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Boynton, W. V.

Publications and source records attributed to Boynton, W. V..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Ground Ice at the Phoenix Landing Site: A Preflight Assessment

One of the objectives of the Mars Scout mission, Phoenix, is to characterize the present state of water in the martian environment, in a location where water may play a significant role in the present and past habitability of Mars. Given the generally dry and cold climate of Mars today any substantial amount of water is expected to occur in the form of ground ice (subsurface ice) within the regolith. The Mars Odyssey Gamma Ray Spectrometer has indicated abundant subsurface hydrogen and inferred ground ice at high latitudes. Therefore, the Phoenix mission will be targeted to land in the northern high latitudes (approximately 65 degrees N - 75 degrees N) where ground ice is expected to be abundantly available for analysis. The lander will be capable of excavating, sampling, and analyzing, dry and water-rich/icy soils. The location and depth of excavation necessary to achieve the goals of sampling and analysis of icy material become important parameters to assess. In the present work we ask two key questions: 1) At what depth within the regolith do we expect to find ice? 2) How might this depth vary over the region of potential landing sites? Numerous lines of evidence can be employed to provide an indication of the presence or absence of shallow ground ice at the potential landing sites. For example geomorphology, neutrons, gamma rays, and theory each contribute clues to an overall understanding of the distribution of ice. Orbital observations provide information on a variety of spatial scales, typically 10 s of meters (patterned ground) to 100 s of kilometers (gamma rays). While information on all of these scales are important, of particular interest is how the presence and depth of ground ice might vary on spatial scales comparable to the lander and its work area. While ground ice may be stable (and present) on a regional scale, local-scale slopes and changes in the physical characteristics of soils can result in significant variations in the distribution of ice.

Mellon, M. T.↗
NASA NTRS2004

Northern and Southern Permafrost Regions on Mars with High Content of Water Ice: Similarities and Differences

The measurements by neutron detectors on Odyssey have revealed two large poleward regions with large depression of flux of epithermal and high energy neutrons [1-3]. The flux of neutrons from Mars is known to be produced by the bombardment of the surface layer by galactic cosmic rays. The leakage flux of epithermal and fast neutrons has regional variation by a factor of 10 over the surface of Mars (e.g. see [3- 5]). These variations are mainly produced by variations of hydrogen content in the shallow subsurface. On Mars hydrogen is associated with water. Therefore, the Northern and Southern depressions of neutron emission could be identified as permafrost regions with very high content of water ice [1-5]. These regions are much larger than the residual polar caps, and could contain the major fraction of subsurface water ice. Here we present the results of HEND neutron data deconvolution for these regions and describe the similarities and differences between them.

Mitrofanov, I. G.↗
NASA NTRS2004

Northern and Southern Permafrost Regions on Mars with High Content of Water Ice: Similarities and Differences

The measurements by neutron detectors on Odyssey have revealed two large poleward regions with large depression of flux of epithermal and high energy neutrons. The flux of neutrons from Mars is known to be produced by the bombardment of the surface layer by galactic cosmic rays. The leakage flux of epithermal and fast neutrons has regional variation by a factor of 10 over the surface of Mars. These variations are mainly produced by variations of hydrogen content in the shallow subsurface. On Mars hydrogen is associated with water. Therefore, the Northern and Southern depressions of neutron emission could be identified as permafrost regions with very high content of water ice. These regions are much larger than the residual polar caps, and could contain the major fraction of subsurface water ice. Here we present the results of HEND neutron data deconvolution for these regions and describe the similarities and differences between them.

Mitrofanov, I. G.↗
NASA NTRS2004

Elemental Composition Variations for Large Dusty and Rocky Regions on Mars Using Gamma-Ray Data from the Mars Odyssey Gamma-Ray Spectrometer

The Gamma-Ray Spectrometer (GRS) on the Mars Odyssey spacecraft has been mapping the elemental composition of the surface materials since June 2002. To study elemental composition variations on the martian surface, seven large regions of Mars were selected: three very dusty ones and four mainly rocky ones. Large regions were used to get good counting statistics on as many gamma-ray peaks as possible from spectrum accumulated by the GRS experiment on Mars Odyssey, including elements with poor counting statistics. Data from TES were used to help select these regions. Gamma-ray peaks for several elements were analyzed. Some results and trends are reported.

Evans, L. G.↗
NASA NTRS2004

Ancient Giant Basin/Aquifer System in the Arabia Region, Mars, and Its Influence on the Evolution of the Highland-Lowland Boundary

Ancient geologic and hydrologic phenomena on Mars observed through the magnetic data provide windows to the ancient past through the younger Argyre and Hellas impacts, the northern plains basement and the rock materials that mantle the basement, and the Tharsis and Elysium magmatic complexes (recently referred to as superplumes). These signatures, coupled with highly degraded macrostructures (tectonic features that energetic planet during its embryonic development (0.5 Ga or so of activity) with an active dynamo and magnetosphere. One such window into the ancient past occurs northwest of the Hellas impact basin in Arabia Tern. Arabia Terra is one of the few water-rich equatorial regions of Mars, as indicated I through impact crater and elemental information. This region records many unique characteristics, including predominately Noachian materials, a highland-lowland boundary region that is distinct from other boundary regions, the presence of very few macrostructures when compared to the rest of the cratered highlands, the largest region of fretted terrain on Mars, outflow channels such as Mamers Valles that do not have obvious origins, and distinct albedo, thermal inertia, gravity, magnetic, and elemental signatures.

Dohm, J. M.↗
NASA NTRS2003

Gamma Rays in a Spectrum from the Mars Odyssey Gamma-Ray Spectrometer

The gamma-ray spectrum from a long sum over the middle latitudes of Mars measured by the Mars Odyssey Gamma Ray Spectrometer was analyzed. About 250 peaks and features were observed, including many seen during the cruise to Mars. The sources of about 85% of these gamma rays were identified. Most were background lines from the Ge detector or from Ti, Mg, and Zn near the detector.

Reedy, R. C.↗
NASA NTRS2003

AGE (Argon Geochronology Experiment): An Instrument for Geochronology on the Surface of Mars

As our knowledge of the planet Mars continues to grow, one parameter that remains elusive is the absolute chronology of the planet s geological history. Although crater counts have provided a robust relative chronology, impactor fluxes are poorly enough known that there are places on Mars where the absolute age is uncertain by a factor of two or more. To resolve these uncertainties, it will be necessary to either analyze well-documented samples returned to the Earth from the Martian surface or to perform in situ measurements with sufficient precision. Sample return is still at least a decade away, and even then it might be from a biologically interesting area that might be geologically complex. Hence an in situ measurement, within an uncertainty of 20% or better, could greatly improve our knowledge of the history of Mars. With funding from the Planetary Instrument Definition and Development Program (PIDDP), we have been working on an instrument to perform potassium-argon (K-Ar) and cosmic-ray exposure (CRE) dating in situ on the surface of Mars. For either of these techniques, it is necessary to measure the abundance of one or more major or minor elements (K in the case of KAr; all majors and minors in the case of CRE) and the abundance and isotopes composition of a noble gas (Ar in the case of K-Ar; He, Ne and Ar for CRE dating). The technology for either of these types of measurements exists, but has never before been integrated for a spacecraft. We refer to the instrument as AGE, the Argon Geochronology Experiment (although we will measure the noble gases He and Ne as well for CRE ages). We report here on the basic components that go into such an instrument, both those that use existing technology and those that had to be developed to create the integrated package.

Swindle, T. D.↗
NASA NTRS2003

Comparison Between North and South Near Polar Regions of Mars from HEND/Odyssey Data

It is known that North and South near polar regions are affected by global redistribution of atmospheric CO2. The maximal thickness of CO2 snow depth may be as high as 1 m at latitudes close to martian poles. It explains why neutron flux above martian poles significantly varies from summer to winter seasons. It occurs because CO2 frost hides upper surface layer from the orbit observations. This fact was used to estimate thickness of CO2 deposit at different latitudes. Here we suggest to make comparison between martian near polar regions in both ways as in terms of subsurface regolith structure as in terms of distribution of CO2 deposits.

Litvak, M. L.↗
NASA NTRS2002

Dar Al Gani 872: Yet Another Eucrite, Yet Another Lesson to Learn?

We present chemical and mineralogical data on a new monomict basaltic eucrite recovered from Libya. In contrast to most other eucrites, it exhibits high shock features, unusually heterogeneous exsolution of pigeonite, and interesting melt pockets. Additional information is contained in the original extended abstract.

Patzer, A.↗
NASA NTRS2002

The NEAR-Shoemaker XGRS Experiment: An End of Mission Overview

We present an overview of the results from the NEAR (Near Earth Asteroid Rendezvous)-Shoemaker remote sensing X-Ray/Gamma-Ray Spectrometer experiment for more than a year of operation in orbit and on the surface of 433 Eros. Additional information is contained in the original extended abstract.

Trombka, J. I.↗
NASA NTRS2002

Elemental Composition Results for the NEAR-Shoemaker Gamma-Ray Spectrometer

Elemental composition results for the surface measurements on 433 Eros by the Near Earth Asteroid Rendezvous (NEAR) gamma-ray spectrometer are reviewed. Extension of the elemental composition results to the whole asteroid using orbital gamma-ray measurements will be considered. Additional information is contained in the original extended abstract.

Evans, L. G.↗
NASA NTRS2001

The Composition of 433 Eros: A Mineralogical-Chemical Synthesis

We report on an effort with the Near-Infrared Spectrometer/Multi-Spectral Imager (NIS/MSI) and X-ray/Gamma-ray Spectrometer (XGRS) teams to synthesize our data sets to constrain the relationship between Eros and meteorites; the mineralogy, abundances and compositions of Eros; and the processes that formed Eros. Additional information is contained in the original extended abstract.

McCoy, T. J.↗
NASA NTRS2001

Preliminary Results of the NEAR Gamma-Ray Spectrometer

The Near Earth Asteroid Rendezvous (NEAR) spacecraft was put into a 35 km orbit on December 13, 2000. This is first opportunity for the Gamma-ray Spectrometer to collect good geochemical data from Eros. Preliminary measurements for a number of key elements are in good agreement with predictions. Additional information is contained in the original extended abstract.

Evans, L. G.↗
NASA NTRS2001

The X-Ray Spectrometer for Mercury MESSENGER

Mercury is the closest planet to the Sun and because it is so close, it is difficult to study from Earth-based observatories. Its proximity to the Sun has also limited the number of spacecraft to visit this tiny planet to just one, Mariner 10, which flew by Mercury twice in 1974 and once in 1975. Mariner 10 provided a wealth of new information about Mercury, yet much still remains unknown about Mercury's geologic history and the processes that led to its formation. The origin of Mercury's metal-rich composition is just one area of investigation awaiting more and improved data to sort between competing hypotheses. Mercury plays an important role in comparative planetology, and many of the processes that were important during its formation are relevant to the Earth's early history. MESSENGER (Mercury Surface, Space Environment, Geochemistry, and Ranging) is a Discovery mission that has been designed to fly by and orbit Mercury. It will launch in March 2004, flyby Mercury in 2007 and 2008 and enter an elliptical orbit in April 2009. During the one-year orbital phase, a suite of instruments on board the MESSENGER spacecraft will study the exosphere, magnetosphere, surface, and interior of Mercury. One of these instruments will be an X-Ray Spectrometer (XRS) that will measure surface elemental abundances. Remote X-ray spectroscopy has been accomplished before on the Apollo 15 and 16 missions, and more recently on NEAR Shoemaker. The MESSENGER XRS will measure characteristic X-ray emissions induced in the surface of Mercury by the incident solar flux. The Ka lines for the elements Mg, Al, Si, S, Ca, Ti, and Fe will be detected with spatial resolution on the order of 40 km when counting statistics are not a limiting factor. These measurements can be used to obtain quantitative information on elemental composition.

Starr, R. D.↗
NASA NTRS2000

Scientific Objectives of the Mars Surveyor 2001 Gamma-Ray Spectrometer

The Gamma-Ray Spectrometer (GRS) is one of the instruments on the Mars Surveyor 2001 Orbiter, which is part of NASA's Mars-Surveyor program. The GRS is really an instrument suite consisting of the GRS, a neutron spectrometer (NS), and a high-energy neutron detector (FIEND). Each of these instruments/sensors are remotely mounted at different locations on the spacecraft and connect to a central electronics box. The GRS will achieve global mapping of the elemental composition of the surface and the abundance of hydrogen in the shallow subsurface. It is an updated design using the same technology as the lost Mars Observer mission. The Martian surface is continuously bombarded by cosmic ray particles; their interactions with the constituents of the soil produces nuclear reaction cascades with fast neutrons being the main secondaries. Those neutrons interact in turn with the nuclei of the elements that make up the soil and they eventually get slowed to thermal energies. In this process they leave the nuclei in an excited state that decays via the emission of characteristic gamma rays. All these processes are precisely known and have been simulated by means of numerical models. Thus, remote gamma-ray spectroscopy is a useful method for quantitatively measuring the geochemical composition of the surface down to a few tens of g/sq cm. Additional information is contained in original extended abstract.

Boynton, W. V.↗
NASA NTRS2000

Differential Scanning Calorimetry and Evolved Gas Analysis at Mars Ambient Conditions Using the Thermal Evolved Gas Analyser (TEGA)

Differential Scanning Calorimetry (DSC) combined with evolved gas analysis (EGA) is a well developed technique for the analysis of a wide variety of sample types with broad application in material and soil sciences. However, the use of the technique for samples under conditions of pressure and temperature as found on other planets is one of current development and cutting edge research. The Thermal Evolved Gas Analyzer (TEGA), which was designed, built and tested at the University of Arizona's Lunar and Planetary Lab (LPL), utilizes DSC/EGA. TEGA, which was sent to Mars on the ill-fated Mars Polar Lander, was to be the first application of DSC/EGA on the surface of Mars as well as the first direct measurement of the volatile-bearing mineralogy in martian soil. Additional information is available in the original extended abstract.

Musselwhite, D. S.↗