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NASA NTRS1993

First results from a laboratory facility for measurement of emission spectra under simulated planetary conditions

We have developed a laboratory spectroscopic facility for the measurement of emission spectra under simulated planetary conditions. Spectral measurements are made from 6 to 13 microns with a scanning grating monochromator equipped with a HgCdTl detector. An environment chamber in service in Hawaii for several years in which we can control the temperature from 77 K to 500 K, the pressure from 10(exp -5) torr to two atmospheres, has been equipped with a 77 K or 273 K cold shield. The shield serves to minimize light reflected off the sample and to aid in development of thermal gradients for obtaining spectra under conditions simulating the thermal environment of airless bodies. Samples are placed in small cups on a temperature controlled substrate allowing measurements of emission due to heating from below by the substrate, or from illumination from a solar simulation source.

Lucey, Paul G.↗

NASA NTRS1993

Remote visual detection of impacts on the lunar surface

We propose a novel method of remotely observing impacts on the airless Moon that may extend the present data base on meteoroids down to 1 m in diameter. Meteorites or comets of radius approximately 1-100 m are burnt away or dispersed in the atmospheres of the Earth and Venus. However, when such objects strike the Moon they deposit their energy in a small initial volume, forming a plasma plume whose visible and infrared radiation may be visible from the Earth. We consider impacts of model SiO2 projectiles on the surface of an SiO2 model Moon.

Melosh, H. Jay↗

NASA NTRS1994

Grain rims on ilmenite in the lunar regolith: Comparison to vapor deposits on regolith silicates

In efforts to understand regolith evolution on airless bodies, increasing attention is now being payed to those processes and events that alter or 'weather' the surfaces of regolith grains. This attention has developed partly out of the ongoing need to optimize models of planetary reflectance spectra and the growing recognition that diverse types of grain coatings and surface alterations occur which can strongly influence mineral reflectance properties. In addition to their implications for optical properties, surface features on regolith grains have provided useful clues to the basic thermal, chemical, and radiation history of regoliths.

Christoffersen, R.↗

NASA NTRS1993

Optical effects of space weathering: The role of the finest fraction

The optical properties of lunar soils are different than those of rocks which they are derived. As a consequence of lunar space weathering, soils are darker and exhibit a distinctive red-sloped continuum and weaker mineral absorption bands. The accumulation of dark glass-welded aggregates (agglutinates) has been thought to account for these optical effects of space weathering on lunar soils. Spectroscopic analyses of agglutinate separates and size fractions for a suite of lunar soils presented here indicate that the agglutinate paradigm is insufficient to fully account for lunar optical alteration. It is the finest fraction of lunar soils (less than 25 microns which constitute approximately 25% wt.) that dominates the optical properties of the bulk soil. Unlike size fractions of most silicates for which the finest fraction is the brightest, the lunar soil size fractions all have comparable albedos in the short-wavelength visible. In the near infrared, however, it is the finest fraction that exhibits the steep red continuum and weak absorption bands. The properties of the finest fraction cannot be duplicated by preparing a fine fraction by grinding larger agglutinate-rich soil particles. These results suggest space weathering on airless bodies is dominated by surface correlated processes (perhaps associated with the developement of fine-grained Fe(dot) on or near the surface of grains), and the accumulation of the large agglutinates is not necessarily required to account for lunar optical alteration.

Pieters, C. M.↗

NASA NTRS1994

Mercury: Evidence for anorthosite and basalt from mid-infrared (7.3-13.5 micrometers) spectroscopy

Spectroscopic observations (7.3-13.5 micrometers) of three locations on the surface of Mercury are reported. The observed spectral radiance emanated from equatorial and low altitude regions between 12 and 32 deg mercurian longitude on 8 December 1990, from the longitudinal region 22-44 deg on 10 December 1990, and from the longitudinal region 110-130 deg on 12 July 1992; all locations are primarily intercrater plains. Spectra indicate compositional differences among these three locations. The emissivity maximum, or Christiansen emission peak, occurs at 8.1 micrometers in the 8 December 1990 spectra, but at shorter wavelengths in the data of 10 December 1990 and 12 July 1992. Emission peaks near 8 micrometers indicate rocks of intermediate or mafic composition. Spectra from 22 to 44 deg longitude resemble spectra of terrestrial basalt and diorite with SiO2 content between 49 and 55%. The Christiansen feature in spectra from near 110-130 deg longitude strongly suggests the presence of plagioclase, in particular labradorite, while the overall spectrum resembles anorthosite. The spectra from all three locations on Mercury show distinct and recognizable features, the principal Christiansen emission peak being the most prominent, but they also contain features that we have not yet identified. The general indication from the spectra is that Mercury's surface consists of minerals more depleted in oxidized iron than those on the Moon. We also explore the theoretical and observational complexities of ground-based mid-infrared spectroscopy of airless bodies in general and Mercury in particular. A spectroscopic study of quartzite in both reflectance and emittance illustrates the practical, spectral validity of Kirchhoff's law.

Sprague, A. L.↗

NASA NTRS1995

Charged Particle Alterations of Surfaces in the Solar System

The surfaces of 'airless' bodies in the solar system are exposed to the ambient plasma, micrometeorites, and the solar UV. The effects of these space weathering agents on surfaces in the solar system has been studied in this project. In the last three years work was carried out on volatile depletion at Mars, on sputtering of the lunar surface, on absorption by implanted S in vapor-deposited H2O and its relevance to observations of Europa's surface in the UV, and on the spectral changes produced on irradiating SO2 and its possible relevance to Io. In addition, the role of plasma-induced charging of E-ring grains was evaluated because of its relevance to E-ring particle source and the lifetime of the E-ring. Finally, the detection of sputtered material from Dione by the CAPS instrument on CASSINI was evaluated as a tool for analysis of satellite surface composition, and the role of sputtering on the ambient OH in the vicinity of the ice satellites and the E-ring was evaluated.

Johnson, R. E.↗

NASA NTRS1996

Galactic Cosmic-Ray-Produced Thermoluminescence Profiles in Meteorites Lunar Samples and a Terrestrial Analog

The long-term radiation shielding properties of common extraterrestrial materials are poorly known, although these materials are the most likely structural elements on airless worlds such as the Moon. We report on radiation dose profiles in meteorites and lunar soil cores using specific minerals as naturally-occurring "dosimeters". We find that radiation profiles are fairly flat in typical meteoroid bodies (less than 85 cm radius) and drop by only about 40% through about 2.5 m of lunar soil. These profiles are produced by primary galactic cosmic rays and the secondary proton cascade but with a significant contribution by secondary neutrons at depths of about 2 m (300 g/sq cm).

Benoit, Paul H.↗

NASA NTRS1999

Mineralogy of the Solar System

The coming decade will witnesses the first sample return missions from solar system bodies in 30 years. These samples will all be very small, some missions return only a few milligrams of total mass. Fortunately, the capability of modem methods to characterize ultra-small samples is well established from analysis of interplanetary dust particles (IDPs), interstellar grains recovered from meteorites, and other materials requiring ultra-sensitive analytical capabilities. Powerful analytical techniques are available that require, under favorable circumstances, single particles of only a few nanograms for entire suites of fairly comprehensive characterizations. A returned sample of greater than 1,000 particles with total mass of just one microgram permits comprehensive quantitative geochemical measurements that are impractical to can-y out in situ by flight instruments. With the Galileo flybys of Gaspra and Ida, it is now recognized that even very small airless bodies have indeed developed a particulate regolith. Acquiring a sample of the bulk regolith, a simple sampling strategy, provides two critical pieces of information about the body. Regolith samples are excellent bulk samples since they normally contain all the key components of the local environment, albeit in particulate form. Furthermore, since this fine fraction dominates remote measurements, regolith samples also provide information about surface alteration processes and are a key link to remote sensing of other bodies. Studies indicate that a statistically significant number of nanogram-sized particles should be able to characterize the regolith of a primitive asteroid, although the presence of larger components within even primitive meteorites (e.g.. Murchison), e.g. chondrules, CAI, large crystal fragments, etc., points out the limitations of using data obtained from nanogram-sized samples to characterize entire primitive asteroids. However, most important asteroidal geological processes have left their mark on the matrix, since this is the finest-grained portion and therefore most sensitive to chemical and physical changes. Thus, the following information can be learned from this fine grain size fraction alone: (1) mineral paragenesis; (2) regolith processes, (3) bulk composition; (4) conditions of thermal and aqueous alteration (if any); (5) relationships to planets, comets, meteorites (via isotopic analyses, including oxygen; (6) abundance of water and hydrated material; (7) abundance of organics; (8) history of volatile mobility, (9) presence and origin of presolar and/or interstellar material.

Zolensky, Michael E.↗

NASA NTRS1999

The Topography and Basin Deposits of the Equatorial Highlands: A MGS-Viking Synergistic Study

One of the greatest unresolved issues concerns the evolution of Mars early in its history; during the time period that accretion was winding down but the frequency of impacting debris was still heavy. Ancient cratered terrain that has only been moderately modified since the period of heavy bombardment covers about a quarter of the planet's surface but the environment during its formation is still uncertain. This terrain was dominantly formed by cratering. But unlike on the airless Moon, the impacting craters were strongly modified by other contemporary surface processes that have produced distinctive features such as: 1) dendritic channel networks, 2) rimless, flatfloored craters, 3) obliteration of most craters smaller than a few kilometers in diameter (except for post heavy-bombardment impacts), and 4) smooth intercrater plains. The involvement of water in these modification processes seems unavoidable, but interpretations of the surface conditions on early Mars range from the extremes of: 1) the "cold" model which envisions a thin atmosphere and surface temperatures below freezing except for local hydrothermal springs; and 2) the "warm" model, which invokes a thick atmosphere, seasonal temperatures above freezing in temperate and equatorial regions, and at least occasional precipitation as part of an active hydrological cycle. The nature of hydrologic cycles, if they occurred on Mars, would have been critically dependent on the environment. The resolution of where along this spectrum the actual environment of early Mars occurred is clearly a major issue, particularly because the alternate scenarios have much different implications about the possibility that life might have evolved on Mars. Additional information is contained in the original extended abstract.

Moore, J. M.↗

NASA NTRS2000

Thermal Emission Spectra of Phobos, Vesta, Ceres, and Pallas: A Comparison

Ultraviolet, visual, and near-infrared spectra of Phobos, obtained by Mariner 9 and Viking Orbiters, were interpreted to suggest a compositional similarity with carbonaceous chrondrites. Such a composition would be inconsistent with the moon's origin in the proto-Mars region, as Mars is composed chiefly of differentiated silicates. This interpretation was used to suggest that the moons originated in the main-asteroid belt, with subsequent capture and orbital evolution into their current locations. Interpretations of more recent visual and near-infrared spectra, obtained by Phobos-2 and Mars Pathfinder, have demonstrated that the Phobos spectrum is more similar to spectra of other classes of asteroids and lunar soils. If lunar mare soil is the correct analogy, then such a composition suggests a formation of Phobos from materials similar to that on Mars, i.e. basalts, and would not require a dynamically difficult capture and orbital evolution. During the science phasing orbits of the Mars Global Surveyor mission Thermal Emission Spectrometer (TES) observations of Phobos were acquired at each of four encounters. The spectral variability observed for localized surface regions on Phobos has been previously reported and is greatest near the northern wall of Stickney crater. Interpretation of the thermal infrared spectra of airless bodies, based upon most existing laboratory measurements, is complicated by the absence of interstitial gases on the celestial objects that would act to minimize potential thermal gradients in the upper layers of the surface. As an aid to interpretation of the TES Phobos spectra are compared to telescopic and airborne thermal infrared spectra of asteroids from several classes, including Ceres (G), Pallas (B), and Vesta (V). The asteroid spectra provide a direct analogy to the physical situation encountered at the surface of Phobos, albeit different thermal gradients may exist for each surface. This work is supported by NASA RTOP's 344-30-30-01 and 344-34-21-08.

Roush, Ted↗

NASA NTRS1999

Topographic Evaluation of Mars 2001 Candidate Landing Sites: A MGS-Viking Synergistic Study

One of the greatest unresolved issues concerns the evolution of Mars early in its history; during the time period that accretion was winding down but the frequency of impacting debris was still heavy. Ancient cratered terrain that has only been moderately modified since the period of heavy bombardment covers about a quarter of the planet's surface but the environment during its formation is still uncertain. This terrain was dominantly formed by cratering. But unlike on the airless Moon, the impacting craters were strongly modified by other contemporary surface processes that have produced distinctive features such as 1) dendritic channel networks, 2) rimless, flatfloored craters, 3) obliteration of most craters smaller than a few kilometers in diameter (except for post heavy-bombardment impacts), and 4) smooth intercrater plains. The involvement of water in these modification processes seems unavoidable, but interpretations of the surface conditions on early Mars range from the extremes of 1) the "cold" model which envisions a thin atmosphere and surface temperatures below freezing except for local hydrothermal springs; and 2) the "warm" model, which invokes a thick atmosphere, seasonal temperatures above freezing in temperate and equatorial regions, and at least occasional precipitation as part of an active hydrological cycle. The nature of hydrologic cycles, if they occurred on Mars, would have been critically dependent on the environment. The resolution of where along this spectrum the actual environment of early Mars occurred is clearly a major issue, particularly because the alternate scenarios have much different implications about the possibility that life might have evolved on Mars.

Moore, J. M.↗

NASA NTRS2001

Did We Really Land on the Moon? Suggestions for Science Teachers

On Feb. 15, 2001, the FOX network broadcast a one hour TV program claiming that the Apollo lunar landings had all been staged in a studio set in Nevada, and that astronauts had never landed on the Moon. This claim can be refuted on many points, focused on the supposed photographic evidence indicating studio lighting or other aspects of the Apollo missions. The TV program ignored the returned lunar samples. Science teachers have been swamped with questions about the program, and this paper has been written to suggest how they can use it to stimulate interest in lunar geology. The article shows how the NASA Lunar Disk kits, available on loan to schools, can be studied by students. These samples are visibly different from terrestrial soils and rocks in several ways. There is no quartz in the lunar soil; there are no true reds and browns resulting from ferric oxides; and the textures of the soil (agglutinates and glass beads) can only be formed on an airless planet. The article has several pictures of the lunar surface and the Apollo samples, and a short bibliography for background reading.

Lowman, Paul D., Jr.↗

NASA NTRS2002

Thermal Modeling on Planetary Regoliths

The thermal region of the spectrum is one of special interest in planetary science as it is the only region where planetary emission is significant. Studying how planetary surfaces emit in the thermal infrared can tell us about their physical makeup and chemical composition, as well as their temperature profile with depth. This abstract will discuss a model of thermal energy transfer in planetary regoliths on airless bodies which includes both conductive and radiative processes while including the time dependence of the solar input function.

Hale, A. S.↗

NASA NTRS1998

Dusty Plasma Dynamics Near Surfaces in Space

The investigation 'Dusty Plasma Dynamics Near Surfaces in Space' is an experimental and theoretical study of the dynamics of dust particles on airless bodies in the solar system in the presence of a photoelectron sheath generated by solar ultraviolet light impinging on the surface. Solar UV illumination of natural and manmade surfaces in space produces photoelectrons which form a plasma sheath near the surface. Dust particles on the surface acquire a charge and may be transported by electric fields in the photoelectron sheath generated by inhomogeneities in the surface or the illumination (such as shadows). The sheath itself has a finite vertical extent leading to (at least) an electric field normal to the illuminated surface. If dust particles are launched from the surface by some other process, such as meteoroid impact, or spacecraft activity on the surface, these grains become charged and move under the influence of gravity and the electric field. This can give rise to suspension of the particles above the surface, loss from the parent body entirely (if accelerated beyond escape velocity), and a different distribution of dust ejecta from what would be expected with purely gravitational dynamics.

Colwell, Joshua E.↗

NASA NTRS1983

Space Technology for Book Preservation

The Library of Congress has patented a process to extend book life. It is called vapor phased deacidification, and involves the use of DEZ (diethyl zinc), a chemical vapor which neutralizes acid and deposits an alkaline reserve on book pages. As the process must be done in an airless environment, the library utilized Goddard Space Flight Center's vacuum chamber for deacidification. The chamber can treat 5,000 books at once, and a new facility is planned. The Library plans to license the technology to private companies; several universities are interested in the process.

Source record↗

NASA NTRS1982

Advanced Welding Tool

Accutron Tool & Instrument Co.'s welder was originally developed as a tool specifically for joining parts made of plastic or composite materials in any atmosphere to include the airless environment of space. Developers decided on induction or magnetic heating to avoid causing deformation and it also can be used with almost any type of thermoplastic material. Induction coil transfers magnetic flux through the plastic to a metal screen that is sandwiched between the sheets of plastic to be joined. When welder is energized, alternating current produces inductive heating on the screen causing the adjacent plastic surfaces to melt and flow into the mesh, creating a bond on the total surface area. Dave Brown, owner of Great Falls Canoe and Kayak Repair, Vienna, VA, uses a special repair technique based on operation of the Induction Toroid Welder to fix canoes. Whitewater canoeing poses the problem of frequent gashes that are difficult to repair. The main reason is that many canoes are made of plastics. The commercial Induction model is a self-contained, portable welding gun with a switch on the handle to regulate the temperature of the plastic melting screen. Welder has a broad range of applications in the automobile, appliance, aerospace and construction industries.

Source record↗

NASA NTRS2003

Space Weathering: An Ultraviolet Indicator

We present evidence suggesting that the spectral slope of airless bodies in the UV-visible wavelength range can be used as an indicator of exposure to space weathering. While space weathering generally produces a reddening of spectra in the visible-NIR spectral regions, it tends to result in a bluing of the UV-visible portion of the spectrum, and may in some cases produce a spectral reversal. The bluing effect may be detectable with smaller amounts of weathering than are necessary to detect the longer-wavelength weathering effects.

Hendrix, A. R.↗

NASA NTRS2004

Space Weathering: An Ultraviolet Indicator

Hendrix, A. R.↗