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Trask, N. J.

Publications and source records attributed to Trask, N. J..

18 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Moon-Mercury - Large impact structures, isostasy and average crustal viscosity

It is shown that Mercury's surface has only 70% as many large craters (of at least 200 km in diameter) as the moon. The density of Mercurian impact craters having diameters over 400 km is 30% of that of the moon, and for craters with diameters between 400 and 700 km, Mercurian density is 21% of that of the moon. The size-frequency distribution curve of Mercury is the same as the lunar cumulative -2 slope. The Mercurian curve, however, lies well below the 10% surface saturation level of the lunar curve. This may indicate that the old, heavily-cratered Mercurian terrain is not presently in a state of cratering equilibrium. The differences in crater and basin densities observed between Mercury and the moon may be functions of crater-production rates or of different crustal histories. The total isostatic compensation of impact craters having diameters of about 800 km suggests that the average viscosity of the Mercurian crust during approximately the past 4 eons was the same as that of the moon.

Schaber, G.↗
NASA NTRS1976

Additional evidence of Mercurian volcanism

Evidence concerned with (1) the character and distribution of terrain surrounding fresh basins; (2) albedo, color, and temporal differences between a basin rim and smooth plains on its floor; and (3) the stratigraphic relations and local distribution of smooth plains in the hilly and lineated terrain are cited as additional evidence for an internal origin of much of the Mercurian smooth plains. Although the question of Mercurian volcanism should be kept open, this evidence together with that presented in an earlier paper suggests that volcanism occurred on Mercury early in its history.

Trask, N. J.↗
NASA NTRS1976

Planetary imaging - Past, present, and future

Recent exploration of the planets has been highlighted by the development of visual imaging systems carried on board the spacecraft. This paper describes the evolution of planetary camera systems from the earliest reconnaissance flight to Mars in 1965 (Mariner 4) through the planned mission to Jupiter and Saturn in 1977. Advances in telecommunication performance, mission planning and operations, and digital processing of images are also discussed. Science objectives and changes in the imaging systems required to meet these objectives are discussed for the Mariner Mars 1971 (Mariner 9), Mariner Venus-Mercury (Mariner 10), Viking 1975 (Mars Orbiter), and Mariner Jupiter-Saturn 1977 missions. The last section of the paper describes future plans for imaging experiments based on cameras using solid-state sensors, particularly charge-coupled devices.

Masursky, H.↗
NASA NTRS1975

Preliminary geologic terrain map of Mercury

A geologic terrain map of Mercury has been constructed by use of the photogeologic methods employed for the moon and Mars. The oldest and most widespread unit, intercrater plains, forms nearly level to rolling surfaces on which are superposed numerous secondary impact craters. This unit may represent a very old surface that predates the last heavy bombardment of the inner planets. The effects of this bombardment are recorded in a second widespread unit, heavily cratered terrain, consisting of closely spaced craters and basins from 30 km to several hundred kilometers in diameter. Units formed by excavation of the 1300-km-diameter Caloris basin are widespread on one hemisphere of the planet. The development of the Caloris basin was followed relatively quickly by emplacement of widespread plains materials, most of which are probably volcanic.

Trask, N. J.↗
NASA NTRS1975

Surface history of Mercury - Implications for terrestrial planets

A plausible surface history of Mercury is presented which is suggested by Mariner 10 television pictures. Five periods are postulated which are delineated by successive variations in the modification of the surface by external and internal processes: accretion and differentiation, terminal heavy bombardment, formation of the Caloris basin, flooding of that basin and other areas, and light cratering accumulated on the smooth plains. Each period is described in detail; the overall history is compared with the surface histories of Venus, Mars, and the moon; and the implications of this history for earth are discussed. It is tentatively concluded that: Mercury is a differentiated planet most likely composed of a large iron core enclosed by a relatively thin silicate layer; heavy surface bombardment occurred about four billion years ago, which probably affected all the inner planets, and was followed by a period of volcanic activity; no surface modifications caused by tectonic, volcanic, or atmospheric processes took place after the volcanic period.

Murray, B. C.↗
NASA NTRS1972

The contributions of Ranger photographs to understanding the geology of the moon

Vidicon photographs returned to earth by Rangers 7, 8, and 9 in 1964 and 1965 were used to study the details of lunar geologic units previously recognized from earth-based telescopic photographs and to make geologic maps at a variety of scales. The photographs from each mission changed continuously in scale as the spacecraft approached impact. The final frames had resolutions some 1,000 times better than the best earthbased photographs. Lunar stratigraphic units mapped at a scale of 1:1,000,000 displayed, at these larger scales, differences in properties and, possibly, in ages, but a clear-cut stratigraphic succession of subunits was not apparent. The plains-forming materials in both terra and mare were divisible into units mainly on the basis of the differences in the total number of superposed craters and in the relative number of craters of various morphologic types.

Trask, N. J.↗
NASA NTRS1971

Imaging of Mercury and Venus from a flyby.

Study of an imaging experiment planned for the 1973 Mariner Venus/Mercury flyby mission. Scientific objectives are presented together with mission constraints, analysis of alternative systems, and the rationale for the final choice. The final selection was a vidicon camera quite similar to that used for Mariner Mars 1971, but with the capability of real time transmission during the Venus and Mercury flybys. Systematic high resolution UV photography of Venus is planned after encounter in an attempt to understand the nature of the mysterious UV markings and their apparent 4- to 5-day rotation period.

Murray, B. C.↗
NASA NTRS1971

Contributions to Astrogeology: Geology of the lunar crater volcanic field, Nye County, Nevada

The Lunar Crater volcanic field in east-central Nevada includes cinder cones, maars, and basalt flows of probably Quaternary age that individually and as a group resemble some features on the moon. Three episodes of volcanism are separated by intervals of relative dormancy and erosion. Changes in morphology of cinder cones, degree of weathering, and superposition of associated basalt flows provide a basis for determining the relative ages of the cones. A method has been devised whereby cone heights, base radii, and angles of slope are used to determine semiquantitatively the age relationships of some cinder cones. Structural studies show that cone and crater chains and their associated lava flows developed along fissures and normal faults produced by tensional stress. The petrography of the basalts and pyroclastics suggests magmatic differentiation at depth which produced interbedded subalkaline basalts, alkali-olivine basalts, and basanitoids. The youngest flows in the field are basanitoids.

Scott, D. H.↗