It is uncertain whether the Moon ever formed a metallic core or generated a core dynamo. The lunar crust and returned samples are magnetized, but the source of this magnetization could be meteoroid impacts rather than a dynamo. Here, we report magnetic measurements and 40Ar/39Ar thermochronological calculations for the oldest known unshocked lunar rock, troctolite 76535. These data imply that there was a long-lived field on the Moon of at least 1 microtesla approximately 4.2 billion years ago. The early age, substantial intensity, and long lifetime of this field support the hypothesis of an ancient lunar core dynamo.

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We derive the depth of the water ice table on Mars by fitting seasonal surface temperature trends acquired by the Mars Climate Sounder and Thermal Emission Imaging System with a two-layer regolith model assuming frozen H 2 O as the lower material. Our results are consistent with widespread water ice at latitudes as low as 35°N/45°S buried sometimes a few centimeters below sand-like material, with high lateral ice depth variability, and correlated with periglacial features. While several investigations have already predicted, identified, and characterized some properties of near-surface ice on Mars, our results constitute a significant advance in the context of the upcoming crewed exploration because (1) they focus on very shallow depths accessible with limited equipment, (2) they provide continuous regional coverage including the midlatitudes, and (3) they yield moderate spatial resolution maps (3 ppd) relevant to landing site selection studies. Plain Language SummaryFrozen water is a very strong heat conductor compared to typical Martian regolith. As a result, near-surface ice measurably influences seasonal surface temperature trends, and the depth of the H 2 O table controls the amplitude of this effect. We leverage this influence on orbital temperature observations using a numerical heat transfer model to derive regional and local maps of the ice depth on Mars, at much higher spatial resolution than previously available. We show that water ice is present sometimes just a few centimeters below the surface, at locations where future landing is realistic, under mobile material that could easily be moved around. This ice could be exploited on-site for drinking water, breathable oxygen, etc., at a much lower cost than if brought from Earth. Key Points: • Shallow subsurface water ice on Mars influences seasonal surface temperatures in a measurable manner with MCS and THEMIS • We leverage this effect to map the depth to the water ice table at middle and high latitudes • Large continuous units of shallow ice are found~35°N and~45°S and could be exploited for future crewed missions Supporting Information: • Supporting Information S1

A 500 km long network of valleys extends from Herschel crater to Gale, Knobel, and Sharp craters.The mineralogy and timing of fluvial activity in these watersheds provide a regional framework for deciphering the origin of sediments of Gale crater's Mount Sharp, an exploration target for the Curiosity rover. Olivine-bearing bedrock is exposed throughout the region, and its erosion contributed to widespread olivine-bearing sand dunes. Fe/Mg phyllosilicates are found in both bedrock and sediments, implying that materials deposited in Gale crater may have inherited clay minerals, transported from the watershed. While some topographic lows of the Sharp-Knobel watershed host chloride salts, the only salts detected in the Gale watershed are sulfates within Mount Sharp, implying regional or temporal differences in water chemistry. Crater counts indicate progressively more spatially localized aqueous activity: large-scale valley network activity ceased by the early Hesperian, though later Hesperian/Amazonian fluvial activity continued near Gale and Sharp craters.

The Curiosity rover has detected diverse lithologies in float rocks and sedimentary units on the Gale crater floor, interpreted to have been transported from the rim. To understand their provenance, we examine the mineralogy and geology of Gale's rim, walls, and floor, using high‐resolution imagery and infrared spectra. While no significant differences in bedrock spectral properties were observed within most Thermal Emission Imaging System and Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) scenes, some CRISM scenes of rim and wall rocks showed olivine‐bearing bedrock accompanied by Fe/Mg phyllosilicates. Hydrated materials with 2.48 μm absorptions in Gale's eastern walls are spectrally similar to the sulfate unit in Mount Sharp (Aeolis Mons). Sedimentary strata on the Gale floor southwest of the landing site, likely coeval with the Bradbury units explored by Curiosity, also are hydrated and/or have Fe/Mg phyllosilicates. Spectral properties of these phyllosilicates differ from the Al‐substituted nontronite detected by CRISM in Mount Sharp, suggesting formation by fluids of different composition. Geologic mapping of the crater floor shows that the hydrated or hydroxylated materials are typically overlain by spectrally undistinctive, erosionally resistant, cliff‐forming units. Additionally, a 4 km impact crater exposes >250 m of the Gale floor, including finely layered units. No basement rocks are exposed, thus indicating sedimentary deposits ≥250 m beneath strata studied by Curiosity. Collectively, the data indicate substantial sedimentary infill of Gale crater, including some materials derived from the crater rim. Lowermost thin layers are consistent with deposition in a lacustrine environment; interbedded hydrated/hydroxylated units may signify changing environmental conditions, perhaps in a drying or episodically dry lake bed.

The Mastcam-Z Camera is a stereoscopic, multispectral camera with zoom capability on NASA’s Mars-2020 Perseverance rover. The Mastcam-Z relies on a set of two deck-mounted radiometric calibration targets to validate camera performance and to provide an instantaneous estimate of local irradiance and allow conversion of image data to units of reflectance (R∗ or I/F) on a tactical timescale. Here, we describe the heritage, design, and optical characterization of these targets and discuss their use during rover operations. The Mastcam-Z primary calibration target inherits features of camera calibration targets on the Mars Exploration Rovers, Phoenix and Mars Science Laboratory missions. This target will be regularly imaged during flight to accompany multispectral observations of the martian surface. The primary target consists of a gold-plated aluminum base, eight strong hollow-cylinder Sm2Co17 alloy permanent magnets mounted in the base, eight ceramic color and grayscale patches mounted over the magnets, four concentric, ceramic grayscale rings and a central aluminum shadow post (gnomon) painted with an IR-black paint. The magnets are expected to keep the central area of each patch relatively free of Martian aeolian dust. The Mastcam-Z secondary calibration target is a simple angled aluminum shelf carrying seven vertically mounted ceramic color and grayscale chips and seven identical, but horizontally mounted ceramic chips. The secondary target is intended to augment and validate the calibration-related information derived from the primary target. The Mastcam-Z radiometric calibration targets are critically important to achieving Mastcam-Z science objectives for spectroscopy and photometric properties.

Recent paleomagnetic studies of Apollo samples have established that a core dynamo existed on the Moon from at least 4.2 to 3.56 billion years (Ga). Because there is no lunar dynamo today, a longstanding mystery has been the origin of magnetization in very young lunar samples (<~200 million years old (Ma)). Possible sources of this magnetization include transient fields generated by meteoroid impacts, remanent fields from nearby rocks magnetized during an earlier dynamo epoch, a weak late dynamo, and spontaneous remanence formed in a near-zero field. To further understand the source of the magnetization in young lunar samples, we conducted paleomagnetic, petrographic, and 40 Ar/ 39 Ar geochronometry analyses on a young impact melt glass rind from the exterior of~3.35 Ga mare basalt 12017. Cosmic ray track densities and our 40 Ar/ 39 Ar and cosmogenic 38 Ar analyses constrain the glass formation age to be <7 Ma and most likely <20 thousand years (kyr), making it likely the youngest extraterrestrial sample yet studied with paleomagnetic methods. Despite its relatively high fidelity magnetic recording properties compared to most lunar rocks, we find that the glass carries no stable primary natural remanent magnetization and that it formed in a field <~7 μT (with a 2 σ upper limit of <11 μT). Given the poor magnetic recording properties of the majority of lunar samples, this provides further evidence that many or perhaps even all previous paleointensity estimates for ≤1.5 Ga rocks are upper limits on the true paleofield and therefore require neither a protracted strong (>10 μT) core dynamo field nor impact-generated fields.

Observations of planetary magnetic fields provide fundamental insights into the origin and evolution of terrestrial planets. However, whether Venus ever hosted a dynamo is unknown. Here we show that crustal remanent magnetism is a potentially observable consequence of an ancient Venusian dynamo, in contrast to previous studies that dismissed this possibility. Past spacecraft measurements only exclude crustal magnetization near the Venera 4 landing site and northward of 50° South latitude for >150‐km coherence scales and strong magnetization intensities. Magnetite grains with sizes commonly observed in volcanic rocks can retain thermoremanent magnetism at Venusian conditions for >1 billion years. Depths to the Curie temperature of magnetite are ~5–40 km and typically less than predicted crustal thicknesses at our analyzed localities. Aerial platforms could detect expected magnetizations at horizontal scales similar to the ~50‐km operating altitude. Any detection would validate models of planetary accretion, geologic processes, and climate history.