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  • 1
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    A slightly more massive young Sun as an explanation for warm temperatures on early Mars (1995)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The valley network channels on the heavily cratered ancient surface of Mars suggest the presence of liquid water approximately 3.8 Gyr ago. However, the implied warm climate is difficult to explain in the context of the standard solar model, even allowing for the maximum CO2 greenhouse heating. In this paper we investigate the astronomical and planetary implications of a nonstandard solar model in which the zero-age, main-sequence Sun had a mass of 1.05 +/- 0.02 Solar Mass. The excess mass was subsequently lost in a solar wind during the first 1.2(-0.2, +0.4) Gyr of the Sun's main sequence phase. The implied mass-loss rate of 4(+3, -2) x 10(exp -11) M/yr, or about 10(exp 3) x that of the current Sun, may be detectable in several nearby young solar type stars.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); p. 5457-5464
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  • 2
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    Global map of eolian features on Mars (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A variety of common eolian features on Mars have been identified from a survey of Mariner 9 and Viking orbiter images, and their regional and global distributions and orientations are discussed. Ten features have been mapped including: light and dark streaks, splotches, barchan and transverse dunes, crescentric and anomalous dunes, yardangs, wind grooves, and deflation pits. The north polar region shows a complex wind regime. Dunes and other ephemeral features reveal winds from the northwest and northeast. In the middle and low northern latitudes, northeasterly winds are the most effective winds. Southeast winds are the effective winds in most southern latitudes. Erosional features in bedrock indicate long-term and perhaps ancient wind trends, whereas depositional features may record relatively more recent winds. Deflation pits in the mantled terrain may contain the best record of both ancient and present-day winds.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 90; 2038-205
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  • 3
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    Speculation on Martian north polar wind circulation and the resultant orientations of polar sand dunes (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: When seen at frost cap minimum, Martian north polar erg dunes north of 80 deg N record east winds, while those south of that latitude record west winds. Many of the transverse dunes are considered to be reversing dunes, and dunes in the two fields may have reversed at least once during the lifetime of the Viking Orbiters. It is proposed that the average polar winds are strong, off-pole northwest winds in the fall, moderate west winds in winter, latitude-dependent weak-to-strong off-pole northeast winds in spring, and weak west winds in summer, as has been largely confirmed by Viking images of near polar clouds. Over millenia, the combination of reversing west and east winds could produce the biomodal distributions of dune orientations observed at the north pole.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 55; Sept
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  • 4
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    Planetological implications of mass loss from the early Sun (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The element lithium is observed to be underabundant in the Sun by a factor of approx. equal to 100. To account for this depletion, Boothroyd et al. (Ap. J., in press 1991) proposed a model in which the Sun's zero-age-main-sequence mass was approx. 1.1 solar magnitude. If this is the explanation for the lithium depletion, then astronomical observations of F/G dwarfs in clusters suggest that the timescale for mass loss is approx. equal to 0.6 Gyr. Assuming this approximate timescale, the authors investigated several planetological implications of the astrophysical model.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Abstracts for the International Conference on Asteroids, Comets, Meteors 1991; p 238
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  • 5
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    Mars and the early Sun (1993)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Global mean temperatures near 273 K on early Mars are difficult to explain in the context of standards solar evolution models. Even assuming maximum CO2 greenhouse warming, the required flux is approximately 15 percent too low. Here we consider two astrophysical models that could increase the flux by this amount. The first model is a nonstandard solar model in which the early Sun had a mass somewhat greater than today's mass (1.02-1.06 solar mass). The second model is based on a standard evolutionary solar model, but the ecliptic flux is increased due to focusing by an (expected) heavily spotted early Sun.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Workshop on Early Mars: How Warm and How Wet?, Part 1; p 23
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  • 6
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    Ground-based near-infrared imaging observations of Venus during the Galileo encounter (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Near-infrared images of Venus, obtained from a global network of ground-based observatories during January and February 1990, document the morphology and motions of the night-side near-infrared markings before, during, and after the Galileo Venus encounter. A dark cloud extended halfway around the planet at low latitudes and persisted throughout the observing program. It had a rotation period of 5.5 + or - 0.15 days. The remainder of this latitude band was characterized by small-scale (400 to 1000 km) dark and bright markings with rotation periods of 7.4 + or - 1 days. The different rotation periods for the large dark cloud and the smaller markings suggest that they are produced at different altitudes. Midlatitudes (+ or - 40 to 60 deg) were usually occupied by bright east-west bands. The highest observable latitudes (+ or - 60 deg to 70 deg) were always dark and featureless, indicating greater cloud opacity. Maps of the water vapor distribution show no evidence for large horizontal gradients in the lower atmosphere of Venus.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 253; 1538-154
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  • 7
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    Radiative transfer modeling constraints on the size of the spoke particles in Saturn's rings (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The spoke particle sizes of Saturn's outer B ring constitute an important parameter for spoke formation and evolution theories, prompting the present effort to find constraining observations. The spokes' apparent optical depths are found to increase with wavelength. A relationship is derived for the contribution of the spokes' small particle optical depth, taking multiple-scatter and flatter spoke-region large-particle phase functions into account; the spokes' optical depths still generally appear to increase or remain constant with increasing wavelength.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 85; 168-190
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  • 8
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    Radiative transfer modeling of Saturn's outer B ring (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The present investigation of Voyager images of the Saturn outer B ring's light-scattering behavior gives attention to the four radial regions formed by brighter and darker areas within and outside the 'spokes'. The B-ring particles are found to have a strongly backscattering phase function and a large-particle scattering albedo of 0.54 in the dark regions and 0.58 in the bright ones; these albedos are interpretable as due to multiple scattering among very pure ice grains covering the ring particle surfaces. It is shown that dark micrometeoroid impacts into the B ring would have darkened the particles to their current spherical albedo in as little as 100 to 200 million years.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 80; 104-135
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  • 9
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    On the quasi-conical flowfield structure of the swept shock wave-turbulent boundary layer interaction (1991)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The swept oblique shock-wave/turbulent-boundary-layer interaction generated by a 20-deg sharp fin at Mach 4 and Reynolds number 21,000 is investigated via a series of computations using both conical and three-dimensional Reynolds-averaged Navier-Stokes equations with turbulence incorporated through the algebraic turbulent eddy viscosity model of Baldwin-Lomax. Results are compared with known experimental data, and it is concluded that the computed three-dimensional flowfield is quasi-conical (in agreement with the experimental data), the computed three-dimensional and conical surface pressure and surface flow direction are in good agreement with the experiment, and the three-dimensional and conical flows significantly underpredict the peak experimental skin friction. It is pointed out that most of the features of the conical flowfield model in the experiment are observed in the conical computation which also describes the complete conical streamline pattern not included in the model of the experiment.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 91-1759
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  • 10
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    The hypersonic shock wave-turbulent boundary layer interaction generated by a sharp fin at Mach 8.2 (1992)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A combined experimental and numerical study has been conducted on the hypersonic shock-wave turbulent-boundary layer interaction at Mach 8.2 generated by a single fin of angles alpha = 10 and 15 deg. Three models are considered: (1) the 3D compressible Reynolds-averaged Navier-Stokes (RANS) equations using the k-epsilon turbulence model, (2) the 3D RANS using the Rodi turbulence model, and (3) the conical RANS using the Baldwin-Lomax algebraic turbulence model. The computations are compared with various experimental data. The computations using models (1) and (2) show quantitatively very similar results and very good agreement with experimental data for surface pressure and skin friction. Comparison with boundary layer profiles of pitot pressure and yaw angle are also generally good, but the peak surface heat transfer is overestimated by up to 48 percent. The effect of the laminar boundary layer on the fin is restricted to the immediate vicinity of the fin surface. Conical calculations using model (3) show substantially poorer agreement with experiment.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 92-0747
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