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Ronald Greeley

Publications and source records attributed to Ronald Greeley.

29 records · Page 2Linked to original sources
USGS1994

Geologic map of the MTM-15147 quadrangle, Mangala Valles region of Mars

The map area is in the Mangala - M e mnonia region (fig. 1), which contains remarkably diverse geologic features and terrain types. Studies of the Mariner 9 images revealed the wide range of ages of the major rock units in this region ; age assignments wer e based on the density of impact craters preserved on the various surfaces ( Mutch and others, 1976, p. 56-60; Scott and Carr , 1978; Mut c h and Morris, 1979). The region includes ancient cratered highlands, more sparsely cratered smooth plains, young volcanic plains, and the Mangala Valles channel system. The sinuosity of the streamlined l an dforms within the Man g ala Valles, combined with braided channels evident throughout the lower reaches of the valley system, were recognized as indicators that he Mangala area was subject to substantial erosion by a flowing fluid, most likely water (Milton, 1973; Baker and Milton, 1974; Sharp and Malin , 1975). Recent global mapping based on the Viking Orbiter images (Scott and Tanaka , 1986 ) has refined the relative ages of many rock units on Mars, but it has modified only slightl y the basic interpretations of features in the Mangala- Memnonia region.

IMAP↗
USGS1992

Lunar impact basins and crustal heterogeneity: New western limb and far side data from Galileo

Multispectral images of the lunar western limb and far side obtained from Galileo reveal the compositional nature of several prominent lunar features and provide new information on lunar evolution. The data reveal that the ejecta from the Orientale impact basin (900 kilometers in diameter) lying outside the Cordillera Mountains was excavated from the crust, not the mantle, and covers pre-Orientale terrain that consisted of both highland materials and relatively large expanses of ancient mare basalts. The inside of the far side South Pole—Aitken basin (>2000 kilometers in diameter) has low albedo, red color, and a relatively high abundance of iron- and magnesium-rich materials. These features suggest that the impact may have penetrated into the deep crust or lunar mantle or that the basin contains ancient mare basalts that were later covered by highlands ejecta.

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USGS1990

Volcanism in Northwest Ishtar Terra, Venus

Soviet Venera 15/16 radar images and topographic data for an area in NW Ishtar Terra, Venus (74°N, 313°E) contain evidence for the existence of a complex volcanic center. Located at the intersection of Akna and Freyja Montes (both elevated ∼4 to 7 km above the planetary reference radius of 6051 km), this volcanic center has a complex caldera system, possibly more than one major eruptive vent, and associated lava flows at lower elevations. Evidence for a volcanic center at NW Ishtar Terra includes: a smooth-surfaced unit with moderate radar brightness; adjacent (possibly associated) bright flows extending northwestward more than 300 km; an irregularly shaped depression 200 by 250 km in size and ∼2.0 km deep; arcuate slopes that appear to mark the rims of several semicircular depressions within the larger depression; and 5.5-km-elevation ridge separating volcanic deposits of northern Lakshmi Planum from those of NW Ishtar Terra. The lack of a notable shield construct at NW Ishtar and the similarity between smooth terrain and undivided plains of Lakshmi Planum suggest that volcanic units at NW Ishtar Terra may represent an earlier (perhaps younger) stage of volcanism than that attributed to Colette and Sacajawea Paterae of Lakshmi Planum. A westward migration in volcanic activity from Sacajewea to Colette NW Ishtar is supported by relative youth of Colette as compared to Sacajawea, the relatively young stage of volcanism at NW Ishtar Terra, and the superposition of this volcano on the banded terrain of Akna and Freyja Montes.

Icarus↗
USGS1987

Geologic map of the eastern equatorial region of Mars

The M ariner 9 mission in the early 1970’s provided the first comprehensive view of the geology of Mars (McCauley and others, 1972, Masursky , 1973) and led to the derivation of the first global geologic map ( Carr and others, 19 73). These preliminary studies were followed by more comprehensive mapping coordinated with the U.S. Geological Survey. Thirty quadrangles at a scale of 1:5 , 0 00,000 were produced in this map series, from which Scott and Carr (1978) compiled a single geologic map at a scale of 1:25,000,000. The reliability of these maps, however, is varied because of the uneven quality of the Mariner 9 data.

IMAP↗
USGS1974

North polar region of Mars: Imaging results from Viking 2

During October 1976, the Viking 2 orbiter acquired approximately 700 high-resolution images of the north polar region of Mars. These images confirm the existence at the north pole of extensive layered deposits largely covered over with deposits of perennial ice. An unconformity within the layered deposits suggests a complex history of climate change during their time of deposition. A pole-girdling accumulation of dunes composed of very dark materials is revealed for the first time by the Viking cameras. The entire region is devoid of fresh impact craters. Rapid rates of erosion or deposition are implied. A scenario for polar geological evolution, involving two types of climate change, is proposed.

Science↗