Explore the vast range of titles available.

The Diviner Lunar Radiometer Experiment onboard the Lunar Reconnaissance Orbiter has measured solar reflectance and mid‐infrared radiance globally, over four diurnal cycles, at unprecedented spatial and temporal resolution. These data are used to infer the radiative and bulk thermophysical properties of the near‐surface regolith layer at all longitudes around the equator. Normal albedos are estimated from solar reflectance measurements. Normal spectral emissivities relative to the 8‐μm Christiansen Feature are computed from brightness temperatures and used along with albedos as inputs to a numerical thermal model. Model fits to daytime temperatures require that the albedo increase with solar incidence angle. Measured nighttime cooling is remarkably similar across longitude and major geologic units, consistent with the scarcity of rock exposures and with the widespread presence of a near‐surface layer whose physical structure and thermal response are determined by pulverization through micrometeoroid impacts. Nighttime temperatures are best fit using a graded regolith model, with a ∼40% increase in bulk density and an eightfold increase in thermal conductivity (adjusted for temperature) occurring within several centimeters of the surface. Key Points LRO Diviner reveals radiative and thermophysical properties of the lunar surface Lunar daytime temperatures require albedo dependence on solar incidence angle Lunar nighttime temperatures require graded structure in upper cm of regolith

Granites are nearly absent in the Solar System outside of Earth. Achieving granitic compositions in magmatic systems requires multi-stage melting and fractionation, which also increases the concentration of radiogenic elements 1 . Abundant water and plate tectonics facilitate these processes on Earth, aiding in remelting. Although these drivers are absent on the Moon, small granite samples have been found, but details of their origin and the scale of systems they represent are unknown 2 . Here we report microwave-wavelength measurements of an anomalously hot geothermal source that is best explained by the presence of an approximately 50-kilometre-diameter granitic system below the thorium-rich farside feature known as Compton–Belkovich. Passive microwave radiometry is sensitive to the integrated thermal gradient to several wavelengths depth. The 3–37-gigahertz antenna temperatures of the Chang’e-1 and Chang’e-2 microwave instruments allow us to measure a peak heat flux of about 180 milliwatts per square metre, which is about 20 times higher than that of the average lunar highlands 3 , 4 . The surprising magnitude and geographic extent of this feature imply an Earth-like, evolved granitic system larger than believed possible on the Moon, especially outside of the Procellarum region 5 . Furthermore, these methods are generalizable: similar uses of passive radiometric data could vastly expand our knowledge of geothermal processes on the Moon and other planetary bodies. Measurements from the Chang’e-1 and Chang’e-2 microwave instruments reveal an anomalously hot geothermal source on the Moon that is best explained by a roughly 50-kilometre-diameter granitic system below the geological feature known as Compton–Belkovich.

This work analyzes the observations from the Lunar Regolith Penetrating Radar (LRPR) onboard Chang’E-5 to reconstruct the subsurface structure of the regolith under the lander at the drilling site. This is the first stationary Ground-Penetrating Radar (GPR) array to operate on the Moon. Imaging results of pre-drilling and post-drilling measurements show that the thickness of local regolith is larger than 2 m. Within the LRPR’s detection range, we do not find any continuous layer. Instead, irregular, high-density zones are identified in the regolith. Two of these zones are on the drilling trajectory at ~30 cm and ~70 cm, consistent with the recorded drilling process. We speculate a rock fragment from the deeper, high-density zone obstructed the drill, which led to an early termination of the drilling. Based on our interpretation of subsurface structure, we modeled the LRPR echoes using a finite-difference time-domain method. The same imaging algorithm was also applied to the simulation data. The modeled data verify our inference of the regolith structure under the lander.

Diviner Lunar Radiometer Experiment surface-temperature maps reveal the existence of widespread surface and near-surface cryogenic regions that extend beyond the boundaries of persistent shadow. The Lunar Crater Observation and Sensing Satellite (LCROSS) struck one of the coldest of these regions, where subsurface temperatures are estimated to be 38 kelvin. Large areas of the lunar polar regions are currently cold enough to cold-trap water ice as well as a range of both more volatile and less volatile species. The diverse mixture of water and high-volatility compounds detected in the LCROSS ejecta plume is strong evidence for the impact delivery and cold-trapping of volatiles derived from primitive outer solar system bodies.

Thermal models for the north polar region of Mercury, calculated from topographic measurements made by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, show that the spatial distribution of regions of high radar backscatter is well matched by the predicted distribution of thermally stable water ice. MESSENGER measurements of near-infrared surface reflectance indicate bright surfaces in the coldest areas where water ice is predicted to be stable at the surface, and dark surfaces within and surrounding warmer areas where water ice is predicted to be stable only in the near subsurface. We propose that the dark surface layer is a sublimation lag deposit that may be rich in impact-derived organic material.

Magnetized rocks can record the history of the magnetic field of a planet, a key constraint for understanding its evolution. From orbital vector magnetic field measurements of Mercury taken by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft at altitudes below 150 kilometers, we have detected remanent magnetization in Mercury's crust. We infer a lower bound on the average age of magnetization of 3.7 to 3.9 billion years. Our findings indicate that a global magnetic field driven by dynamo processes in the fluid outer core operated early in Mercury's history. Ancient field strengths that range from those similar to Mercury's present dipole field to Earth-like values are consistent with the magnetic field observations and with the low iron content of Mercury's crust inferred from MESSENGER elemental composition data.

Many regions near the lunar poles are currently cold enough that surface water ice would be stable against sublimation losses for billions of years. However, most of these environments are currently too cold to efficiently drive ice downward by thermal diffusion, leaving impact burial as the primary means of protection from surface loss processes. In this respect, most of the present near‐surface thermal environments on the Moon may actually be quite poor traps for water ice. This was not always the case. Long‐term orbital changes have dramatically altered the lunar polar thermal environment. We develop a simple model of the evolution of the lunar orbit and spin axis to examine the thermal environments available for volatile deposition and retention in the past. Our calculations show that some early lunar polar environments were in the right temperature regime to have collected subsurface ice if a supply were available. However, a high‐obliquity period, which occurred when the Moon was at about half its present distance from the Earth, would either have driven this ice out into space or deep into the lunar subsurface. Since that time, as the lunar obliquity has slowly decreased to its present value, environments have undergone their own thermal evolution, and each of the current cold traps experienced a period when they were most efficient at thermally burying ice. We examine the thermal history of a lunar polar crater to provide a framework for examining other processes effecting volatiles in the Moon's near‐surface cold traps. Key Points The lunar polar environment has not always been stable for ice deposition The thermal environment of the moon is the primary control of ice stability Some periods in the Moon's history may have been better for collecting ice

Juno's microwave radiometer experiment (MWR) provided the first spatially resolved observations beneath the surface of Ganymede's ice shell. The results indicate that scattering is a significant component of the observed brightness temperature, which is a combination of the upwelling ice emission and reflected emission from the sky and from Jupiter's synchrotron emission (Brown et al., 2023). Retrieval of the sub‐surface ice temperature profile requires that these confounding signals are estimated and removed to isolate the thermal signature of the ice. We present data analysis and model results to estimate the reflected synchrotron emission component. Our results indicate reflected emission over a broad range of observed angles, due to surface roughness and internal scattering. Based on viewing geometry, direct specular reflection from a smooth surface at a narrow angle is not observed. A microwave‐reflective medium is indicated, that is, a very rough surface and/or non‐homogeneous subsurface. Plain Language Summary On 7 June 2021, Juno had a close flyby of Jupiter's moon Ganymede, flying approximately 1,000 km above the surface. During the flyby, Juno's six channel Microwave Radiometer (MWR) mapped a portion of Ganymede, providing the first resolved observations of Ganymede's sub‐surface ice shell. The observed brightness temperature is composed of upwelling thermal emission from the ice shell and reflected radiation from the sky and from Jupiter's synchrotron emission. To study the sub‐surface ice shell temperature profile, we present data analysis and model results to estimate the reflected radiation component. The radiation is reflected diffusively by a very rough surface and/or non‐homogeneous subsurface. Key Points Reflected radiation from the sky and from Jupiter's synchrotron is an important component for Juno microwave radiometer experiment (MWR) observations at 0.6 and 1.2 GHz Absence of specular reflection indicating that Ganymede has a rough surface Reflections originate mostly from internal scattering

In a series of laboratory experiments, we measure thermal diffusivity, thermal conductivity, and heat capacity of icy regolith created by vapor deposition of water below its triple point and in a low pressure atmosphere. We find that an ice‐regolith mixture prepared in this manner, which may be common on Mars, and potentially also present on the Moon, Mercury, comets and other bodies, has a thermal conductivity that increases approximately linearly with ice content. This trend differs substantially from thermal property models based of preferential formation of ice at grain contacts previously applied to both terrestrial and non‐terrestrial subsurface ice. We describe the observed microphysical structure of ice responsible for these thermal properties, which displaces interstitial gases, traps bubbles, exhibits anisotropic growth, and bridges non‐neighboring grains. We also consider the applicability of these measurements to subsurface ice on Mars and other solar system bodies. Key Points First measured thermal properties of icy regolith as a function of ice content Thermal conductivity of vapor deposited ice varies linearly with ice content These measurements differ from currently used models of icy planetary regolith