Martian deglaciation as an indicator of climatic variability
Mars contains abundant evidence of glaciation at virtually all latitudes, but the highest concentration of glacial features are present in the mid-latitudes (~30-60°). Inside many glaciated craters, young geologic features indicate deglaciation and subsequent modification that are induced by deglaciation. This modification indicates the presence of a paraglacial period on Mars. On Earth, the paraglacial period describes how an environment responds to instabilities introduced by the loss of ice that occurs when a region is deglaciated. Paraglacial modification acts over similar timeframes and creates a suite of similar geological features, so assessing the paraglacial response in a region can yield much information about the climate and nature of an environment. Through assessing the suite of features that frequently form in deglaciated craters, the martian paraglacial period can be identified and characterized.
Evidence of paraglacial activity is present at virtually all longitudes on Mars in the mid-latitudes of both hemispheres, but the distribution and association of paraglacial features is not constant across the planet. The distribution of paraglacial features appear to be dependent on regional accumulation and ablation patterns. See this recent LPSC abstract for more information.
Recently glaciated terrains on Mars represent potentially useful human exploration destinations as they contain abundant deposits of near-surface ice. This ice could be extracted and utilized by humans, cutting down on consumables transported from Earth. The wide distribution of glaciated terrains at a variety of latitudes provide abundant exploration targets.
Characterizing endmember volcanism on the Moon
The Aristarchus plateau is widely agreed to be the most complex volcanic center on the Moon, containing the largest pyroclastic deposit and the longest, widest, and deepest sinuous rille. While the complex stratigraphy and multitude of volcanic features in the region may formed through multiple eruptions or several disparate stages, evidence of large irregular cone-like features just south of Cobra Head suggest that the major volcanic features could have formed through a single, continuous fire-fountain eruption. In this large, continuous eruption, partly cooled erupted material would accumulate near the volcanic vent and form welded spatter cones. The morphology and physical characteristics of these irregular cone features agrees with a formation via spatter accumulation, and the location and distribution of these features can be used to infer conditions about the volcanic eruption. For more information see my recent LPSC abstract.
Understanding the physical conditions of the largest explosive eruption on the Moon is critical when considering future human exploration targets, as detailed knowledge of eruption that created the pyroclastic deposit on Aristarchus may contain useful resources that may be extracted and utilized by future astronauts.
Examining spectral variations of localized lunar pyroclastic deposits
The localized lunar dark mantle deposits (DMDs) in Alphonsus, J. Herschel, and Oppenheimer craters were analyzed using visible-near-infrared spectroscopy data from the Moon Mineralogy Mapper (M3). Spectra of these localized DMDs were analyzed for compositional and mineralogical variations within the deposits and were compared with nearby mare basalt units. Spectra of the three localized DMDs exhibited mafic absorption features indicating iron-rich compositions, although the DMDs were spectrally distinct from nearby mare basalts. All of the DMDs contained spectral signatures of glassy materials, suggesting the presence of volcanic glass in varying concentrations across the individual deposits. In addition, the albedo and spectral signatures were variable within the Alphonsus and Oppenheimer crater DMDs, suggesting variable deposit thickness and/or variations in the amount of mixing with the local substrate. Two previously unidentified localized DMDs were discovered to the northeast of Oppenheimer crater. The identification of high concentrations of volcanic glass in multiple localized DMDs in different locations suggests that the distribution of volcanic glass across the lunar surface is much more widespread than has been previously documented. The presence of volcanic glass implies an explosive, vulcanian eruption style for localized DMDs, as this allows volcanic glass to rapidly quench, inhibiting crystallization, compared to the larger hawaiian-style eruptions typical of regional DMD emplacement where black beads indicate a higher degree of crystallization. Improved understanding of the local and global distributions of volcanic glass in lunar DMDs will further constrain lunar degassing and compositional evolution throughout lunar volcanic history.
Co-authors on this work: Sebastien Besse, Lisa R. Gaddis, Jessica M. Sunshine, James W. Head, and Sara Mazrouei
The relationship between radar scattering and surface roughness of lunar volcanic features
Lunar roughness measurements derived from the Lunar Orbiter Laser Altimeter (LOLA) are compared to 12.6 cm wavelength radar data (S-band) collected by the Miniature Radio Frequency instrument and 70 cm wavelength radar data (P-band) collected by the Arecibo Observatory. These data are compared to assess how surface and subsurface roughness are correlated and affected by parameters including age and composition at length scales between 0.1-100 m. A range of features are analyzed including volcanic domes (Marius Hills, Rümker Hills, Gruithuisen, and Mairan Domes); mare (Imbrium, Serenitatis, and Oceanus Procellarum); pyroclastic dark mantle deposits (Sinus Aestuum, Sulpicius Gallus, and Mare Vaporum); and two young craters (Copernicus and Tycho). Statistically significant positive correlations exist between topographic roughness and both P- and S-band circular polarization ratios. The strongest correlation is observed at the longest length scales. Correlations weaken as length scales become less similar, potentially due to distinct processes controlling surface modification. Roughness is not significantly correlated with local slope. Although the Marius Hills are compositionally distinct from the Gruithuisen and Mairan domes, they are indistinguishable in roughness characteristics. Conversely, the Rümker Hills, mare, and dark mantle deposits are smoother at the length scales examined, possibly due to fine-grained mantling of regolith or pyroclastic deposits. The floor and ejecta of Tycho crater are the roughest surfaces measured in this study, while the floor and ejecta of Copernicus crater overlap the roughness distribution of the volcanic features. This study shows that many factors control the evolution of roughness over time on various length scales.
Co-authors on this work: Walter S. Kiefer, Caleb I. Fassett, D. Benjamin J. Bussey, Joshua T. S. Cahill, M. Darby Dyar, Samuel J. Lawrence, and Paul D. Spudis