Reflectance spectroscopy in planetary science: Review and strategy for the future

Reflectance spectroscopy is a remote sensing technique used to study the surfaces and atmospheres of solar system bodies. It provides first-order information on the presence and amounts of certain ions, molecules, and minerals on a surface or in an atmosphere. Reflectance spectroscopy has become one of the most important investigations conducted on most current and planned NASA Solar System Exploration Program space missions. This book reviews the field of reflectance spectroscopy, including information on the scientific technique, contributions, present conditions, and future directions and needs

Research in planetary astronomy

The objective is the continuation of a long-term research program designed to study the composition, structure and processes operating on the surfaces of solar system objects using the Mauna Kea Observatory with techniques and modern instrumentation. Reflectance spectroscopy and multispectral imaging in the spectral region, 0.3 to 5.0 micrometer are the major techniques used, although thermal (10 micrometer and 20 micrometer) radiometry are used in some aspects of the research. Some specific projects include: (1) systematic spectral imaging observations of the Moon; (2) systematic spectral imaging and spectral monitoring of the Martian surface; (3) thermal radiometry of asteroids as part of the IRAS follow-up and other target specific programs; (4) searches for asteroid satellites and dust belts using a stellar coronagraph; and (5) studies of circumstellar disks using a stellar coronagraph. Progress for each of the programs included is discussed. minerals; (2) completed observations of lunar multi-ringed basins and crater deposits in search of high-Ca spectral anomalies; (3) completed data reduction of an additional 5 asteroids observed by the coronagraphic technique in the search for asteroids satellites and debris clouds; and (4) completed the reduction and calibration of 350 asteroids observed at 10 micron and 20 micron using the NASA IRTF

Color differences on the lunar surface

Both a detailed literature survey and a new observational study were performed to determine and extend the knowledge of spectral reflectivity differences (color differences) on the lunar surface in the extended visible wavelength region. A survey of the extensive and disorganized literature revealed few positively known facts and indicated the need for an accurate, multi-passband observational study of a number of lunar areas of differing morphology. A 21-filter (0.4µ- 0.8µ), double beam photoelectric photometer was designed and constructed to observe differentially 83 lunar areas, some many times, to an accuracy of 0.1% to 0.3%. Some results were the discovery of: (1) many color variations up to 10% with some to about 60%, (2) a dependence of relative color on phase angle but no temporally varying luminescence, (3) broadband absorption features on spectral reflectivity curves and possibly some less broad, low amplitude (0.2%- 0.5%) humps, (4) a dependence of spectral curve shape on lunar morphology and, (5) no universal dependence of color on brightness, although some mare areas show this tendency. These results indicate that color differences are caused mainly by compositional differences and that the shapes of the spectral reflectivity curves give some indications of the rock and mineral composition of the lunar surface

Reflectance spectra of mafic silicates and phyllosilicates from .6 to 4.6 microns

The results of spectral measurements for mafic silicates are given. The study provided valuable spectral reflectance information about mafic silicates and phyllosilicates in the 2.5 to 4.6 micron wavelength region. It was shown that the reflectance of these materials is strongly affected by the presence of H2O and OH. Therefore, the identification of these absorbing species is greatly enhanced

Planetary Instrument Definition and Development Program (PIDDP). Instrument for future planetary flight missions: A visible-infrared imaging spectrometer for planetary missions

The objective of this project is to develop and prove a small, light-weight, efficient imaging spectrometer design to cover the VIS/NIR spectral range for applications particularly but not exclusively to NASA inner solar system space missions. A design and a brassboard prototype will be developed and tested. Progress over the first year of this project includes design specification, optical design layout, grating specifications, infrared detector selection, and mechanical design. Mechanical and grating manufacturing drawings were begun. We developed an agreement in principle to cooperate with the German space group, DLR, to apply some of their electronics microminiaturization technology to this imaging spectrometer project, mostly or entirely at their expense. Funds from NASA for the second year of this effort have been received and the effort is on track. Release of funds for the third year of this award will be requested later this year in order to accelerate this work and bring it to a conclusion in time for new NASA missions considerations as well as to make effective use of the DLR contributions

Two-Dimensional Silicon Vidicon Astronomical Photometer

We have developed and successfully used an integrating two-dimensional silicon diode array vidicon photometer which is exceptionally well suited for use with telescopes. The video signal is read out from the 1-cm silicon target of the vidicon through a current mode preamplifier and then converted to digital form and stored on magnetic tape. The 256 × 256 element frames are recorded at 20,000 eight-bit words/sec. The vidicon tube has a published quantum efficiency ranging from 85% at 0.5 µ to 6% at 1.1 µ and must be cooled to about -65°C to eliminate thermal dark current. The minimum detectable signal in the present system is about 1000 carriers per resolution element, limited by preamplifier and other system noise. The system is used as a single-frame camera. The large dynamic range (>10^3), linear response, high quantum efficiency over a large spectral region, and low cost of the system make it well suited for digital direct image and spectroscopy as well as for a laboratory digitizer of two-dimensional material

Differences between proposed Apollo sites: 1. Synthesis

Recent observations of the spectral reflectivity and emissivity of the five prime Apollo landing sites are evaluated in the context of similar observations of other localities on the moon and of data returned from unmanned lunar probes. We conclude that those five sites differ significantly only in minor constituents and/or relative valence states and that those differences are more modest than the differences that characterize mare regions generally. Recommendations of priorities for the five prime Apollo sites are made based on their uniqueness for sample return. Sampling of other lunar localities displaying anomalous emissivities and extreme color differences will be required to ascertain the full range of lithologies that constitute the lunar surface

Evidence of Titan's Climate History from Evaporite Distribution

Water-ice-poor, 5-$\mu$m-bright material on Saturn's moon Titan has previously been geomorphologically identified as evaporitic. Here we present a global distribution of the occurrences of the 5-$\mu$m-bright spectral unit, identified with Cassini's Visual Infrared Mapping Spectrometer (VIMS) and examined with RADAR when possible. We explore the possibility that each of these occurrences are evaporite deposits. The 5-$\mu$m-bright material covers 1\% of Titan's surface and is not limited to the poles (the only regions with extensive, long-lived surface liquid). We find the greatest areal concentration to be in the equatorial basins Tui Regio and Hotei Regio. Our interpretations, based on the correlation between 5-$\mu$m-bright material and lakebeds, imply that there was enough liquid present at some time to create the observed 5-$\mu$m-bright material. We address the climate implications surrounding a lack of evaporitic material at the south polar basins: if the south pole basins were filled at some point in the past, then where is the evaporite

Near-Infrared Mapping and Physical Properties of the Dwarf-Planet Ceres

We study the physical characteristics (shape, dimensions, spin axis direction, albedo maps, mineralogy) of the dwarf-planet Ceres based on high-angular resolution near-infrared observations. We analyze adaptive optics J/H/K imaging observations of Ceres performed at Keck II Observatory in September 2002 with an equivalent spatial resolution of ~50 km. The spectral behavior of the main geological features present on Ceres is compared with laboratory samples. Ceres' shape can be described by an oblate spheroid (a = b = 479.7 +/- 2.3 km, c = 444.4 +/- 2.1 km) with EQJ2000.0 spin vector coordinates RA = 288 +/- 5 deg. and DEC = +66 +/- 5 deg. Ceres sidereal period is measured to be 9.0741 +/- 0.0001 h. We image surface features with diameters in the 50-180 km range and an albedo contrast of ~6% with respect to the average Ceres albedo. The spectral behavior of the brightest regions on Ceres is consistent with phyllosilicates and carbonate compounds. Darker isolated regions could be related to the presence of frost.Comment: 11 pages, 8 Postscript figures, Accepted for publication in A&