Lunar and Planetary Institute

In the absence of structural asymmetry, the lunar tidal Love numbers should be order independent. Through careful analysis of GRAIL’s non-static gravity field, a recent study by Park et al. (2025; Nature) extracted statistically different ordered Love numbers for the monthly Moon tides, indicative of large scale laterally varying internal structure. In their study, they inverted for variations in shear modulus within the lunar mantle and interpreted these variations in the context of temperature variations. In a complementary, though distinct vein, we jointly invert these new Love numbers, augmented with the same Love numbers for the yearly tides, in tandem with the free-air gravity field and the center-of-mass to center-of-figure offset, to produce a long-wavelength tomographic model of the Moon’s mantle density, elastic, and anelastic properties. To do this, we adapted a normal mode perturbation theory able to predict tidal deformation derived for the Earth that incorporates the Moon's rotation, lateral variations in density, shear and bulk moduli, attenuation, and boundary topography such as the crustal-mantle interface and the core-mantle boundary (Lau et al., 2015; GJI). Since we self-consistently solve for density, shear modulus and attenuation, we are able to interpret our results in the context of both temperature and compositional variations, finding a lower contribution to variations in temperature than in Park et al.’s work and independent density variations within the nearside-farside mantle asymmetry.

The petrography and geochemistry of Northwest Africa (NWA) 12593 reveals association with the ferroan anorthosite and magnesian suites, as well as highlands-type clasts that are compositionally distinct from Apollo highlands material, re-affirming previous observations of increased compositional diversity in lunar crustal rocks outside of the Apollo sampled region. A large number of apatite grains were identified in lunar meteorite NWA 12593, in texturally pristine condition and associated with lithic clasts and the impact melt matrix. Chlorine and hydrogen isotope compositions obtained on apatite in NWA 12593 (δ 37 Cl = + 11.3 ‰ to + 53.1 ‰; δD = − 368 ‰ to + 1030 ‰) are significantly greater than in Apollo samples and basaltic lunar meteorites, with a broad range of volatile abundances spanning two orders of magnitude (Cl = 1053-12337 ppm; H 2 O = 143-4486 ppm). These volatile signatures reveal new insights into the distribution and isotopic heterogeneity of highly volatile elements in areas of the lunar surface not sampled previously and indicate that the lunar interior may have been equally heterogenous throughout its evolution. The variety of impact melt and lithic material in this sample implies a complex impact history that can contribute to future lunar exploration (e.g., Artemis III) surface activity goals of determining the lunar record of Inner Solar System impact history and volatile distribution throughout the lunar surface and interior.

Nominally anhydrous minerals (NAMS), such as plagioclase, may represent a significant volatile reservoir as their low intrinsic volatile content is multiplied many times by their large volumetric abundance. This study reports the volatile concentration of CO 2 , H 2 O, F, P 2 O 5 , S, and Cl in shocked plagioclase from three paired lunar troctolites, Northwest Africa (NWA) 5744, NWA 8676, and NWA 10140, to assess the volatile inventory of the early lunar crust. Measured volatile abundances are typically < 5 ppm, except for P 2 O 5 , which is as high as ∼ 300 ppm. Calculated parental melt estimates range from ∼ 3.2 to 238 ppm H 2 O, 2.3 to 213 ppm F, and 0.13 to 1971 ppm Cl. Whilst the lower ends of these ranges are in keeping with literature values, the higher ends of these ranges may indicate heterogeneity in the early Moon's volatile distribution. The cause or causes of any heterogeneity will remain poorly defined until complementary isotopic data (e.g., H, Cl) and distribution coefficients are known for lunar conditions.

Context. Observations by Parker Solar Probe (PSP) of electrostatic waves suggest that electrostatic instabilities, including the ion-ion-acoustic instability (IIAI) frequently observed in the inner heliosphere, play an important role in plasma heating and particle acceleration. Aims. Our aim is to explore the application of single spacecraft diagnostics to the IIAI, in anticipation of its application to two of the current missions operating in the inner heliosphere, PSP and Solar Orbiter. Methods. We applied the field-particle correlation (FPC) technique to fully kinetic simulations of IIAI. We characterized the conversion of energy between the electric field and particle species, allowing the differentiation between oscillatory and secular energy transfer to and from the particles and highlighting the role of resonant energy exchange. We then identified the characteristic IIAI signatures for the proton and electron distributions, and related them to our previous knowledge of IIAI onset and energy exchange mechanisms. Results. Applying the FPC technique to our simulations that were run in a parameter regime compatible with solar wind conditions, we identified IIAI signatures that would enable efficient recognition of IIAI in observations. This task is left for future missions, since the timescale over which IIAI signatures develop is too fast for the sampling rates of current missions.

Context . Jupiter’s atmosphere has strong zonal flows and exhibits marked differential rotation. The dynamic effects of these flows on Jupiter’s gravity field and internal structure have been extensively investigated in order to interpret Juno gravity field data. However, static effects arising from differential rotation are generally ignored in interior modeling. Along with precise measurements of Jupiter’s gravity field, it is of interest to explore the static effects on Jupiter’s shape, gravity field, and interior structure. Aims . We aim to incorporate differential rotation into the fifth-order theory of figures (TOF5) to self-consistently derive planetary shapes and gravitational harmonics. Using Juno gravity field data as constraints, we further investigate the static effects of differential rotation on Jupiter’s shape, gravity field, and interior structure. Methods . We propose a simplified differential rotation model with one free parameter characterizing the intensity of differential rotation. TOF5 is extended to account for differential rotation and is subsequently integrated into Jupiter’s interior models. Results . Our analysis reveals that differential rotation systematically increases Jupiter’s oblateness, with the degree of flattening dependent on the intensity of differential rotation. Absolute values of even gravitational harmonics | J 2 n | increase with the intensity of differential rotation, and higher-order ones exhibit a more pronounced response. Constrained by the Juno gravity data, we find that differential rotation significantly alters Jupiter’s shape and interior structure compared to the results of rigid rotation. The atmospheric metallicity of Jupiter is generally reduced by differential rotation. This implies that a higher 1 bar temperature or a density deficit in part of the molecular envelope is required to interpret the Galileo atmospheric measurement. Furthermore, incorporating differential rotation allows for more heavy elements in Jupiter’s interior, which are mainly concentrated in the metallic hydrogen envelope and the diluted core region. This enrichment is accompanied by a corresponding reduction of heavy elements in the compact core and molecular atmosphere.

We aim to characterize the nearby (23.78 pc), low-mass planetary system GJ,7 (TOI-198), which consists of an M0-type star and a terrestrial planet. Using photometric data from three sectors of the Transiting Exoplanet Survey Satellite TESS ) and a follow-up on the planetary transit observed by the Characterizing ExOPlanets Satellite ( CHEOPS ), along with 87 precise radial velocities obtained with the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO) spectrograph, we confidently confirm the planet and infer its properties. Planet GJ,7,b has a mass of M_p = 3.17 ^ +0.64 _ -0.65 M_⊕ and a radius of R_p = 1.36 ± 0.13 R_⊕. It orbits at a distance of a = 0.0675 ^ +0.0067 _ -0.0082 au from its host star with an orbital period of P = 10.215213 ^ +0.000011 _ -0.000010 d. We impose a 3σ upper limit on the planetary eccentricity of e łe 0.15. These parameters imply that GJ,7,b has a high density, ̊ho_p = 6.89 ^ +4.27 _ -2.78 g,cm -3 $, positioning it within the region of the rocky, Earth-like planets on the mass--radius diagram and interior to the inner edge of the habitable zone around its parent star. Additionally, we find that the host star is a slow rotator and is slightly metal-depleted ( Fe/H = -0.66 ± 0.10 dex), making GJ,7 one of the few planetary systems accurately characterized in the domain of subsolar iron abundances. TESS photometry does not show additional transit-like features attributable to planets with radii greater than ≈90,% that of Earth. The high number of radial velocity measurements enables us to determine that possible transiting and non-transiting planet candidates with masses lower than half the mass of GJ,7,b would have eluded detection in our in-depth study. The stellar activity, although moderate, shows a significant radial velocity amplitude of about 4 m,s$^ -1 and poses a challenge for detecting planets with masses lower than Earth around GJ,7.

Context . Pebbles play a crucial role in planetary and planetesimal formation, as planetesimals and their remnants form from the gravitational collapse of a pebble cloud. Understanding the compressibility and strength of pebble piles is essential not only for elucidating these processes, but also for collisional evolution studies. Aims . We aim to characterise the compressibility and tensile strength of pebble-pile samples under static compression. Methods . We generated different-sized silica pebbles in the laboratory to assemble pebble-pile samples. The samples were compressed to derive their crush curves, then determine the tensile strength of the compressed samples using the Brazilian disk test. Additionally, we calculated the tensile strength through discrete element method simulations (DEM) and compared the results with our experimental findings. Results . We obtain a new empirical relation linking tensile strength with the volume filling factor, consistent with previous results at low pressures but extended to higher compaction levels. Our findings show that tensile strength is independent of pebble size within the tested range. We also establish a new relationship for tensile strength as a function of pressure in pebble piles, which provides a better fit at higher pressures than previous approximations. The DEM simulations reproduce experimental results with good agreement. Conclusions . The tensile strength of pebble piles, at moderate to high compaction, converges with those of dust aggregates, indicating partial or complete disintegration of the pebbles. Our results provide physically consistent scaling laws that describe relationships between pressure, porosity, and tensile strength.

The Rosetta spacecraft escorted comet 67P/Churyumov-Gerasimenko for two years, gathering a rich and variable dataset. Amongst the data from the Rosetta Plasma Consortium (RPC) suite of instruments are measurements of the total electron density from the Mutual Impedance Probe (MIP) and Langmuir Probe (LAP). At low outgassing, the plasma density measurements can be explained by a simple balance between the production through ionisation and loss through transport. Ions are assumed to travel radially at the outflow speed of the neutral gas. Near perihelion, the assumptions of this field-free chemistry-free model are no longer valid, and plasma density is overestimated. This can be explained by enhanced ion transport by an ambipolar electric field inside the diamagnetic cavity, where the interplanetary magnetic field does not reach. In this study, we explore the transition between these two regimes, at intermediate outgassing ($5.4 \times10^{26}~\mathrm{s^{-1}}$), when the interaction between the cometary and solar wind plasma influences the transport of the ions. We use a 3D collisional test-particle model, adapted from Stephenson et al. 2022 to model the cometary ions with input electric and magnetic fields from a hybrid simulation for 2.5-3 au. The total plasma density from this model is then compared to data from MIP/LAP and to the field-free chemistry-free model. In doing so, we highlight the limitations of the hybrid approach and demonstrate the importance of modelling collisional cooling of the electrons to understand the ion dynamics close to the nucleus.

The primary source of heating in the upper atmospheres (thermospheres) of giant planets has been subject of long debate. The conundrum (or 'energy crisis') consists in observed thermosphere temperatures at low and mid latitudes exceeding values expected from solar heating by several hundred Kelvins (Yelle and Miller, 2004), suggesting the presence of another energy source. Several theories have been proposed to explain the high temperatures, from heating by upward propagating gravity or acoustic waves (Young et al., 1997; Matcheva et al., 1999; Schubert et al., 2003) to heating of auroral regions by magnetosphere-atmosphere coupling (Yelle and Miller, 2004; Mueller-Wodarg et al., 2019). While the latter provides sufficient energy, the problem became one of global energy redistribution. On a rapidly rotating planet, Coriolis forces act to 'trap' auroral energy in the polar regions, heating up the poles but leaving the equator cold (Smith et al., 2007; 2009; Mueller-Wodarg et al., 2019). On Saturn, the redistribution of energy from pole to equator was achieved by invoking zonal Rayleigh drag, possibly related to atmospheric waves (Mueller-Wodarg et al., 2019). Using a new General Circulation Model of Jupiter, we reproduce well the observed low and mid latitude thermosphere temperatures without the need to invoke Rayleigh drag. We identify for the first time the role played by a planet's magnetic field in affecting the global energy redistribution in thermospheres.