Processes governing the VIS/NIR spectral reflectance behavior of lunar swirls

Hess, Marcel; Wöhler, Christian; Bhatt, Megha; Berezhnoy, A. A.; Grumpe, A.; Wohlfarth, K.; Bhardwaj, Anil; Шевченко, В. В.

doi:10.1051/0004-6361/201937299

Cited by 19 publications

(39 citation statements)

References 71 publications

(126 reference statements)

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“…Similar to previous studies (e.g., Li and Garrick-Bethell 2019), recent results by Hess et al (2020) indicate a weaker 3-µm band at the swirl locations than on the surrounding surface. This finding supports the assumption that the magnetic field locally reduces the flux of solar wind protons, leading to a reduced rate of OH/H 2 O formation in the regolith.…”

Section: Local Anomaliessupporting

confidence: 90%

“…This would lead to soil compaction and, according to the model by Hapke (2008), increased surface albedo without changing the mafic band depths and spectral slope. Additionally, the cometary gas may also remove the uppermost, highly matured regolith layer and reveal immature material, which would be consistent with the observation by Hess et al (2020) that spectra indicating a low surface maturity occur at all studied swirls. Using spectra of the lunar surface acquired by the Yutu rover at different distances from the Chang'E-3 lander, Wu and Hapke (2018) demonstrated that a landing rocket jet causes exactly this effect.…”

Section: Local Anomaliessupporting

confidence: 90%

“…This finding supports the assumption that the magnetic field locally reduces the flux of solar wind protons, leading to a reduced rate of OH/H 2 O formation in the regolith. However, Hess et al (2020) also showed that the spectral appearance of the northeastern parts of the Reiner Gamma swirl can be better explained by regolith compaction rather than by immature soil, due to the absence of variations in spectral reddening and in the depth of the mafic absorption bands between on-swirl and off-swirl surfaces. Furthermore, they described a small swirl structure in the western part of Mare Moscoviense that is not associated with a magnetic anomaly and does not show reduced OHIBD values compared to the surrounding surface.…”

Section: Local Anomaliesmentioning

confidence: 98%

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Water Group Exospheres and Surface Interactions on the Moon, Mercury, and Ceres

et al. 2021

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Water ice, abundant in the outer solar system, is volatile in the inner solar system. On the largest airless bodies of the inner solar system (Mercury, the Moon, Ceres), water can be an exospheric species but also occurs in its condensed form. Mercury hosts water ice deposits in permanently shadowed regions near its poles that act as cold traps. Water ice is also present on the Moon, where these polar deposits are of great interest in the context of future lunar exploration. The lunar surface releases either OH or H2O during meteoroid showers, and both of these species are generated by reaction of implanted solar wind protons with metal oxides in the regolith. A consequence of the ongoing interaction between the solar wind and the surface is a surficial hydroxyl population that has been observed on the Moon. Dwarf planet Ceres has enough gravity to have a gravitationally-bound water exosphere, and also has permanently shadowed regions near its poles, with bright ice deposits found in the most long-lived of its cold traps. Tantalizing evidence for cold trapped water ice and exospheres of molecular water has emerged, but even basic questions remain open. The relative and absolute magnitudes of sources of water on Mercury and the Moon remain largely unknown. Exospheres can transport water to cold traps, but the efficiency of this process remains uncertain. Here, the status of observations, theory, and laboratory measurements is reviewed.

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Section: Local Anomaliessupporting

confidence: 90%

Section: Local Anomaliessupporting

confidence: 90%

Section: Local Anomaliesmentioning

confidence: 98%

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Water Group Exospheres and Surface Interactions on the Moon, Mercury, and Ceres

et al. 2021

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“…On-swirl regions in our study areas are higher in feldspar and orthopyroxene (Lemelin et al, 2019) and are depleted in FeO (Lemelin et al, 2019), TiO 2 (Sato et al, 2017), and OH (Hess et al, 2020;Kramer et al, 2011a). Of particular interest, is the abundance of submicroscopic (≤1 μm) iron particles.…”

mentioning

confidence: 83%

Topographic Correlations Within Lunar Swirls in Mare Ingenii

Domingue

Weirich

Chuang

et al. 2022

Geophysical Research Letters

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The Moon's bright albedo markings, known as swirls, are defined by broad, bright, on‐swirl areas separated by darker off‐swirl lanes. Their formation mechanism has long been debated and is key for understanding the processing of the lunar surface, the mobility of the lunar soil particles, and the effects of the space environment on planetary surfaces. Here we present, for the first time, evidence that these features do not necessarily cross the surface without regard to topography or local terrain. Within portions of Mare Ingenii on the lunar far‐side, brighter on‐swirl areas have statistically lower mean elevations than adjacent, darker, off‐swirl lanes. These topographic characteristics provide constraints on the plausible formation mechanisms for the swirls in Mare Ingenii, which in turn provide insight into lunar soil migration and evolution. We believe this correlation with topography argues for highly mobile dust transport across the lunar surface.

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“…Spectral parameters in the UV (e.g., [3,4]) or in the NIR (e.g., [5]) can also be used to estimate the elemental abundances, but should be used with care. For example, according to the TiO 2 maps of Sato et al [4] the swirl Reiner Gamma is deprived of TiO 2 compared to its surroundings, which is physically implausible, as the optical differences are likely due to a difference in maturity and/or compaction [53]. Setting a prior, however, does not rule out solutions that do not confirm with prior knowledge, as long as the probability of the prior does not become zero.…”

Section: Priormentioning

confidence: 99%

Uncertainty Introduced by Darkening Agents in the Lunar Regolith: An Unmixing Perspective

et al. 2021

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On the Moon, in the near infrared wavelength range, spectral diagnostic features such as the 1-μm and 2-μm absorption bands can be used to estimate abundances of the constituent minerals. However, there are several factors that can darken the overall spectrum and dampen the absorption bands. Namely, (1) space weathering, (2) grain size, (3) porosity, and (4) mineral darkening agents such as ilmenite have similar effects on the measured spectrum. This makes spectral unmixing on the Moon a particularly challenging task. Here, we try to model the influence of space weathering and mineral darkening agents and infer the uncertainties introduced by these factors using a Markov Chain Monte Carlo method. Laboratory and synthetic mixtures can successfully be characterized by this approach. We find that the abundance of ilmenite, plagioclase, clino-pyroxenes and olivine cannot be inferred accurately without additional knowledge for very mature spectra. The Bayesian approach to spectral unmixing enables us to include prior knowledge in the problem without imposing hard constraints. Other data sources, such as gamma-ray spectroscopy, can contribute valuable information about the elemental abundances. We here find that setting a prior on TiO2 and Al2O3 can mitigate many of the uncertainties, but large uncertainties still remain for dark mature lunar spectra. This illustrates that spectral unmixing on the Moon is an ill posed problem and that probabilistic methods are important tools that provide information about the uncertainties, that, in turn, help to interpret the results and their reliability.

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Processes governing the VIS/NIR spectral reflectance behavior of lunar swirls

Cited by 19 publications

References 71 publications

Water Group Exospheres and Surface Interactions on the Moon, Mercury, and Ceres

Water Group Exospheres and Surface Interactions on the Moon, Mercury, and Ceres

Topographic Correlations Within Lunar Swirls in Mare Ingenii

Uncertainty Introduced by Darkening Agents in the Lunar Regolith: An Unmixing Perspective

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