Local and regional lunar regolith characteristics at Reiner Gamma Formation: Optical and spectroscopic properties from Clementine and Earth‐based data

Abstract

Abstract. A detailed remote sensing survey of the Reiner Gamma Formation (RGF) region by means of Earth-based telescopic and Clementine multispectral imaging has been made in the UVvisible-near-infrared domain. The spectral mixture analysis reveals the existence of three basic end-members relevant for modeling the observed spectral variations in the RGF vicinity. These are MB (mare background), SWS (southwest swirl), and RGS (Reiner Gamma soil). The first two components exhibit spectral characteristics consistent with a prevailing contribution of mature mare soils for the surroundings (MB) and of immature mare crater-like soils (RGS) at RGF. The third intermediate-albedo component (SWS) has general characteristics of a mature mare soil, but with a redder continuum slope. The reported observation can be modeled by a mechanism which would remove the finest fraction in the soil (particle diameter < 45 [tm) at RGF and redistribute it in the vicinity with a laterally variable proportion and local accumulations such as at SWS site. According to the available set of in situ data documenting variations in the chemical composition, in the distribution of particle sizes, and in the degree of maturity with depth in the mare regolith, the characteristics depicted at RGF are those of a subsurface soil layer from a depth of the order of 0.3 -0.8 m. In our view, the simplest way to account for the whole body of information available from the present work lies in the proposition that in the area of RGF the uppermost layer of the regolith has been optically and mechanically modified by a process involving the fall of fragments of a low-density cometary nucleus previously disrupted by tidal interaction in the Earth-Moon system. We recognize, however, that in the present state of knowledge, one cannot rule out the hypothesized existence of a zone of seismically modified terrain peripheral to the Imbrium or Orientale basins just beneath the mare surface that would be the actual source of the RGF magnetic anomaly.

Lunar Clinopyroxene and Plagioclase: Surface Distribution and Composition

“…The same can be said about the swirl Reiner Gamma, where some excess of CPx is observed in comparison with the surrounding mare regions. This agrees well with the age of the swirl: it is one of the youngest formations on the lunar surface (Pinet et al, 2000;Starukhina and Shkuratov, 2004). The soil in the South Pole-Aitken basin (the lower corners of the mosaic) contains a lot of CPx.…”

Formation of lunar swirls by magnetic field standoff of the solar wind

“…The mid-infrared Diviner data presented here place tight constraints on the swirl formation process and must be accounted for by any proposed swirl formation mechanism. The proposed feldspathic dust lofting 7 , meteoroid/comet swarm [4][5][6] and hybrid 41 swirl formation mechanisms would likely result in thermophysical and spectral properties that are inconsistent with the Diviner measurements. The proposed dust lofting and hybrid processes cannot account for the observed CF shift in Diviner data while the meteoroid/comet swarm and hybrid processes cause regolith disturbance that would result in a substantial thermal anomaly in the night-time Diviner data.…”

“…Discussion Previous spectroscopic observations of the swirls at visible and near-infrared wavelengths have been used to argue for the solar wind standoff model 3,14,24 , the micrometeoroid/comet swarm model [4][5][6] or the feldspathic dust pile model. More recently, M 3 spectra have been used to propose a hybrid model for swirl formation that invokes both regolith disturbance and dust lofting 41 .…”

“…Intermediate morphologies occur near Airy and Gerasimovich craters 2 . Several swirl formation mechanisms have been proposed, including (1) solar wind standoff due to the presence of local magnetic fields, preventing solar wind sputtering and implantation, nanophase iron formation, and the resulting surface darkening associated with space weathering 3 , (2) recent comet impacts or micrometeoroid swarms that scoured the lunar surface, leaving a fine-gained, unweathered material and possibly imparting a remnant magnetization [4][5][6] , and (3) electrostatic levitation and deposition of high-albedo, fine-grained, feldsparenriched dust 7 . The association of all swirls with magnetic field anomalies of varying strength [8][9][10] has driven the development of each of these hypotheses.…”

3d Pic Simulations of Collisionless Shocks at Lunar Magnetic Anomalies and Their Role in Forming Lunar Swirls

“…The features are distinctive due to their fluid or wispy structure that is unlike either craters or impact ejecta. Their form has been determined to be unrelated to geographical topography and appears to overprint on both mountainous and plateau terrains (Bell & Hawke 1987;Pinet et al 2000;Blewett et al 2007). Although not all magnetic field anomalies have identifiable lunar swirl patterns, no lunar swirls have been found that are not coincident with similarly sized areas of anomalous crustal magnetic field (Blewett et al 2007;Kramer et al 2011a).…”