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Jakosky, B. M.

Publications and source records attributed to Jakosky, B. M..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Viking Landers and remote sensing

Thermal and radar remote sensing signatures of the materials in the lander sample fields can be crudely estimated from evaluations of their physical-mechanical properties, laboratory data on thermal conductivities and dielectric constants, and theory. The estimated thermal inertias and dielectric constants of some of the materials in the sample field are close to modal values estimated from orbital and earth-based observations. This suggests that the mechanical properties of the surface materials of much of Mars will not be significantly different that those of the landing sites.

Moore, H. J.↗
NASA NTRS1986

On the thermal properties of Martian fines

Theoretical models are developed for the thermal conductivity of grains smaller than 30 microns diameter and over 1 mm diameter in order to aid in the understanding of the thermal inertia of the surface regolith of Mars. The thermal inertia is a function of the thermal conductivity of the surface materials, and is discussed in terms of pore sizes below and above the mean free path of gas molecules (GMFP). The models are limited to surface deposits which consist of non-bonded materials at Martian surface pressures. The calculations indicate that a particulate surface with grains having pores smaller than the GMFP will be proportional to the pore or grain size. The thermal conductivity of a surface made of grains larger than the GMFP will be independent of the particle size. The results for the larger grain sizes is supported by available laboratory data. Further experiments are recommended in order to test the validity of the models for the smaller grain surfaces.

Jakosky, B. M.↗
NASA NTRS1986

Are the Viking Lander sites representative of the surface of Mars?

Global remote sensing data of the Martian surface, collected by earth- and satellite-based instruments, are compared with data from the two Viking Landers to determine if the Lander data are representative of the Martian surface. The landing sites are boulder-strewn and feature abundant fine material and evidence of strong eolian forces. One site (VL-1) is in a plains-covered basin which is associated with volcanic activity; the VL-2 site is in the northern plains. Thermal IR, broadband albedo, color imaging and radar remote sensing has been carried out of the global Martian surface. The VL-1 data do not fit a general correlation observed between increases in 70-cm radar cross-sections and thermal inertia. A better fit is found with 12.5-cm cross sections, implying the presence of a thinner or discontinuous duricrust at the VL-1 site, compared to other higher-inertia regions. A thin dust layer is also present at the VL-2 site, based on the Lander reflectance data. The Lander sites are concluded to be among the three observed regions of anomalous reflectivity, which can be expected in low regions selected for the landings. Recommendations are furnished for landing sites of future surface probes in order to choose sites more typical of the global Martian surface.

Jakosky, B. M.↗
NASA NTRS1986

Composition and stability of the condensate observed at the Viking Lander 2 site on Mars

Surface energy balance and near-surface temperature data from the Viking Lander 2 site taken during the first winter that condensated were observed and analyzed to determine the relative stability of CO2 and H2O frosts. The CO2 frost stability is calculated with an equilibrium surface energy balance model, i.e., the total energy incident on a frost surface is compared with the blackbody energy emitted by the surface. The energy sources considered were IR emission from the atmosphere, sunlight, and the sensible heat flux from the atmosphere. H2O stability was examined as a function of buoyant diffusion and turbulent mixing processes which could remove saturated near-surface gases. The CO2 frost is found to be sufficiently unstable at the time the condensate was observed on the ground, so all CO2 ice deposited at night would boil away in a few hours of sunlight. CO2 ice would not form during a dust storm. Water frost would be stable during the condensate observations, since sublimation would occur at a rate below 1 micron/day. A stable winter thickness of 10 microns is projected for the water ice.

Hart, H. M.↗
NASA NTRS1986

Global duricrust on Mars - Analysis of remote-sensing data

A study is conducted of the infrared thermal emission, radio thermal emission, and radar reflection data sets with the objective to obtain a simple and self-consistent model for the Mars surface. The results are compared with in situ observations at the Viking Lander sites. Attention is given to thermal inertia values, the abundance of surface rocks, radar/thermal correlations, diurnal temperature deviations, and radio emission data. It is suggested that all of the global remote-sensing data sets considered can be reconciled on the basis of variations in the degree of formation of a case-hardened crust or duricrust. On the other hand, no other model which has been proposed in conjunction with any individual data set can satisfy all of the constraints discussed.

Jakosky, B. M.↗
NASA NTRS1985

Possible precipitation of ice at low latitudes of Mars during periods of high obliquity

Most of the old cratered highlands of Mars are dissected by branching river valleys that appear to have been cut by running water, yet liquid water is unstable everywhere on the Martian surface. In the equatorial region, where most of the valleys are observed, even ice is unstable. It has been suggested, therefore, that Mars had an early denser atmosphere with sufficient greenhouse warming to allow the existence of liquid water. Here, it is suggested instead that during periods of very high obliquities, ice could accumulate at low latitudes as a result of sustained sublimation of ice from the poles and transport of the water vapor equatorwards. At low latitudes, the water vapor would saturate the atmosphere and condense onto the surface, where it would accumulate until lower obliquities prevailed. The mechanism is efficient only at the very high obliquities that occurred before formation of Tharsis very early in the planet's history, but limited equatorial ice accumulation could also have occurred at the highest obliquities during the rest of the planet's history. Partial melting of the ice could have provided runoff to form the channels or replenish the groundwater system.

Jakosky, B. M.↗
NASA NTRS1985

The seasonal cycle of water on Mars

A review of the behavior of water in the Mars atmosphere and subsurface is appropriate now that data from the Mariner and Viking spacecraft have been analyzed and discussed for several years following completion of those missions. Observations and analyses pertinent to the seasonal cycle of water vapor in the atmosphere of Mars are reviewed, with attention toward transport of water and the seasonal exchange of water between the atmosphere and various non-atmospheric reservoirs. Possible seasonally-accessible sources and sinks for water include water ice on or within the seasonal and residual polar caps; surface or subsurface ice in the high-latitude regions of the planet; adsorbed or chemically-bound water within the near-surface regolith; or surface or subsurface liquid water. The stability of water within each of these reservoirs is discussed, as are the mechanisms for driving exchange of the water with the atmosphere and the timescales for exchange. Specific conclusions are reached about the distribution of water and the viability of each mechanism as a seasonal reservoir. Discussion is also included of the behavior of water on longer timescales, driven by the variations in solar forcing due to the quasi-periodic variations of the orbital obliquity. Finally, specific suggestions are made for future observations from spacecraft which would further define or constrain the seasonal cycle of water.

Jakosky, B. M.↗
NASA NTRS1985

Martian atmospheric photochemistry and composition during periods of low obliquity

During periods of low obliquity, previous work has shown that martian CO2 partial pressures decreased to 0.1 mbar; CO2 partial pressures decreased to 0.02 mbar prior to the formation of the Tharsis bulge. The permanent polar caps act as a cold trap and projected global average water vapor abundances drop to possibly as low as 0.00001 precipitable micron. As a result, the odd hydrogen catalytic cycle would not be effective at recombining CO and O back into CO2, and as much as 0.12 mbar of CO and 0.06 mbar of O2 could exist. These increased abundances would radically affect surface oxidation, change the lower atmospheric thermal structure, and completely alter the upper atmosphere.

Lindner, B. L.↗
NASA NTRS1984

Comparison of ground-based and Viking Orbiter measurements of Martian water vapor - Variability of the seasonal cycle

Earth-based observations of Mars atmospheric water vapor are presented for the 1975-1976, 1977-1978, and 1983 apparitions. Comparisons are made with near-simultaneous spacecraft measurements made from the Viking Orbiter Mars Atmospheric Water Detection experiment during 1976-1978 and with previous earth-based measurements. Differences occur between the behavior in the different years, and may be related to the Mars climate. Measurements during the southern summer in 1969 indicate a factor of three times as much water as is present at this same season in other years. This difference may have resulted from the sublimation of water from the south polar residual cap upon removal of most or all of the CO2 ice present; sublimation of all of the CO2 ice during some years could be a result of a greater thermal load being placed on the cap due to the presence of differing amounts of atmospheric dust.

Jakosky, B. M.↗
NASA NTRS1983

Mars - Subsurface properties from observed longitudinal variation of the 3.5-mm brightness temperature

Extensive 3.5-mm measurements are reported which show a variation in the brightness temperature of Mars, with the Central Meridian Longitude that is generally in phase with the variation at 2.8 cm and is opposite in sign from the variations at 20 microns. It is pointed out that the phase result is not unexpected, since 3.5 mm is longer than the wavelength at which the phase behavior is expected to change. The result that the 3.5-mm rotation curve amplitude is larger than the amplitudes at both 20 microns and 2.8 cm, however, is unexpected. This result, it is noted, can be explained as a consequence of subsurface scattering from rocks smaller than 1.5 cm in radius. A correlation of subsurface scatterers with the location of the high-thermal inertial regions would be consistent with the hypothesis that rock abundance predominates in determining the thermal inertia.

Epstein, E. E.↗
NASA NTRS1983

Variability of carbon monoxide in the Mars atmosphere

Recent measurements and reanalyses of past measurements are used to derive estimates of the variability of CO concentrations in the Martian atmosphere. The J = 1 - 2 rotational transition of CO in the microwave spectrum of Mars was observed in January, 1982, and abundances were calculated through surface and atmospheric temperature modeling. A column density of 4.6 + or - 2.0 x 10 to the 20th/sq cm is obtained, which is contrasted with values of 3.0 + or - 1.0 x 10 to the 20th/sq cm in 1980 and 1.7 x + or - 0.9 x 10 to the 20th/sq cm in 1975 obtained by reanalysis of the J = 0 - 1 transition observed by Good and Schloerb (1981) and Kakar et al. (1977), respectively. It is noted that due to the uncertainties in global atmospheric average temperatures, results are consistent with a CO variability of from 0 to 100 percent over a time scale of several years. It is suggested that simultaneous measurements of the J = 0 - 1 and J = 1 - 2 transitions may provide stronger constraints on the CO abundance and atmospheric temperature of Mars.

Clancy, R. T.↗
NASA NTRS1982

The seasonal and global behavior of water vapor in the Mars atmosphere - Complete global results of the Viking atmospheric water detector experiment

A key question regarding the evolution of Mars is related to the behavior of its volatiles. The present investigation is concerned with the global and seasonal abundances of water vapor in the Mars atmosphere as mapped by the Viking Mars Atmospheric Water Detector (MAWD) instrument for almost 1-1/2 Martian years from June 1976 to April 1979. Attention is given to the implications of the observed variations for determining the relative importance of those processes which may be controlling the vapor cycle on a seasonal basis. The processes considered include buffering of the atmosphere water by a surface or subsurface reservior of ground ice, physically adsorbed water, or chemically bound water. Other processes are related to the supply of water from the residual or seasonal north polar ice cap, the redistribution of the vapor resulting from atmospheric circulation, and control of the vapor holding capacity of the atmosphere by the local atmospheric temperatures.

Jakosky, B. M.↗
NASA NTRS1981

A comparison of the thermal and radar characteristics of Mars

Results of thermal infrared sensing and radar observations of the Martian surface are compared for the region centered on +22 deg latitude. Values of the apparent thermal inertia of the surface were derived from surface brightnesses observed by the Viking Orbiter Infrared Thermal Mapper, while radar cross sections were obtained in earth-based experiments at wavelengths of 3.8, 12.5 and 70 cm. A correlation between the thermal inertia and radar cross section values is observed which is strongest with the 70-cm radar data except between longitudes of 10 and 90 deg, where a slight anticorrelation is found. The mixing of small (much less than 70 cm) rocks into a surface of fine material can account for the data between 90 and 370 deg longitude, with as much as 50% of the surface covered by rock in Syrtis Major, Isidis Planitia and parts of Elysium Planitia, and little or no rock cover near Olympus Mons, Elysium Mons, and Amazonis Planitia. The remaining longitudes may be explained in terms of the effects of atmospheric dust on the surface temperature or the effects of local variations in large-scale roughness or scattering from rocks. Data from the 90 to 370 deg longitude region are consistent with the division of the Martian surface into two types of terrain, possibly related to the erosional or depositional nature of the regions.

Jakosky, B. M.↗
NASA NTRS1980

The longitudinal variation of the thermal inertia and of the 2.8 centimeter brightness temperature of Mars

The spatial variations on Mars of the surface thermal inertia and radiometric albedo are used to predict the variation with sub-earth longitude of the 2.8 cm whole-disk brightness temperature. The maximum variation predicted, about 8 K, agrees well with observations. The sub-earth longitudes at which the temperature maxima and minima are predicted to occur nearly agree with the observations. There are, however, differences in the overall form of the variation with longitude. These discrepancies can be reduced by an ad hoc assumption of spatial variations in either the fraction of the surface covered by rock or the amount of atmospheric dust.

Jakosky, B. M.↗
NASA NTRS1979

The effects of nonideal surfaces on the derived thermal properties of Mars

The paper examines the effects of the observed brightness temperatures and the derived thermal inertias of some of the nonideal properties of the Martian surface. Attention is given to thermal models used for calculating the temperatures of the ideal and nonideal surfaces. Surfaces temperatures and derived thermal inertias for the various nonideal surfaces are presented. In addition, discussion covers the application of these models to the surface of Mars, the VL-1 landing site, the caldera atop Arsia Mons volcano, and the global relationships between thermal inertia and surface elevation.

Jakosky, B. M.↗
NASA NTRS1979

Planetary atmospheres

The present paper deals with some of the principal data on extraterrestrial atmospheres obtained during the period 1975-1978. The atmospheres of Venus, Mars, Jupiter, and the Jovian satellites are examined, showing that many first-order questions concerning composition, physical state, and kinematics of these atmospheres have been answered.

Ingersoll, A. P.↗