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James, P. B.

Publications and source records attributed to James, P. B..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Effects of Atmospheric Dust on Residual South Polar Cap Stability

The Martian polar caps have been studied from the time of Herschel. Neither polar cap normally disappears in summer. The Residual North Polar Cap (portion that remains through summer) is composed of a mixture of water ice and dust, and its interannual stability is due to its low sublimation rate at the summer temperatures in the North Polar Region. The Residual South Polar Cap (RSPC) is more enigmatic, surviving the relatively hot perihelic summer season despite being composed of much more volatile CO2. It is able to do so because of its unusually high albedo, which is larger than that of other bright regions in the seasonal cap (e.g. Mountains of Mitchel). The proximity of the albedo of the RSPC to the critical albedo for stability raises the question of whether the RSPC exists in every Martian year. The ground based record is somewhat ambivalent. Douglass and Lowell reported that RSPC suddenly vanished at Ls=297deg in 1894 and did not reappear until Ls=0deg [1], and Kuiper reported that it disappeared in 1956 [2]; but both observations were questioned by contemporaries, who tended to attribute them to obscuring dust. Barker [3] reported a large amount of water vapor over the south polar cap in 1969 that could be attributed to exposure of near surface water ice during partial removal of the CO2 in the RSPC in 1969.

Bonrv, B. P.↗
NASA NTRS2003

Effects of Atmospheric and Surface Dust on the Sublimation Rates of CO2 on Mars

We present an overview of our modeling work dedicated to study the effects of atmospheric dust on the sublimation of CO2 on Mars. The purpose of this study is to better understand the extent to which dust storm activity can be a root cause for interannual variability in the planetary CO2 seasonal cycle, through modifying the springtime regression rates of the south polar cap. We obtain calculations of the sublimation fluxes for various types of polar surfaces and different amounts of atmospheric dust. These calculations have been compared qualitatively with the regression patterns observed by Mars Global Surveyor (MGS) in both visible and infrared wavelengths, for two years of very different dust histories (1999, and 2001).

Bonev, B. P.↗
NASA NTRS2003

Yearly Comparisons of the Mars North Polar Cap: 1999, 2001, and 2003 MOC Observations

The seasonal cycle of the martian north polar cap has been studied since the time of William Herschel, who published the first quantitative observations of the seasonal recession of the polar caps in 1784. Ground-based observations made after Herschel were summarized by Slipher in 1962. More recent ground-based observations of the north polar cap have been done by Iwasaki et al. Mariner 9 and Viking also made north polar observations. Cantor et al. used Hubble Space Telescope observations between 1990 and 1997 to determine several north polar recessions and Lambert albedos of the cap. Mars Global Surveyor went into orbit around Mars in September 1997. The wide-angle cameras on the Mars Orbiter Camera (MOC) acquire images of the entire planet every day at a resolution of approx. 7.5 km/pixel in both red (575 nm - 625 nm) and blue (400 nm - 450 nm) bandpasses (WAR and WAB). Some polar cap observations were acquired during the aerobraking (AB) and science phasing (SPO) of MGS before systematic mapping began in March, 1999 at Ls = 110 .

Benson, J. L.↗
NASA NTRS2000

The Residual Polar Caps of Mars: Geological Differences and Possible Consequences

The Martian polar regions have been known to have thick layered sequences (presumed to consist of silicates and ice), CO2 seasonal frost, and residual frosts that remain through the summer: H2O in the north, largely CO2 in the south. The relationship of the residual frosts to the underlying layered deposits could not be determined from Viking images. The Mars Orbiter Camera on Mars Global Surveyor has provided a 50-fold increase in resolution that shows more differences between the two poles. The north residual cap surface has rough topography of pits, cracks, and knobs, suggestive of ablational forms. This topography is less than a few meters in height, and grades in to surfaces exposing the layers underneath. In contrast, the south residual cap has distinctive collapse and possibly ablational topography emplaced in four or more layers, each approx. two meters thick. The top surface has polygonal depressions suggestive of thermal contraction cracks. The collapse and erosional forms include circular and cycloidal depressions, long sinuous troughs, and nearly parallel sets of troughs. The distinctive topography occurs throughout the residual cap area, but not outside it. Unconformities exposed in polar layers, or other layered materials, do not approximate the topography seen on the south residual cap. The coincidence of a distinct geologic feature, several layers modified by collapse, ablation, and mass movement with the residual cap indicates a distinct composition and/or climate compared to both the remainder of the south polar layered units and those in the north.

Thomas, P. C.↗
NASA NTRS1993

Observed climatic activity pertaining to the evolution of the northern plains

Although most of the landforms observed by Viking were probably formed long before the advent of present climatic conditions, it is possible that some modifications occurred more recently and may continue to the present. Also, present climate activity provides another dataset for hypothesizing earlier climatic conditions. Observations of climatic activity in the northern plains from 1905 to 1993 are summarized. Data from Earthbound telescopes and from spacecraft, including the Hubble Space Telescope (HST), were used.

Martin, L. J.↗
NASA NTRS1993

Northern hemisphere dust storms on Mars

Dust storms in the northern hemisphere of Mars appear to be less common than the more familiar southern hemisphere storms, and essentially, no activity north of about 30 latittude has been documented. The data are, however, subject to an observational bias because Mars is near aphelion during oppositions, which occur during the most likely seasons for dust activity in the north. The amount of dust activity in the northern hemisphere is clearly very relevant to the role of atmospheric transport in the dust cycle. The classic global storms that occur during spring in the southern hemisphere are observed to transport dust from sources in the southern hemisphere to sinks or temporary depositories in the north. The question of whether atmospheric transport can close the dust cycle, i.e., return the dust to the southern hemisphere sources on some timescale, is clearly relevant to the solution of the puzzle of how the dust storm cycle is modulated, i.e., why storms occur in some years but not in others. There are data that suggest that the spring/early summer season in the northern hemisphere of Mars during the year following the major 1977 storms observed by Viking was very dusty. A number of observations of the vicinity of the receding north polar cap showed clear evidence of substantial dust activity in the sub-Arctic region.

James, P. B.↗
NASA NTRS1992

Observed changes in limb clouds immediately prior to the onset of planet-encircling dust storms

Of the several size and nomenclature groupings of Martian dust storms, it is the plane-encircling or truly runaway dust storms that are of most concern to both the theoreticians and mission planners. Once believed to be regularly seasonal, it is now known that they are not annual occurrences and that the few we know about occurred within at least one-third of Mars' seasonal cycle. We cannot confirm that any were observed before 1956, and not one has been observed since 1982 (the classification of that event as 'encircling' is an interpretation of observation from a single point on the planet's surface). If these storms occur in cycles, we do not know the lengths or causes of the cycles. Regional and local dust storms occur more frequently and throughout the Martian year, but the underlying question is how do some become runaways, encircling the planet, while the others die out, usually within a few days. An investigation of this topic is presented.

Martin, L. J.↗
NASA NTRS1992

Condensation phase of the Martian south polar cap

One type of database that can be useful in limiting models of the Mars surface-atmosphere system is the time dependent boundary of CO2 frost for the polar caps. Data acquired by the thermal infrared sensors on spacecraft are not limited by the lighting problems that hamper visual observations. The surface temperature of solid CO2 is limited by Clapeyron's equation as a function of the local partial pressure of CO2 gas. The growth was studied of the Martian south polar cap using the Viking IRTM dataset. These data are available in five bands, four of which should correspond to surface radiation in clear conditions; the 20 micron data was examined in the first phase.

Capuano, J.↗
NASA NTRS1992

The interannual variability of polar cap recessions as a measure of Martian climate and weather: Using Earth-based data to augment the time line for the Mars observer mapping mission

The recessions of the polar ice caps are the most visible and most studied indication of seasonal change on Mars. Circumstantial evidence links these recessions to the seasonal cycles of CO2, water, and dust. The possible advent of a planet encircling storm during the Mars Observer (MO) mission will provide a detailed correlation with a cap recession for that one Martian year. That cap recession will then be compared with other storm and nonstorm years. MO data will also provide a stronger link between cap recessions and the water and CO2 cycles. Cap recession variability might also be used to determine the variability of these cycles. After nearly a century of valiant attempts at measuring polar cap recessions, including Mariner 9 and Viking data, MO will provide the first comprehensive dataset. In contrast to MO, the older data are much less detailed and precise and could be forgotten, except that it will still be the only information on interannual variability. By obtaining simultaneous Earth-based observations (including those from Hubble) during the MO mission, direct comparisons can be made between the datasets.

Martin, L. J.↗
NASA NTRS1987

The direction of water transport on Mars: A possible pumping mechanism

It is suggested that an atmospheric pumping mechanism might be at work in which water is preferentially transported into the north by a mass outflow wind (due to sublimation from polar cap) that is stronger during southern spring than it is during northern spring. The mechanism is provided by the asymmetric seasonal temperature distribution produced by the eccentric martial orbit and by the associated seasonal asymmetry in the carbon dioxide cycle. The alternating condensation and sublimation of CO2 at the poles produces condensation winds which, in turn, contribute to the meridional transport of water vapor.

James, P. B.↗
NASA NTRS1987

The great dust storm of 1986

It is reported that on the global scale, no major dust storm activity was seen during telescopic observations of Mars during the several months or so preceeding this conference. However, the corresponding season on Mars was early fall, which is at the beginning of the dust storm season. It was too early to tell, therefore, if a great dust storm was going to occur that year. Current observations and what they show about present atmospheric conditions and the recession of the South Polar Cap is discussed.

Martin, L. J.↗
NASA NTRS1985

The Martian hydrologic cycle - Effects of CO2 mass flux on global water distribution

The Martian CO2 cycle, which includes the seasonal condensation and subsequent sublimation of up to 30 percent of the planet's atmosphere, produces meridional winds due to the consequent mass flux of CO2. These winds currently display strong seasonal and hemispheric asymmetries due to the large asymmetries in the distribution of insolation on Mars. It is proposed that asymmetric meridional advection of water vapor on the planet due to these CO2 condensation winds is capable of explaining the observed dessication of Mars' south polar region at the current time. A simple model for water vapor transport is used to verify this hypothesis and to speculate on the effects of changes in orbital parameters on the seasonal water cycle.

James, P. B.↗
NASA NTRS1984

Some photometric properties of the Martian south polar cap region during the 1971 apparition

High-quality earth-based photographs from the Lowell Observatory Planetary Research Center collection have been analyzed to derive some photometric parameters for the Martian south polar cap region during the 1971 apparition. The optical thickness of the atmosphere above the cap varied with wavelength from 0.35 + or - 0.05 in red light to 0.58 + or 0.06 in UV light. The effective geometric albedo is calculated from the 30 deg phase data assuming isotropic scattering: it varies from 0.85 + or - 0.04 (in red light) to 0.63 + or 0.05 (in UV light).

Lumme, K.↗
NASA NTRS1983

Polarization catastrophe model of static electrification and spokes in the B-ring of Saturn

A Clausius-Mossotti polarization catastrophe is presented as the operative charging mechanism in the Saturn B-ring. A review is undertaken of the polarization effect appearing in ice at the crystallization temperature. The ice crystals in the Saturn rings are in the 68-85 K temperature range, close to the ferroelectric transition temperature. An analytical treatment of the interaction of the ice crystals with the Saturn electric discharge field indicates that once polarization is initiated, it propagates toward the direction of the initial polarization. The spokes form in the radial direction, following the radial direction of the Saturn electric field. The polarization is cancelled by free plasma in the planet shadow. The charges are freed and are observed as the Saturn electric discharge phenomena, which has a periodicity which corresponds with the superrotation of the Saturn ionosphere.

Handel, P. H.↗
NASA NTRS1982

Recession of Martian north polar cap - 1979-1980 Viking observations

The polar regression curve for the Martian northern polar cap, derived from Viking observations for the 1979-1980 regression, is discussed, and comparisons with previous regression curves are made. Differences in the curves may be due to dust storms affecting the deposition of the cap. It is not possible to unambiguously ascribe differences between the curves to dynamical effects, since detailed information on the longitudinal dependence, which was an uncontrolled variable, is not available.

James, P. B.↗
NASA NTRS1982

The seasonal CO2 cycle on Mars - An application of an energy balance climate model

Energy balance climate models of the Budyko-Sellers variety are applied to the carbon-dioxide cycle on Mars. Recent data available from the Viking mission, in particular the seasonal pressure variations measured by Viking landers, are used to constrain the models. No set of parameters was found for which a one-dimensional model parameterized in terms of ground temperature gave an adequate fit to the observed pressure variations. A modified, two-dimensional model including the effects of dust storms and the polar hood reasonably reproduces the pressure curve, however. The implications of these results for Martian climate changes are discussed.

James, P. B.↗