Mercury's hollows: Constraints on formation and composition from analysis of geological setting and spectral reflectance. Issue 5 (22nd May 2013)

• Record Type: Journal Article
• Authors: Blewett, David T.; Vaughan, William M.; Xiao, Zhiyong; Chabot, Nancy L.; Denevi, Brett W.; Ernst, Carolyn M.; Helbert, Jörn; D'Amore, Mario; Maturilli, Alessandro; Head, James W.; Solomon, Sean C.
• Is Part Of: Journal of geophysical research. Volume 118:Issue 5(2014:May)
• Page Start: 1013
• Page End: 1032
• Publication Date: 2013-05-22
• Subjects: Mercury (planet) -- hollows -- volatiles -- spectral reflectance -- MESSENGER -- sulfides; Planets -- Periodicals; Geophysics -- Periodicals; 559.9
• DOI: 10.1029/2012JE004174
• Languages: English
• ISSNs: 2169-9097

Abstract

Abstract: [1] 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. Key Points: Hollows are shallow depressions with relatively high reflectance and blue color Hollows are found in units with reflectance lower than the global average Sulfide minerals could contribute to Mercury's spectral characteristics