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The long-term cyclicity and temporal succession of glacial-periglacial (or deglacial) periods or epochs are keynotes of Quaternary geology on Earth. Relatively recent work has begun to explore the histories of the mid- to higher-latitudinal terrain of Mars, especially in the northern hemisphere, for evidence of similar cyclicity and succession in the Mid to Late Amazonian Epoch. Here, we carry on with this work by focusing on Protonilus Mensae [PM] (43-490 N, 37-590 E). More specifically, we discuss, describe and evaluate an area within PM that straddles a geological contact between two ancient units: [HNt], a Noachian-Hesperian Epoch transition unit; and [eHT] an early Hesperian Epoch transition unit. Dark-toned terrain within the eHt unit (HiRISE image ESP_028457_2255) shows continuous coverage by structures akin to clastically-sorted circles [CSCs]. The latter are observed in permafrost regions on Earth where the freeze-thaw cycling of surface and/or near-surface water is commonplace and cryoturbation is not exceptional. The crater-size frequency distribution of the dark-toned terrain suggests a minimum age of ~100 Ma and a maximum age of ~1 Ga. The age estimates of the candidate CSCs fall within this dispersion. Geochronologically, this places the candidate CSCs amongst the oldest periglacial landforms identified on Mars so far., Comment: 71 pages, 15 figures, published in Icarus

We used infrared data from the Lunar Reconnaissance Orbiter (LRO) Diviner Lunar Radiometer Experiment to globally map thermophysical properties of the Moon's regolith fines layer. Thermal conductivity varies from 7.4$\times$10$^{-4}$ W m$^{-1}$ K$^{-1}$ at the surface, to 3.4$\times$10$^{-3}$ W m$^{-1}$ K$^{-1}$ at depths of $\sim$1 m, given density values of 1100 kg m$^{-3}$ at the surface, to 1800 kg m$^{-3}$ at 1-m depth. On average, the scale height of these profiles is $\sim$7 cm, corresponding to a thermal inertia of 55 $\pm$2 J m$^{-2}$ K$^{-1}$ s$^{-1/2}$ at 273 K, relevant to the diurnally active near-surface layer, $\sim$4-7 cm. The temperature-dependence of thermal conductivity and heat capacity leads to a $\sim$2$\times$ diurnal variation in thermal inertia at the equator. On global scales, the regolith fines are remarkably uniform, implying rapid homogenization by impact gardening of this layer on timescales $<$ 1 Gyr. Regional and local scale variations show prominent impact features $<$ 1 Gyr old, including higher thermal inertia ($>$ 100 J m$^{-2}$ K$^{-1}$ s$^{-1/2}$) in the interiors and ejecta of Copernican-aged impact craters, and lower thermal inertia ($<$ 50 J m$^{-2}$ K$^{-1}$ s$^{-1/2}$) within the lunar cold spots identified by Bandfield et al. (2014). Observed trends in ejecta thermal inertia provide a potential tool for age-dating craters of previously unknown age, complementary to the approach suggested by Ghent et al. (2014). Several anomalous regions are identified in the global 128 pixels-per-degree maps presented here, including a high-thermal inertia deposit near the antipode of Tycho crater., Comment: Accepted for publication in Journal of Geophysical Research - Planets

We model the primary crater production of small (D < 100 m) primary craters on Mars and the Moon using the observed annual flux of terrestrial fireballs. From the size-frequency distribution (SFD) of meteor diameters, with appropriate velocity distributions for Mars and the Moon, we are able to reproduce martian and lunar crater-count chronometry systems (isochrons) in both slope and magnitude. We include an atmospheric model for Mars that accounts for the deceleration, ablation, and fragmentation of meteors. We find that the details of the atmosphere or the fragmentation of the meteors do not strongly influence our results. The downturn in the crater SFD from atmospheric filtering is predicted to occur at D ~ 10-20 cm, well below the downturn observed in the distribution of fresh craters detected by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) or the Mars Reconnaissance Orbiter (MRO) Context Camera (CTX). Crater counts conducted on the ejecta blanket of Zunil crater on Mars and North Ray crater on the Moon yielded crater SFDs with similar slopes and ages (~1 Ma, and ~58 Ma, respectively) to our model, indicating that the average cratering rate has been constant on these bodies over these time periods. Since our Monte Carlo simulations demonstrate that the existing crater chronology systems can be applied to date young surfaces using small craters on the Moon and Mars, we conclude that the signal from secondary craters in the isochrons must be relatively small, as our Monte Carlo model only generates primary craters., Comment: Under review with Icarus

The decay of the martian atmosphere - which is dominated by carbon dioxide - is a component of the long-term environmental change on Mars from a climate that once allowed rivers to flow to the cold and dry conditions of today. The minimum size of craters serves as a proxy for palaeopressure of planetary atmospheres, because thinner atmospheres permit smaller objects to reach the surface at high velocities and form craters. The Aeolis Dorsa region near Gale crater on Mars contains a high density of preserved ancient craters interbedded with river deposits and thus can provide constraints on atmospheric density around the time of fluvial activity. Here we use high-resolution orthophotos and digital terrain models from the Mars Reconnaissance Orbiter to identify ancient craters in Aeolis Dorsa that date to about 3.6 Gyr ago and compare their size distribution with models of atmospheric filtering of impactors. We obtain an upper limit of 0.9$\pm$0.1 bar, rising to 1.9$\pm$0.2 bar if rimmed circular mesas - interpreted to be erosionally-resistant fills of floors of impact craters - are excluded. We assume target properties appropriate for desert alluvium: if sediment had rock-like rock-mass strength similar to bedrock at the time of impact, the upper limit increases by a factor of up to two. If Mars did not have a stable multibar atmosphere at the time that the rivers were flowing - as suggested by our results - then the warm and wet CO2/H2O greenhouse is ruled out, and long-term average temperatures were most likely below freezing.

Lunar Reconnaissance Orbiter (LRO) Diviner Radiometer, Mini-RF, and LRO Camera data were used to identify and characterize rocky lunar deposits that appear well separated from any potential source crater. Two regions are described: 1) A approximate 18,000 sq km area with elevated rock abundance and extensive melt ponds and veneers near the antipode of Tycho crater (167.5 deg E, 42.5 deg N). This region has been identified previously, using radar and aging data. 2) A much larger and more diffuse region, covering approximately 730,000 sq km, centered near 310 deg E, 35 deg S, containing elevated rock abundance and numerous granular flow deposits on crater walls. The rock distributions in both regions favor certain slope azimuths over others, indicating a directional component to the formation of these deposits. The spatial distribution of rocks is consistent with the arrival of ejecta from the west and northwest at low angles (approximately 10-30 deg) above the horizon in both regions. The derived age and slope orientations of the deposits indicate that the deposits likely originated as ejecta from the Tycho impact event. Despite their similar origin, the deposits in the two regions show significant differences in the datasets. The Tycho crater antipode deposit covers a smaller area, but the deposits are pervasive and appear to be dominated by impact melts. By contrast, the nearside deposits cover a much larger area and numerous granular flows were triggered. However, the features in this region are less prominent with no evidence for the presence of impact melts. The two regions appear to be surface expressions of a distant impact event that can modify surfaces across wide regions, resulting in a variety of surface morphologies. The Tycho impact event may only be the most recent manifestation of these processes, which likely have played a role in the development of the regolith throughout lunar history