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↗

USGS1987

Geologic map of the polar regions of Mars

These geologic maps of the north and south polar regions of Mars, extend ing to 55 ˚ north and south latitudes, overlap by 2 ˚ the geologic maps of the western and eastern regions, which extend to lat ± 57 ˚ . The maps were compiled from Viking medium-resolution photomosaics at scales of 1:2,000,000 and from higher resolution Viking images. The quality and resolution of the Viking pictures are superior to those of Mariner 9 used to prepare the previous maps (Scott and Carr , 1978) that includes these two regions. Because of the Viking orbital configuration, a vast number of high-resolution images of the area within 10 ˚ of the north pole was obtained, whereas many areas in lower northern latitudes were covered only by low-resolution images. In contrast, the south polar region is nearly completely covered by images at medium resolution but is not image d at high resolution.

IMAP↗

USGS1986

Geomorphic evidence for the distribution of ground ice on Mars

High-resolution Viking orbiter images show evidence for quasi-viscous relaxation of topography. The relaxation is believed to be due to creep deformation of ice in near-surface materials. The global distribution of the inferred ground ice shows a pronounced latitudinal dependence. The equatorial regions of Mars appear to be ice-poor, while the heavily cratered terrain poleward of ± 30° latitude appears to be ice-rich. The style of creep poleward of ± 30° varies with latitude, possibly due to variations in ice rheology with temperature. The distribution suggests that ice at low latitudes, which is not in equilibrium with the present atmosphere, has been lost via sublimation and diffusion through the regolith, thereby causing a net poleward transport of ice over Martian history.

Science↗

USGS1981

Survey for bright Mars-crossing asteroids

A new method of search for relatively bright Mars-crossing asteroids with the Palomar 46-cm Schmidt camera was initiated in 1980. Selected fields photographed with the 46-cm Schmidt were systematically reduced for all asteroids detected on the films. The 46-cm Schmidt fields have an effective diameter of 8 3/4 degrees. Kodak 11a-D film was exposed with a yellow plexiglass filter. The films were scanned with a specially designed stereomicroscope that permits recognition of asteroids by stereopsis. Stereoscopic pairs of films were exposed with a time separation of 30 minutes; over this interval the parallax in position relative to the background stars allows easy recognition of asteroids at distances ranging from near the Earth through the main belt. Optimum exposure for each film was found to be 10 minutes on the f/2 Schmidt.

Book chapter↗

USGS1980

Geologic map of the Sinus Sabaeus quadrangle of the Mars

The area included in the Sinus Sabaeus quadrangle represents an ancient cratered surface that has been modified by a combination of impact cratering, fluvial, eolian, and, probably, volcanic processes. Impact cratering has been the dominant process. Cumulative frequencies of craters larger than 20 km for the entire quadrangle (fig. 4) are only about a factor of two below the idealized lunar steady-s ta te curve (Moor e , 1964; Trask, 1966). Two of the units mapped (hilly, channeled , and cratered material a n d hilly and cratered material) have cumulative frequencies of craters larger than 40 km that are near the same as the idealized steady-state curve. The young map units (smooth plains material and units of the crater Bakhuysen ) have cumul ative frequencies of craters a distributions that are similar in form and magnitude to the average frequency distributions of lunar maria. Ages of surfaces recorded by craters larger than 5 km (fig. 4) are probably measured in several billions of years. Direct comparison with lunar cra t ers would place the age of the young units (smooth plains material and units of Bakhuysen ) i n the range 3.2 to 3.5 billion years, but procedures for making such a comparison are controversial. (See, for example, Soderblom and others, 1974 ; Neukum and Wise, 1976). These units may be either a few tenths of a billion years older or about a billion years younger than the average lunar maria. The more cratered units (hilly, channel e d, and cratered material and hill y and cratered material) may represent the cumulative result of about 4 billion years of cratering (Soderblom and others, 1974 ; Neukem and Wise, 1976).

IMAP↗

USGS1979

Chemical composition of Mars

The composition of Mars has been calculated from the cosmochemical model of Ganapathy and Anders (1974) which assumes that planets and chondrites underwent the same 4 fractionation processes in the solar nebula. Because elements of similar volatility stay together in these processes, only 4 index elements (U, Fe, K and Tl or Ar 36 ) are needed to calculate the abundances of all 83 elements in the planet. The values chosen are U = 28 ppb , K = 62 ppm (based on K U = 2200 "> KU= 2200 from orbital γ-spectrometry and on thermal history calculations by Toksöz and Hsui (1978) Fe = 26.72% (from geophysical data), and Tl = 0.14 ppb (from the Ar 36 and Ar 40 abundances measured by Viking). The mantle of Mars is an iron-rich [ Mg /( Mg + Fe ) = 0.77] garnet wehrlite ( ρ = 3.52−3.54 g / cm 3 ), similar to McGetchin and Smyth's (1978) estimate but containing more Ca and Al. It is nearly identical to the bulk Moon composition of Morgan et al. (1978b). The core makes up 0.19 of the planet and contains 3.5% S—much less than estimated by other models. Volatiles have nearly Moon-like abundances, being depleted relative to the Earth by factors of 0.36 (K-group, T cond = 600–1300 K ) or 0.029 (Tl group, T cond < 600 K ). The water abundance corresponds to a 9 m layer, but could be higher by as much as a factor of 11. Comparison of model compositions for 5 differentiated planets (Earth, Venus, Mars, Moon, and eucrite parent body) suggests that volatile depletion correlates mainly with size rather than with radial distance from the Sun. However, the relatively high volatile content of shergottites and some chondrites shows that the correlation is not simple; other factors must also be involved.

Geochimica et Cosmochimica Acta↗