Based on results of the Viking mission, the soil layer of Mars has been thought to be fairly homogeneous and to consist of a mixture of as few as two components, a 'dark gray' basaltic material and a 'bright red' altered material. However, near-infrared reflectance spectra measured recently both telescopically and from spacecraft indicate compositional heterogeneity beyond what can be explained by just two components. In particular, data from the ISM imaging spectrometer, which observed much of the equatorial region at a spatial resolution of approximately 22 km, indicate spatial differences in the presence and abundance of Fe-containing phases, hydroxylated silicates, and H2O. The ISM data was used to define, characterize, and map soil 'units' based on their spectral properties. The spatial distribution of these 'units' were compared to morphologic, visible color, and thermal inertia features recognized in Viking data

Murchie, S.

Mustard, J.

Saylor, R.

English

NASA Technical Reports Server

32 Results from the MSATT Progrom
intermediate values of FeO/(FeO + Fe.,O3) are shown in Figs. I and
2. Their M6ssbauer spectra show more comparable amounts of
hematite and pyroxene than the heavily and slightly oxidized samples.
The reflectivity data for both have a band minimum near 910 nm,
which could result from (1) a composite of hematite (840-870-nm)
and pyroxene (940-rim) bands; (2) a different pyroxene character-
ized by a 910-nm band; (3) a composite band derived from a
pyroxene ferrous band and a pyroxene ferrous-ferric charge transfer
band; and (4) another ferric mineral (e.g., goethite) having a band
in this region. Alternative (4) is excluded by the MOssbauer data
specifically for the case of goethite. None of the other ahematives
can be excluded. However, a pyroxene 910-nm band usually implies
a second band near 1800 nm [13], which we would probably ob-
serve, and [12] did not observe ferrous-ferric charge transfer tran-
sitions in two-band pyroxenes they subjected to thermal oxidation
in air. Thus, there is some evidence to favor the interpretation
involving composite hematite-pyroxene bands. This is particularly
the case for MAN-74-217, where the 750-nm relative reflectivity
maximum and 620- and 520-nm inflections are evidence for a strong
spectral contribution from hematite.
Implications for Interpretation of Martian Spectral Data:
Visible and near-IR martian bright-region spectral data (400 to
-2000 rim) returned from groundbased telescopes and the Phobos-
2 encounter are characterized by a shallow band minimum in the
near-IR whose position varies between approximately 850 and
1000 nm [14,15]. It is reasonable to assign these endmember band
positions to hematite and pyroxene respectively [8,14,15]. Assign-
ment of band positions near 910 nm is more equivocal. Murchie et
al. and Geissler et al. [14,16] favor another ferric phase (like
goethite) as the interpretation for Phobos-2 bands in the region of
910 nm, although they do not exclude composite hematite-pyroxene
bands. The results of this study show for naturally occurring mate-
rials that composite hematite-pyroxene bands have minima in the
91 O-rim region. Thus, many of the anomalous Phobos-2 spectra can
be explained by assemblages whose endmembers (hematite and
pyroxene) are accepted to be present on Mars. Furthermore, our
results show that a mineralogically diverse suite of rocks can be
generated at essentially constant composition, which implies that
variations in martian surface mineralogy do not necessarily imply
variations in chemical composition.
References: [I]Floranetal.(1978)JGR,83,2737_[2]Phinney
et al. (1978) LPS IX, 2659. [3] Pohl et al. (1977) Impact and
Explosion Cratering, 343. [4] Newsom et al. (1986) Proc. LPS 17th,
in JGR, 91, E239. [5] Newsom (1980) Icarus, 44, 207. [6] Kieffer
and Simonds (1980) Rev. Geophys. Space Phys., 18, 143. [7] Allen
et al. (1982)JGR, 87, 10083. [8] Morris et al. (1989) JGR, 94, 2760.
[9] Morris et al. ( 1993)GCA, in press. [10] Morris et al. (1985)JGR,
90, 3126 [ ! I ] Golden et al. (1993) JGR, 98, 3401. [ 12] Straub et al.
(1991) JGR, 96, 18819. [13] Cloutis and Gaffey (1991) JGR, 96,
22809. [14] Murchie et al. (1993) Icarus, in press. [15] Bell et al.
(1990)JGR, 95, 14447. [16] Geissler et al. (1993)Icarus, in press.
N94-332' 0
MARTIAN SPECTRAL UNITS DERIVED FROM ISM
IMAGING SPECTROMETER DATA. S. Murchie x, J.
Mustard 2, and R. Saylor 3, 1Lunar and Planetary Institute, Houston
TX 77058, USA, 2Brown University, Providence RI 02912, USA,
3Western Kentucky University, Bowling Green KY 42101,USA.
Introduction: Based on results of the Viking mission, the soil
layer of Mars has been thought to be fairly homogeneous and to
consist of a mixture of as few as two components, a "dark gray"
basaltic material and a "bright red" altered material [ 1,2]. However,
near-infrared reflectance spectra measured recently both telescopi-
cally and from spacecraft indicate compositional heterogeneity be-
yond what can be explained by just two components [3,4]. In
particular, data from the ISM imaging spectrometer [4,5], which
observed much of the equatorial region at a spatial resolution of
-22 kin, indicate spatial differences in the presence and abundance
of Fe-containing phases, hydroxylated silicates, and H20 [4,6.-8].
We have used the ISM data to define, characterize, and map soil
"units" based on their spectral properties. The spatial distributions
of these "units" were compared to morphologic, visible color, and
thermal inertia features recognized in Viking data.
Analysis: We investigated ISM data "windows" that covei"
eastern Tharsis, Vales Marineris, Arabia, Syrtis Major, Isidis, and
Amenthes. These areas contain examples of most of the variations
in color, reflectance, and thermal inertia recognized in Viking data
[2]. The windows were registered with the digital topographic map
of Mars using spacecraft pointing information and correlation of
topographic relief features with variations in depth of the 2.0-pro
atmospheric CO 2 absorption. The ISM data were reduced to a suite
of"parameter" images that describe key sources of spectral variabil-
ity, including reflectance, strength of a narrow absorption at 2.2 pm
attributed to metal-OH, depth of the 3.0-pro H20 absorption, depth
of the broad 2-pro absorption attributed to Fe in pyroxene, and NIR
spectral slope. Representative spectra were extracted for regions
displaying different spectral characteristics to validate these differ-
ences and to characterize the shape and position of the I-pro and 2-
pm absorptions due to ferric and ferrous iron.
The parameterized ISM data were then classified using principal
components analysis. Three principal components were found ca-
pane of accounting for most of the observed variations in NIR
spectral properties. Spatial variations in the contributions or "load-
ings" of the principal components define coherent regions of soils
having distinctly different spectral properties.
• Results: The observed martian soils can be divided into broad
groupings (Table I) based on systematic, spatially coherent differ-
ences in their spectral attributes. The two largest groupings corre-
spond with materials that are "bright red" and "dark gray" at visible
wavelengths. "Normal bright soil" exhibits a high albedo, an inter-
mediate 3.0-pro absorption, a relatively strong 2.2-pro absorption,
and a fiat spectral slope: "'normal dark soils" exhibit a strong 2-1Jm
pyroxene absorption and a relatively weak 3.0-pro absorption. Each
group can be subdivided further based on position and shape of the
ferric iron absorption in bright regions, and in dark regions, spectral
slope, strength of the 3.0-pro absorption, and position and shape of
the l-pro and 2-pro absorptions due to Fe in pyroxene. "Transi-
tional" soils, which occur largely at borders of "normal" bright and
dark soils, are intermediate to "normal" bright and dark soils in most
respects but have a negative spectral slope.
https://ntrs.nasa.gov/search.jsp?R=19940028714 2020-06-16T12:15:03+00:00Z
LPI Technical Report 93-06, Part I 33
TABLE 1. Properties and geologic correlations of ISM spectral units.
3-pro
Arbitrary Unit "'Water"
Designation Band Depth
2-pro 2.2-pm
"'Pyroxene" Spectral "'M-OH" Centerof
Band Depth Slope Band Depth Ferric Band
Geologic
Correlations
Low Albedo
Normal dark ! Weak
Normal dark I! Weak
Normal dark Ilt Intermed.
High Albedo
Normal bright I lntermed./strong
Normal bright II lntermedJstrong
Transitional lnlermedJstrong
Strong/v. strong Intemaed. Weak/absent
lntermed./strong Negative/v. negative Weak,'absem
lntermed./strong Negative Weak/absent
Weak/absent Rat Strong
Weak/absent Very Flat Strong
Weak lntem_:lJv, negative lntermed./strong
Anomalous
Hydrated dark Strong V. strong Flat/very fiat Weak'absent
Intermediate Imermed. Intermed. Flat/intermed. Weak]absent
Hydrated bright i V. strong Weak/absent Flat Strong/v. strong
Hydrated bright II V. strong Inter. Very flat Inter.
Hydrated bright Iil V. strong Weak/absem Very flat Internxxl.
Hydrated bright IV V. strong Weak Negative/v. negative Weak/absent
0.85 pm
0.92 pm
i
-..0.86 pm
i
0.89 pm?
Parts of plateau plains, floor of Valles
Marineris
Parts of plateau plains
Plateau plains in Arabia
Low-thermal-inertia regions of
Tharsis;parts of Amenthes
Low-thermal-inertia regions of Arabia
Libya Montes: parts of Amenthes:
bright-dark borders
Layered material in Melas. Eos. Ch.
Layered material in Hebes. C. Candor
Ch.
Basin fill oflsidis
"Dark red" plains in Western Arabia
"Dark red" plains in Lunae Planum
Layered material in E. W Candor Ch.
The remainder of the data, about 15% of the observed surface,
are "anomalous" and can be divided into as many as six additional
groupings, which are distinct spectrally from "normal" bright, "nor-
mal" dark, and "transitional" soils. Parts of Lunae Planum and
western Arabia with a "'dark red" visible color are intermediate to
"normal" bright and dark soils in some respects, but, unlike "tran-
sitional" areas, they have a flat spectral slope and they exhibit a
stronger 3.0-pm absorption than do either "normal bright" or "nor-
mal dark" soils. Low-albedo layered materials in Valles Marineris
have a stronger 2-pro pyroxene absorption than most dark regions,
yet also a stronger 3-pro absorption than most bright regions. High-
albedo layered materials are very heterogeneous, with some regions
characterized by a higher albedo and very strong 3.0-pm absorption,
and others exhibiting an intermediate albedo and a 2-pro pyroxene
absorption, lsidis resembles "normal bright soil" in most respects,
but has a much stronger 3.0-pro absorption.
Discussion: "Normal bright soils" are correlated spatially with
low-thermal-inertia regions .interpreted as accumulations of "dust"
by airfall [2,9,10]. The ferric absorption at 0.85 pm throughout the
Tharsis region and in Amenthes is indicative of hematite, but the
absorption at 0.92 pm throughout Arabia indicates the presence of
one or more additional Fe phases, possibly goethite or ferrihydrite
[8,1 I]. This difference implies that all low-thermal-inertia regions
cannot be airfall derived from a single, well-mixed reservoir, and
that regional lithologic differences have survived eolian mixing.
The intermediate albedo and absorption strengths in "transitional"
soils appear to a first order to be consistent with mixture of local
"normal" bright and dark components; their negative spectral slope
is consistent with a bright component either coating or mixed
intimately with a darker substrate [ 12,13].
In contrast, "anomalous" soils are mostly intermediate to high
albedo, but lie outside the low-inertia regions. They exhibit greater
spectral heterogeneity than "normar' bright and dark soils, they are
distinctive from "transitional" soils, and they are correlated spa-
tially with independemly identified high-thermal-inertia features
and geologic units. As such they may represent indurated materials
and/or exposures of specific geologic deposits. For example, inter-
mediate-albedo "dark red" soils in Lunae Planum and Arabia cor-
respond to high thermal inertia surfaces previously interpreted as
cemented duricrust [2]. Their strong 3.0-pro absorptions suggest
enrichment in a water-bearing phase, perhaps hydrated salts that act
as the duricrust's "cement" [cf. 14]. The lsidis unit also corresponds
with a thick, unconformable, basin-filling deposit [ 15] having anoma-
lously high thermal inertia [2,10]. This unit's high inertia and strong
3.0-pro absorption would also be consistent with induration of soil
by water-bearing cement, but its high albedo and relatively strong
2.2-pro absorption indicate a different compositon of cemented
particulates than in "dark red" soils.
The "intermediate," "hydrated dark," and "hydrated bright"
units in Valles Marineris correspond with different plateaus of
eroded layered materials. Previous analysis of ISM data covering
these deposits has also shown that their absorptions due to Fe vary
in position and strength, indicating the presence of pyroxenes of
different composition [6,7] and local enrichments of ferric minerals
[16]. This heterogeneity in the layered materials' spectral properties
supports previous inferences based on stratigraphic relations that
layered materials were emplaced under differing environmental
regimes [17,18].
References: [I] Arvidson R. et al. (1982) JGR, 87, 10149.
[2] Christensen P. and Moore H. (1992) in Mars (H. Kieffer et al.,
34 Resuhs from the MSATT Program
eds.), 686, Univ. of Arizona, Tucson. [3] Bell J. (1992) Icarus, 100,
575. [4] Erard S. et al. (1991) LPSXXI, 437. [5] Bibring J.-P. et al.
(1990) LPSXX, 461. [6] Murchie S. et al. (1992) LPSXXIII, 941.
[7] Mustard J. et al. (1993) LPS XXIV, 1039. [8] Murchie S. et al.
(1993) Icarus, in press. [9] Pailuconi F. and Kieffer H. (1978)
Icarus, 45, 415. [10] Christensen P. (1986) Icarus, 68, 217.
[ l l ] Morris R. et al. ( 1985)JGR, 90, 3126. [12] Singer R. and Roush
T. (1983) LPSXIV, 708. [13] Morris R. and Neely S. (1982) LPS
XIII, 548. [14] Merenyi E. et al. (1992)LPSXXIII, 897. [ i 5] Grizzaffi
P. and Schultz P. 0989) Icarus, 77, 358. [16] Geissler P. et al.
(1993) Icarus, in press. [ 17] Witbeck N. et al. ( 1991 ) U.S.G.S. Misc.
Inv. Ser. Map 1-2010. [ 18] Komatsu G. et al. ( 1993)JGR. 98. I 1105.
N94- 33221
EDDY TRANSPORT OF WATER VAPOR IN THE MAR-
TIAN ATMOSPHERE. J.R. Murphy 1.2 and R. M. Haberle l,
ISJSU Foundation, 2NASA Ames Research Center, Moffeti Field
,O_ CA 94035' USA"Viking orbiter measurements of the martian atmosphere suggest
that the residual north polar water-ice cap is the primary source of
atmospheric water vapor, which appears at successively lower north-
ern latitudes as the summer season progresses [ I ]. Zonally symmet-
ric studies of water vapor transport indicate that the zonal mean
meridional circulation is incapable (due to its weakness at high
latitudes) of transporting from north polar regions to low latitudes
the quantity of water vapor observed [2]. This result has been
interpreted as implying the presence of nonpolar sources of water,
namely subsurface ice and adsorbed water, at northern middle and
subtropical latitudes. Another possibility, which has not been ex-
plored, is the ability of atmospheric wave motions, which are not
accounted for in a zonally symmetric framework, to efficiently
accomplish the transport from a north polar source to the entirety of
the northern hemisphere. The ability or inability of the full range of
atmospheric motions to accomplish this transport has important
implications regarding the questions of water sources and sinks on
Mars: if the full spectrum of atmospheric motions proves to be
incapable of accomplishing the transport, it strengthens arguments
in favor of additional water sources.
Preliminary results from a three-dimensional atmospheric dy-
namical/water vapor transport numerical model will be presented.
The model accounts for the physics of a subliming water-ice cap, but
does not yet incorporate recondensation of this sublimed water.
Transport of vapor away from this water-ice cap in this three-
dimensional framework will be compared with previously obtained
zonally symmetric (two-dimensional) results to quantify effects of
water vapor transport by atmospheric eddies.
References: [1] Jakosky and Farmer (1982) JGR, 87, 2999-
3019. [2] Haberle and Jakosky (1990) JGR, 95, 1423-1437.
, N94-33222
IRTM BRIGHTNESS TEMPERATURE MAPS OF THE
MARTIAN SOUTH POLAR REGION DURING TIlE
POLAR NIGHT: THE COLD SPOTS DON'T MOVE. D.A.
Paige 1, D. Crisp -_,M. L. Santee 2, and M. I. Richardson I, 1Department
of Earth and Space Sciences, UCLA, Los Angeles CA 90024, USA,
-_Jet Propulsion Laboratory, Pasadena CA 91106, USA.
The Viking Infrared Thermal Mapper (IRTM) polar winter
season observations in the 20-pm channel showed considerable
temporal and spatial structure, with minimum brightness tempera-
tures well below the surface CO 2 frost point of -148 K [1,2].
Brightness temperatures as low as 134 K in the south and 128 K in
the north were observed. To date, these low brightness temperatures
have not been uniquely explained. In the i976 paper, Kieffer et al.
[!] suggested three mechanisms: (I) low surface emissivities,
(2) presence of high-altitude clouds, and (3) depressed solid-vapor
equilibrium CO 2 frost kinetic temperatures due to reduced atmo-
spheric CO_ partial pressures at the surface. Hess [3] cast doubt on
mechanism (3) by showing that vertical and horizontal gradients in
average molecular weight of the polar atmosphere could only be
stable under special circumstances.
In 1979, Ditteon and Kieffer [4] published infrared transmission
spectra of thick, solid CO 2 samples grown in the laboratory. The
results showed that in wavelengths away from the strong CO 2
absorption features, the transmissivity of their samples was quite
high, and concluded that the low brightness temperature observa-
lions could be explained by low surface frost emissivity. Warren el
al. [5] have used Ditteon and Kieffer's laboratory data in conjunc-
tion with scattering models to show that the spectral emissivities of
martian CO 2 frosts could take on almost any value from 0 to I
depending on CO 2grain size, dust and water ice content, or viewing
angle.
Hunt [61 showed that the polar night brightness temperatures
could be explained by the radiative effects of CO 2 clouds. Using the
results of a one-dimensional atmospheric model in conjunction with
IRTM observations, Paige [7,81 showed that the spatial and tempo-
ral occurrence of low brightness temperatures are consistent with
the notion that they are due to CO 2 clouds. Subsequently, Pollack et
al. [91 published the results of Global Circulation Model (GCM)
experiments that showed that CO 2 should condense in the atmos-
phere over the winter pole and that this condensation is enhanced by
the presence of dust.
In the 1977 paper, Kieffer et al. [2] published midwinter bright-
ness temperature maps that showed some evidence of temporal
variation. These temporal variations have since been interpreted by
others as illustrating dynamic motions of the lowest of the low
brightness temperature regions. However, Kieffer et al. [2] state
that the possible motion of individual features cannot be established
from the analysis presented in the 1977 paper.
In this study, we have examined a series of IRTM south polar
brightness temperature maps obtained by Viking Orbiter 2 during
a 35-day period during the southern fall season in 1978 (L, 47.3 to
62.7, Julian Date 2443554 to 2443588). These maps represent the
best spatial and temporal coverage obtained by IRTM during a polar-
night season that have not been analyzed in previous studies. The
maps show a number of phenomena that have been identified in
previous studies, including day-to-day brightness temperature varia-
tions in individual low-temperature regions [ I ], and the tendency for


Martian spectral units derived from ISM imaging spectrometer data

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