The apparent lack of lunar-like swirls on Mercury: Implications for the formation of lunar swirls and for the agent of space weathering

Blewett, D. T.; Denevi, Brett W.; Robinson, M. S.; Ernst, C. M.; Purucker, Michael E.; Solomon, Sean C.

doi:10.1016/j.icarus.2010.03.008

Cited by 36 publications

(24 citation statements)

References 63 publications

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“…Therefore, models of swirl formation that invoke comet‐related impacts are not favored. Blewett et al [2010] also argue that the apparent lack of swirls on Mercury is evidence against the comet impact hypothesis. Further, Nicholas et al [2007] found that the degree of magnetization required to produce the observed field over Reiner Gamma would be unrealistically high for a thin layer of surface material modified by interaction with a comet.…”

Section: Discussionmentioning

confidence: 97%

Characterization of lunar swirls at Mare Ingenii: A model for space weathering at magnetic anomalies

et al. 2011

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[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. (2) 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.

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Section: Discussionmentioning

confidence: 97%

Characterization of lunar swirls at Mare Ingenii: A model for space weathering at magnetic anomalies

et al. 2011

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“…Information on the nature of lunar swirls continues to emerge, but definitive conclusions about the origin of swirls cannot yet be drawn. We currently favor hypotheses for swirl formation that involve the influence of a crustal magnetic anomaly on the solar wind [cf., Blewett et al , 2010a]. Key questions concerning lunar swirls and crustal magnetic anomalies that need to be answered include the following: (1) Are the crustal magnetic anomalies truly capable of causing an important decrease in the solar wind flux reaching the surface?…”

Section: Discussionmentioning

confidence: 99%

Lunar swirls: Examining crustal magnetic anomalies and space weathering trends

et al. 2011

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[1] We have used multispectral images from Clementine and data from Lunar Prospector's magnetometer to conduct a survey of lunar crustal magnetic anomalies, prominent lunar swirls, and lesser known swirl markings to provide new information on the nature of swirls and their association with magnetic anomalies. We find that all swirls and swirl-like albedo patterns are associated with areas of magnetized crust, but not all areas of magnetized crust are colocated with swirl-like albedo anomalies. All observed swirls exhibit spectral characteristics similar to immature material and generally have slightly lower FeO values compared with their surroundings as determined with a multispectral iron-mapping method. We discuss these results in relation to the various hypotheses for swirl formation. The comet impact hypothesis for lunar swirls would not predict a difference in the spectrally determined FeO content between swirls and nearby ordinary surfaces. The compositional difference could be explained as a consequence of (1) magnetic shielding of the surface from the solar wind, which could produce anomalous space weathering (little darkening with limited reddening) and potentially alter the predictions of the multispectral iron-mapping algorithm while the compositional contrast could be enhanced by delivery of lower-FeO ejecta from outside the swirl; and (2) accumulation of fine plagioclase-rich dust moving under the influence of electric fields induced by solar wind interactions with a magnetic anomaly. Therefore, we cannot at present clearly distinguish between the solar wind shielding and electrostatic dust accumulation models for swirl formation. We describe future measurements that could contribute to solution of the puzzle of swirl origin.

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“…Inspection of low‐spatial‐resolution data from MESSENGER's first Mercury flyby led initially to the association of high‐reflectance, bluish material primarily with the floors of impact craters [ Robinson et al ., ; Blewett et al ., , ]. However, the subsequent flybys and especially the orbital phase of the mission revealed that in addition to floors, hollows occur in a variety of settings in and around craters as well as in locations not directly linked with impact structures.…”

Section: Hollows: Geological Settingsmentioning

confidence: 99%

“…These data have much better radiometric calibration and a larger number of wavelengths than did the Mariner 10 images. The MESSENGER flyby data confirmed the presence of the unusual bright, bluish materials in those patches identified with Mariner 10 images, and a number of additional occurrences were noted [ Robinson et al ., ; Blewett et al ., , ], for example, on the floor of Sander crater and on the peak ring of the Raditladi impact basin (Figures and ).…”

Section: Introductionmentioning

confidence: 99%

Mercury's hollows: Constraints on formation and composition from analysis of geological setting and spectral reflectance

et al. 2013

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Landforms unique to Mercury, hollows are shallow, flat‐floored irregular depressions notable for their relatively high reflectance and characteristic color. Here we document the range of geological settings in which hollows occur. Most are associated with impact structures (simple bowl‐shaped craters to multiring basins, and ranging from Kuiperian to Calorian in age). Hollows are found in the low‐reflectance material global color unit and in low‐reflectance blue plains, but they appear to be absent from high‐reflectance red plains. Hollows may occur preferentially on equator‐ or hot‐pole‐facing slopes, implying that their formation is linked to solar heating. Evidence suggests that hollows form because of loss of volatile material. We describe hypotheses for the origin of the volatiles and for how such loss proceeds. Intense space weathering and solar heating are likely contributors to the loss of volatiles; contact heating by melts could promote the formation of hollows in some locations. Lunar Ina‐type depressions differ from hollows on Mercury in a number of characteristics, so it is unclear if they represent a good analog. We also use MESSENGER multispectral images to characterize a variety of surfaces on Mercury, including hollows, within a framework defined by laboratory spectra for analog minerals and lunar samples. Data from MESSENGER's X‐Ray Spectrometer indicate that the planet's surface contains up to 4% sulfur. We conclude that nanophase or microphase sulfide minerals could contribute to the low reflectance of the low‐reflectance material relative to average surface material. Hollows may owe their relatively high reflectance to destruction of the darkening agent (sulfides), the presence of alteration minerals, and/or physical differences in particle size, texture, or scattering behavior.

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The apparent lack of lunar-like swirls on Mercury: Implications for the formation of lunar swirls and for the agent of space weathering

Cited by 36 publications

References 63 publications

Characterization of lunar swirls at Mare Ingenii: A model for space weathering at magnetic anomalies

Characterization of lunar swirls at Mare Ingenii: A model for space weathering at magnetic anomalies

Lunar swirls: Examining crustal magnetic anomalies and space weathering trends

Mercury's hollows: Constraints on formation and composition from analysis of geological setting and spectral reflectance

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