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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, Ina, 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. [ABSTRACT FROM AUTHOR]

We investigate the physical properties, and changes through time, of lunar impact ejecta using radar and thermal infrared data. We use data from two instruments on the Lunar Reconnaissance Orbiter (LRO) – the Diviner thermal radiometer and the Miniature Radio Frequency (Mini-RF) radar instrument – together with Earth-based radar observations. We use this multiwavelength intercomparison to constrain block sizes and to distinguish surface from buried rocks in proximal ejecta deposits. We find that radar-detectable rocks buried within the upper meter of regolith can remain undisturbed by surface processes such as micrometeorite bombardment for >3 Gyr. We also investigate the thermophysical properties of radar-dark haloes, comprised of fine-grained, rock-poor ejecta distal to the blocky proximal ejecta. Using Diviner data, we confirm that the halo material is depleted in surface rocks, but show that it is otherwise thermophysically indistinct from background regolith. We also find that radar-dark haloes, like the blocky ejecta, remain visible in radar observations for craters with ages >3 Ga, indicating that regolith overturn processes cannot replenish their block populations on that timescale. [ABSTRACT FROM AUTHOR]

The northern floor and wall of Amundsen crater, near the lunar south pole, is a permanently shaded region (PSR). Previous study of this area using data from the Lunar Orbiter Laser Altimeter (LOLA), Diviner and LAMP instruments aboard Lunar Reconnaissance Orbiter (LRO) shows a spatial correlation between brighter 1064 nm albedo, annual maximum surface temperatures low enough to enable persistence of surface water ice (<110 K), and anomalous ultraviolet radiation. We present results using data from Diviner that quantify the differential emissivities observed in the far-IR (near the Planck peak for PSR-relevant temperatures) between the PSR and a nearby non-PSR target in Amundsen Crater. We find features in far-IR emissivity (50–400 μm) could be attributed to either, or a combination, of two effects (i) differential regolith emissive behavior between permanently-shadowed temperature regimes and those of normally illuminated polar terrain, perhaps related to presence of water frost (as indicated in other studies), or (ii) high degrees of anisothermality within observation fields of view caused by doubly-shaded areas within the PSR target that are colder than observed brightness temperatures. The implications in both cases are compelling: The far-IR emissivity curve of lunar cold traps may provide a metric for the abundance of "micro" cold traps that are ultra-cool, i.e. shadowed also from secondary and higher order radiation (absorption and re-radiation or scattering by surrounding terrain), or for emissive properties consistent with the presence of surface water ice. • We explore far-IR emissivity of permanently- and partially- shaded targets in the lunar south polar crater Amundsen. • 50–400 micron emissivity trends of the permanently shadowed region (PSR) target are different than for the non-PSR target. • Unlike the non-PSR target, emissivity of the PSR target shows apparent temperature dependence between ~30–40 K. • Results are consistent with anisothermality due to sub-FOV scale ultra-cold terrain, and surface water ice. [ABSTRACT FROM AUTHOR]