¹Elyse Allender, ¹Tomasz F. Stepinski
Icarus (in Press) Link to Article [http://dx.doi.org/10.1016/j.icarus.2016.08.022]
¹Space Informatics Lab, University of Cincinnati, Cincinnati, OH 45221-0131, USA
Copyright Elsevier

Martian spectroscopic and mineralogical analysis is usually performed using Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) browse products – false color images which show the spatial distribution of absorption features at key wavelengths. This manual, time-consuming method is ill-suited for exploratory surveys of a large number of images – for such surveys an automatic methodology is needed. In this paper we propose a method for exploratory but fully automatic mineralogical mapping of CRISM images. In our approach pixels are characterized by vectors of CRISM summary product values instead of spectral functions, and mineralogical units are discovered using a clustering principle. Moreover, the rare class discovery algorithm DEMUD is used in place of a standard clustering algorithm to identify mineralogical units – enabling the identification of only scientifically interesting, possibly rare, mineralogical deposits. The method outputs a map for each site showing the spatial distribution of mineralogical units – areas characterized by similar mineralogy. It also provides, without using a spectral library, semantic labels for each unit. We envision our method as a focus-of-attention tool to facilitate fast exploratory surveys of a large number of images. An analyst needs only to examine manually regions within an image where our pipeline indicates the existence of mineral units of interest. In this paper the method for our computational pipeline is described in detail and its performance is evaluated using a sample of 20 CRISM images – the mineralogical content of which is known from manual analysis. We find that our pipeline identifies most deposits found through manual analysis as well as some additional deposits which were not targeted by those analyses. Overall, we conclude that our fully automatic mineralogical mapper works well for exploratory purposes. Thus, it adds a new, valuable functionality to existing tools for CRISM imagery analysis.

¹N.G. Rudraswami, ¹M. Shyam Prasad, ²R.H. Jones, ³K. Nagashima
Geochimica et Cosmochimica Acta (in Press)   Link to Article [http://dx.doi.org/10.1016/j.gca.2016.08.024]
¹National Institute of Oceanography (Council of Scientific and Industrial Research), Dona Paula, Goa 403004, India
²School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
³Hawaii Institute of Geophysics and Planetology, University of Hawaii at Manoa, 1680 East-West-Road, Honolulu, HI 96822, USA
Copyright Elsevier

Cosmic spherules collected from deep sea sediments of the Indian Ocean having different textures such as scoriaceous (4), relict-bearing (16), porphyritic (35) and barred olivine (2) were investigated for petrography, as well as high precision oxygen isotopic studies on olivine grains using secondary ion mass spectrometry (SIMS). The oxide FeO/MgO ratios of large olivines (> 20μm) in cosmic spherules have low values similar to those seen in the olivines of carbonaceous chondrite chondrules, rather than matching the compositions of matrix. The oxygen isotope compositions of olivines in cosmic spherules have a wide range of δ18O, δ17O and Δ17O values as follows: −9 to 40‰, −13 to 22‰ and -11 to 6‰. Our results suggest that the oxygen isotope compositions of the scoriaceous, relict-bearing, porphyritic and barred spherules show provenance related to the carbonaceous (CM, CV, CO and CR) chondrites. The different types of spherules that has experienced varied atmospheric heating during entry has not significantly altered the Δ17O values. However, one of the relict-bearing spherules with a large relict grain has Δ17O = 5.7‰, suggesting that it is derived from 16O-poor material that is not recognized in the meteorite record. A majority of the spherules have Δ17O ranging from −4 to −2‰, similar to values in chondrules from carbonaceous chondrites, signifying that chondrules of carbonaceous chondrites are the major contributors to the flux of micrometeorites, with an insignificant fraction derived from ordinary chondrites. Furthermore, barred spherule data shows that during atmospheric entry an increase in ∼10‰ of δ18O value surges Δ17O value by ∼1‰.