ISSN:0148-0227    

DOI:10.1029/JB084iB14p07909

年代:1979

数据来源: WILEY

ISSN:0148-0227    

DOI:10.1029/JB084iB14p07911

年代:1979

数据来源: WILEY

摘要:

The primary mission of the Viking project, with two orbiters and two landers at Mars, was completed in November 1976, but operations have since been extended in a series of stages, and they are still continuing as of November 1979. The lander investigations that searched for evidence of living organisms and organic chemicals in the surface material and determined the chemical composition of the atmosphere were completed early in 1977. Since then a major emphasis has been on the study of the weather on Mars, with instruments on all four spacecraft contributing. The acquisition of samples for the inorganic analysis of surface material, the manipulation of the sampling tool to investigate the physical and magnetic properties of the surface, and the seismic measurements were terminated a year later, but other investigations were continued. Orbiters and landers have acquired large quantities of photographs of the surface and of atmospheric phenomena. Viking Orbiter 2 ceased to operate in July 1978; Viking Orbiter 1 was shut down temporarily in February 1979 but resumed operations in July for an additional 3 months or more. Both landers have been programmed to continue for another decade, but only Viking Lander 1 will yield scientific data. This paper discusses the operation and chronology of the Viking mission. The scientific results are discussed in a companion paper.

ISSN:0148-0227    

DOI:10.1029/JB084iB14p07917

年代:1979

数据来源: WILEY

摘要:

Any model for the tectonic evolution of Mars must account for two major crustal elements: the Tharsis bulge and the topographically low and lightly cratered northern third of the planet. Ages determined by crater density indicate that both of these elements came into existence very early in Martian history, a conclusion that holds no matter which of the current crater density versus age curves is used. The size of these two major crustal elements and their sequential development suggest that both may be related to a global‐scale internal process. It is proposed that the resurfacing of the northern third of Mars is related to subcrustal erosion and isostatic foundering during the life of a first‐order convection cell. With the demise of the cell, denser segregations of metallic materials began to coalesce as a gravitatively unstable layer which finally overturned to form the core. In the overturn, lighter crustal material was shifted laterally and underplated beneath Tharsis to cause rapid and permanent isostatic rise. This was followed by a long‐lived thermal phase produced by the hot underplate and by the gravitative energy of core formation slowly making its way to the surface to produce the Tharsis volc

ISSN:0148-0227    

DOI:10.1029/JB084iB14p07934

年代:1979

数据来源: WILEY

摘要:

Considerable controversy has arisen regarding the existence of water and water ice below the surface of Mars. Results of laboratory internal friction measurements on strongly outgassed rocks, recently made as part of an effort to interpret the high seismicQvalues observed in the lunar crust, show that moisture absorbed in pores and cracks causes the lowQvalues. Unfortunately, the Viking seismology investigation found a surprisingly inactive planet. This note makes the case for active seismic exploration in order to ascertain the existence of liquid water in the crust fromQdeterminations.

ISSN:0148-0227    

DOI:10.1029/JB084iB14p07940

年代:1979

数据来源: WILEY

摘要:

Satellite geodesy techniques previously applied to artificial earth satellites have been extended to obtain a high‐resolution gravity field for Mars. Two‐way Doppler data collected by 10 Deep Space Network (DSN) stations during Mariner 9 and Viking 1 and 2 missions have been processed to obtain a twelfth degree and order spherical harmonic model for the martian gravitational potential. The quality of this model was evaluated by examining the rms residuals within the fit and the ability of the model to predict the spacecraft state beyond the fit. Both indicators show that more data and higher degree and order harmonics will be required to further refine our knowledge of the martian gravity field. The model presented shows much promise, since it resolves local gravity features which correlate highly with the martian topography. An isostatic analysis based on this model, as well as an error analysis, shows rather complete compensation on a global (long wavelength) scale. Though further model refinements are necessary to be certain, local (short wavelength) features such as the shield volcanos in Tharsis appear to be uncompensated. These are interpreted to place some bounds on the internal structure of M

ISSN:0148-0227    

DOI:10.1029/JB084iB14p07943

年代:1979

数据来源: WILEY

摘要:

Special photogrammetric techniques have been developed to portray Mars topography, using Mariner and Viking imaging and nonimaging topographic information and earth‐based radar data. Topography is represented by the compilation of maps at three scales: global, intermediate, and very large scale. The global map is a synthesis of topographic information obtained from Mariner 9 and earth‐based radar, compiled at a scale of 1:25,000,000 with a contour interval of 1 km; it gives a broad quantitative view of the planet. At intermediate scales, Viking Orbiter photographs of various resolutions are used to compile detailed contour maps of a broad spectrum of prominent geologic features; a contour interval as small as 20 m has been obtained from very high resolution orbital photography. Imagery from the Viking lander facsimile cameras permits construction of detailed, very large scale (1:10) topographic maps of the terrain surrounding the two landers; these maps have a contour interval of 1 cm. This paper presents several new detailed topographic maps of M

ISSN:0148-0227    

DOI:10.1029/JB084iB14p07955

年代:1979

数据来源: WILEY

摘要:

Detailed geomorphic mapping from Viking imagery of selected portions of Kasei Vallis, Maja Vallis, and vicinity reveals numerous similarities of channel morphology to erosional and depositional features of the Channeled Scabland. Characteristic scabland landforms which occur in Kasei and Maja Valles include erosional grooves, streamlined uplands and hills, scour zones around flow obstacles, inner channels with erosional head cuts, breached ridges and basin (crater) rims, pendant forms (bars?), erosional terracing of streamlined hills and channel margins, and possible midchannel bars. These features constitute an assemblage of landforms which on earth is most characteristic of catastrophic flood channeling in jointed bedrock. Prominent mass wastage and sapping features are associated with the high‐wall relief in lower Kasei Vallis. Many cliffs along the channel margins exhibit steep upper slopes and gentler lower talus slopes which form the spur‐and‐gully topography that has also been described along chasma walls in the Valles Marineris. Landslides, debris fans, and debris cones can also be recognized. Much less wall modification occurs in the shallower Maja Vallis. Probably, the steep escarpments of Kasei were created by tectonic processes and subsequent channel incision. These escarpments later receded by mass wasting and sa

ISSN:0148-0227    

DOI:10.1029/JB084iB14p07961

年代:1979

数据来源: WILEY

摘要:

The large‐scale water flows implied by the morphology of the Martian outflow channels could have produced the observed assemblage of erosional bed forms by a combination of ice processes, macroturbulence, streamlining, and cavitation. Although pure liquid water would not be stable under present Martian environmental conditions, evaporative cooling would probably lead to a variety of ice processes, including erosive ice drives and ice jamming at flow constrictions, sharp bends, and islands. Macroturbulence in the deep, high‐velocity flood flows might consist of kolks, rollers in zones of flow separation, and longitudinal arrays of vortices. These processes would contribute to the development of the scabland‐type bed forms on the channel floors, including longitudinal grooves, inner channels, and cataracts. Streamlined uplands are preferentially developed and preserved in this turbulent regime because they minimize flow separation. The Martian streamlined uplands are somewhat more elongate than those in the Channeled Scabland, perhaps indicating formation by flows of higher Reynold's number. The large variety of possible thermodynamic states, flow dynamics, and local pressure environments for the Martian flood flows appears to have been ideal for cavitation inception and bubble collapse. The combination of relatively low gravity and low atmospheric pressure would facilitate Martian fluvial cavitation at much lower velocities than are required for cavitation inception in terrestrial rivers. Cavitation erosion was probably localized on the stream bed by flow constriction‐expansion effects and by macroturbulent flow st

ISSN:0148-0227    

DOI:10.1029/JB084iB14p07985

年代:1979

数据来源: WILEY

摘要:

The Lunae Planum‐Chryse Planitia region provides the opportunity to study a sequence of channeling events and to determine their temporal and genetic relationships to plains units in the northern hemisphere of Mars. Two sets of small channels and four major channel systems can be divided into four periods of channeling by superposition and contact relationships to the plains. All of the channels are considered to have formed by water erosion. The first two channeling events occurred early in the history of this area and formed small, narrow channels within the old rugged terrain. These channel events were separated by deposition of a mantle unit. The small channels probably formed by runoff of surface water or by a sapping process. These channels preceded the emplacement of vast volcanic plains in both Lunae Planum and Chryse Planitia. Channels postdating the plains are Vedra, Maumee, Bahram, and Maja valles; the first three of these deposited a sedimentary unit on the western slope of Chryse Planitia that was eroded by Maja Vallis. These large‐scale channels were probably formed predominantly by catastrophic floods and may represent two periods of water release from Juventae Chasma. The origin of Bahram Vallis remains uncert

ISSN:0148-0227    

DOI:10.1029/JB084iB14p07994

年代:1979

数据来源: WILEY