William Abbey

Classification of Organic and Biological Materials with Deep Ultraviolet Excitation

We show that native fluorescence can be used to differentiate classes or groups of organic molecules and biological materials when excitation occurs at specific excitation wavelengths in the deep ultraviolet (UV) region. Native fluorescence excitation–emission maps (EEMs) of pure organic materials, microbiological samples, and environmental background materials were compared using excitation wavelengths between 200–400 nm with emission wavelengths from 270 to 500 nm. These samples included polycyclic aromatic hydrocarbons (PAHs), nitrogen- and sulfur-bearing organic heterocycles, bacterial spores, and bacterial vegetative whole cells (both Gram positive and Gram negative). Each sample was categorized into ten distinct groups based on fluorescence properties. Emission spectra at each of 40 excitation wavelengths were analyzed using principal component analysis (PCA). Optimum excitation wavelengths for differentiating groups were determined using two metrics. We show that deep UV excitation at 235 (±2) nm optimally separates all organic and biological groups within our dataset with >90% confidence. For the specific case of separation of bacterial spores from all other samples in the database, excitation at wavelengths less than 250 nm provides maximum separation with >6σ confidence.

SHERLOC: Scanning habitable environments with Raman & luminescence for organics & chemicals

SHERLOC is an arm-mounted fluorescence and Raman spectrometer that was recently selected to be part of the payload for the next proposed NASA rover mission to Mars, scheduled for launch in 2020. SHERLOC enables non-contact, spatially resolved, high sensitivity detection and characterization of organics and minerals on the Martian surface. The investigation goals are to assess past aqueous history, detect the presence and preservation potential of biosignatures, and support the selection of samples for caching and potential return to Earth.

Probabilistic surface classification for rover instrument targeting

Communication blackouts and latency are significant bottlenecks for planetary surface exploration; rovers cannot typically communicate during long traverses, so human operators cannot respond to unanticipated science targets discovered along the route. Targeted data collection by point spectrometers or high-resolution imagery requires precise aim, so it typically happens under human supervision during the start of each command cycle, directed at known targets in the local field of view. Spacecraft can overcome this limitation using onboard science data analysis to perform autonomous instrument targeting. Two critical target selection capabilities are the ability to target priority features of a known geologic class, and the ability to target anomalous surfaces that are unlike anything seen before. This work addresses both challenges using probabilistic surface classification in traverse images. We first describe a method for targeting known classes in the presence of high measurement cost that is typical for power- and time-constrained rover operations. We demonstrate a Bayesian approach that abstains from uncertain classifications to significantly improve the precision of geologic surface classifications. Our results show a significant increase in classification performance, including a seven-fold decrease in misclassification rate for our random forest classifier. We then take advantage of these classifications and learned scene context in order to train a semi-supervised novelty detector. Operators can train the novelty detection to ignore known content from previous scenes, a critical requirement for multi-day rover operations. By making use of prior scene knowledge we find nearly double the number of abnormal features detected over comparable algorithms. We evaluate both of these techniques on a set of images acquired during field expeditions in the Mojave Desert.

Reflectance spectroscopy and optical functions for hydrated Fe-sulfates

Abstract Visible and near-infrared wavelength (VNIR, λ = 0.35-5 mm) laboratory diffuse reflectance spectra and corresponding optical functions (real and imaginary refractive indices) for several iron sulfates (natural K- and Na-jarosite, szomolnokite, rhomboclase) are presented. On Mars, jarosite has been identified in Meridiani Planum, Mawrth Vallis, Melas Chasma, and Eridania Basin; szomolnokite has been found as distinct layers at Columbus Crater and as outcrops at Juventae Chasma, and rhomboclase has been identified at Gusev Crater. Constraining the mineralogy and chemistry (Fe- vs. Mg-rich) of the sulfates on Mars may contribute to our understanding of the environmental and aqueous conditions present on Mars during their formation. The data presented here will help to constrain the mineralogy, abundance, and distribution of sulfates on the martian surface, which will lead to improvements in understanding the pressure, temperature, and humidity conditions and how active frost, groundwater, and atmospheric processes once were on Mars.

Radiocarbon dating of glacial dust layers and soils at Kilimanjaro’s Northern Ice Field

As the African climate history recorded in Kilimanjaro’s Northern Ice Field (NIF) is rapidly lost, the age of the glacier remains disputed. Current age estimates from ice core data and glacial dynamics modeling disagree by an order of magnitude (11,700 vs ~1000 years old). We present radiocarbon dates of glacial dust and proximal soil samples collected from in and around the edge of the NIF that support the hypothesis that the peripheral portions of the NIF glacier are younger and more dynamic than the center. Samples of a dust-rich ice layer, 1.5 m above the base at the edge of the ~40 m high glacier ice cliff were found to be 1600–790 years old. These dates agree with the prediction of significant growth and shrinkage in glacial coverage over the last millennium. The variation in radiocarbon ages likely arises from heterogeneity in the summit volcanic soils, the main source of the dust recovered from the glacier, and cryoconite microbial activity. Sediment samples of a supraglacial pond had modern radiocarbon ages, further demonstrating the impact of cryoconite microbial communities on radiocarbon measurements of glacial samples. After accounting for the variability in the sample ages and the effects of microbial activity, we contend that the lower (i.e. younger) limit of the radiocarbon age range is the most reliable assessment of the age of the ice in which it was trapped.

The Mojave Vadose Zone: A Subsurface Biosphere Analogue for Mars

If life ever evolved on the surface of Mars, it is unlikely that it would still survive there today, but as Mars evolved from a wet planet to an arid one, the subsurface environment may have presented a refuge from increasingly hostile surface conditions. Since the last glacial maximum, the Mojave Desert has experienced a similar shift from a wet to a dry environment, giving us the opportunity to study here on Earth how subsurface ecosystems in an arid environment adapt to increasingly barren surface conditions. In this paper, we advocate studying the vadose zone ecosystem of the Mojave Desert as an analogue for possible subsurface biospheres on Mars. We also describe several examples of Mars-like terrain found in the Mojave region and discuss ecological insights that might be gained by a thorough examination of the vadose zone in these specific terrains. Examples described include distributary fans (deltas, alluvial fans, etc.), paleosols overlain by basaltic lava flows, and evaporite deposits.

Development of a Deep Drill System with Integrated Deep UV/Raman Spectrometer for Mars and Europa

SPECTROMETER FOR MARS. Joey Palmowski, Boleslaw Mellerowicz, Evan Eshelman, Kris Zacny, Gale Paulsen, Michael Malaska, John C Priscu, William Abbey, Ivria Doloboff, Arthur L Lane, Luther W Beegle, Lauren P DeFlores, Brandi L Carrier, Peter Ngo, Paul Chow, Robert Huddleston, Albert Ridilla, Alexander Wang, Jameil Bailey, Huey Nguyen, Rohit Bhartia Honeybee Robotics, Altadena, CA, United States, NASA Jet Propulsion Laboratory, Pasadena, CA, United States, Montana State University, Land Resources and Environmental Science, Bozeman, MT, United States

The structure and chemical layering of Proterozoic stromatolites in the Mojave Desert

The Proterozoic carbonate stromatolites of the Pahrump Group from the Crystal Spring formation exhibit interesting layering patterns. In continuous vertical formations, there are sections of chevron-shaped stromatolites alternating with sections of simple horizontal layering. This apparent cycle of stromatolite formation and lack of formation repeats several times over a vertical distance of at least 30 m at the locality investigated. Small representative samples from each layer were taken and analysed using X-ray diffraction (XRD), X-ray fluorescence (XRF), environmental scanning electron microscopy - energy dispersive X-ray spectrometry, and were optically analysed in thin section. Optical and spectroscopic analyses of stromatolite and of non-stromatolite samples were undertaken with the objective of determining the differences between them. Elemental analysis of samples from within each of the four stromatolite layers andthe four intervening layersshowsthatthe two typesof layers arechemicallyand mineralogically distinct. In the layers that contain stromatolites the Ca/Si ratio is high; in layers without stromatolites the Ca/Si ratio is low. In the high Si layers, both K and Al are positively correlated with the presence and levels of Si. This, together with XRD analysis, suggested a high K-feldspar (microcline) content in the non-stromatolitic layers. This variation between these two types of rocks could be due to changes in biological growth rates in an otherwise uniform environment or variations in detrital influx and the resultant impact on biology. The current analysis does not allow us to choose between these two alternatives. A Mars rover would have adequate resolution to image these structures and instrumentation capable of conducting a similarelemental analysis.