Supervolcanoes Within an Ancient Volcanic Province in Arabia Terra, Mars

Several irregularly shaped craters located within Arabia Terra, Mars represent a new type of highland volcanic construct and together constitute a previously unrecognized martian igneous province. Similar to terrestrial supervolcanoes, these low-relief paterae display a range of geomorphic features related to structural collapse, effusive volcanism, and explosive eruptions. Extruded lavas contributed to the formation of enigmatic highland ridged plains in Arabia Terra. Outgassed sulfur and erupted fine-grained pyroclastics from these calderas likely fed the formation of altered, layered sedimentary rocks and fretted terrain found throughout the equatorial region. Discovery of a new type of volcanic construct in the Arabia volcanic province fundamentally changes the picture of ancient volcanism and climate evolution on Mars. Other eroded topographic basins in the ancient Martian highlands that have been dismissed as degraded impact craters should be reconsidered as possible volcanic constructs formed in an early phase of widespread, disseminated magmatism on Mars

The dynamic geophysical environment of (101955) Bennu based on OSIRIS-REx measurements

The top-shaped morphology characteristic of asteroid (101955) Bennu, often found among fast-spinning asteroids and binary asteroid primaries, may have contributed substantially to binary asteroid formation. Yet a detailed geophysical analysis of this morphology for a fast-spinning asteroid has not been possible prior to the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission. Combining the measured Bennu mass and shape obtained during the Preliminary Survey phase of the OSIRIS-REx mission, we find a notable transition in Bennu’s surface slopes within its rotational Roche lobe, defined as the region where material is energetically trapped to the surface. As the intersection of the rotational Roche lobe with Bennu’s surface has been most recently migrating towards its equator (given Bennu’s increasing spin rate), we infer that Bennu’s surface slopes have been changing across its surface within the last million years. We also find evidence for substantial density heterogeneity within this body, suggesting that its interior is a mixture of voids and boulders. The presence of such heterogeneity and Bennu’s top shape are consistent with spin-induced failure at some point in its past, although the manner of its failure cannot yet be determined. Future measurements by the OSIRIS-REx spacecraft will provide insight into and may resolve questions regarding the formation and evolution of Bennu’s top-shape morphology and its link to the formation of binary asteroids

Evidence for widespread hydrated minerals on asteroid (101955) Bennu

Early spectral data from the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission reveal evidence for abundant hydrated minerals on the surface of near-Earth asteroid (101955) Bennu in the form of a near-infrared absorption near 2.7 µm and thermal infrared spectral features that are most similar to those of aqueously altered CM-type carbonaceous chondrites. We observe these spectral features across the surface of Bennu, and there is no evidence of substantial rotational variability at the spatial scales of tens to hundreds of metres observed to date. In the visible and near-infrared (0.4 to 2.4 µm) Bennu’s spectrum appears featureless and with a blue (negative) slope, confirming previous ground-based observations. Bennu may represent a class of objects that could have brought volatiles and organic chemistry to Earth

Young lunar volcanic features: Thermophysical properties and formation

Irregular mare patches (IMPs) are small volcanic features on the lunar nearside with young model ages. Several formation mechanisms have been proposed including: caldera collapse, explosive outgassing, lava flow inflation, pyroclastic eruption, and regolith drainage. We present new observations of the four largest IMPs (Sosigenes, In a, Cauchy-5, and Maskelyne) using the Lunar Reconnaissance Orbiter (LRO) Diviner Lunar Radiometer (Diviner) and evaluate the formation hypotheses in the context of both previous results and the results presented here. We find that the IMPs have a rock abundance slightly higher than their surrounding terrain. Comparison of the Diviner data with thermal models excludes the possibility of extensive competent rocks within ∼15 cm of the surface at the IMPs. We also derive the thermal inertia at the four largest IMPs. Three appear to have thermal inertias slightly higher than typical regolith due to alteration by nearby craters or mass wasting from surrounding steep slopes, but Ina has a thermal inertia lower than the surrounding terrain. In particular, the largest smooth mound in Ina is the area with the lowest thermal inertia, suggesting that the material on the mound is less consolidated than typical regolith and/or contains fewer small rocks ( < 1 m). Formation by lava flows or regolith drainage is not expected to result in material with a lower thermal inertia than pre-existing regolith, so some other process such as explosive outgassing or pyroclastic eruptions must have occurred

Young lunar volcanic features: Thermophysical properties and formation

Irregular mare patches (IMPs) are small volcanic features on the lunar nearside with young model ages. Several formation mechanisms have been proposed including: caldera collapse, explosive outgassing, lava flow inflation, pyroclastic eruption, and regolith drainage. We present new observations of the four largest IMPs (Sosigenes, In a, Cauchy-5, and Maskelyne) using the Lunar Reconnaissance Orbiter (LRO) Diviner Lunar Radiometer (Diviner) and evaluate the formation hypotheses in the context of both previous results and the results presented here. We find that the IMPs have a rock abundance slightly higher than their surrounding terrain. Comparison of the Diviner data with thermal models excludes the possibility of extensive competent rocks within ∼15 cm of the surface at the IMPs. We also derive the thermal inertia at the four largest IMPs. Three appear to have thermal inertias slightly higher than typical regolith due to alteration by nearby craters or mass wasting from surrounding steep slopes, but Ina has a thermal inertia lower than the surrounding terrain. In particular, the largest smooth mound in Ina is the area with the lowest thermal inertia, suggesting that the material on the mound is less consolidated than typical regolith and/or contains fewer small rocks ( < 1 m). Formation by lava flows or regolith drainage is not expected to result in material with a lower thermal inertia than pre-existing regolith, so some other process such as explosive outgassing or pyroclastic eruptions must have occurred

Highly silicic compositions on the Moon.

Using data from the Diviner Lunar Radiometer Experiment, we show that four regions of the Moon previously described as "red spots" exhibit mid-infrared spectra best explained by quartz, silica-rich glass, or alkali feldspar. These lithologies are consistent with evolved rocks similar to lunar granites in the Apollo samples. The spectral character of these spots is distinct from surrounding mare and highlands material and from regions composed of pure plagioclase feldspar. The variety of landforms associated with the silicic spectral character suggests that both extrusive and intrusive silicic magmatism occurred on the Moon. Basaltic underplating is the preferred mechanism for silicic magma generation, leading to the formation of extrusive landforms. This mechanism or silicate liquid immiscibility could lead to the formation of intrusive bodies