ABSTRACT: Understanding the history of impact crater modification and alteration
can provide insights into planet scale processes that have occurred
throughout Martian history. We have identified a unique class of Martian
craters with flat, high thermal inertia floors, mafic mineralogies, and
degraded morphologies. By using physical material properties in
combination with morphologic and mineralogical data, it is possible to
constrain the formation and modification history of these craters and
better understand the crater modification processes, including
post-impact volcanism, chemical weathering and hydrothermal alteration.
This class of crater is prevalent throughout the southern highlands of
Mars. The craters studied have degraded walls and rims, no central peak,
no clearly visible ejecta deposits, an average diameter of ~52km
(ranging in size from 18.5km to 179km), and occur almost exclusively in
the southern highlands indicating an old formation age. The thermal
inertia values derived from Thermal Emission Imaging System (THEMIS)
measurements of crater floors are consistent with competent rocky
material, while the walls and surrounding plains are composed of a less
cohesive material. We have used THEMIS, Compact Reconnaissance Imaging
Spectrometer for Mars (CRISM), and Thermal Emission Spectrometer (TES)
data to constrain the compositional variability of ~60 sites with the
highest thermal inertia values. In general, the crater floors have
higher abundances of mafic minerals (e.g. pyroxenes and olivine), while
the surrounding plains have lower abundances of mafic minerals but show
an increase in high-Si phase abundance. The composition, morphology, and
distribution suggest that old, flat floored craters were resurfaced by a
post-impact process that resulted in material significantly more mafic
than the surrounding terrain. A possible formation mechanism may be
related to inflationary volcanism associated with the impact [Schultz,
1976]. In this model, during the impact event, the crust is fractured
providing a conduit for magma to erupt onto the surface and infill the
original crater floor. The source of this magma is not well constrained
and may be related to the unloading of the early Martian mantle and
crust, resulting in partial melting of the underlying material. The
mineralogy of these materials is consistent with a picritic basalt and
indicates a primitive magma source, such as the Martian mantle. We have
identified and characterized a unique class of Martian craters that has
gone previously unstudied. If the distribution of this crater type is
considered and the proposed model is correct, it is likely that
inflationary volcanism is an important widespread process on Mars that
has gone previously undocumented. This process could be responsible for
extended periods of hydrothermal activity, a source of energy for
altering materials, and may indicate high crustal heat flow early in
Mars history. Schultz, P. H. (1976), Floor-fractured lunar craters,
Earth, Moon, and Planets, 15(3).
AGU Fall Meeting Abstracts. 11/2010; -1:1531.
ABSTRACT: Global acquisition of infrared spectra and high-resolution visible and infrared imagery has enabled the placement of compositional information within stratigraphic and geologic context. Mare Serpentis, a low albedo region located northwest of Hellas Basin, is rich in spectral and thermophysical diversity and host to numerous isolated exposures of in situ rocky material. Most martian surfaces are dominated by fine-grained particulate materials that bear an uncertain compositional and spatial relationship to their source. Thus location and characterization of in situ rock exposures is important for understanding the origin of highland materials and the processes which have modified those materials. Using spectral, thermophysical and morphologic information, we assess the local and regional stratigraphy of the Mare Serpentis surface in an effort to reconstruct the geologic history of the region. The martian highlands in Mare Serpentis are dominated by two interspersed surface units, which have distinct compositional and thermophysical properties: (1) rock-dominated surfaces relatively enriched in olivine and pyroxene, and depleted in high-silica phases, and (2) sediment or indurated material depleted in olivine and pyroxene, with relatively higher abundance of high-silica phases. This is a major, previously unrecognized trend which appears to be pervasive in the Mare Serpentis region and possibly in other highland areas. The detailed observations have led us to form two hypotheses for the relationship between these two units: either (1) they are related through a widespread mechanical and/or chemical alteration process, where less-mafic plains materials are derived from the mafic bedrock, but have been compositionally altered in the process of regolith formation, or (2) they are stratigraphically distinct units representing separate episodes of upper crust formation. Existing observations suggest that the second scenario is more likely. In this scenario, plains materials represent older, degraded, and possibly altered, "basement" rock, whereas the rocky exposures represent later additions to the crust and are probably volcanic in origin. These hypotheses should be further testable with decimeter-resolution imagery and meter-resolution short wavelength infrared spectra.
Icarus 01/2009; 200:446-462. · 3.38 Impact Factor
ABSTRACT: Chlorides commonly precipitate during the evaporation of surface water or groundwater and during volcanic outgassing. Spectrally distinct surface deposits consistent with chloride-bearing materials have been identified and mapped using data from the 2001 Mars Odyssey Thermal Emission Imaging System. These deposits are found throughout regions of low albedo in the southern highlands of Mars. Geomorphologic evidence from orbiting imagery reveals these deposits to be light-toned relative to their surroundings and to be polygonally fractured. The deposits are small (< approximately 25 km(2)) but globally widespread, occurring in middle to late Noachian terrains with a few occurrences in early Hesperian terrains. The identification of chlorides in the ancient southern highlands suggests that near-surface water was available and widespread in early Martian history.
Science 03/2008; 319(5870):1651-4. · 31.20 Impact Factor
ABSTRACT: We have identified and mapped a number of spectrally distinct deposits
(~250) in mid-infrared data acquired by the 2001 Odyssey Thermal
Emission Imaging System (THEMIS). These deposits are interpreted to
contain a chloride salt component based on their spectral signatures in
THEMIS and Mars Global Surveyor Thermal Emission Spectrometer (TES)
data. Thermal inertia derived from THEMIS nighttime observations,
indicate that the chloride-bearing materials are possibly cemented or
indurated. Individually, most chloride-bearing deposits are small in
area (<~25 km2), but they are globally widespread, as we have
identified them throughout low albedo regions of the southern highlands
of Mars. These regions correspond to mid-to-late Noachian terrains, as
well as early Hesperian ridged plains units. The chloride-bearing
deposits commonly occur in topographic lows relative to the surrounding
terrain, and some appear to follow channel-like outlines. Less
typically we observe them in small crater floors. Images acquired by the
Mars Orbiter Camera (MOC) and the High Resolution Imaging Science
Experiment (HiRISE) indicate geomorphology consistent with formation in
an evaporitic environment. HiRISE imagery (at 25.3 cm/pixel) over a
large exposure in Terra Sirenum shows the chloride-bearing materials to
be light-toned and highly fractured. The fracturing is sub-polygonal and
is similar to desiccation cracks in evaporitic environments. Cross
cutting relationships indicate that the chloride-bearing materials are
older than the surrounding basaltic materials, and commonly appear to
have been exposed by erosion. In the HiRISE image we observe additional
occurrences of chloride materials within the regional terrain,
indicating that the chloride deposits are likely more extensive than
what is discernable at THEMIS IR scales. The origin and diagenesis of
each chloride deposit is likely complex, however it is probable that
water played a role in each instance, either via direct precipitation of
ground water or standing water, or via efflorescence from evaporative
pumping, volcanic out gassing, or atmospheric-surface interactions. Many
chloride salts are extremely hygroscopic and can be further modified by
fluctuations in humidity. Identification of a hygroscopic chloride could
indicate brine activity subsequent to initial deposition. The
identification of another water-related material in the ancient cratered
terrain of Mars is further evidence that Mars once had a hydrologic
cycle (albeit possibly short in duration) that was more active than at
AGU Fall Meeting Abstracts. 11/2007; -1:1563.
ABSTRACT: Compositional mapping of Mars at the 100-metre scale with the Mars Odyssey Thermal Emission Imaging System (THEMIS) has revealed a wide diversity of igneous materials. Volcanic evolution produced compositions from low-silica basalts to high-silica dacite in the Syrtis Major caldera. The existence of dacite demonstrates that highly evolved lavas have been produced, at least locally, by magma evolution through fractional crystallization. Olivine basalts are observed on crater floors and in layers exposed in canyon walls up to 4.5 km beneath the surface. This vertical distribution suggests that olivine-rich lavas were emplaced at various times throughout the formation of the upper crust, with their growing inventory suggesting that such ultramafic (picritic) basalts may be relatively common. Quartz-bearing granitoid rocks have also been discovered, demonstrating that extreme differentiation has occurred. These observations show that the martian crust, while dominated by basalt, contains a diversity of igneous materials whose range in composition from picritic basalts to granitoids rivals that found on the Earth.
Nature 07/2005; 436(7050):504-509. · 36.28 Impact Factor
ABSTRACT: The Miniature Thermal Emission Spectrometer (Mini-TES) has provided remote measurements of mineralogy, thermophysical properties, and atmospheric temperature profile and composition of the outcrops, rocks, spherules, and soils surrounding the Spirit and Opportunity Rovers. The mineralogy of volcanic rocks provides insights into the composition of the source regions and the nature of martian igneous processes. Carbonates, sulfates, evaporites, and oxides provide information on the role of water in the surface evolution. Oxides, such as crystalline hematite, provide insight into aqueous weathering processes, as would the occurrence of clay minerals and other weathering products. Diurnal temperature measurements can be used to determine particle size and search for the effects of sub-surface layering, which in turn provide clues to the origin of surficial materials through rock disintegration, aeolian transport, atmospheric fallout, or induration. In addition to studying the surface properties, Mini-TES spectra have also been used to determine the temperature profile in the lower boundary layer, providing evidence for convective activity, and have determined the seasonal trends in atmospheric temperature and dust and cloud opacity.
ABSTRACT: The Miniature Thermal Emission Spectrometer (Mini-TES) on Opportunity investigated the mineral abundances and compositions of outcrops, rocks, and soils at Meridiani Planum. Coarse crystalline hematite and olivine-rich basaltic sands were observed as predicted from orbital TES spectroscopy. Outcrops of aqueous origin are composed of 15 to 35% by volume magnesium and calcium sulfates [a high-silica component modeled as a combination of glass, feldspar, and sheet silicates (approximately 20 to 30%)], and hematite; only minor jarosite is identified in Mini-TES spectra. Mini-TES spectra show only a hematite signature in the millimeter-sized spherules. Basaltic materials have more plagioclase than pyroxene, contain olivine, and are similar in inferred mineral composition to basalt mapped from orbit. Bounce rock is dominated by clinopyroxene and is close in inferred mineral composition to the basaltic martian meteorites. Bright wind streak material matches global dust. Waterlain rocks covered by unaltered basaltic sands suggest a change from an aqueous environment to one dominated by physical weathering.
Science 01/2005; 306(5702):1733-9. · 31.20 Impact Factor
ABSTRACT: An abundance of impact craters on the martian surface and shock effects
in the martian meteorites indicate that the surface of Mars has been
shocked. The thermal infrared (TIR) spectra of plagioclase feldspars
experimentally shocked to various pressures have enabled the amount of
shock to be correlated with changes in the TIR spectra [Johnson et al.,
2002, 2003]. With these, estimates on the amount of shocked plagioclase
feldspar on the martian surface has been investigated [Johnson et al.,
in press]. However, in relation to the use of shocked plagioclase
feldspars as end-members for the deconvolution of remote TIR data,
similar work need to be performed on the laboratory spectra of shocked
rocks and subsequent deconvolutions with these shocked mineral
end-members. In this work, laboratory TIR spectra of a shocked
terrestrial basalt and it unshocked counterpart are deconvolved and
compared to assess the possibility of removing the spectral contribution
of shocked plagioclase feldspar from a shocked martian basalt spectrum.
It has been suggested that the modal abundances of martian meteorite Los
Angeles [Rubin et al., 2000] are similar to mineral abundances derived
from the deconvolution of Thermal Emission Spectrometer (TES) Surface
Type 1 (ST1) [Bandfield, 2002]. TIR spectra of shocked basalt from Lonar
Crater, India were collected and deconvolved with an end-member library
containing experimentally shocked calcic plagioclase feldspars [Johnson
et al., 2002]. The deconvolution-derived mineral abundances were
compared to those from deconvolutions of unshocked basalt, and it was
determined that the spectrum of the original, unshocked bulk rock could
be replicated by removing from the spectrum of a shocked basalt the
shocked plagioclase end-member spectrum (scaled by its abundance). The
same methodology was performed on another shocked basalt, martian
meteorite Los Angeles. The TIR spectra of Los Angeles was deconvolved
with an end-member library containing shocked plagioclase feldspar
(An75), revealing an abundance of maskelynite (~46%) that closely
matches modal abundances from petrographic studies (~45%) [Rubin et al.,
2000]. TIR spectra of shocked intermediate calcic plagioclase feldspars
such as those found in Los Angeles (An56-38) do not exist and therefore
are not contained within the spectral library used here. A mean
percentage of 46% of the shocked plagioclase feldspar end-member was
removed from the bulk rock spectra of Los Angeles and replaced with
unshocked labradorite. Similar to the Lonar Crater basalts, this should
recreate the spectra of the pre-impact, unshocked basalt. This
end-member replacement results in a TIR spectrum of a basalt with a
Christiansen feature moved to lower wavenumbers, agreeing with previous
work that suggested the position of this feature varies with the amount
of shock [Johnson et al., 2002]. The new "unshocked" Los Angeles TIR
spectrum is not an exact match for ST1, but it is more similar to TES
spectra than a shocked Los Angeles spectrum is. Whereas laboratory TIR
spectra of shergottites provide poor matches to orbital TES data
[Hamilton et al., 2003], using this unshocked basalt spectrum as an
end-member might provide additional constraints on the source region of
Los Angeles. Further, it is suggested here that TIR spectra be acquired
for various experimentally shocked end members of plagioclase feldspar
solid solution series for better deconvolutions of shocked rocks.
AGU Fall Meeting Abstracts. 11/2004; -1:0954.
ABSTRACT: The Miniature Thermal Emission Spectrometer (Mini-TES) on Spirit has studied the mineralogy and thermophysical properties at Gusev crater. Undisturbed soil spectra show evidence for minor carbonates and bound water. Rocks are olivinerich basalts with varying degrees of dust and other coatings. Dark-toned soils observed on disturbed surfaces may be derived from rocks and have derived mineralogy (+/-5 to 10%) of 45% pyroxene (20% Ca-rich pyroxene and 25% pigeonite), 40% sodic to intermediate plagioclase, and 15% olivine (forsterite 45% +/-5 to 10). Two spectrally distinct coatings are observed on rocks, a possible indicator of the interaction of water, rock, and airfall dust. Diurnal temperature data indicate particle sizes from 40 to 80 microm in hollows to approximately 0.5 to 3 mm in soils.
Science 09/2004; 305(5685):837-42. · 31.20 Impact Factor
ABSTRACT: Mini-TES observations have been acquired of both the Gusev and Meridiani
landing sites. The most recent results from the surface mineralogy,
thermophysical properties, and atmospheric observations will be
ABSTRACT: We present results from the retrieval of atmospheric dust and water-ice
optical depth from THEMIS infrared images. Data from THEMIS complements
the concurrent MGS TES data by offering a later local time and much
higher spatial resolution.
ABSTRACT: The objective of this study was to identify and map possible source
regions for all 5 known martian meteorite lithologies (basalt,
lherzolite, clinopyroxenite, orthopyroxenite, and dunite) using data
from the Mars Global Surveyor Thermal Emission Spectrometer (MGS TES).
We deconvolved the TES data set using laboratory spectra of 6 martian
meteorites (Los Angeles, Zagami, ALH A77005, Nakhla, ALH 84001, and
Chassigny) as end members, along with atmospheric and surface spectra
previously derived from TES data. Global maps (16 pixels/degree) of the
distribution of each meteorite end member show that meteorite-like
compositions are not present at or above TES detectability limits over
most of the planet's dust-free regions. However, we have confidently
identified local-scale (100s1000s km2) concentrations of olivine-
and orthopyroxene-bearing materials similar to ALH A77005, Chassigny,
and ALH 84001 in Nili Fossae, in and near Ganges Chasma, in the Argyre
and Hellas basin rims, and in Eos Chasma. Nakhla-like materials are
identified near the detection limit throughout the eastern Valles
Marineris region and portions of Syrtis Major. Basaltic shergottites
were not detected in any spatially coherent areas at the scale of this
study. Martian meteorite-like lithologies represent only a minor portion
of the dust-free surface and, thus, are not representative of the bulk
composition of the ancient crust. Meteorite-like spectral signatures
identified above TES detectability limits in more spatially restricted
areas (<tens of km) are targets of ongoing analysis.
Meteoritics & planetary science 05/2003; 38:871-885. · 2.72 Impact Factor
ABSTRACT: Scattering by atmospheric aerosols can contribute a substantial fraction of the visible-light radiance observed in any remote sensing of Mars. Our objective is to develop techniques to separate this aerosol component from the surface-reflectance component in Mars Odyssey's THEMIS Visible Imaging Subsystem (THEMIS-VIS) dataset. The primary purpose of this study is the production of accurate surface reflectance data in order to allow for reliable color and mineralogical unit mapping. The second principal goal is to study the feasibility of using VIS measurements to derive quantitative information about ice and dust aerosol properties such as particle size and optical depth.
ABSTRACT: Methods refined and adapted from the TES investigation are used to develop a surface-atmosphere separation strategy for THEMIS image analysis and atmospheric temperature and opacity retrievals. Additional information is contained in the original extended abstract.
ABSTRACT: A gradation of surface units represents either (1) an influx of basaltic sediment from southern highlands, deposited on andesitic volcanics, or (2) incompletely weathered basalt marking the geographic extent of submarine alteration of basaltic crust. Additional information is contained in the original extended abstract.
ABSTRACT: Basalt and andesite surface compositions are identified within individual low albedo intracrater features and adjacent dark wind streaks. High resolution mapping of compositional heterogeneities may help constrain origin hypotheses for these features. Additional information is contained in the original extended abstract.
ABSTRACT: The Thermal Emission Spectrometer (TES) instrument is a Fourier transform Michelson interferometer operating with 10 or 5 cm(exp -1) sampling in the thermal infrared spectral region from 1700 to 200 cm(exp -1) (-6 to 50 micrometers) where virtually all minerals have characteristic fundamental vibrational absorption bands. The TES data used in this paper are among the 6 x 10(exp 7) spectra collected during the early mapping phase of the Mars Global Surveyor (MGS) mission from southern hemisphere winter to early summer (aerocentric longitude, L(sub s), 107 deg to 297 deg. The methodology for separating the surface and atmospheric components of the radiance from Mars, which allows detailed analysis and interpretation of surface mineralogy, is described in previous paper. Additional information is contained in original extended abstract.
Meteoritics and Planetary Science Supplement. 06/2000; 35:171.
ABSTRACT: The Thermal Emission Spectrometer on board the Mars Global Surveyor has observed "White Rock" and the data do not indicate the presence of evaporite minerals. We suggest it is a deposit of compacted or weakly cemented aeolian sediment.
ABSTRACT: Successful operation of the Mars Global Surveyor spacecraft, beginning in September 1997, has permitted extensive infrared observations of condensation clouds during the martian southern summer and fall seasons (184 deg less than L(sub s) less than 28 deg). Initially, thin (normal optical depth less than 0.06 at 825/ cm) ice clouds and hazes were widespread, showing a latitudinal gradient. With the onset of a regional dust storm at L(sub s) = 224 deg, ice clouds essentially vanished in the southern hemisphere, to reappear gradually after the decay of the storm. The thickest clouds (optical depth approx. 0.6) were associated with major volcanic features. At L(exp s) = 318 deg, the cloud at Ascraeus Mons was observed to disappear between 21:30 and 09:30, consistent with historically recorded diurnal behavior for clouds of this type. Limb observations showed extended optically thin (depth less than 0.04) stratiform clouds at altitudes up to 55 km. A water ice haze was present in the north polar night at altitudes up to 40 km; this probably provided heterogeneous nucleation sites for the formation of CO2 clouds at altitudes below the 1 mbar pressure level, where atmospheric temperatures dropped to the condensation point of CO2.