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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Mariner 9 television observations of Phobos and Deimos. II.

Analyses of the Mariner 9 pictures of the Martian satellites have yielded much new information: improved ephemerides, estimates of their principal axes, information about the texture of their surfaces, and estimates of the structural strength of their interiors. Both satellites are found to be in synchronous rotation, as was expected from tidal theory. A close examination of the preorbital satellite pictures has failed to show any unknown satellite. The photometric behavior of Phobos and Deimos indicates that they have intricate surface layers consistent with the presence of a regolith. Morphological features on Phobos and the expected collisional history of both satellites imply that both are made of well-consolidated material.

Pollack, J. B.↗
NASA NTRS1974

Infrared observations of Phobos from Mariner 9

Radiometric measurements of Phobos at 10 and 20 microns show that the surface is covered by a material whose conductivity is extremely low, around .000001 cal per cm per sec per deg K. It is concluded that Phobos is covered with a layer of dust at least 1 mm thick.

Gatley, I.↗
NASA NTRS1975

Accuracy of estimating the masses of Phobos and Deimos from multiple Viking orbiter encounters

The problem was investigated of estimating the masses of Phobos and Deimos from Doppler and onboard optical measurements during the Viking extended mission. A Kalman filter was used to analyze the effects of gravitational uncertainties and nongravitational accelerations. These accelerations destroy the dynamical integrity of the orbit, and multibatch or limited memory filtering is preferred to single batch processing. Optical tracking is essential to improve the relative orbit geometry. The masses can be determined to about 10% and 25% respectively for Phobos and Deimos, assuming satellite densities of about 3 gr/cu cm.

Tolson, R. H.↗
NASA NTRS1975

Accuracy of estimating the masses of Phobos and Deimos from multiple Viking orbiter encounters

This paper addresses the problem of estimating the masses of Phobos and Deimos from Doppler and onboard optical measurements during the Viking extended mission. A Kalman filter is used to analyze the effects of gravitational uncertainties and nongravitational accelerations. These accelerations destroy the dynamical integrity of the orbit and multi-batch or limited memory filtering is preferred to single batch processing. Optical tracking is essential to improve the relative orbit geometry. The masses can be determined to about 10% and 25% respectively for Phobos and Deimos, assuming satellite densities of about 3 g per cu cm.

Tolson, R. H.↗
NASA NTRS1977

The equilibrium figures of Phobos and other small bodies

Computations of figures of hydrostatic equilibrium for isolated rotating bodies are discussed. It is shown that the theoretical figure of equilibrium for Phobos is a triaxial ellipsoid whose a and b axes differ by about 25% and that this difference is less than 2% for Deimos. A density of less than 3.9 g/cu cm is estimated for Phobos. Equilibrium figures are also examined for the inner satellites of Jupiter and Saturn as well as for small asteroids.

Soter, S.↗
NASA NTRS1977

Phobos - Surface density of impact craters

Revised crater counts for Phobos are presented which are based on uniform Mariner 9 imagery and Duxbury's (1974) map of the satellite. The contiguous portion of the satellite's surface on which all craters down to the limiting resolution of 0.2 to 0.3 km in diameter would be expected to be identified is delineated and found to contain 87 identifiable craters larger than 0.2 km in diameter. Analysis of the crater size distribution shows that the surface appears to be saturated for craters exceeding 1 km in diameter but the crater counts definitely fall below the saturation curve for smaller craters. Reasons for this fall-off are considered, and it is noted that too few craters are visible in Mariner 9 images of Deimos to permit meaningful crater counts on that satellite's surface. It is concluded that, contrary to a previous assertion, the surfaces of Phobos and Deimos are not known to be saturated with craters larger than 0.2 km in diameter.

Thomas, P.↗
NASA NTRS1977

Phobos and Deimos

Ground-based and spacecraft observations of Phobos and Deimos are reviewed and the satellites' origin is discussed. The crater densities of both bodies are close to the saturation level. The largest impact events may have caused extensive fracturing of their surfaces. The surfaces are at least 1.5 billion years old and may date back to the early history of the solar system. The Martian satellites display large deviations from sphericity. As a result of tidal processes, they are in synchronous rotation. Several independent lines of evidence show that they have regoliths. Despite some provocative arguments, their internal strengths and the nature of their interior are poorly known at present. Photometric measurements suggest that they are made of either carbonaceous chondritic material or a basalt. Sinclair (1972), Born and Duxbury (1975) and Shor (1975) apparently have successfully determined Phobos' secular acceleration. Their value of approximately .001 deg/year/year implies that the interior of Mars has a low specific dissipation factor (about 100), may indicate that a portion of the Martian interior is experiencing partial melting. The low inclination of the satellites' orbits indicates that they were formed as part of the same process that resulted in Mars.

Pollack, J. B.↗
NASA NTRS1977

Phobos and Deimos - Geodesy

Results of geodesy studies of Phobos and Deimos based on Mariner 9 imaging data are presented. This analysis includes a review of the surface coverage and high resolution pictures obtained and the determined sizes, shapes, topographies, and librations of the two Martian satellites. Also, exploration of Phobos and Deimos by missions such as Viking is discussed.

Duxbury, T. C.↗
NASA NTRS1977

Are striations on Phobos evidence for tidal stress

A series of striations or grooves over a great part of the surface of Phobos, the inner satellite of Mars, can be observed on Viking orbiter photographs. It is suggested that some of these features are related to a readjustment of the satellite's figure with increasing tidal stress as the orbit evolves inwards under the action of tidal friction. If the width of the grooves is in fact due to tidal readjustments of the figure of Phobos, then the older craters should be systematically deformed from their initial nearly circular shapes.

Soter, S.↗
NASA NTRS1977

Viking Observations of Phobos and Deimos: Preliminary Results

The improved resolution of the Viking images has led to the discovery of a number of unusual surface features on Phobos. The features include elongated rill-like depressions associated with the crater Stickney, chains and clusters of irregular elongated craters, and linear striations or grooves. Crater counts are also considered. A total of 27 craters ranging in size from 0.3 to 1.4 km are visible on the best Deimos frame available. Craters ranging from 50 m to 4.9 km in diameter can be observed on the best of the Phobos images.

Veverka, J.↗
NASA NTRS1978

Origin of the grooves on Phobos

The age, surface density, and association with the 10-km crater Stickney of the grooves (long linear depression) on Phobos are investigated, and the results support the cratering hypothesis of groove formation and seem to rule out a tidal mechanism. The appearance of the grooves is described. The age of the grooves is estimated from the density of superimposed impact craters; the density of impact craters within the grooves is compared with the average value for all of Phobos. The old age of the grooves as well as their evident association with the crater Stickney are considered to be inconsistent with the tidal hypothesis.

Thomas, P.↗
NASA NTRS1978

Spacecraft imaging of Phobos and Deimos

A series of lower- and higher-resolution pictures of Phobos and Deimos taken from Viking spacecraft is presented. The imaging data imply that the two asteroid-size bodies may indeed have originated in the asteroid belt and may be composed of primordial material from the solar nebula. There is now sufficient knowledge on Phobos and Deimos to consider them as candidate targets for future sample/return missions or for locating bases to monitor Mars.

Duxbury, T. C.↗
NASA NTRS1978

The surfaces of Phobos and Deimos

Knowledge acquired from spacecraft observations of the surfaces of Phobos and Deimos is reviewed. Consideration is given to: the first spacecraft data - Mariner 7; the first systematic exploration - Mariner 9; surface texture and composition from Mariner 9 data; surface morphology from Mariner 9; and Viking results. A series of Viking photographs of Phobos and Deimos is presented.

Veverka, J.↗
NASA NTRS1979

Grooves on Phobos - Their distribution, morphology and possible origin

The global distribution, morphology, age, possible origin and significance of the long, linear depressions termed grooves on the surface of Phobos are discussed, based on Viking Orbiter data. The grooves, which consist of linear strings of coalesced and separate depressions in a loose regolith up to 100-200 m in depth, are observed to define the intersection of several sets of parallel planes with the surface of Phobos, with the widest and deepest grooves occurring just outside the rim of the 10-km crater, Stickney. The superposition of the grooves on older craters, crater density within the grooves and the intersections of groove sets suggest that the grooves are all of the same age, with their formation closely following that of Stickney. The evidence of groove morphology and distribution is used to attribute their formation to the enlargement of preexisting fractures or the formation of new fractures by the Stickney impact, causing the mobilization of the regolith along the fractures. The lack of observable grooves on Deimos is explained by the absence of a crater large enough to have severly fractured its surface.

Thomas, P.↗
NASA NTRS1981

The unusual dynamical environment of Phobos and Deimos

A three-dimensional numerical model is used to study the dynamical environment of Phobos and Deimos. Surface gravity, escape speeds, and ejecta impact contours are calculated both for the satellites at their present orbit distances, and for orbit distances they may have had in the past. Impact loci for Stickney ejecta are also calculated and compared with the observed groove locations in order to evaluate a possible secondary-impact origin for the grooves on Phobos. Attention is also given to the possible influence of the dynamical environment on shaping the satellites' surfaces.

Davis, D. R.↗
NASA NTRS1984

Phobos: Close encounter imaging from the Viking Orbiters

The shape and orbital characteristics of Phobos, the larger and innermost of Mars' two irregular moons, are discussed and illustrated. Also presented are the high resolution pictures of Phobos that were obtained during the close flybys of Viking Orbiters 1 and 2. The viewing geometry is also given for each picture.

Duxbury, T. C.↗
NASA NTRS1986

Phobos and Deimos: Satellites of Mars

The physical characteristics of Phobos and Deimos, satellites of Mars, are discussed. Phobos and Deimos are used as an example to discuss the probable internal structure of objects of this type and the structural formations on their surfaces. The history of astronomical observations of Mars is also described.

Zharkov, V. M.↗
NASA NTRS1988

Manned Mars Explorer project: Guidelines for a manned mission to the vicinity of Mars using Phobos as a staging outpost; schematic vehicle designs considering chemical and nuclear electric propulsion

The Manned Mars Explorer (MME) project responds to the fundamental problems of sending human beings to Mars in a mission scenario and schematic vehicle designs. The mission scenario targets an opposition class Venus inbound swingby for its trajectory with concentration on Phobos and/or Deimos as a staging base for initial and future Mars vicinity operations. Optional vehicles are presented as a comparison using nuclear electric power/propulsion technology. A Manned Planetary Vehicle and Crew Command Vehicle are used to accomplish the targeted mission. The Manned Planetary Vehicle utilizes the mature technology of chemical propulsion combined with an advanced aerobrake, tether and pressurized environment system. The Crew Command Vehicle is the workhorse of the mission performing many different functions including a manned Mars landing, and Phobos rendezvous.

Nolan, Sean↗