Geology topics

Kenneth E. Herkenhoff

Publications and source records attributed to Kenneth E. Herkenhoff.

131 records · Page 8Linked to original sources

USGS1999

Observations of Phobos, Deimos, and bright stars with the Imager for Mars Pathfinder

The Imager for Mars Pathfinder (IMP) was used to observe several objects during the Martian night. The satellites, Phobos and Deimos, were observed on two occasions each, through the IMP geological filters covering the wavelength range 440 nm to 1 μm. The observations were converted to geometric albedo using triaxial ellipsoid models of the satellites and phase functions derived from Viking Orbiter images. The spectral slopes over the full wavelength range were 7.9(±0.5)% (100 nm) −1 and 9.6(±0.6)% (100 nm) −1 , respectively, referenced to 600 nm. In the Deimos spectra, some evidence for decreased reddening toward the trailing hemisphere was found. The geometric albedoes of Phobos and Deimos were found to be 0.065 (±0.010) and 0.068 (±0.009), respectively, averaged over 440 and 600 nm, in good agreement with previous measurements. The nighttime optical depth was investigated using observations of stars. A mean value of 0.56 (±0.09) was determined from measurements at different airmass. A possible maximum in the optical depth near 0200 local time was found, which may result from condensation during the night. A measurement of the egress of Phobos from eclipse was made. Modeling of the light curve gave a scale height for the scatterers of 10–15 km. The exact time of the eclipse reappearance over the limb could be reconstructed from the measurements and was in reasonable accord with predictions, although a small modification to the predicted position of Phobos of 6.8 (±6.0) km would have produced better agreement.

Journal of Geophysical Research E: Planets↗

USGS1998

Geologic map of the MTM -85280 quadrangle, Planum Australe region of Mars

The polar deposits on Mars are of great interest because they probably record martian climate variations (Thomas and others, 1992). The area shown on this map includes polar layered deposits with distinct low-albedo features and a sharp boundary between the layered deposits and the moderately cratered unit that forms the floor of Chasma Australe. Detailed mapping of this quadrangle was undertaken to further investigate the geologic relations between the albedo features and the layered deposits and to better constrain the recent geologic history of the south polar region. Dark dunes in the north polar region appear to be derived from erosion of the layered deposits, but the source of dark material in the south polar region is less clear (Thomas and Weitz, 1989). The presence of dark material in the brighter, redder layered deposits is paradoxical (Herkenhoff and Murray, 1990a); resolving this paradox is likely to result in a better understanding of the origin and evolution of the layered deposits and, therefore, the mechanisms by which global climate variations are recorded. Published geologic maps of the south polar region of Mars have been based on images acquired by either Mariner 9 (Condit and Soderblom, 1978; Scott and Carr, 1978) or the Viking Orbiters (Tanaka and Scott, 1987). The extent of the layered deposits mapped previously from Mariner 9 data is different from that mapped using Viking Orbiter images, and the present map agrees with the map by Tanaka and Scott (1987): the floor of Chasma Australe is not mapped as layered deposits. The residual polar ice cap, areas of partial frost cover, the layered deposits, and two nonvolatile surface units - the dust mantle and the dark material - were mapped by Herkenhoff and Murray (1990a) at 1:2,000,000 scale using a color mosaic of Viking Orbiter images. This mosaic and an additional Viking color mosaic were used to confirm the identification of the nonvolatile Amazonian units for this map and to test hypotheses for their origin and evolution. The colors and albedos of these units, as measured in places outside this map area, are presented in table 1 and figure 1. Accurately measuring the color and albedo of the units in this map area was not possible due to low signal/noise in the part of the red/violet mosaic (corrected for atmospheric scattering) that includes this area (Herkenhoff and Murray, 1990a). However, color/albedo unit boundaries in this area are visible in color mosaics that have not been corrected for atmospheric scattering effects. Therefore, while the color and albedo of various units on this map cannot be precisely quantified and compared with the values in table 1 and figure 1, color/albedo units can still be recognized. Because the resolution of the color mosaics is not sufficient to map these units in detail at 1:500,000 scale, contacts between them were recognized and mapped using higher resolution black-and-white Viking and Mariner 9 images. Only two possible impact craters in the layered deposits have been found in the area mapped; both are slightly elongate rather than circular. One, 1.6 km in diameter at lat 86.6° S., long 268°, was recognized by Plaut and others (1988); the other, about 3 km in diameter, is at lat 82.8° S., long 277°. Although the crater statistics are poor (only 16 likely impact craters found in the entire south polar layered deposits), these observations generally support the conclusions that the south polar layered deposits are Late Amazonian in age and that some areas have been exposed for at least 120 million years (Plaut and others, 1988; Herkenhoff and Murray, 1992, 1994). However, the recent cratering flux on Mars is poorly constrained, so inferred ages of surface units are uncertain. The Viking Orbiter 2 images used to construct the base were taken during the southern summer of 1977, with resolutions no better than 180 m/pixel. (The "less than 100 m per picture element" in Notes on Base of the controlled photomosaic base [U.S. Geological Survey, 1986] is incorrect.) A digital mosaic of Mariner 9 images was also constructed to aid in mapping. The Mariner 9 images were taken during the southern summer of 1971-72 and have resolutions as high as 90 m/pixel. However, usefulness of the Mariner 9 mosaic is limited by incomplete coverage and atmospheric dust opacity.

IMAP↗

USGS1997

Results from the Mars Pathfinder camera

Images of the martian surface returned by the Imager for Mars Pathfinder (IMP) show a complex surface of ridges and troughs covered by rocks that have been transported and modified by fluvial, aeolian, and impact processes. Analysis of the spectral signatures in the scene (at 440- to 1000-nanometer wavelength) reveal three types of rock and four classes of soil. Upward-looking IMP images of the predawn sky show thin, bluish clouds that probably represent water ice forming on local atmospheric haze (opacity ∼0.5). Haze particles are about 1 micrometer in radius and the water vapor column abundance is about 10 precipitable micrometers.

Science↗

USGS1997

Structure and kinematics of a complex impact crater, Upheaval Dome, southeast Utah

Two vastly different phenomena, impact and salt diapirism, have been proposed for the origin of Upheaval Dome, southeast Utah. Detailed geologic mapping, seismic refraction data, and the presence of shock metamorphosed rocks indicate that the dome originated by collapse of a transient cavity formed by impact. Evidence is: (1) the occurrence of a lag deposit of rare impactites, (2) fan-tailed fracture surfaces (shatter surfaces) and rare shatter cones are present near the center of the structure, (3) the top of the underlying salt horizon is at least 500 m below the surface at the center of the dome and there are no exposures of salt or associated rocks of the Paradox Formation in the dome to support the possibility that a salt diapir has ascended through it, (4) sedimentary strata in the center of the structure are pervasively imbricated by top-toward-the-center thrust faulting and are complexly folded as well, (5) top-toward-the-center normal faults are found at the perimeter of the structure, and 6) clastic dikes are widespread. We show that the dome formed mainly by centerward motion of rock units along listric faults. Outcrop-scale folding and upturning of beds, especially common in the center, are largely a consequence of this motion. We have also detected some centerward motion of fault-bounded wedges resulting from displacements on subhorizontal faults that conjoin and die out within horizontal bedding near the perimeter of the structure. The observed deformation corresponds to the central uplift and the encircling ring structural depression seen in complex impact craters.

Utah↗

USGS1994

Geologic map of the MTM -85080 quadrangle (revised), Planum Australe region of Mars

Published geologic maps of south polar region of Mars have been based on either Mariner 9 (Condit Soderblom, 1978; Scott and Carr, 1978) or Viking Orbiter (Tanaka and Scott, 1987) images. The mapped extent of the southern layered deposits differs in many places on these maps and on our maps. These differences reflect the difficulty in accurately determining the location of the contact between the layered deposits and subjacent units. The polar layered deposit gradually thin toward their margin in many places, and the smooth surface features that characterize the layered deposits are also found on other sedimentary blankets in the south polar region (Murray and others, 1972; Sharp, 1973). Previous workers have also reached different conclusions regarding the origin of the lower member of the Dorsa Argentea Formation, which was named by Tanaka and Scott (1987) and interpreted by them as volcanic in origin (based on observation of flow fronts in areas far outside this quadrangle). The lower member, previously called pitted material, and other sedimentary, and other sedimentary units were recognized in Mariner 9 images and described by Murray and others (1972), Sharp (1973), and Cutts (1973b). Sharp (1973) argued for exhumation of pits by wind, perhaps aided by sublimation of volatiles. He concluded that the massive pitted sediments of the lower member unconformably overlie older massive units. We have mapped one of these older units ridged and knobby material. Condit and Soderblom (1978) found some layered deposits within pits, which indicates that erosion of the pits was completed before accumulation of the layered deposits commenced. Howard’s (1981) suggestion that the pits may be formed by basal melting of ground ice is consistent with either a volcanic or sedimentary origin for the lower (pitted) member. Plaut and others (1988) mapped the extent of the pitted material and found that it overlies volcanic plains wherever the contact is visible. They concluded that the pitted material is no more than 1 km thick and is about 3.3 billion years old (Late Hesperian).

IMAP↗