arXiv subjects

Adrian J. Brown

Publications and source records attributed to Adrian J. Brown.

At least 19 recordsLinked to original sources

arXiv2022

Properties of the Nili Fossae Olivine-clay-carbonate lithology: orbital and in situ at Séítah

We examine the observed properties of the Nili Fossae olivine-clay-carbonate lithology from orbital data and in situ by the Mars 2020 rover at the Séítah unit in Jezero crater, including: 1) composition (Liu, 2022) 2) grain size (Tice, 2022) 3) inferred viscosity (calculated based on geochemistry collected by SuperCam (Wiens, 2022)). Based on the low viscosity and distribution of the unit we postulate a flood lava origin for the olivine-clay-carbonate at Séítah. We include a new CRISM map of the clay 2.38 μm band and use in situ data to show that the clay in the olivine cumulate in the Séítah formation is consistent with talc or serpentine from Mars 2020 SuperCam LIBS and VISIR and MastCam-Z observations. We discuss two intertwining aspects of the history of the lithology: 1) the emplacement and properties of the cumulate layer within a lava lake, based on terrestrial analogs in the Pilbara, Western Australia, and using previously published models of flood lavas and lava lakes, and 2) the limited extent of post emplacement alteration, including clay and carbonate alteration (Clave, 2022; Mandon, 2022).

astro-ph.EP↗

arXiv2022

Using asymmetric band analysis to interpret the electronic spectroscopy of the Olivine family

This paper discusses the mathematical aspects of band fitting and introduces the mathematics of the Asymmetric Gaussian shape and its tangent space for the first time. First, we derive an equation for an Asymmetric Gaussian shape. We then use this equation to derive a rule for the resolution of two Gaussian shaped bands. We then use the Asymmetrical Gaussian equation to derive a Master Equation to fit two overlapping bands. We identify regions of the fitting space where the Asymmetric Gaussian fit is optimal, sub optimal and not optimal. We then demonstrate the use of the Asymmetric Gaussian to fit four overlapping Gaussian bands, and show how this is relevant to the olivine spectral complex at 1 micron. We develop a new model of the olivine family spectrum based on previous work by Runciman and Burns. The limitations of the asymmetric band fitting method and a critical assessment of three commonly used numerical minimization methods are also provided.

cond-mat.mtrl-sci↗

arXiv2020

Mars2020 and Mars Sample Return

Mars Sample Return consists of three separate missions, the first of which is the Mars2020 rover which will land at Jezero crater on February 18, 2021. We describe here our remote sensing study of a particular unit that outcrops in Jezero crater that is likely to be part of the return sample suite. We report on our efforts to characterize the olivine unit using data from the CRISM instrument, including the grain size and Fe/Mg (Fo) number of the olivine. We also discuss the astrobiological significance of the unit by analogy with the stromatolite-bearing early Archean Warrawoona group in Western Australia. We also discuss the current state of the MSR architecture.

astro-ph.EP↗

arXiv2020

Ancient Australian Rocks and the Search for Life on Mars

We discuss the results of a remote sensing study that has revealed new details about an important rock unit dominated by two minerals that can be associated with volcanism (olivine) and life (carbonate). The study, which used a new analysis technique on CRISM data, identified a region where no carbonates or clays are present, only large grain size olivine. This discovery shines new light on the formation and history of the olivine-carbonate rock within Jezero crater that will be explored by the Mars 2020 rover.

astro-ph.EP↗

arXiv2020

The case for a multi-channel polarization sensitive LIDAR for investigation of insolation-driven ices and atmospheres

All LIDAR instruments are not the same, and advancement of LIDAR technology requires an ongoing interest and demand from the community to foster further development of the required components. The purpose of this paper is to make the community aware of the need for further technical development, and the potential payoff of investing experimental time, money and thought into the next generation of LIDARs.

astro-ph.IM↗

arXiv2020

Ultramafic talc-carbonate unit -- The North Pole Dome and Dresser Formation

Here we describe the ultramafic talc-carbonate unit of the North Pole Dome. The North Pole Dome (NPD) is located in the centre of the East Pilbara Terrane (Van Kranendonk et al., 2007). The NPD is a structural dome of bedded, dominantly mafic volcanic rocks of the Warrawoona and Kelly Groups that dip gently away from the North Pole Monzogranite exposed in the core of the dome (Figure 1) (Van Kranendonk, 1999, 2000). Average dips vary from 30 to 60 degrees in the inner part of the dome to about 60 to 80 degrees in the outer part of the dome (Van Kranendonk, 2000). The North Pole Monzogranite is interpreted to represent a syn-volcanic laccolith to the Panorama Formation (Thorpe et al., 1992) and has been estimated to extend approximately 1.5km below the surface, based on gravity surveys (Blewett et al., 2004). Felsic volcanic formations are interbedded with the greenstones (Hickman, 1983), and these are capped by cherts that indicate hiatuses in volcanism (Barley, 1993; Van Kranendonk, 2006). An overall arc-related model for hydrothermal activity is favored by Barley (1993), whereas more recent studies have indicated a mantle-plume model for igneous and hydrothermal activity at the North Pole Dome (Van Kranendonk et al., 2002, 2007; Smithies et al., 2003; Van Kranendonk and Pirajno, 2004).

astro-ph.EP↗

arXiv2019

Olivine-Carbonate Mineralogy of the Jezero Crater Region

A well-preserved, ancient delta deposit, in combination with ample exposures of carbonate rich materials, make Jezero Crater in Nili Fossae a compelling astrobiological site. We use Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) observations to characterize the surface mineralogy of the crater and surrounding watershed. Previous studies have documented the occurrence of olivine and carbonates in the Nili Fossae region. We focus on correlations between these two well studied lithologies in the Jezero crater watershed. We map the position and shape of the olivine 1 μm absorption band and find that carbonates are only found in association with olivine which displays a 1 μm band shifted to long wavelengths. We then use THEMIS coverage of Nili Fossae and perform tests to investigate whether the long wavelength shifted olivine signature is correlated with high thermal inertia outcrops. We find no correlation between thermal inertia and the unique olivine signature. We discuss a range of formation scenarios, including the possibility that these olivine and carbonate associations are products of serpentinization reactions on early Mars. These lithologies provide an opportunity for deepening our understanding of early Mars, and, given their antiquity, may provide a framework to study the formation of valley networks, and the thermal history of the martian crust and interior from the early Noachian to today.

astro-ph.EP↗

arXiv2018

Olivine-Carbonate Mineralogy of Jezero Crater

A well-preserved, ancient delta deposit, in combination with ample exposures of Mg-carbonate rich materials, make Jezero Crater in Nili Fossae a compelling astrobiological site and a top candidate for future landed missions to Mars. We use CRISM observations to characterize the surface mineralogy of the crater and surrounding watershed. We have identified a three- endmember sequence of olivine-bearing lithologies that we hypothesize are distinguished by their Mg content. We find that Mg-carbonates are consistently identified in association with one of the olivine-bearing lithologies, although that lithology is not fully carbonatized. Surprisingly, this lithology contains relatively Fe-rich olivine. We address a range of formation scenarios, including the possibility that these olivine and carbonate associations are indicators of serpentinization on early Mars. These deposits provide an opportunity for deepening our understanding of early Mars by revealing the thermal history of the martian interior and potentially changes in its tectonic regime with time.

astro-ph.EP↗

arXiv2017

Observations of a new stabilizing effect for polar water ice on Mars

Using the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), we map the temporal variability of water ice absorption bands over the near-polar ice mound in Louth crater, Mars. The absorption band depth of water ice at 1.5 microns can be used as a proxy for ice grain size and so sudden reductions can time any switches from ablation to condensation. A short period of deposition on the outer edge of the ice mound during late spring coincides with the disappearance of seasonal water frost from the surrounding regolith suggesting that this deposition is locally sourced. The outer unit at Louth ice mound differs from its central regions by being rough, finely layered, and lacking wind-blown sastrugi. This suggests we are observing a new stabilizing effect wherein the outer unit is being seasonally replenished with water ice from the surrounding regolith during spring. We observe the transport distance for water migration at Louth crater to be ~4km, and we use this new finding to address why no water ice mounds are observed in craters <9km in diameter.

astro-ph.EP↗

arXiv2017

Circular Polarization and Coherent Backscattering

We extend the work of Mishchenko et al. (2000) regarding the exact results of the polarization effect, using the theory of Amic et al. (1997) to derive a model prediction for the polarization coherent opposition effect at small angles. Our extension is to assess the effect of circular polarized light, thus completing exact derivation of the full Müller matrix for the semi infinite slab of Rayleigh sized particles. We find the circular polarization peak is narrower than the coherent backscattering intensity peak, and weaker in intensity.

astro-ph.IM↗

arXiv2016

Detection and Quantification of Volatiles at Mars using a multispectral LIDAR

We present a concept for using a polarization sensitive multispectral lidar to map the seasonal distribution and exchange of volatiles among the reservoirs of the Martian surface and atmosphere. The LIDAR instrument will be a multi-wavelength, altitude-resolved, active near-infrared (NIR, with 10 bands around 1.6 microns) instrument to measure the reflected intensity and polarization of backscattered radiation from planetary surfaces and atmospheres. The proposed instrument would be ideally suited for a mission to Mars to comprehensively investigate the nature and seasonal distributions of volatiles and aerosols. The investigation would include the abundance of atmospheric dust and condensed volatiles, surface and cloud/aerosol grain sizes and shapes, ice and dust particle microphysics and also variations in atmospheric chemistry during multiple overflight local times throughout polar night and day. Such an instrument would be ideal for mapping and detection of recently detected CO2 frost phenomena and H2O and CO2 precipitation events in the polar regions of Mars. Herein we discuss the applicability of this instrument to detect and map sublimation/deposition 'mode flips' recently discovered by Brown et al. (2016) using the CRISM passive infrared sensor on Mars Reconnaissance Orbiter.

astro-ph.EP↗

arXiv2016

Martian north polar cap summer water cycle

A key outstanding question in Martian science is 'are the polar caps gaining or losing mass and what are the implications for past, current and future climate?' To address this question, we use observations from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) of the north polar cap during late summer for multiple Martian years, to monitor the summertime water cycle in order to place quantitative limits on the amount of water ice deposited and sublimed in late summer. We establish here for the first time the summer cycle of water ice absorption band signatures on the north polar cap. We show that in a key region in the interior of the north polar cap, the absorption band depths grow until Ls=120, when they begin to shrink, until they are obscured at the end of summer by the north polar hood. This behavior is transferable over the entire north polar cap, where in late summer regions 'flip' from being net sublimating into net condensation mode. This transition or 'mode flip' happens earlier for regions closer to the pole, and later for regions close to the periphery of the cap. The observations and calculations presented herein estimate that on average a water ice layer ~70 microns thick is deposited during the Ls=135-164 period. This is far larger than the results of deposition on the south pole during summer, where an average layer 0.6-6 microns deep has been estimated by Brown et al. (2014).

astro-ph.EP↗

arXiv2015

Correlations of atmospheric water ice and dust in the Martian Polar regions

We report on the interannual variability of the atmospheric ice/dust cycle in the Martian polar regions for Mars Years 28-30. We used CRISM emission phase function measurements to derive atmospheric dust optical depths and data from the MARCI instrument to derive atmospheric water ice optical depths. We have used autocorrelation and cross correlation functions in order to quantify the degree to which dust and ice are correlated throughout both polar regions during Mars Years 28-29. We find that in the south polar region, dust has the tendency to "self clear", demonstrated by negative autocorrelation around the central peak. This does not occur in the north polar region. In the south polar region, dust and ice are temporally and spatially anti correlated. In the north polar region, this relationship is reversed, however temporal correlation of northern dust and ice clouds is weak - 6 times weaker than the anticorrelation in the south polar region. Our latitudinal autocorrelation functions allow us to put average spatial sizes of event cores and halos. Dust events in the south are largest, affecting almost the entire pole, whereas dust storms are smaller in the north. Ice clouds in north are similar in latitudinal extent to those in the south (both have halos < 10°). Using cross-correlation functions of water ice and dust, we find that dust events temporally lag ice events by 35-80 degrees of solar longitude in the north and south poles, which is likely due to seasonality of dust and ice events.

astro-ph.EP↗

arXiv2015

Quantification of summertime water ice deposition on the Martian north polar ice cap

We use observations from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) of the north polar cap during late summer for two Martian years, to monitor the complete summer cycle of albedo and water ice grain size in order to place quantitative limits of the amount of water ice deposited in late summer. We establish here for the first time the complete spring to summer cycle of water ice grain sizes on the north polar cap. The apparent grain sizes grow until Ls=132, when they appear to shrink again, until they are obscured at the end of summer by the north polar hood. Under the assumption that the shrinking of grain sizes is due to the deposition of find grained ice, we quantify the amount of water ice deposited per Martian boreal summer, and estimate the amount of water ice that must be transported equatorward. Interestingly, we find that the relative amount of water ice deposited in the north cap during boreal summer (0.7-7 microns) is roughly equivalent to the average amount of water ice deposited on the south polar cap during austral summer (0.6-6 microns).

astro-ph.EP↗

arXiv2014

Equivalence relations for Mueller matrix symmetries of laboratory, LIDAR and planetary scattering geometries

Symmetry relationships for optical observations of matter generally fall into several common scattering geometries. The 'planetary' configuration is preferred among a group of observers of extraterrestrial planets, 'laboratory' observations are performed in the biomedical research field and the LIDAR configuration is preferred among those using lasers to probe optical properties of horizontal surfaces with mirror or axial symmetry. This paper starts with the Stokes matrix formalism and uses symmetries of Mueller matrix scattering to establishes links between the mathematical symmetries of each geometric configuration.

physics.optics↗

arXiv2014

Interannual observations and quantification of summertime H2O ice deposition on the Martian CO2 ice south polar cap

The spectral signature of water ice was observed on Martian south polar cap in 2004 by the Observatoire pour l'Mineralogie, l'Eau les Glaces et l'Activite (OMEGA) (Bibring et al., 2004). Three years later, the OMEGA instrument was used to discover water ice deposited during southern summer on the polar cap (Langevin et al., 2007). However, temporal and spatial variations of these water ice signatures have remained unexplored, and the origins of these water deposits remains an important scientific question. To investigate this question, we have used observations from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on the Mars Reconnaissance Orbiter (MRO) spacecraft of the southern cap during austral summer over four Martian years to search for variations in the amount of water ice. We report below that for each year we have observed the cap, the magnitude of the H2O ice signature on the southern cap has risen steadily throughout summer, particularly on the west end of the cap. The spatial extent of deposition is in disagreement with the current best simulations of deposition of water ice on the south polar cap (Montmessin et al., 2007). This increase in water ice signatures is most likely caused by deposition of atmospheric H2O ice and a set of unusual conditions makes the quantification of this transport flux using CRISM close to ideal. We calculate a 'minimum apparent' amount of deposition corresponding to a thin H2O ice layer of 0.2mm (with 70 percent porosity). This amount of H2O ice deposition is 0.6-6 percent of the total Martian atmospheric water budget. We compare our 'minimal apparent' quantification with previous estimates. This deposition process may also have implications for the formation and stability of the southern CO2 ice cap, and therefore play a significant role in the climate budget of modern day Mars.

astro-ph.EP↗

arXiv2014

Symmetry relations revealed in Mueller Matrix hemispherical maps

The hemispherical Mueller matrix map for light reflected from a plane-parallel planetary atmosphere is shown to obey several symmetry properties that provide a straightforward method to check their physical realizability. The mirror scattering relation and the reciprocity relation are employed to support the symmetry rules for hemispherical Mueller matrix maps. Additionally, two classes of experiments are identified in which the symmetry rules can be applied, namely, when the incident beam is at zenith and off- zenith angles and the scattering particles are spheres and randomly oriented hexagonal particles.

physics.optics↗

arXiv2014

The science case for a modern, multi-wavelength, polarization-sensitive LIDAR in orbit around Mars

We present the scientific case to build a multiple-wavelength, active, near-infrared (NIR) instrument to measure the reflected intensity and polarization characteristics of backscattered radiation from planetary surfaces and atmospheres. We focus on the ability of such an instrument to enhance, perhaps revolutionize, our understanding of climate, volatiles and astrobiological potential of modern-day Mars.

astro-ph.EP↗