215 research outputs found
Recovery of surface reflectance spectra and evaluation of the optical depth of aerosols in the near-IR using a Monte-Carlo approach: Application to the OMEGA observations of high latitude regions of Mars
We present a model of radiative transfer through atmospheric particles based
on Monte Carlo methods. This model can be used to analyze and remove the
contribution of aerosols in remote sensing observations. We have developed a
method to quantify the contribution of atmospheric dust in near-IR spectra of
the Martian surface obtained by the OMEGA imaging spectrometer on board Mars
Express. Using observations in the nadir pointing mode with significant
differences in solar incidence angles, we can infer the optical depth of
atmospheric dust, and we can retrieve the surface reflectance spectra free of
aerosol contribution. Martian airborne dust properties are discussed and
constrained from previous studies and OMEGA data. We have tested our method on
a region at 90{\deg}E and 77{\deg}N extensively covered by OMEGA, where
significant variations of the albedo of ice patches in the visible have been
reported. The consistency between reflectance spectra of ice-covered and
ice-free regions recovered at different incidence angles validates our
approach. The optical depth of aerosols varies by a factor 3 in this region
during the summer of Martian year 27. The observed brightening of ice patches
does not result from frost deposition but from a decrease in the dust
contamination of surface ice and (to a lower extent) from a decrease in the
optical thickness of atmospheric dust. Our Monte Carlo-based model can be
applied to recover the spectral reflectance characteristics of the surface from
OMEGA spectral imaging data when the optical thickness of aerosols can be
evaluated. It could prove useful for processing image cubes from the Compact
Reconnaissance Imaging Spectrometer for Mars (CRISM) on board the Mars
Reconnaissance Orbiter (MRO)
An Extremely Elongated Cloud over Arsia Mons Volcano on Mars: I. Life Cycle
We report a previously unnoticed annually repeating phenomenon consisting of
the daily formation of an extremely elongated cloud extending as far as 1800 km
westward from Arsia Mons. It takes place in the Solar Longitude (Ls) range of
~220-320, around the Southern solstice. We study this Arsia Mons Elongated
Cloud (AMEC) using images from different orbiters, including ESA Mars Express,
NASA MAVEN, Viking 2, MRO, and ISRO Mars Orbiter Mission (MOM). We study the
AMEC in detail in Martian Year (MY) 34 in terms of Local Time and Ls and find
that it exhibits a very rapid daily cycle: the cloud growth starts before
sunrise on the western slope of the volcano, followed by a westward expansion
that lasts 2.5 hours with a velocity of around 170 m/s in the mesosphere (~45
km over the areoid). The cloud formation then ceases, it detaches from its
formation point, and continues moving westward until it evaporates before the
afternoon, when most sun-synchronous orbiters observe. Moreover we
comparatively study observations from different years (i.e. MYs 29-34) in
search of interannual variations and find that in MY33 the cloud exhibits lower
activity, whilst in MY34 the beginning of its formation was delayed compared to
other years, most likely due to the Global Dust Storm. This phenomenon takes
place in a season known for the general lack of clouds on Mars. In this paper
we focus on observations, and a theoretical interpretation will be the subject
of a separate paper
Yearly and seasonal variations of low albedo surfaces on Mars in the OMEGA/MEx dataset: Constraints on aerosols properties and dust deposits
The time variations of spectral properties of dark martian surface features
are investigated using the OMEGA near-IR dataset. The analyzed period covers
two Mars years, spanning from early 2004 to early 2008 (includes the 2007
global dust event). Radiative transfer modeling indicates that the apparent
albedo variations of low to mid-latitude dark regions are consistent with those
produced by the varying optical depth of atmospheric dust as measured
simultaneously from the ground by the Mars Exploration Rovers. We observe only
a few significant albedo changes that can be attributed to surface phenomena.
They are small-scaled and located at the boundaries between bright and dark
regions. We then investigate the variations of the mean particle size of
aerosols using the evolution of the observed dark region spectra between 1 and
2.5 {\mu}m. Overall, we find that the observed changes in the spectral slope
are consistent with a mean particle size of aerosols varying with time between
1 and 2 {\mu}m. Observations with different solar zenith angles make it
possible to characterize the aerosol layer at different altitudes, revealing a
decrease of the particle size of aerosols as altitude increases
Dynamics of the extremely elongated cloud on Mars Arsia Mons volcano
Starting in September 2018, a daily repeating extremely elongated cloud was observed extending
from the Mars Arsia Mons volcano. We study this Arsia Mons Elongated Cloud (AMEC) using
images from VMC, HRSC, and OMEGA on board Mars Express, IUVS on MAVEN, and MARCI on
MRO. We study the daily cycle of this cloud, showing how the morphology and other parameters
of the cloud evolved with local time. The cloud expands every morning from the western slope of
the volcano, at a westward velocity of around 150m/s, and an altitude of around 30-40km over the
local surface. Starting around 2.5 hours after sunrise (8.2 Local True Solar Time, LTST), the
formation of the cloud resumes, and the existing cloud keeps moving westward, so it detaches
from the volcano, until it evaporates in the following hours. At this time, the cloud has expanded
to a length of around 1500km. Short time later, a new local cloud appears on the western slope of
the volcano, starting around 9.5 LTST, and grows during the morning.
This daily cycle repeated regularly for at least 90 sols in 2018, around Southern Solstice (Ls
240-300) in Martian Year (MY) 34. According with these and previous MEx/VMC observations, this
elongated cloud is a seasonal phenomenon occurring around Southern Solstice every Martian
Year. We study the interannual variability of this cloud, the influence of the Global Dust Storms in
2018 on the cloud’s properties (Sánchez-Lavega et al., Geophys. Res. Lett. 46, 2019), and its validity
as a proxy for the global state of the Martian atmosphere (Sánchez-Lavega et al., J. Geophys. Res.,
123, 3020, 2018). We discuss the physical mechanisms behind the formation of this peculiar cloud
in Mars
Dynamics of the extremely elongated cloud on Mars Arsia Mons volcano
Starting in September 2018, a daily repeating extremely elongated cloud was observed
extending up to 1800km from the Mars Arsia Mons volcano. We study this Arsia Mons
Elongated Cloud (AMEC) using images from VMC, HRSC, and OMEGA on board Mars
Express, IUVS on MAVEN, MCC on Mars Orbiter Mission (MOM), MARCI on MRO,
and Visible Camera on Viking 2 orbiter. We study the daily cycle of this cloud, showing
how the morphology and other parameters of the cloud evolved rapidly with local time.
The cloud expands every morning from the western slope of the volcano, at a westward
velocity of around 160m/s, and an altitude of around 45km over martian areoid. The
expansion starts with sunrise, and resumes around 2.5 hours later, when cloud formationresumes and the elongated tail detaches from the volcano and keeps moving westward
until it evaporates before afternoon, when most sun-synchronous missions observe. This
daily cycle repeated regularly for at least 80 sols in 2018 (Martian Year 34). We find in
images from past years that this AMEC is an annually repeating phenomenon that takes
place around the Solar Longitude range 220º-320º. We study the AMEC in Martian Year
34 in terms of Local Time and Solar Longitude, and then compare with observations from
previous years, in search for interannual variations, taking into account the possible
influence of the recent Global Dust Storm
Martian atmosphere as observed by VIRTIS‐M on Rosetta spacecraft
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95134/1/jgre2651.pd
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Soil Diversity and Hydration as Observed by ChemCam at Gale Crater, Mars
Abstract: The ChemCam instrument, which provides insight into martian soil chemistry at the submillimeter scale, identified two principal soil types along the Curiosity rover traverse: a fine-grained mafic type and a locally derived, coarse-grained felsic type. The mafic soil component is representative of widespread martian soils and is similar in composition to the martian dust. It possesses a ubiquitous hydrogen signature in ChemCam spectra, corresponding to the hydration of the amorphous phases found in the soil by the CheMin instrument. This hydration likely accounts for an important fraction of the global hydration of the surface seen by previous orbital measurements. ChemCam analyses did not reveal any significant exchange of water vapor between the regolith and the atmosphere. These observations provide constraints on the nature of the amorphous phases and their hydration.Keywords: Water, Allophane, Chemistry, X-ray spectrometer, Surface, Instrument suite, Chemical composition, Emission spectrometer data, Hydrous minerals, Martian Regolit
Volatile and Organic Compositions of Sedimentary Rocks in Yellowknife Bay, Gale crater, Mars
H₂O, CO₂, SO₂, O₂, H₂, H₂S, HCl, chlorinated hydrocarbons, NO and other trace gases were evolved during pyrolysis of two mudstone samples acquired by the Curiosity rover at Yellowknife Bay within Gale crater, Mars. H₂O/OH-bearing phases included 2:1 phyllosilicate(s), bassanite, akaganeite, and amorphous materials. Thermal decomposition of carbonates and combustion of organic materials are candidate sources for the CO₂. Concurrent evolution of O₂ and chlorinated hydrocarbons suggest the presence of oxychlorine phase(s). Sulfides are likely sources for S-bearing species. Higher abundances of chlorinated hydrocarbons in the mudstone compared with Rocknest windblown materials previously analyzed by Curiosity suggest that indigenous martian or meteoritic organic C sources may be preserved in the mudstone; however, the C source for the chlorinated hydrocarbons is not definitively of martian origin
The Petrochemistry of Jake_M: A Martian Mugearite
“Jake_M,” the first rock analyzed by the Alpha Particle X-ray Spectrometer instrument on the
Curiosity rover, differs substantially in chemical composition from other known martian igneous
rocks: It is alkaline (>15% normative nepheline) and relatively fractionated. Jake_M is
compositionally similar to terrestrial mugearites, a rock type typically found at ocean islands and
continental rifts. By analogy with these comparable terrestrial rocks, Jake_M could have been
produced by extensive fractional crystallization of a primary alkaline or transitional magma at
elevated pressure, with or without elevated water contents. The discovery of Jake_M suggests that
alkaline magmas may be more abundant on Mars than on Earth and that Curiosity could encounter
even more fractionated alkaline rocks (for example, phonolites and trachytes)
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