Space weathering on airless bodies

Pieters, C. M.; Noble, S. K.

doi:10.1002/2016je005128

Cited by 382 publications

(310 citation statements)

References 108 publications

(152 reference statements)

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“…Based on the (admittedly limited) work presented here and by Donaldson Hanna et al (), this does not appear to be the case, although a more thorough analysis of relevant materials is certainly warranted in future work. It is well known that space weathering causes both darkening and reddening (Pieters & Noble, ) or, in some cases, just darkening (Lucey & Riner, ) of airless body surfaces. The degree of weathering is primarily dependent on the degree solar wind and micrometeoroid bombardment.…”

Section: Discussionmentioning

confidence: 99%

MGS‐TES Spectra Suggest a Basaltic Component in the Regolith of Phobos

et al. 2018

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The origins of the Martian moons Phobos and Deimos have been the subjects of considerable debate. Visible and near‐infrared spectra of these bodies are dark and nearly featureless, with red slopes of varying degrees. These spectra are generally consistent with those of carbonaceous asteroids, leading to the hypothesis that Phobos and Deimos are captured carbonaceous asteroids. The shapes and inclinations of the orbits of Phobos and Deimos present problems for the asteroid capture hypothesis. This had led researchers to suggest that Phobos and Deimos coaccreted with Mars or that they are the result of an impact with Mars or in the Mars vicinity. In this work, we reexamine Mars Global Surveyor Thermal Emission Spectrometer (MGS‐TES) data of Phobos and compare spectra of the Phobos surface to mid‐IR spectra of the ungrouped C2 meteorite Tagish Lake (a suggested analog for D‐class asteroids) and particulate basalt and phyllosilicate samples (mixed with carbon black to reduce their visible albedos) acquired in a simulated airless body environment. We find that Tagish Lake is a poor mid‐IR spectral analog to Phobos and that major spectral features in the Phobos spectrum are best matched by a silicate transparency feature similar to that found for finely particulate basalt. Other features in the spectrum are likely best explained by a phyllosilicate component. We suggest that these results indicate that at a portion of the Phobos surface regolith is derived from the Martian crust.

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Section: Discussionmentioning

confidence: 99%

MGS‐TES Spectra Suggest a Basaltic Component in the Regolith of Phobos

et al. 2018

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“…Based on lunar sample studies, one of the primary metallic byproducts of space weathering is iron metal (Keller & McKay, ; Keller & McKay, ; Noble et al, ; Taylor et al, ), although iron silicides (e.g., hapkeite) and rare metallic Si also make up a minor fraction of metallic space weathering products (Anand et al, ; Gopon et al, ). The iron metal produced through space weathering occurs along a continuum of nanophase iron particles that coarsen through Ostwald ripening to larger particles (Lucey & Noble, ; Noble et al, ; Pieters et al, ; Pieters & Noble, ). In addition to metal particles, sulfides and halides have also been reported to form through space weathering processes based on studies of samples returned from the asteroid Itokawa by the Hayabusa spacecraft (Noguchi et al, ; Noguchi, Kimura, Hashimoto, Konno, Nakamura, Zolensky, Okazaki, & Ishibashiet, ; Noguchi, Kimura, Hashimoto, Konno, Nakamura, Zolensky, Tsuchiyama, & Okadaet, ).…”

Section: Secondary Processes That Could Have Affected the O/si Ratio mentioning

confidence: 99%

“…The MESSENGER GRS data on which our O/Si ratio is based provide chemical information on the upper ten to several tens of centimeters of the surface of Mercury (Solomon et al, ). In contrast, metallic space weathering products typically form in the outer hundreds of nanometers of an exposed particle (Keller & McKay, ; Keller & McKay, ; Noble et al, ; Pieters & Noble, ; Pieters et al, ; Taylor et al, ). The contrast in scales of the space weathering process and the GRS analysis requires that we consider the volume of material from which O has been lost and how it relates to mass.…”

Section: Secondary Processes That Could Have Affected the O/si Ratio mentioning

confidence: 99%

A Low O/Si Ratio on the Surface of Mercury: Evidence for Silicon Smelting?

et al. 2017

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Data from the Gamma‐Ray Spectrometer (GRS) that flew on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft indicate that the O/Si weight ratio of Mercury's surface is 1.2 ± 0.1. This value is lower than any other celestial surface that has been measured by GRS and suggests that 12–20% of the surface materials on Mercury are composed of Si‐rich, Si‐Fe alloys. The origin of the metal is best explained by a combination of space weathering and graphite‐induced smelting. The smelting process would have been facilitated by interaction of graphite with boninitic and komatiitic parental liquids. Graphite entrained at depth would have reacted with FeO components dissolved in silicate melt, resulting in the production of up to 0.4–0.9 wt % CO from the reduction of FeO to Fe0—CO production that could have facilitated explosive volcanic processes on Mercury. Once the graphite‐entrained magmas erupted, the tenuous atmosphere on Mercury prevented the buildup of CO over the lavas. The partial pressure of CO would have been sufficiently low to facilitate reaction between graphite and SiO2 components in silicate melts to produce CO and metallic Si. Although exotic, Si‐rich metal as a primary smelting product is hypothesized on Mercury for three primary reasons: (1) low FeO abundances of parental magmas, (2) elevated abundances of graphite in the crust and regolith, and (3) the presence of only a tenuous atmosphere at the surface of the planet within the 3.5–4.1 Ga timespan over which the planet was resurfaced through volcanic processes.

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“…Fresh craters on Ceres are spectrally blue and exhibit distinct optical properties compared to older surface regions, indicating that some process of space weathering or regolith gardening homogenizes the surface . A different group of surface and space weathering processes including lateral mixing, micrometeorite bombardment and contamination, thermal cycling, and sublimation likely dominate on Ceres as compared to inner solar system bodies that experience the formation of nanophase metallic iron (npFe 0 ) or other nanophase particles ( Pieters and Noble, 2016 JID: YICAR [m5G;November 6, 2017;12:24 ] surface materials is most likely to significantly lower the albedo of faculae over relevant timescales. We estimated the timescale over which impact-induced lateral mixing and direct impacts are expected to bury or disseminate newly emplaced faculae by using the Ceres crater production function .…”

Section: Darkening and Disappearance Of Faculaementioning

confidence: 99%

The Formation and Evolution of Bright Spots on Ceres

Stein¹,

Ehlmann²,

Palomba³

et al. 2017

Geological Society of America Abstracts With Programs

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a b s t r a c tThe otherwise homogeneous surface of Ceres is dotted with hundreds of anomalously bright, predominantly carbonate-bearing areas, termed "faculae," with Bond albedos ranging from ∼0.02 to > 0.5. Here, we classify and map faculae globally to characterize their geological setting, assess potential mechanisms for their formation and destruction, and gain insight into the processes affecting the Ceres surface and near-surface. Faculae were found to occur in four distinct geological settings, associated predominantly with impact craters: (1) crater pits, peaks, or floor fractures (floor faculae), (2) crater rims or walls (rim/wall faculae), (3) bright ejecta blankets, and (4) the mountain Ahuna Mons. Floor faculae were identified in eight large, deep, and geologically young (asteroid-derived model (ADM) ages of < 420 ± 60 Ma) craters: Occator, Haulani, Dantu, Ikapati, Urvara, Gaue, Ernutet, and Azacca. The geometry and geomorphic features of the eight craters with floor faculae are consistent with facula formation via impact-induced heating and upwelling of volatile-rich materials, upwelling/excavation of heterogeneously distributed subsurface brines or their precipitation products, or a combination of both processes. Rim/wall faculae and bright ejecta occur in and around hundreds of relatively young craters of all sizes, and the geometry of exposures is consistent with facula formation via the excavation of subsurface bright material, possibly from floor faculae that were previously emplaced and buried. A negative correlation between rim/wall facula albedo and crater age indicates that faculae darken over time. Models using the Ceres crater production function suggest initial production or exposure of faculae by large impacts, subsequent dissemination of facula materials to form additional small faculae, and then burial by impact-induced lateral mixing, which destroys faculae over timescales of less than 1.25 Gyr. Cumulatively, these models and the observation of faculae limited to geologically young craters indicate relatively modern formation or exposure of faculae, indicating that Ceres' surface remains active and that the near surface may support brines in the present day.

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Space weathering on airless bodies

Cited by 382 publications

References 108 publications

MGS‐TES Spectra Suggest a Basaltic Component in the Regolith of Phobos

MGS‐TES Spectra Suggest a Basaltic Component in the Regolith of Phobos

A Low O/Si Ratio on the Surface of Mercury: Evidence for Silicon Smelting?

The Formation and Evolution of Bright Spots on Ceres

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