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Boyce, J.

Publications and source records attributed to Boyce, J..

14 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2017

Exploring the Largest Mass Fraction of the Solar System: the Case for Planetary Interiors

Why explore planetary interiors: The typical image that comes to mind for planetary science is that of a planet surface. And while surface data drive our exploration of evolved geologic processes, it is the interiors of planets that hold the key to planetary origins via accretionary and early differentiation processes. It is that initial setting of the bulk planet composition that sets the stage for all geologic processes that follow. But nearly all of the mass of planets is inaccessible to direct examination, making experimentation an absolute necessity for full planetary exploration.

Danielson, L. R.↗
NASA NTRS2010

The Interaction of Impact Melt, Impact-Derived Sediment, and Volatiles at Crater Tooting, Mars

We are producing a 1:200K geologic map of Tooting crater, Mars. This work has shown that an incredible amount of information can be gleaned from mapping at even larger scales (1:10K 1:25K) using CTX and HiRISE data. We have produced two new science papers (Morris et al., 2010; Mouginis-Mark and Boyce, 2010) from this mapping, and additional science questions continue to arise from our on-going analysis of Tooting crater: 1) What was the interplay of impact melt and volatile-rich sediments that, presumably, were created during the impact? Kieffer and Simonds [1980] predicted that melt would have been destroyed during impacts on Mars because of the volatiles present within the target we seek to understand if this is indeed the case at Tooting crater. We have identified pitted and fractured terrain that formed during crater modification, but the timing of the formation of these materials in different parts of the crater remains to be resolved. Stratigraphic relationships between these units and the central peak may reveal deformation features as well as overlapping relationships. 2) Morris et al. [2010] identified several lobate flows on the inner and outer walls of Tooting crater. It is not yet clear what the physical characteristics of the source areas of these flows really are; e.g., what are the sizes of the source areas, what elevations are they located at relative to the floor of the crater, are they interconnected, and are they on horizontal or tilted surfaces? 3) What were the details of dewatering of the inner wall of Tooting crater (Fig. 1)? We find evidence within Tooting crater of channels carved by water release, and the remobilization of sediment (which is inferred to have formed during the impact event). Sapping can be identified along the crest of unit 8 near the floor of the crater (Fig. 2a, 2b). This unit displays amphitheater-headed canyons that elsewhere on Mars are typically attributed to water leaking from the substrate [Laity and Malin, 1985; Malin and Edgett, 2000].

Mouginis-Mark, P.↗
NASA NTRS2003

Origin of Outer Solar System

We feel that at the present moment the available theoretical models of the Kuiper belt are still in advance of the data, and thus our main task has been to conduct observational work guided by theoretical motivations. Our efforts over the past year can be divided into four categories: A) Wide-field Searches for Kuiper Belt Objects; B) Pencil-beam Searches for Kuiper Belt Objects; C) Wide-field Searches for Moons of the Outer Planets; D) Pencil-beam Searches for Faint Uranian and Neptunian Moons; E) Recovery Observations. As of April 2002, we have conducted several searches for Kuiper belt objects using large-format mosaic CCD camera on 4-meter class telescopes. In May 1999, we used the Kitt Peak 4-meter with the NOAO Mosaic camera we attempted a search for KBOs at a range of ecliptic latitudes. In addition to our wide-field searches, we have conducted three 'pencil-beam' searches in the past year. In a pencil-beam search we take repeated integrations of the same field throughout a night. After preprocessing the resulting images we shift and recombine them along a range of rates and directions consistent with the motion of KBOs. Stationary objects then smear out, while objects moving at near the shift rate appear as point sources. In addition to our searches for Kuiper belt objects, we are completing the inventory of the outer solar system by search for faint satellites of the outer planets. In August 2001 we conducted pencil beam searches for faint Uranian and Neptunian satellites at CFHT and CTIO. These searches resulted in the discover of two Neptunian and four Uranian satellite candidates. The discovery of Kuiper belt objects and outer planet satellites is of little use if the discoveries are not followed by systematic, repeated astrometric observations that permit reliable estimates of their orbits.

Holman, Matthew J.↗
NASA NTRS2002

Mineralogic and Petrologic Studies of Meteorites

This report lists publications related to work done under NASA grant. Topics as indicated by title include: condensation in fractionated nebular systems, nebular processes in different constituents of the CH chondrite NWA 470, growth mechanism and additional constraints on FeNi metal condensation in the solar nebula, the ZONMET thermodynamic and kinetic model of metal condensation, the first occurrence of CaAl2O4 in a CAI (calcium aluminum inclusion) from the new CH chondrite NWA 470.

Wood, John↗
NASA NTRS2001

Three Classes of Kuiper Belt Objects: Theory and Observations

As part of the Origins of Solar Systems program our team conducted a dynamically motivated search for three classes of Kuiper belt objects (distant comets near and beyond the orbit of Neptune). Our strategy has been to exploit variations in the sky density of Kuiper belt that result from the gravitational influence of Neptune. By searching two regions of the sky, one nearly 90 degrees from Neptune and one nearly opposite Neptune, and comparing the number of objects discovered in each region we are able to constrain the relative populations of resonant and non-resonant objects, a fundamental quantity in Kuiper belt formation models. In addition, by searching at a variety of angles above the plane of the solar system we have constrained the inclination distribution of Kuiper belt objects. We have conducted four searches for this program. One was in February 1999 and August 2000 at the Canada-France-Hawaii telescope (3.6-meter), and another was in May 1999 and Oct. 2000 at the Kitt Peak National Observatory (4-meter). In addition, a search for Uranian satellites was conducted.

Holman, Mathew J.↗
NASA NTRS1996

Mars Together 2001: Joint US-Russian Team

While the US and USSR have collaborated in human space flight and Earth application missions, this is the first time in the cultural relations between our two countries that American and Russian specialists have been authorized to work together on a joint space science mission. A study was commissioned to investigate the possibility of a combined US/Russian mission in the 2001 opportunity. A basic option for a proposed mission (abbreviated as MT 2001) was adopted. This option is described.

Mars Russia↗
NASA NTRS1986

Separation of biological materials in microgravity

Partition in aqueous two phase polymer systems is a potentially useful procedure in downstream processing of both molecular and particulate biomaterials. The potential efficiency of the process for particle and cell isolations is much higher than the useful levels already achieved. Space provides a unique environment in which to test the hypothesis that convection and settling phenomena degrade the performance of the partition process. The initial space experiment in a series of tests of this hypothesis is described.

Brooks, D. E.↗
NASA NTRS1986

Demixing of aqueous polymer two-phase systems in low gravity

When polymers such as dextran and poly(ethylene glycol) are mixed in aqueous solution biphasic systems often form. On Earth the emulsion formed by mixing the phases rapidly demixes because of phase density differences. Biological materials can be purified by selective partitioning between the phases. In the case of cells and other particulates the efficiency of these separations appears to be somewhat compromised by the demixing process. To modify this process and to evaluate the potential of two-phase partitioning in space, experiments on the effects of gravity on phase emulsion demixing were undertaken. The behavior of phase systems with essentially identical phase densities was studied at one-g and during low-g parabolic aircraft maneuvers. The results indicate the demixing can occur rather rapidly in space, although more slowly than on Earth. The demixing process was examined from a theoretical standpoint by applying the theory of Ostwald ripening. This theory predicts demizing rates many orders of magnitude lower than observed. Other possible demixing mechanisms are considered.

Bamberger, S.↗
NASA NTRS1982

A new look at the Saturn system - The Voyager 2 images

Images of the Saturn system acquired by Voyager 2 in its encounter in August 1981 are presented and information gained from the imagery on the atmosphere, satellites, and rings of Saturn is discussed. The images have shown the Saturn atmosphere to contain persistent oval clouds similar to those of Jupiter, and small irregular features indicative of a pattern of zonal winds that is symmetric about the equator and appears to extend to great depths. The atmosphere of Titan is found to possess an upper haze layer above the main haze, a hemispherical brightness asymmetry, and a dark band in the north polar region. Other satellite observations included relatively high resolution coverage of Enceladus and Tethys, moderate resolution views of Hyperion and Iapetus, and the first observations of Phoebe, as well as views of the eight minor satellites associated with the orbits of Dione, Tethys and Mimas, and the F and A rings. Images of various ring structures were obtained, most notably the birth of a spoke and variable ringlet structures in the outer B ring. The observations may be used to deduce the collisional and thermal history of the rings and satellites.

Smith, B. A.↗
NASA NTRS1981

Encounter with Saturn - Voyager 1 imaging science results

As Voyager 1 flew through the Saturn system it returned photographs revealing many new and surprising characteristics of this complicated community of bodies. Saturn's atmosphere has numerous, low-contrast, discrete cloud features and a pattern of circulation significantly different from that of Jupiter. Titan is shrouded in a haze layer that varies in thickness and appearance. Among the icy satellites there is considerable variety in density, albedo, and surface morphology and substantial evidence for endogenic surface modification. Trends in density and crater characteristics are quite unlike those of the Galilean satellites. Small inner satellites, three of which were discovered in Voyager images, interact gravitationally with one another and with the ring particles in ways not observed elsewhere in the solar system. Saturn's broad A, B, and C rings contain hundreds of 'ringlets', and in the densest portion of the B ring there are numerous nonaxisymmetric features. The narrow F ring has three components which, in at least one instance, are kinked and crisscrossed. Two rings are observed beyond the F ring, and material is seen between the C ring and the planet.

Smith, B. A.↗
NASA NTRS1979

The Galilean satellites and Jupiter - Voyager 2 imaging science results

Continuous global observations of Jupiter were made by Voyager 2 for a period of 63 days. Voyager 2 provided images that both complement and supplement the Voyager 1 images. The combined Voyager 1 and 2 observations of Jupiter provide an almost continuous record, over a 6-month period, of the behavior of the Jovian atmosphere at a resolution far better than can be obtained from earth-based studies. The present report briefly describes the changes in the cloud morphologies and local atmospheric motions. On Io, changes are observed in eruptive activity, plume structure, and surface albedo patterns. Europa's surface retains little or no record of intense meteorite bombardment, but reveals a system of overlapping bright and dark linear features. Ganymede exhibits at least one unit of heavily cratered terrain on a surface that otherwise suggests widespread tectonism. Except for two large ringed basins, Callisto's entire surface is heavily cratered.

Smith, B. A.↗
NASA NTRS1979

Standard techniques for presentation and analysis of crater size-frequency data

In September 1977 a crater studies workshop was held for the purpose of developing standardized data analysis and presentation techniques. The present report contains the unanimous recommendations of the participants. Recommendations are devoted primarily to crater size-frequency data and refer to cumulative and relative size-frequency distribution plots and to morphological analysis.

Arvidson, R.↗
NASA NTRS1978

Reports of planetary geology program, 1977-1978

A compilation of abstracts of reports which summarizes work conducted by Planetary Geology Principal Investigators and their associates is presented. Full reports of these abstracts were presented to the annual meeting of Planetary Geology Principal Investigators and their associates at the Universtiy of Arizona, Tucson, Arizona, May 31, June 1 and 2, 1978.

Strom, R.↗