Michael D. Kraft

• Arizona State University

The mound of material in Gale Crater formed by tectonic uplift rather than sedimentary deposition and erosion.

Models of Thermal Emission Spectrometer (TES) data suggest that poorly-crystalline weathering products allophane and aluminosilicate gel occur in several low-albedo regions of Mars. The presence of allophane in TES models indicates that the martian surface experienced low-temperature chemical weathering at low water-to-rock ratios and mildly acidic...

We have identified several exposed dikes in Thaumasia Planum Mars using THEMIS, CTX, HiRISE and CRISM data. These dikes extend from tens to ∼100 kilometers in length with average widths of ∼50 m. They display classic ‘en echelon’ patterns while cross-cutting preexisting geologic features, including extensive wrinkle ridges. Both the dikes and assoc...

The detection of clay minerals and other secondary silicates in light-toned surfaces at Mawrth Vallis from near-infrared (NIR) spectroscopy indicates that this surface experienced aqueous alteration. The types of alteration products can help constrain past aqueous environments to assess habitability. NIR data from OMEGA and CRISM show a Fe/Mg-smect...

Nanocrystalline alteration products form in a range of soil and regolith weathering environments on Earth. In some weathering systems, poorly crystalline aluminosilicates such as allophane are distributed heterogeneously, as a function of depth in a vertical weathering profile or as a function of micro-environmental factors. Both of these factors c...

Models of TES and Mini-TES spectra with libraries containing allophanes and gel suggest these weathering products occur in several regions of Mars. The presence of allophane indicates that weathering has proceeded under moderate pH conditions.

Allophane is an alteration product of volcanic glass and a clay mineral precursor that is commonly found in basaltic soils on Earth. It is a poorly-crystalline or amorphous, hydrous aluminosilicate with Si/Al ratios ranging from ~0.5-1 [Wada, 1989]. Analyses of thermal infrared (TIR) spectra of the Martian surface from TES show high-silica phases a...

It has been suggested that allophane or related poorly crystalline aluminosilicates are present on Mars, and that they comprise the high-silica phase detected by the Thermal Emission Spectrometer (TES) in Surface Type 2 materials (Kraft et al., 2003; Michalski et al., 2005). Using new laboratory spectra of allophanic materials, we (Rampe et al., th...

Known compositional differences in high-silica materials of Acidalia Planitia are explored in detail with THEMIS data. They are closely correlated to periglacial features, suggesting aqueous alteration in icy soil environments in northern Acidalia.

We synthesized allophane, a terrestrial aqueous alteration product, and measured a thermal IR emission spectrum for the public spectral library. The use of this spectrum in martian spectral models can help constrain chemical alteration environments.

Subzero to low temperature acid-weathering of olivine is explored experimentally, taking into account pH, temperature, and dissolution effects. The findings are applied to possible acid-weathering on Mars in its often very low temperatures.

Introduction. A variety of secondary silicates have been identified on Mars using Vis-NIR spectroscopic data from the Observatoire pour la Mineralogie, l'Eau, les Glaces et l'Activite (OMEGA) on Mars Express and the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on Mars Reconnaissance Orbiter, including smectite, chlorite, kaolinite,...

While much attention has been given to chemical alteration and the state of water on early Mars, it remains important to understand aqueous processes throughout Martian history, including the recent geologic past. It has been suggested that the Amazonian was marked primarily by anhydrous, oxidative weathering because Amazonian surfaces, such as the...

We compare measured chemical compositions and weathering trends of terrestrial basalts to those derived from TIR spectral models. Deriving true chemistry and weathering trends from TIR models of weathered surfaces on Mars may be impractical.

Features of mid-infrared spectra from a large suite of weathered basalt can be indexed to distinguish weathered and unweathered surfaces, suggesting that weathering can be studied on Mars without using spectral modeling methods.

Interpretations of visible/near-infrared (VNIR) spectral data from OMEGA and CRISM identify a variety of phyllosilicate minerals in Noachian terrains on Mars, including Fe/Mg smectites, montmorillonite, kaolinite, muscovite or illite, and chlorite [Bibring et al., 2005 and 2006, Poulet et al., 2006, Wray et al., 2008, Mustard et al., 2008, and Ehlm...

We examine the possibility that crystalline hematite (α-Fe2O3) deposits on Mars were derived from the precursor iron oxyhydroxide minerals akaganéite (β-FeOOH) or lepidocrocite (γ-FeOOH) and compare them to an earlier study of goethite (α-FeOOH) and magnetite (Fe3O4) precursors. Both the mid-infrared and visible/near infrared spectra of hematite ar...

Mineralogical and geomorphological data from higher latitude regions of Mars are consistent with aqueous weathering occurring in ice-rich soils.

We investigate the effects of chemical weathering on the ability to detect igneous minerals in thermal infrared spectral models of physical mixtures. Weathering products affect modeled relative abundances of plagioclase, pyroxene, and olivine.

The Martian surface may be chemically altered on regional scales. Thermal infrared (TIR) spectroscopy and spectral deconvolution are commonly used to determine mineral abundances of the surface. Chemically weathered surfaces tend to be intimate mixtures of igneous minerals and fine-grained alteration products. To understand how alteration products...

Infrared spectroscopy is a critical tool for Martian mineralogy. Because it is crucial to evaluate the history of water on Mars, mineralogical study of weathering and alteration is among the most important topics of Mars spectroscopy. The state of alteration of the Martian surface is evaluated by the presence or absence of alteration phases and the...

We examine the thermal transformations of lepidocrocite and akaganeite to hematite to determine if these minerals are viable precursors to Martian crystalline hematite. This is an extension of the work of Glotch et al. (2004) who demonstrated that precursor mineralogy and temperature of hematite formation have a strong influence on the infrared emi...

Silica coatings on basaltic materials can explain thermal and near-infrared observations of the northern plains of Mars. Coatings could form in recent soil environments.

We investigate the effects of small amounts of secondary silicates on TIR spectroscopy and spectral models of mixtures of primary and secondary phases. Modeled primary mineral abundances are dependent on the secondary phase present in the mixtures.

Modeled mineralogy of TIR spectra of physical mixtures containing secondary silicates show secondary silicates affect modeled primary mineralogy and cause identification of primary glass. These results support Surface Type 2 as a weathered basalt.

Basalt coated by hydrous silica shows large effects on thermal-IR laboratory spectra but little effect on near-IR spectra. TES type 2 surfaces are consistent with such coatings, perhaps indicating liquid water on Mars has been recent and widespread.

Recent scientific investigations of Mars, including those conducted by TES, OMEGA, and the MER lander missions, have expanded the discussion about aqueous alteration on Mars. Results from these missions indicate that the styles and/or intensity of water-rock interactions on Mars have changed over time, and they provide evidence for geographical dif...

Spectral data suggest that the Martian surface may be chemically altered. However, TES data show evidence for abundant primary glass, and Mini-TES data from MER Spirit in the Columbia Hills identify primary basaltic glass in rocks that are believed to be altered (Haskin et al., 2005, Ming et al., 2006, Wang et al., 2006). Debate over whether the pr...

We investigated the mineralogy of basalt weathering rinds and fresh basaltic rocks using visible/near-infrared (VNIR) (λ = 0.4–2.5 μm) and thermal emission (λ = 6–30 μm) spectroscopy to 1) constrain the effects of chemical weathering on rock spectra, and 2) further understand the context of infrared spectra of Mars, which may contain evidence for w...

To understand the aqueous history of Mars, it is critical to constrain the alteration mineralogy of the Martian surface. Previously published analyses of thermal infrared (λ = 6-25 μm) remote sensing data of Mars suggest that dark regions have ~15-20% clay minerals. However, near-infrared (λ = 1-3 μm) spectral results generally do not identify wide...

Mineral spectra from lightly weathered basalt surfaces mix nonlinearly, making it challenging to model primary and secondary mineralogy.

We are performing mineral mixing experiments to better understand the effects of thermal emission spectral mixing for spectra from weathered surfaces.

Thermal emission spectroscopy has provided crucial information about the mineralogical composition of the Martian surface. Portions of that surface may be chemically weathered, and it is, therefore, important that the influence of chemical weathering on thermal infrared observations be recognized and understood. To this end, we have examined a suit...

On Earth, subaerially exposed basaltic rocks (from arid-to-tropical regions) develop weathering rinds and rock coatings that affect spectroscopic measurements of their natural surfaces. Similarly, basaltic rocks and basaltic soil particles on Mars may have rinds and coatings that are spectroscopically observable. Thermal emission spectroscopy, beca...

The Thermal Emission Spectrometer (TES) has observed a high-silica material in the dark regions of Mars that is spectrally similar to obsidian glass and may have a volcanic origin. An alternate interpretation is that the spectrally amorphous material consists of clay minerals or some other secondary material, formed by chemical alteration of surfac...

In weathering rinds of crystalline basalts, we find poorly crystalline secondary silicates, similar to palagonites. Small volumes of these products cause rinds to have "glassy" thermal-IR spectra. Similar spectral surfaces on Mars may be altered.

Poorly crystalline silicate alteration products may be widespread on Mars. We discuss spectral evidence for these materials in weathered terrestrial basalts, similarities to spectra of Mars, and the implications for chemical alteration on Mars.

Thermal infrared spectra of some layered materials in Acidalia Planitia suggest a mineralogy dominated by high-silica-poorly crystalline materials, intermediate-composition feldspars, and sulfates. These spectra are similar in shape to the Acidalia Planitia-type global spectral component (ST2) previously identified by Bandfield et al. [2000], but a...

Mineralogy of Natural Basalt Weathering Rinds With Application to Thermal Emission Spectra of Mars M.D. Kraft, J.R. Michalski, T.G. Sharp, (and P.R. Christensen?) Chemically weathered rocks have been suggested to cover a significant portion of the Martian surface based on orbiter observations, and rocks investigated by the Mars Exploration Rover at...

TES surface type-2 spectra of Mars have been interpreted previously as weathered basalt or unweathered andesite. We conclude that evidence for smectite clays from TES is lacking. Silica-rich weathering products are consistent with TES observations.

TES observations of silicic Martian surfaces may result from silica-rich rock coatings. The conditions required to form silica coatings may occur on Mars. Silica coatings would form by chemical weathering of Martian dust under low water conditions.

(1) On Mars, silica derived from chemical weathering could precipitate to coat rocks and particles. We suggest that rock coatings of secondary amorphous silica may account for a widespread Martian surface spectral unit previously modeled as andesite or weathered basalt. In a laboratory study, we investigated the effects of synthetic silica coatings...

Thermal Emission Spectrometer (TES) data have been fundamental to understanding Martian surface mineralogy. These data, however, require careful modeling based on laboratory spectroscopic measurements, and modeling of some minerals for Mars has been equivocal. Due to high degrees of spectral similarity, it is difficult to distinguishing silicate gl...

[1] The possible existence of silica-rich rocks on Mars requires consideration of all of the candidate forms of silica that might exist there. We synthesized coesite and cristobalite, and obtained natural samples of tridymite, opal-A, and opal-CT. The thermal emission spectra of these silica phases were analyzed and related to their crystal structu...

Among the most important discoveries made during the Mars Global Surveyor (MGS) mission was that the rocky materials of Mars are broadly divisible into two distinct rock types. The geological significance of this finding is dependent on the mineralogy of these rock types as well as their geographic and stratigraphic positions. Much work has yet to...

Results from the Thermal Emission Spectrometer (TES) show that Martian dark regions are composed of two distinct components. One is accepted to be basalt. The other is controversial, having been interpreted as andesite/basaltic andesite and as chemically weathered basalt. This second component, referred to here as S2, occurs most prominently in the...

Thermal emission spectra were taken of an oxidized olivine. The oxidized olivine maintains the spectral characteristics of forsteritic olivine. Finding olivine on Mars does not preclude alteration processes from having occurred.

Sand-size particles are considered to exist on the surface of Mars, as indicated by the presence of numerous dunes and duneforms, as well as other evidence.

Ventifacts and rock coatings coexist at the Mars Pathfinder site. Coatings may be salt-cemented, varnish-like, or silica. Experiments show that coatings abrade more easily than rock. The soil layer has deflated. Recent aeolian abrasion is minimal.

Fundamental to the exploration of Mars and other solid planets for astrobiology is the desire to locate sites where rocks have been aqueously altered or where aqueous sediments exist. One material that is common and abundant on Earth, and that is likely to occur in any environment where silicate rocks have interacted with water, is silica. Silica i...