The Plethora of Science Afforded by a Lunar Swirl (original) (raw)
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The Lunar Swirls A White Paper to the NASA Decadal Survey
2009
The lunar swirls are high albedo curvilinear surface features that are not associated with a particular lithology or typical lunar surface process. Each swirl is coincident with a local region of strong remanent magnetism on a body that does not currently generate its own magnetic field. There are at least three different models for swirl formation. Determining the true nature and formation mechanism of the swirls, their occurrence on the lunar surface, and why they are associated with magnetic anomalies will affect our understanding of the history of the EarthMoon system, the interaction of planetary surfaces with the solar wind, and how we explore planetary surfaces. List of Abbreviations Ga Billions of years ago
Formation of lunar swirls by magnetic field standoff of the solar wind
Nature Communications, 2015
Lunar swirls are high-albedo markings on the Moon that occur in both mare and highland terrains; their origin remains a point of contention. Here, we use data from the Lunar Reconnaissance Orbiter Diviner Lunar Radiometer to support the hypothesis that the swirls are formed as a result of deflection of the solar wind by local magnetic fields. Thermal infrared data from this instrument display an anomaly in the position of the silicate Christiansen Feature consistent with reduced space weathering. These data also show that swirl regions are not thermophysically anomalous, which strongly constrains their formation mechanism. The results of this study indicate that either solar wind sputtering and implantation are more important than micrometeoroid bombardment in the space-weathering process, or that micrometeoroid bombardment is a necessary but not sufficient process in space weathering, which occurs on airless bodies throughout the solar system.
2020
Submitted for the DPP20 Meeting of The American Physical Society Lunar Swirl Formation with Irregular Shaped Dusty Plasma Medium1 CALVIN CARMICHAEL, JENS SCHMIDT, GRAESON GRIFFIN, LORIN MATTHEWS, TRUELL HYDE, Baylor University — On the lunar surface, features with high albedos aptly named Lunar Swirls, have been observed near anomalous lunar magnetic fields. Although the formation mechanism for Lunar Swirls remains in question, numerical models suggest that complex plasmas interacting with local magnetic fields may be accountable for these lunar features via dust transport and weathering of regolith. Identifying the actual relationship between dusty plasma and these lunar magnetic fields would lend insight into the formation of lunar swirls. At Baylor University, a GEC RF Reference Cell and an Inductively Coupled Plasma Generator (IPG-B) are being used to experimentally study the interaction between dusty plasma and simulated lunar magnetic fields on non-conducting surfaces similar ...
Characterization of lunar swirls at Mare Ingenii: A model for space weathering at magnetic anomalies
Journal of Geophysical Research, 2011
1] Analysis of spectra from the Clementine ultraviolet-visible and near-infrared cameras of small, immature craters and surface soils both on and adjacent to the lunar swirls at Mare Ingenii has yielded the following conclusions about space weathering at a magnetic anomaly. (1) Despite having spectral characteristics of immaturity, the lunar swirls are not freshly exposed surfaces. The swirl surfaces are regions of retarded weathering, while immediately adjacent regions experience accelerated weathering. (3) Weathering in the off-swirl regions darkens and flattens the spectrum with little to no reddening, which suggests that the production of larger (>40 nm) nanophase iron dominates in these locations as a result of charged particle sorting by the magnetic field. Preliminary analysis of two other lunar swirl regions, Reiner Gamma and Mare Marginis, is consistent with our observations at Mare Ingenii. Our results indicate that sputtering/vapor deposition, implanted solar wind hydrogen, and agglutination share responsibility for creating the range in npFe 0 particle sizes responsible for the spectral effects of space weathering.
Minimagnetospheres above the Lunar Surface and the Formation of Lunar Swirls
Physical Review Letters, 2012
In this paper we present in-situ satellite data, theory and laboratory validation that show how small scale collisionless shocks and mini-magnetospheres can form on the electron inertial scale length. The resulting retardation and deflection of the solar wind ions could be responsible for the unusual "lunar swirl" patterns seen on the surface of the Moon.
Processes governing the VIS/NIR spectral reflectance behavior of lunar swirls
Astronomy and Astrophysics, 639, A12, pp.1-18 , 2020
We investigated six bright swirls associated with magnetic anomalies of variable strength using Chandrayaan-1 Moon Mineralogy Mapper (M 3) hyperspectral image data. We examined the 3 µm absorption band generally ascribed to solar wind-induced OH/H 2 O and spectral trends in the near-infrared wavelength range at on-swirl and off-swirl locations. We found that the 3 µm absorption band is weaker at on-swirl than at off-swirl locations and shows only weak variations with time-of-day. This result is consistent with magnetic anomaly shielding that reduces solar wind interaction with the surface. For a small swirl structure in Mare Moscoviense, we found the 3 µm absorption band to be similar to that of its surroundings due to the absence of strong magnetic shielding. Our spectral analysis results at on-swirl and off-swirl locations suggest that the spectral trends at on-swirl and off-swirl locations cannot always be explained by reduced space-weathering alone. We propose that a combination of soil compaction possibly resulting from the interaction between the surface and cometary gas and subsequent magnetic shielding is able to explain all observed on-swirl vs. off-swirl spectral trends including the absorption band depth near 3 µm. Our results suggest that an external mechanism of interaction between a comet and the uppermost regolith layer might play a significant role in lunar swirl formation.
Lunar Swirls, Magnetic Anomalies, and the Reiner Gamma Formation
2006
Reiner Gamma is the only near side example of the elusive Lunar Swirl features. There exist only three other known examples, two on the moons far side, and another on Mercury. The origin of these surface deposits and their related magnetic anomalies are a matter of debate, which most likely will not be settled until future lunar missions. We shall here consider their nature and possible origins.
A small lunar swirl and its implications for the formation of the Reiner Gamma magnetic anomaly
Icarus, 2019
The Moon does not currently possess a dynamo, but its crust contains numerous magnetic anomalies detected from orbit. The geologic origins of these anomalies are still unknown, including the archetypal Reiner Gamma magnetic anomaly. To gain insight, we study a small magnetic anomaly, herein called the octopus, which is possibly associated with Reiner Gamma. The octopus has curving bright albedo patterns characteristic of features known as swirls. We use high cadence 9 Hz Lunar Prospector magnetometer data, along with constraints provided by this swirl's albedo pattern, to perform inversions for the swirl's magnetic source body characteristics. We use three different inversion methods, and they all return similar results. We also estimate the depth of magnetization from characteristics of the horizontal component of the magnetic field and the albedo pattern. We find that performing inversion for source body properties at small swirls has advantages compared to larger anomalies, or anomalies without albedo markings. We find the octopus is magnetized in the same direction as the main Reiner Gamma anomaly (within 1σ uncertainties), suggesting they formed contemporaneously. The large spatial distance between these coeval anomalies and their inferred shallow source body depths are compatible with formation in a hot ejecta deposit that cooled in the presence of a dynamo field, as suggested by Hood et al. (2001). However, a key remaining enigma is why the northeastern Reiner Gamma "tail" formation has a magnetization direction ∼60°different from the main body and octopus.
Analysis of Magnetization Directions of Lunar Swirls
2020
Lunar Swirls are high albedo markings on the Moon that exist in the regions of some crustal magnetic anomalies. The precise mechanism responsible for the swirl features is unknown but a prevailing theory is solar wind standoff, where the magnetic field from subsurface magnetized sources protects the lunar surface from solar wind ions, leading to their lesser maturation and brighter appearance. If this theory is correct, the magnetic field of the anomalies should heavily influence the appearance of the swirl. To better understand the cause of swirls, the magnetization direction of the source creating the field is analyzed. This study uses differences of the vector fields measured along satellite orbits (20-40 km above the lunar surface), which have lesser noise because time-varying external fields in the lunar environment are nearly the same for short times between consecutive data points. The magnetization of the magnetic features is derived by best-fitting fields from a set of unidirectional magnetized dipoles. The best-fit is judged by comparing computed vector fields with the observed vector fields (their misfit) and their correlation coefficient. Magnetization directions of the magnetic features analyzed in the study do show a strong relationship between the magnetization directions and the appearance of the swirl. After obtaining the magnetization directions, the corresponding magnetic paleopoles were determined. The paleopole locations do not coincide with the current rotational axis of the Moon (assuming a dipolar core field) and are fairly spread out over the Moon. If the Moon did possess an early dipolar core dynamo then it was most likely not aligned with the present rotational axis. The uncertainty in the magnetization directions and derived paleopole locations as judged by best-fit magnetization directions using different criteria is fairly large.
Geophysical Research Letters, 2007
We describe a strong crustal magnetic anomaly, recently identified in Lunar Prospector magnetometer data, that is associated with a previously unreported albedo feature near the crater Airy in the lunar nearside highlands. Other workers have demonstrated a correlation between magnetic anomalies and the enigmatic bright markings known as lunar swirls. We have used Earth-based telescopic spectra and Clementine multispectral images to investigate the compositional and optical maturity characteristics of the Airy swirl. The Airy albedo feature does not exhibit the complex sinuous structure of well-known swirls such as the Reiner Gamma Formation, but does possess a bright loop and central dark lane. Another strong magnetic anomaly, in the Apollo 16/Descartes region, corresponds to a simple diffuse bright albedo spot. On this basis we suggest that a continuum of swirl morphologies exists on the Moon, with the Airy feature representing an intermediate or incipient swirl form.