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At least 199 records · Page 11
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NASA NTRS1975

The new Martian nomenclature of the International Astronomical Union

A new nomenclature for Martian regions and topographic features uncovered by Mariner 9, as officially adopted by the International Astronomical Union, is described. About 180 craters generally of diameters greater than 100 km have been named, as well as 13 classes of topographic features designated catena, chasma, dorsum, fossa, labyrinthus, mensa, mons, patera, planitia, planum, tholus, vallis, and vastitas. In addition seven craters and the Kepler Dorsum are named on Phobos, and two craters on Deimos. Coordinates and maps of each named feature are displayed.

De Vaucouleurs, G.↗
NASA NTRS1976

Infrared observations of Monoceros R2

A cluster of compact infrared sources plus extended emission has been found at the peak of the molecular cloud in Mon R2. The extended emission is probably due to heated dust associated with PKS 0605-06, a compact H II region embedded in the molecular cloud. Several of the compact infrared sources have properties indicative of protostars. For one of these, the associated dust is apparently seen in projection against the H II region.

Beckwith, S.↗
NASA NTRS1976

Further observations of the 10830-A helium line in stars and their significance as a measure of stellar activity

Measurements of the 10830-A He line in 198 stars are given along with data on other features in that spectral range. Nearly 80 per cent of all G and K stars show some 10830-A absorption or emission; of these, half are variable and one-quarter show emission. The results of Vaughan and Zirin (1968) are confirmed that the 10830-A line is not found in M stars, is weak in F stars, and is particularly strong in close binaries. The line is found in emission in extremely late M and S stars along with P-gamma, but the latter is not in emission in the G and K stars with 10830-A emissions. Variable He emission along with Ti I emission is found in the RV Tauri variables R Sct and U Mon. In R Aqr, the Fe XIII coronal line at 10747 A is found in emission along with a line at 11012 A, which may be singlet He or La II, as well as the 10830-A and P-gamma lines. There is possibly a five-year period in the appearance of 10830-A emission in theta Her. The nature of coronae or hot chromospheres in the various stars is extensively discussed without definite conclusion, except that the 10830-A intensity must be more or less proportional to the energy deposited in the chromosphere-corona by nonthermal processes.

Zirin, H.↗
NASA NTRS1976

Temperatures of the Martian surface and atmosphere - Viking observation of diurnal and geometric variations

Selected observations made with the Viking infrared thermal mapper after the first landing are reported. Atmospheric temperatures measured at the latitude of the Viking 2 landing site (48 deg N) over most of a Martian day reveal a diurnal variation of at least 15 K, with peak temperatures occurring near 2.2 hours after noon, implying significant absorption of sunlight in the lower 30 km of the atmosphere by entrained dust. The summit temperature of Arsia Mons varies by a factor of nearly two each day; large diurnal temperature variation is characteristic of the south Tharsis upland and implies the presence of low-thermal-inertia material. The thermal inertia of material on the floors of several typical large craters is found to be higher than for the surrounding terrain; this suggests that craters are somehow effective in sorting aeolian material. Brightness temperatures of the Viking 1 landing area decrease at large emissions angles; the intensity of reflected sunlight shows a more complex dependence on geometry than expected, implying atmospheric as well as surface scattering.

Kieffer, H. H.↗
NASA NTRS1977

Orbital changes of the gaseous ring around Be stars

In order to understand the seemingly erratic V/R variations and radial velocity curves of emission edges and central absorption of some Be stars, we have advanced, for the changes of structure of the gaseous ring around these stars, a theory that is based on the interaction between the existing ring and the newly ejected matter from the star. It shows that the structural change of the ring is completely controlled by the angular-momentum input factor and the dissipation factor. In light of this understanding, we have gone on to interpret the observed results of Beta-1 Mon and Pi Aqr.

Huang, S.-S.↗
NASA NTRS1977

Relative crater production rates on planets

The relative numbers of impacts on different planets, estimated from the dynamical histories of planetesimals in specified orbits (Wetherill, 1975), are converted by a described procedure to crater production rates. Conversions are dependent on impact velocity and surface gravity. Crater retention ages can then be derived from the ratio of the crater density to the crater production rate. The data indicate that the terrestrial planets have crater production rates within a factor ten of each other. As an example, for the case of Mars, least-squares fits to crater-count data suggest an average age of 0.3 to 3 billion years for two types of channels. The age of Olympus Mons is discussed, and the effect of Tharsis volcanism on channel formation is considered.

Hartmann, W. K.↗
NASA NTRS1977

Further observations of new sources in the AFCRL survey

Salient aspects of follow-up observations carried out on new sources discovered earlier in the AFCRL rocket IR sky survey are summarized. Ground-based searches, studies of class properties of the new AFCRL sources (galactic distribution, IR spectra, time variation), and closer examination of some 'unusual objects' are discussed. Brief descriptions are offered of some unusual objects: possible protostars, and specifically CRL 877; H2O masers in the Mon R2 cloud; the Egg Nebula (CRL 2688); CRL 618, with featureless IR spectrum and optical spectrum reminiscent of a planetary nebula; CRL 437 and other objects associated with multiple-reflection nebulae.

Kleinmann, S. G.↗
NASA NTRS1977

Infrared studies of star formation

Infrared observations at wavelengths of a few microns to 1 mm are reviewed which pertain to the problem of star formation. The data considered include observations of large gas and dust clouds within which stars may be forming and detailed studies of individual objects within these clouds. Stages of star formation are outlined, the IR luminosity of forming stars is examined, and criteria for selecting interstellar regions for IR studies are discussed along with the importance of dust in the IR energy distributions of star-formation regions. Detailed results, including IR maps, are evaluated for the Orion Molecular Cloud 1 (OMC-1), W3, OMC-2, Mon R2, RCW 57, M17, CRL 2591, and NGC 7538. Some general properties of star-formation regions are summarized, and observational techniques for IR astronomy are described. It is noted that the discovery of possible pre-main-sequence (PMS) objects in the densest central portions of larger clouds supports the generally accepted premise of gravitational collapse as the driving mechanism for the star-formation process and that the observed properties of possible PMS objects agree qualitatively with the predictions of detailed models based on gravitational collapse.

Werner, M. W.↗
NASA NTRS1977

Martian Dynamical Phenomena During June-November 1976: Viking Orbiter Imaging Results

A summary is presented of the orbital imaging observations of dynamical phenomena on Mars during the Viking primary mission. Clouds in the Tharsis/Amazonis regions are examined and the observation of an area of unusually high brightness to the southwest of Arsia Mons is considered. Attention is given to clouds and surface frost in the south polar region, the north polar cap, and aspects of dust storm activity.

Briggs, G.↗
NASA NTRS1977

A Study of Variable Features on Mars During the Viking Primary Mission

The Viking coverage revealed numerous wind streaks on the surface of Mars. The Viking images have provided the first good examples of very distinctive mixed tone streaks which appear to consist of a tapered light streak bordered by two dark side lobes. Attention is given to a general lack of eolian activity, eolian activity on the slopes of the Tharsis volcanos, spectacular albedo changes since 1972, more subtle albedo changes, surface detail and wind flow patterns in Hellas, wind flow in the vicinity of Olympus Mons, and a comparison of the 1972 and 1976 wind streak patterns.

Veverka, J.↗
NASA NTRS1978

Observations of interstellar chlorine and phosphorus

Copernicus observations of interstellar Cl I, Cl II, and P II UV lines toward 10 stars are reported. Column densities are estimated for each species, and upper limits are computed for HCl column densities. Derivation of the gas-phase abundances of chlorine and phosphorus indicates that the averages of both the chlorine and the phosphorus logarithmic abundances relative to hydrogen are between 5.0 and 5.1. It is suggested that interstellar chlorine may be depleted by about a factor of 3 relative to the solar abundance and that interstellar phosphorus is depleted by a factor of 2 to 3. The results are shown to support the prediction that chlorine is ionized in regions containing primarily atomic oxygen and is neutral in regions where there is a significant amount of molecular hydrogen. The photoionization rate of neutral chlorine toward 15 Mon is estimated, and it is concluded that most chlorine is contained within the gas phase.

Jura, M.↗
NASA NTRS1978

Orbital changes of the gaseous ring around Be stars. II - Apsidal motion and slow drift of the orbital elements

It is shown that the observed data about the apsidal motion of gaseous rings around some Be stars, like Beta(1) Mon and Pi Aqr, cannot be explained solely by the influence of the equatorial bulge. This fact has prompted the development of a theory of apsidal motion and slow drift of orbital elements that is based on the mixing of slowly escaping gases from the central star with gases in the emission ring around it. Thus, the basic physical idea in this paper follows closely what has been advanced in the first paper of this series but the mathematical treatment has been broadened in order to deal with the actual orbits, instead of osculating orbits, of particles in the ring. In accordance with this theory, it is believed that in cases where no mixing of gases takes place, the apsidal motion is controlled solely by the equatorial bulge. But in cases where mixing takes place, the apsidal motion depends upon the manner of gas mixing as well.

Huang, S.-S.↗
NASA NTRS1978

Investigations of Mars dynamics and geodesy via the Viking spacecraft

Results are reported for analyses of Doppler, ranging, and tracking data from the Viking landers and orbiters of relevance to the dynamics and geodesy of Mars. Highly improved numerical results are given for the orientation of the spin axis of Mars, the planet's sidereal rotation rate, and the earth-Mars ephemeris. A refined definition of the global gravitational field of Mars is discussed, a local gravitational survey based on Viking Orbiter 2 tracking data is described, and a mass anomaly near Olympus Mons is noted. Radius data are examined which suggest an asymmetry in the figure of Mars characterized by generally higher topography in the southern than in the northern hemisphere. The mass of Phobos is determined on the basis of Orbiter 1 orbital perturbations, and the mean density of this Martian satellite is found to be approximately 2.0 g/cu cm, which is suggestive of primitive carbonaceous chondrites and, if true, implies that Phobos was formed in the asteroid belt.

Michael, W. H., Jr.↗
NASA NTRS1978

Martian lithospheric thickness from elastic flexure theory

The thickness of the elastic lithosphere in the Tharsis region of Mars is estimated from effects due to the surface load of Olympus Mons. Deformation (vertical displacement) and stress are calculated using elastic flexure theory for a range of possible lithospheric thicknesses (T), modeling the lithosphere as a thin elastic shell and the interior as a Newtonian fluid. For T below 150 km, displacement and stress rise rapidly with decreasing thickness. For T near 100 km, deformation of the region surrounding the volcano would be clearly visible in the topography, and resulting tensional stresses exceeding 5 kbar should produce observable fracturing at the surface. In contrast, for T near 200 km deformation is minimal and the tensional stress, being less than a kilobar, would not result in extensive fracturing. Since significant deformation and fracturing are not observed, it is concluded that the Martian elastic lithosphere is at least 150 km in thickness. Seismic, tectonic, and gravity observations all suggest a thick Martian lithosphere as well.

Thurber, C. H.↗
NASA NTRS1978

Lava flow materials in the Tharsis region of Mars

Lava-flow materials in the Tharsis region of Mars were studied from moderate-resolution (100-280 m/pixel) Viking Orbiter imagery. Individual eruptive sequences were recognized primarily by stratigraphic relations, density of superimposed impact craters, flow morphology, flow trend, and variations in surface albedo. Nine detailed maps of lava flows based on delineation of flow scarps were compiled for a total area of 7.25 million sq km. Two thirds of this area was covered by mappable flows representing at least 14 distinct eruptive sequences. Assuming a rate of crater production twice that of the moon, the observed range of superimposed crater densities (90 to 3200 craters at least 1 km in diameter per sq km) indicates an age range of 100 m.y. to several billion years for these flows. The youngest lavas are associated with flood lavas filling the depression surrounding the Olympus Mons shield. Flow thicknesses range from less than 5 meters to 20 meters on steeper shield slopes (0.5 to 4.5 deg) and from 20 to 65 meters on relatively flat (less than 0.5 deg slope) terrain.

Schaber, G. G.↗
NASA NTRS1978

Mars gravity - Additional resolution from Viking Orbiter I

Doppler radio tracking data taken from Viking Orbiter I at a 300 km periapsis altitude are now capable of resolving shorter wavelength features such as Olympus Mons and Alba Patera. The number of data is limited as is the area of high resolution which forms a narrow band near 35 deg N latitude. The masses of 71 disks, placed in a geometric pattern on the surface, were estimated. Location of each disk, the mass estimate, and the corresponding uncertainty are given for each disk mass included in the estimator. The new gravity results are compared with previous gravity reductions. The corresponding acceleration surface at 350 km altitude is displayed. It is concluded that systematic postfit residuals imply that further information can be extracted with more detailed modeling.

Sjogren, W. L.↗
NASA NTRS1979

Far-infrared observations of optical emission-line stars - Evidence for extensive cool dust clouds

Far-infrared observations (40-160 microns) of eight optical emission-line stars are presented. Six of these stars, LkH-alpha 198, T Tau, LkH-alpha 101, V380 Ori, R Mon, and MWC 1080, show substantially more far-infrared emission than would be expected on the basis of a blackbody extrapolation of their 10-20-micron fluxes. Additionally, in three cases, the far-infrared emission is shown to be spatially extended (greater than 40 arcsec). A simple model of the thermal emission from cool circumstellar dust (30-70 K) shows that these stars are surrounded by material left over from the star formation process; this result confirms the extreme youth of these stars. MWC 349 was detected at a level consistent with the expected free-free flux from its surrounding H II region, and RY Tau was not detected in the far-infrared; there is little circumstellar dust with temperatures of 20-100 K in these objects.

Harvey, P. M.↗
NASA NTRS1979

Analysis of Viking infrared thermal mapping data of Mars. The effects of non-ideal surfaces on the derived thermal properties of Mars

The thermal interia of the surface of Mars varies spatially by a factor of eight. This is attributable to changes in the average particle size of the fine material, the surface elevation, the atmospheric opacity due to dust, and the fraction of the surface covered by rocks and fine material. The effects of these non-ideal properties on the surface temperatures and derived thermal inertias are modeled, along with the the effects of slopes, CO2 condensed onto the surface, and layering of fine material upon solid rock. The non-ideal models are capable of producing thermal behavior similar to that observed by the Viking Infrared Thermal Mapper, including a morning delay in the post-dawn temperature rise and an enhanced cooling in the afternoon relative to any ideal, homogeneous model. The enhanced afternoon cooling observed at the Viking-1 landing site is reproduced by the non-ideal models while that atop Arsia Mons volcano is not, but may be attributed to the observing geometry.

Muhleman, D. O.↗