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  • 1
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    The state of SO2on Io's surface (1996)
    American Geophysical Union
    Details
    Publication Date: 1996-03-01
    Print ISSN: 0148-0227
    Electronic ISSN: 2156-2202
    Topics: Geosciences
    Published by American Geophysical Union
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    PAPER CURRENT
  • 2
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    A generalized behavioral model for rotating short period comets with spectral orbital elements and axial orientation (1984)
    In:  CASI
    Details
    Publication Date: 2006-04-06
    Description: A generalized model for short period comets is developed which integrates in a fairly rigorous manner the isolation history of regions on rotating comets with specified axial orientation and the complex feedback processes involving heat, gas and dust transport, dust mantle development and coma opacity. Attention is focused on development, reconfiguration and partial or complete launching of dust mantles and the reciprocal effects of these three processes on ice surface temperature and gas and dust production. The dust mantle controls the H2O flux not only by its effect on the temperature at the ice interface but (dominantly) by its dynamic stability which strongly influences vapor diffusivity. The model includes the effects of latitude, rotation and spin axis orientation are included and applied to an initially homogeneous sphere of H2O ice and silicate using the orbital parameters of comet Encke. Numerous variations of the model, using combinations of grain size distribution, dust-to-ice ratio, latitude and spin axis orientation, are presented and discussed. Resulted for a similar nonrotating, constant Sun orientation models are also included.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA. Washington Repts. of Planetary Geol. Program; p 54-55
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Is regolith absorbtion the explanation for the transition from early to present Mars climate (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Experimental data is presented for CO2 adsorption on palagonites (now thought to provide the most acceptable spectral match to Mars weathering products). When corrected for great differences in specific surface area, the adsorptive behavior exhibited by palogonites, nontronite, and basalt with respect to CO2 can be (approx.) described by the same generic equation. Using this relationship normalized to a Mars soil surface area, and the dependence of subsurface temperatures on latitude and depth, the current inventory of regolith absorbed CO2 was estimated.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., MECA Symposium on Mars: Evolution of its Climate and Atmosphere; p 35-36
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    The role of regolith adsorption in the transition from early to late Mars climate (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Researchers reexamined radiative transfer models of early Mars that were advanced to show the existance of a greenhouse effect. These models were reexamined with regard to the effect that regolith adsorption may have had. It is argued that while the precipitation of carbonates has probably been an important process during Mars history, the rates at which this process could have taken place under early Mars conditions would have dropped sharply once liquid water was fairly scarce. Furthermore, conditions under which liquid water was available may have involved efficient recycling of carbonate so that steady state conditions rather than irreversible CO2 removal prevailed. In contrast, the growth of regolith surface area demands corresponding and predictable CO2 removal from the atmosphere-cap system and is fully capable of terminating any enhanced temperature regime on early Mars in the absence of any other effects.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1986; p 161-162
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    The loss and depth of CO2 ice in comet nuclei (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: An analytical model was developed to simulate the material differentiation of a cometary nucleus composed of water ice, putative unclathrated CO2 ice and silicate dust in specified proportions. Selective sublimation of any free CO2 ice present in a comet would produce a surface layer of water ice and dust overlying the original CO2 rich material. This surface layer reduces the temperature of buried CO2 ice and restricts the outflow of gaseous CO2. On each orbit, water sublimation at smaller heliocentric distances temporarily reduces the thickness of the water ice and dust layer and liberates dust. The model includes the effects of nucleus rotation, arbitrary orientation of the rotation axis, latitude, heat conduction into the deep interior of the nucleus and restriction of CO2 gas outflow by the water ice and dust layer. The effects of the permeability of the surface water ice layer, the nucleus rotation rate, and the latitude were investigated. Comparison of these and similar results with observations could yield information regarding the permeability and chemical composition of cometary material and suggest sampling strategies to minimize fractionation effects.
    Keywords: ASTROPHYSICS
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1986; p 69
    Format: application/pdf
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  • 6
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    Temperatures and minimum thickness of the inactive surface layer of comet Halley (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The effects of a nonvolatile mantle on the thermal state of a comet nucleus are investigated. The original computer model was modified so that temperatures can be computed through a thin dust mantle to the center of a 5 km spherical nucleus in the orbit of P/Halley. No attempt is made to simulate the formation of the mantle. Results are obtained for various specified values of initial mantle thickness and thermal conductivity to determine their effects on temperature profiles through the mantle. The minimum thickness of mantle that can withstand ejection by sublimating gasses is also calculated as a function of mantle thermal conductivity. Calculations were performed for ten or more orbits until temperatures in the mantle reached a near steady state. Results indicate that mantles as thin as 4 cm and 14 cm, for thermal conductivities of 600 and 6000 ergs/cm/s K, respectively, will remain intact. Surface temperatures as high as 511 K at perihelion and 400 K at the position of spacecraft encounter were computed at 0 degree latitude for an upright, rotating nucleus. Ice interface temperatures were raised by different amounts during each orbit, depending on mantle thickness and thermal conductivity, until steady state was reached. These results imply that relatively small nonvolatile masses emplaced randomly in comet nuclei could produce an irregular, permanently mantled surface and could also account for the apparently random location of active areas.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1986; p 65
    Format: application/pdf
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  • 7
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    An Idealized Short Period Comet Model: Surface Insolation, H2O Flux, Dust Flux and Mantle Evolution (1985)
    In:  CASI
    Details
    Publication Date: 2014-09-30
    Description: The present cometary activity model integrates feedback processes that involve the transport of heat, gas, and dust, as well as dust mantle development, and includes the effects of latitude, rotation, and spin orientation. Attention is given to the development, structural change, and distribution of dust mantles and their mutual interaction with ice surface temperature and gas and dust production. The results obtained suggest that an initially homogeneous, short period comet with a cosmic dust to water ice ratio, as well as typical orbit, rotation rate, and grain size distribution, would develop only a thin, less than 1 mm cyclic mantle at all points on the nucleus. Most H2O dust histories deduced from brightness data are noted to be in reasonable agreement with the model, allowing for uncertainty in radius and albedo. The exceptional case of Comet Encke is discussed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington Repts. of Planetary Geol. and Geophys. Program, 1984; p 86-87
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    Mars: Long Term Changes in the State and Distribution of H2O (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: A model for H2O distribution and migration on Mars was formulated which takes into account: (1) thermal variations at all depths in the regolith due to variations in obliquity, eccentricity and the solar constant; (2) variations in atmospheric PH2O caused by corresponding changes in polar surface insolation; and (3) the finite kinetics of H2O migration in both the regolith and atmosphere. Results suggest that regolith H2O transport rates are more strongly influenced by polar-controlled atmospheric PH2O variations than variations in pore gas PH2O brought about by thermal variations at the buried ice interface. The configuration of the ice interface as a function of assumed soil parameter and time is derived. Withdrawal of ice proceeds to various depths at latitudes less than 50 deg and is accompanied by filling of regolith pores at latitudes greater than 50 deg and transfer of H2O to the polar cap. The transfer has a somewhat oscillatory character, but only less than 1g/sq cm is shifted into and out the regolith during each obliquity cycle. It is concluded that this process combined with periodic thermal cycles played a major role in development of the fretted terrain, deflationary features in general, patterned ground, the north polar cap and the layered terrain.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington Repts. of Planetary Geol. and Geophys. Program, 1984; p 337
    Format: text
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    NASA TECHNICAL REPORTS
  • 9
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    Seasonal carbon dioxide exchange between the regolith and atmosphere of Mars - Experimental and theoretical studies (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: CO2 penetration rate measurements have been made through basalt-clay soils under conditions simulating the penetration of the cap-induced seasonal CO2 pressure wave through the topmost regolith of Mars, and results suggest that existing theoretical models for the diffusion of a gas through a porous and highly adsorbing medium may be used to assess the importance of the Martian seasonal regolith-atmosphere CO2 exchange. The maximum effect of thermally driven exchange between the topmost seasonally (thermally) affected regolith and the atmosphere shows that, while this may be of greater importance than the isothermal exchange, the thermally driven exchange would be recognizable only if the pressure wave from CO2 exchanged at high latitudes did not propagate atmospherically faster than the rate at which the exchange itself occurred. This is an unreasonable assumption.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 10
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    An idealized short-period comet model - Surface insolation, H2O flux, dust flux, and mantle evolution (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The present cometary activity model integrates feedback processes that involve the transport of heat, gas, and dust, as well as dust mantle development, and includes the effects of latitude, rotation, and spin axis orientation. Attention is given to the development, structural change, and distribution of dust mantles and their mutual interaction with ice surface temperature and gas and dust production. The results obtained suggest that an initially homogeneous, short period comet with a cosmic dust-to-water ice ratio, as well as typical orbit, rotation rate, and grain size distribution, would develop only a thin, less than 1 mm cyclic mantle at all points on the nucleus. Most H2O dust histories deduced from brightness data are noted to be in reasonable agreement with the model, allowing for uncertainty in radius and albedo. The exceptional case of Comet Encke is discussed.
    Keywords: ASTRONOMY
    Type: Icarus (ISSN 0019-1035); 60; 476-511
    Format: text
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