matrix regions show that band positions of the 3-μm feature and Si-O stretch Reststrahlen band (RB) systematically vary with alteration. Additional data from spatially correlated electron microprobe and μ-FTIR measurements tie spectral variations to specific cation substitutions in serpentines: the 3-μm feature shifts from 2.78 to 2.70 μm with increased Mg/Fe in octahedral sites, and the Si-O stretch RB shifts from 10.8 to 9.8 μm with increased Si/Fe³⁺ in tetrahedral sites. Co-variation of these features across the studied CM lithologies defines two successive alteration stages: (1) the Si-O stretch RB and 3-μm feature shift to longer and shorter wavelengths, respectively, as Mg- and cronstedtite-rich phyllosilicates form from incipient chondrule alteration; (2) Si-O stretch RB shifts to shorter wavelengths as Mg-serpentines replace cronstedtite and Mg-rich chondrules. These patterns align with inferred changes in composition and redox state for altering fluids on the CM parent body. Similar features in the spectra of C-type asteroids may reveal information about conditions of aqueous alteration and constrain models of their evolution.

Thermal tides are global-scale atmospheric waves with periods that are subharmonic to a solar day. Among them, short-period tides (e.g., 6-hr and 4-hr) correspond to higher-order harmonics. Based on temperature profiles from Emirates Mars InfraRed Spectrometer (EMIRS) observations, which provide comprehensive local time coverage, we investigate the 6-hr and 4-hr migrating tides in the Martian atmosphere. These short-period migrating tides exhibit distinct seasonal variations: the 6-hr tide reaches a maximum amplitude of ∼0.7 K around the winter solstice, while the 4-hr tide peaks around the equinoxes with an amplitude of ∼0.5 K. Hough mode decomposition reveals that both the 6-hr and 4-hr migrating tides are dominated by low-order, vertically evanescent modes, consistent with the observed feature that their phases remain nearly constant with altitude. Analysis suggests that the amplitudes of these short-period tides are likely modulated by atmospheric dust and water ice clouds. Furthermore, our results provide observational evidence that the superposition of 6-hr and 4-hr tidal winds around the autumn equinox contributes to the pronounced tropical surface pressure enhancements near 8 a.m. and 8 p.m.

We explored the effect of oscillatory loading on the frictional response of polycrystalline water ice and ice + ammonia to better understand the behavior of tidally modulated strike-slip faults on the icy satellites of the outer solar system, particularly Saturn's moon Enceladus. Ice-on-ice friction experiments were conducted between temperatures of 98 and 248 K at a normal stress of 100 kPa (equivalent to ∼1 km depth in the ice shell). A sinusoidal sliding rate was applied over a range of amplitudes and frequencies at a median velocity of 10 μm/s. We calculated the rate-and-state friction parameters for the amplitude-frequency combinations and found that oscillatory loading alters frictional stability relative to steady-state loading, leading to potentially more unstable slip behavior. We observe a full spectrum of slip behavior, from creep to slow slip to stick-slip. Our system shows a temperature- and velocity-dependent phase lag between the sinusoidal sliding rate and frictional response, which may help explain the phase lag between plume activity and peak stresses on the tiger stripes of Enceladus. Through forward modeling of a sinusoidally-driven slider block, using a rate-and-state dependent friction formulation and experimentally derived parameters, we extrapolate the higher-frequency oscillations in the laboratory experiments to lower frequencies analogous to diurnal tidal stresses on icy satellites. We explore the effect of oscillatory friction on frictional heating rates and fault failure depth with implications for the conditions under which shallow frictional melt generation may be favorable.

Laboratory-based mid-infrared (MIR) spectroscopy of terrestrial and planetary analogue materials, combined with chemical and spectral insights from mission-derived data, provides critical tools for advancing our knowledge of planetary surfaces. The returned lunar samples provide information on the chemical variability of the lunar surface. Lunar basalts are notably enriched in TiO₂ when compared to their terrestrial equivalents, and are ideal candidates to study the influence of composition on MIR spectral features. We characterized 25 synthetic lunar glasses with variable TiO₂ (0.6–18.7 wt%) and SiO₂ (35.6–52.1 wt%) in the thermal infrared range using micro-Fourier Transform Infrared Spectrometry (μ-FTIR). Our data reveal a strong linear relationship between the intensity of a spectral shoulder at 14.25 μm (702 cm⁻¹) and the TiO₂ content of the analyzed glasses. We suggest that the relationship in our samples reflects an increased distortion of the silicate network with increasing TiO₂ concentrations. We observe that TiO₂ acts as a network former in specific concentration intervals, thereby affecting the intensity of the observed spectral features in the MIR. This linear relationship is virtually nonexistent in samples that are developing stages of short-range order in the glasses and those samples that show only moderate to low amounts of TiO₂. Comparison with data sets from Earth and Mercury analogue materials confirms that the Christiansen Feature (CF) consistently correlates with the SiO₂ content, underscoring its robustness as a proxy for glass polymerization across planetary compositions. Finally, we emphasize that incipient crystal nucleation in glassy surfaces affects spectral features in the MIR range.

The topographic influence of the radiation environment on the Martian surface radiation is crucial for future human exploration. Topographic maps help assess radiation flux variations, aiding in hazard evaluation. Creating a global radiation map requires accounting for seasonally varying atmospheric density, heliospheric modulation, and topography. Here, we use a radiation model to derive the flux of secondary downward particles generated by the interaction of primary protons with the Martian atmosphere. Our model examines two key factors: (a) the dependence of atmospheric column depth on the zenith angle, affecting radiation directionality as horizon-arriving particles traverse more atmosphere than vertical ones and (b) atmospheric conditions at surface heights in Gale Crater, crucial for developing radiation dose maps that incorporate topographic effects. Our model is validated against Radiation Assessment Detector measurements and benchmarked with existing models. We construct response matrices representing the ratio of secondary particles at the Martian surface to primary inputs across zenith angles, assessing atmospheric effects. We combine these matrices with the incident spectrum to compute secondary particle fluxes from all zenith angles for Galactic Cosmic Rays and Solar Energetic Particles. These fluxes will be integrated into a topographic map of Mars in a follow-up study, providing a detailed representation of surface radiation levels across different terrains. This approach aids mission planners in identifying safe landing sites for astronauts.

The magnetic main field (MF) and secular variation (SV) models for Jupiter can be used to gain insights about the internal dynamo and the flow that drives the field. We use two such models computed from Juno observations up to spherical harmonic degrees 16 and 8 for the MF and SV, respectively. We solve the radial magnetic induction equation in the frozen-flux approximation at the dynamo region outer boundary assuming zero radial velocity for four large-scale physical flow assumptions- unconstrained, toroidal, tangentially geostrophic and columnar. We find flows with root mean square velocity varying between 100 and 400 km/yr (0.3–1.3 cm/s) when the dynamo region spherical boundary is taken at 0.83 Jupiter radius. Equatorially symmetric, toroidal and non-zonal velocity components are larger than the anti-symmetric, poloidal and zonal components, respectively, for almost all cases. Toroidal and tangentially geostrophic flows display similar velocity values and patterns, despite relying on different physical assumptions. The four inverted solutions indicate that the Jovian interior has dominant eastward flows near the Great Blue Spot, in agreement with previous studies. In addition, our more complex flow models shed light on some new features such as a large non-zonal component, meridional flows in the southern hemisphere and field-aligned flows in the north. Finally, our unconstrained flow solution suggests upwelling near the south pole, consistent with thermal wind theory.

This paper provides key hypotheses to guide future missions to Enceladus for the current decadal cycle and beyond. Enceladus is a high priority target for the fields of astrobiology and planetary science because it contains the three basic ingredients for life as we understand it: organic materials, a liquid solvent, and an energy source. This prioritization is reflected in the National Academies of Sciences, Engineering, and Medicine 2023–2032 Planetary Science and Astrobiology Decadal Survey, which highlights Enceladus in the list of destinations for a NASA New Frontiers class mission and recommends an Enceladus Orbilander mission as the second priority Flagship mission. In 2021 the science definition team behind the Enceladus Vent Explorer, a concept funded under NASA's Innovative Advanced Concepts program, held three workshops to discuss high priority science for Enceladus. Resulting from these workshops was a list of investigations addressing two science goals: (a) “How has the thermal evolution of Enceladus impacted the moon's ability to sustain a liquid ocean and recycle nutrients?” and (b) “How has the astrobiological potential of Enceladus changed over time?” Herein we detail the science background, proposed hypotheses, objectives, and physical parameters for each proposed investigation. In addition, we introduce a novel approach to describe the organic state of a planetary body to facilitate the development of hypotheses related to the emergence of life and to contextualize putative biosignatures. Finally, we provide recommendations for further development of technology and research for ocean world exploration.

Dust storms near Mars' South Pole during the perihelion and summer solstice seasons (L_s ∼ 250–290°) are phenomenologically distinct from martian dust storms in other locations and seasons. While they have previously been observed to increase atmospheric dust loading and warm the south polar atmosphere, they have no notable impact on the middle latitudes, tropics, or northern hemisphere. Here, we use a combination of multiple remote sensing instruments, atmosphere reanalyses, and general circulation modeling to study the evolution of dust storms near the Martian South Pole during Mars Year 30 (a prototypical year for such storms). Dust lifting preferentially occurs in the eastern hemisphere (180°–320°E) and follows the retreating seasonal CO₂ polar cap to higher latitudes as the season progresses—implicating the strong cap edge thermal forcing and katabatic flows as well as surface dust availability in driving dust lifting. Dust remains confined to the high southern latitudes during this season with strong diurnal variability in both latitudinal and vertical extents. Dust is entrained in the southern circumpolar jet stream, creating filamentation and longitudinal mixing and controlling the flow of dust back onto the polar cap. The diurnally varying atmospheric circulation (Ferrel cell) limits the mixing of dust to lower latitudes and prevents a global thermal response.

Martian magmas compositionally resemble those from terrestrial continental hotspot magmatic suites, characterized by low OH and high Cl and S contents. The magmatic gases exsolved from such magmas transport a variety of metal complexes and, upon cooling, precipitate vapor-deposits into vugs and fractures within rocks and on the surfaces of pyroclastics, which are then added to surface fines. Experiments investigated trace element behavior during magmatic degassing as a potential signature of this magmatic process. Low-pressure experimental degassing of P-rich basaltic magma containing Cl, Br, S, minor OH, and trace elements (Sr, Ge, Ga, Zn, Pb, Rb, Cs, Se, Cu, La, and Lu) demonstrated that the gas-transported trace metals become incorporated into vapor-deposited Cs-Pb-Zn-Rb-bearing halides, Ge-Ga-bearing iron oxides, Zn-Se-Cu-bearing sulfides, alkali and iron sulfates, Ge-bearing silicates, rare earth phosphates, and elemental metals. Low-OH and high-Cl magmatic systems produce a variety of halides but inhibit Fe-oxide formation. S-rich systems produce vapor-deposited Na-, K-, and Fe-sulfates, Zn-Cu-Se bearing sulfides, and iron oxides. These results provide a signature for determining the possibility of a significant role for magmatic gas in producing secondary minerals and volatile trace element enrichment in the Gusev plains, Columbia Hills, Jezero crater, and Gale crater. A hallmark of vapor-deposited phases is the presence of local heterogeneities in “alteration” phases and in trace element signatures due to the superposition of high and low temperature phases.

NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging mission has revealed that about 27% of the surface of Mercury is covered by smooth plains, which are mostly volcanic in origin. These plains are mainly located in the northern hemisphere, as well as within and around major impact basins. We used Mercury Atmospheric and Surface Composition Spectrometer data to perform an exhaustive spectral analysis of five major impact basins: Caloris, Rembrandt, Beethoven, Tolstoj, and Rachmaninoff. We highlighted the existence of a new high-reflectance spectral unit, that had previously only been identified within the Rembrandt basin, as a major unit being more widespread. We named this new unit Young High-reflectance Red Plains. We found a common sequence of volcanic episodes that infilled the basins and shaped their current surface spectral properties. We have shown that the size of the basin and the age of the volcanic infills are likely important parameters for the layering of different volcanic plains, defining the surface spectral units. Our study gives access to mantle properties, and we suggest that heterogeneity in the mantle is certainly not necessary to explain the spectral properties of effusive volcanism associated with impact basins. Future observations by the ESA-JAXA-BepiColombo mission are eagerly awaited to better constrain the planet's spectral, compositional, morphological, and geophysical surface properties.