David Carl Humm

Hydrated silicate minerals on Mars observed by the Mars Reconnaissance Orbiter CRISM instrument

Phyllosilicates, a class of hydrous mineral first definitively identified on Mars by the OMEGA (Observatoire pour la Mineralogie, L’Eau, les Glaces et l’Activitié) instrument, preserve a record of the interaction of water with rocks on Mars. Global mapping showed that phyllosilicates are widespread but are apparently restricted to ancient terrains and a relatively narrow range of mineralogy (Fe/Mg and Al smectite clays). This was interpreted to indicate that phyllosilicate formation occurred during the Noachian (the earliest geological era of Mars), and that the conditions necessary for phyllosilicate formation (moderate to high pH and high water activity) were specific to surface environments during the earliest era of Mars’s history. Here we report results from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) of phyllosilicate-rich regions. We expand the diversity of phyllosilicate mineralogy with the identification of kaolinite, chlorite and illite or muscovite, and a new class of hydrated silicate (hydrated silica). We observe diverse Fe/Mg-OH phyllosilicates and find that smectites such as nontronite and saponite are the most common, but chlorites are also present in some locations. Stratigraphic relationships in the Nili Fossae region show olivine-rich materials overlying phyllosilicate-bearing units, indicating the cessation of aqueous alteration before emplacement of the olivine-bearing unit. Hundreds of detections of Fe/Mg phyllosilicate in rims, ejecta and central peaks of craters in the southern highland Noachian cratered terrain indicate excavation of altered crust from depth. We also find phyllosilicate in sedimentary deposits clearly laid by water. These results point to a rich diversity of Noachian environments conducive to habitability.

Initial observations with the Global Ultraviolet Imager (GUVI) in the NASA TIMED satellite mission

[1] The Global Ultraviolet Imager (GUVI) instrument carried aboard the NASA TIMED satellite measures the spectral radiance of the Earth’s far ultraviolet airglow in the spectral region from 120 to 180 nm using a cross-track scanning spectrometer design. Continuous operation of the instrument provides images of the Earth’s disk and limb in five selectable spectral bands. Also, spectra at fixed scanning mirror position can be obtained. Initial results demonstrate the quantitative functionality of the instrument for studies of the Earth’s dayglow, aurora, and ionosphere. Moreover, through forward modeling, the abundance of the major constituents of the thermosphere, O, N2, and O2 and thermospheric temperatures can be retrieved from observations of the limb radiance. Variations of the column O/N2 ratio can be deduced from sunlit disk observations. In regions of auroral precipitation not only can the aurora regions be geographically located and the auroral boundaries identified, but also the energy flux Q, the characteristic energy Eo, and a parameter fo that scales the abundance of neutral atomic oxygen can be derived. Radiance due to radiative recombination in the ionospheric F region is evident from both dayside and nightside observations of the Earth’s limb and disk, respectively. Regions of depleted F-region electron density are evident in the tropical Appleton anomaly regions, associated with so-called ionospheric ‘‘bubbles.’’ Access to the GUVI data is provided through the GUVI website www.timed.jhuapl.edu\guvi. INDEX TERMS: 0310 Atmospheric Composition and Structure: Airglow and aurora; 0355 Atmospheric Composition and Structure: Thermosphere—composition and chemistry; 0358 Atmospheric Composition and Structure: Thermosphere—energy deposition; 2407 Ionosphere: Auroral ionosphere (2704); KEYWORDS: airglow, aurora, ultraviolet, imaging, satellite, atmosphere

A hematite-bearing layer in Gale Crater, Mars: Mapping and implications for past aqueous conditions

Oversampled Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) visible and near-infrared hyperspectral data over Mount Sharp in Gale Crater, Mars, were used to generate spatially sharpened maps of the location of red crystalline hematite within the uppermost stratum of an ∼6.5-km-long ridge on the mound’s northern flank. Finely layered strata underlie the ridge to the north and have dips consistent with the nearby Mount Sharp sedimentary sequence. Fe-Mg smectites are exposed in a valley to the south of the ridge. Emplacement of the hematite is hypothesized to result either from exposure of anoxic Fe^(2+)-rich groundwater to an oxidizing environment, leading to precipitation of hematite or its precursors, or from in-place weathering of precursor silicate materials under oxidizing conditions. These hypotheses and implications for habitability will be testable with in situ measurements by the Mars rover Curiosity when it reaches Mount Sharp.

CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) on MRO (Mars Reconnaissance Orbiter)

CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) is a hyperspectral imager that will be launched on the MRO (Mars Reconnaissance Orbiter) spacecraft in August 2005. MRO’s objectives are to recover climate science originally to have been conducted on the Mars Climate Orbiter (MCO), to identify and characterize sites of possible aqueous activity to which future landed missions may be sent, and to characterize the composition, geology, and stratigraphy of Martian surface deposits. MRO will operate from a sun-synchronous, near-circular (255x320 km altitude), near-polar orbit with a mean local solar time of 3 PM. CRISM’s spectral range spans the ultraviolet (UV) to the mid-wave infrared (MWIR), 383 nm to 3960 nm. The instrument utilizes a Ritchey-Chretien telescope with a 2.12° field-of-view (FOV) to focus light on the entrance slit of a dual spectrometer. Within the spectrometer, light is split by a dichroic into VNIR (visible-near-infrared, 383-1071 nm) and IR (infrared, 988-3960 nm) beams. Each beam is directed into a separate modified Offner spectrometer that focuses a spectrally dispersed image of the slit onto a two dimensional focal plane (FP). The IR FP is a 640 x 480 HgCdTe area array; the VNIR FP is a 640 x 480 silicon photodiode area array. The spectral image is contiguously sampled with a 6.6 nm spectral spacing and an instantaneous field of view of 61.5 μradians. The Optical Sensor Unit (OSU) can be gimbaled to take out along-track smear, allowing long integration times that afford high signal-to-noise ratio (SNR) at high spectral and spatial resolution. The scan motor and encoder are controlled by a separately housed Gimbal Motor Electronics (GME) unit. A Data Processing Unit (DPU) provides power, command and control, and data editing and compression. CRISM acquires three major types of observations of the Martian surface and atmosphere. In Multispectral Mapping Mode, with the gimbal pointed at planet nadir, data are collected at frame rates of 15 or 30 Hz. A commandable subset of wavelengths is saved by the DPU and binned 5:1 or 10:1 cross-track. The combination of frame rates and binning yields pixel footprints of 100 or 200 m. In this mode, nearly the entire planet can be mapped at wavelengths of key mineralogic absorption bands to select regions of interest. In Targeted Mode, the gimbal is scanned over ±60° from nadir to remove most along-track motion, and a region of interest is mapped at full spatial and spectral resolution. Ten additional abbreviated, pixel-binned observations are taken before and after the main hyperspectral image at longer atmospheric path lengths, providing an emission phase function (EPF) of the site for atmospheric study and correction of surface spectra for atmospheric effects. In Atmospheric Mode, the central observation is eliminated and only the EPF is acquired. Global grids of the resulting lower data volume observation are taken repeatedly throughout the Martian year to measure seasonal variations in atmospheric properties.

Validation of remote sensing products produced by the Special Sensor Ultraviolet Scanning Imager (SSUSI): a far UV-imaging spectrograph on DMSP F-16

Operational sensors are designed and intended to reliably produce the measurements needed to develop high-value key environmental parameters. The Special Sensor Ultraviolet Spectrographic Imager (SSUSI) is slated to fly on the next five Defense Meteorological Satellite Program launches (beginning with the launch of F16 in Fall 2001). SSUSI will routinely produce maps of ionospheric and upper atmospheric composition and image the aurora. In this paper we describe these products and our validation plans and the process through which we can assure our sponsors and data products users of the reliability and accuracy of these products.

MRO/CRISM Retrieval of Surface Lambert Albedos for Multispectral Mapping of Mars With DISORT-Based Radiative Transfer Modeling: Phase 1—Using Historical Climatology for Temperatures, Aerosol Optical Depths, and Atmospheric Pressures

We discuss the DISORT-based radiative transfer pipeline (ldquoCRISM_LambertAlbrdquo) for atmospheric and thermal correction of MRO/CRISM data acquired in multispectral mapping mode (~200 m/pixel, 72 spectral channels). Currently, in this phase-one version of the system, we use aerosol optical depths, surface temperatures, and lower atmospheric temperatures, all from climatology derived from Mars Global Surveyor Thermal Emission Spectrometer (MGS-TES) data and from surface altimetry derived from MGS Mars Orbiter Laser Altimeter (MOLA). The DISORT-based model takes the dust and ice aerosol optical depths (scaled to the CRISM wavelength range), the surface pressures (computed from MOLA altimetry, MGS-TES lower atmospheric thermometry, and Viking-based pressure climatology), the surface temperatures, the reconstructed instrumental photometric angles, and the measured I/F spectrum as inputs, and then a Lambertian albedo spectrum is computed as the output. The Lambertian albedo spectrum is valuable geologically because it allows the mineralogical composition to be estimated. Here, I/F is defined as the ratio of the radiance measured by CRISM to the solar irradiance at Mars divided by pi; if there was no martian atmosphere, I/F divided by the cosine of the incidence angle would be equal to the Lambert albedo for a Lambertian surface. After discussing the capabilities and limitations of the pipeline software system, we demonstrate its application on several multispectral data cubes-particularly, the outer reaches of the northern ice cap of Mars, the Tyrrhena Terra area that is northeast of the Hellas basin, and an area near the landing site for the Phoenix mission in the northern plains. For the icy spectra near the northern polar cap, aerosols need to be included in order to properly correct for the CO2 absorption in the H2O ice bands at wavelengths near 2.0 mum. In future phases of software development, we intend to use CRISM data directly in order to retrieve the spatiotemporal maps of aerosol optical depths, surface pressure, and surface temperature. This will allow a second level of refinement in the atmospheric and thermal correction of CRISM multispectral data.

Correction to “Extensive MRO CRISM observations of 1.27 µm O2 airglow in Mars polar night and their comparison to MRO MCS temperature profiles and LMD GCM simulations”

The Martian polar night distribution of 1.27 μm (0-0) band emission from O 2 singlet delta [O 2 ( 1 Δ g )] is determined from an extensive set of Mars Reconnaissance Orbiter (MRO) Compact Reconnaissance Imaging Spectral Mapping (CRISM) limb scans observed over a wide range of Mars seasons, high latitudes, local times, and longitudes between 2009 and 2011. This polar nightglow reflects meridional transport and winter polar descent of atomic oxygen produced from CO 2 photodissociation. A distinct peak in 1.27 μm nightglow appears prominently over 70-90NS latitudes at 40-60 km altitudes, as retrieved for over 100 vertical profiles of O 2 ( 1 Δ g ) 1.27 μm volume emission rates (VER). We also present the first detection of much (x80±20) weaker 1.58 μm (0-1) band emission from Mars O 2 ( 1 Δ g ). Co-located polar night CRISM O 2 ( 1 Δ g ) and Mars Climate Sounder (MCS, McCleese et al, 2007) temperature profiles are compared to the same profiles as simulated by the Laboratoire de Meteorologie Dynamique (LMD) general circulation/photochemical model (e.g., Lefevre et al, 2004). Both standard and interactive aerosol LMD simulations (Madeleine et al, 2011) underproduce CRISM O 2 ( 1 Δ g ) total emission rates by 40%, due to inadequate transport of atomic oxygen to the winter polar emission regions. Incorporation of interactive cloud radiative forcing on the global circulation leads to distinct but insufficient improvements in modeled polar O 2 ( 1 Δ g ) and temperatures. The observed and modeled anti-correlations between temperatures and 1.27 μm band VER reflect the temperature dependence of the rate coefficient for O 2 ( 1 Δ g ) formation, as provided in Roble (1995).

Performance of the wedge-and-strip microchannel plate detectors and electronics for the Global Ultraviolet Imager

This paper describes the design and performance of the detectors and electronics developed for the Global UV Imager (GUVI) aboard the NASA TIMED spacecraft, to be launched in May 2000. GUVI employs two alternate design detectors that are compact sealed units with MgF windows, CsI photocathodes, and wedge-and-strip anodes. The focal plane is 15.6 mm X 16.5 mm with images quantized to 176 spectral by 14 spatial pixels, although access to image data over the entire 25-mm dia active area is provided. Moderate detector resolution is achieved at a relatively low gain. Science emphasis is on high throughput, good image stability, and high radiometric accuracy. Significant detector aging is anticipated over an extended mission with sustained high counting rates. Custom hybrid front-end electronics were developed to enable direct coupling to the wedge-and-strip anodes. This eliminates inter-electrode potentials and the associated image distortion and shift with counting rate. A parallel fast channel provides pulse pile-up rejection. XY position, binning, and compression algorithms are performed in software by a fast, radiation- hardened RISC processor. A full-custom ASIC counts input and output rates for each detector.

On-orbit calibration of the Special Sensor Ultraviolet Scanning Imager (SSUSI): a far-UV imaging spectrograph on DMSP F-16

The Special Sensor Ultraviolet Spectrographic Imager (SSUSI) is currently slated for launch on the Defense Meteorological Satellite Program (DMSP) F-16 in November 2001. This instrument consists of a scanning imaging spectrograph (SIS) whose field-of-view is scanned from horizon-to-horizon and a nadir-looking photometer system (NPS). It will provide operational information about the state of the atmosphere above 100 km. The unique problems incurred by the observational requirements (e.g. that we be able to make daytime and nighttime observations) and the design trade-offs needed to meet those requirements were strong drivers on calibration requirements. Those design trade-offs and the expectation that the instrument calibration will change appreciably in-flight have led to the requirement to perform a large instrument characterization in-flight using only natural sources. We focus, in this paper, on the flight characterization of the SSUSI instrument. This includes discussions of the stellar calibration approach for radiometric calibration, measurements of internally scattered light, sensitivity to the South Atlantic Anomaly, measurements of changing pulse height distributions, and measuring changing reflectivity of a nadir viewing scan mirror. In addition, the calibration of the NPS system using natural sources is addressed.

Total photoabsorption cross section of molecular nitrogen near 83.4 nm

The photoabsorption cross section of molecular nitrogen near 83.4 nm has been measured at room temperature. The cross sections at the wavelengths of the 2s2p4 4P5/2, 4P3/2, and 4P1/2 (all - 2s²2p³ 4So3/2) O+ emission lines are measured to be 10.1 ± 1.6 Mb, 0.29 ± 0.02 Mb, and 0.049 ± 0.008 Mb respectively. These measurements were made with an O+ emission discharge source, and repeated using a synchrotron radiation source. Both measurements were made with the 0.008-nm resolution 6.65-m spectrometer at the SURF II storage ring of the National Institute for Standards and Technology.