A (44 KBytes)
|
Tithonium/Ius Chasmata (Orbit 13, Image 3)On October 3, 1997, the MOC acquired this image of the western Tithonium Chasma/Ius Chasma portion of the Valles Marineris, centered at 6.6°S, 90.4°W, at 1:16 PM PDT. Although the lighting beneath the spacecraft was very poor, the camera was canted towards the sun, and the illumination was equivalent to roughly 5 PM local time (the sun was about 17° above the horizon). In the image, the canyon floors are mostly shadowed, but steep slopes in the area are exquisitely highlighted.The area outlined in (A), the highest resolution view of the region previously available, is 6.6 km (4 miles) wide by 55.6 km (34.5 miles) long. The ridges to the north and south are about 4000 m (13,000 feet) above the floor of the troughs, but in the area photographed, the relief is slightly lower (about 3000 m, or 10,000 feet). The top portion of the image is shown in (B), and a section of that image is shown enlarged in (C). The scale is 6.45 m/pixel across the image by 9.65 m/pixel down the image. Most remarkable about the MOC image is the discovery of light and dark layers in the rock outcrops of the canyon walls. In the notable, triangular mountain face [center of (B) and at the top of (C)), some 80 layers, typically alternating in brightness and varying in thickness from 5 to 50 meters (16 to 160 feet), are clearly visible. This shear mountain cliff, over 1000 m (3200 ft) tall, is only one of several outcrops that, together, indicate layering almost the entire depth of the canyon. This type of bedrock layering has never been seen before in Valles Marineris. It calls into question common views about the upper crust of Mars, for example, that there is a deep layer of rubble underlying most of the martian surface, and argues for a much more complex early history for the planet. Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO. |
A (83 KBytes)
|
Schiaparelli Crater (Orbit 23, Image 6)This view of Mars, showing a small area immediately south of the large crater Schiaparelli, was taken by the Mars Orbiter Camera during its 23rd pass close to the planet. It was acquired on October 18, 1997, at 3:42 PM PST, about 10 minutes after closest approach. The image covers an area 4.6 km (2.9 miles) wide by 21.1 km (13.1 miles) high, at a resolution of 4.5 m by 7.9 m (14.75 X 25.9 feet) per picture element, and is centered at 5.5°S, 340.7°W. The local time of the acquisition was about 4:50 PM.(A) shows the location in the best available image from the Viking Orbiters (approximately 240 m/pixel). (B) is the full image, while (C) is an enlarged portion of (B). There are two exciting results seen in this image. First, the small dunes moving from left to right (north to south) along the canyon floor are apparently derived from bright deposits within Schiaparelli crater. They are brighter than most martian dunes and may represent a unique composition. The shape of the dunes, and their relationships to one another, strongly suggest that these dunes have been active recently, although whether that means within the past year or the past century cannot be told from these images alone. The second discovery made in this image are the small depressions found in the upper left and center of image [best seen in (C)] with faint dark lines crossing lighter floors. These depressions, and the pattern of lines, are similar to dry lake beds seen throughout the deserts of the southwestern United States. The light material may be salts or other minerals deposited as the lake evaporated, and the dark lines may be cracks created as the material dried out. Alternative explanations for the dark lines, involving freezing and thawing of water-saturated soil, are equally intriguing. In both cases, these features are the examples of a suite of such forms that can be used to diagnose the amount and distribution of surficial water that may have once ponded on Mars. |
A (95 KBytes)
|
Ganges Chasma (Orbit 28, Image 2)Complex Floor Deposits Within Western Ganges Chasma, Valles Marineris. On October 26, 1997, MOC took this image of Mars 10 minutes after its closest approach to the planet (1:46 AM PST). The view shows the floor of western Ganges Chasma (7.8°S 51.8°W), covering an area 2.6 km (1.6 miles) wide by 45.4 km (28.2 miles) long at a resolution of 5 by 7.4 meters (16.4 by 24.3 feet) per picture element. The local time on Mars when the picture was taken was 4:35 PM.This image, portions of which are presented in (B) and (C) at full resolution, is roughly 50 times better than the previous best image, shown in (A). (B) shows the area near the canyon wall, where large block of the upland surface have slumped down into the canyon. Close inspection of this image shows numerous small dark dots that are in fact individual rocks on the surface of Mars. These rocks vary from the size of a small automobile to the size of a house, have fallen down steep slopes. (C) shows a remarkable landscape of ridges and troughs that very closely resemble folded and warped sediments on Earth. This is the first time such warped beds have been seen on Mars, and neither their origin nor their occurrence within Ganges Chasma is understood. It is possible these are beds folded by a large landslide, but that would be very unusual. Alternatively, these may be folded sedimentary beds, similar to horizontal beds seen elsewhere in Ganges Chasma. However, what forces then folded these particular beds while leaving the others undeformed is unknown. Future imaging within this and the other Valles Marineris will be used to address such issues. |
During each passage through the upper atmosphere, the spacecraft points the delicate science instruments in the direction away from the motion (the aerobraking attitude). Again, the camera cannot take pictures of Mars in this orientation, since it is always looking away from the planet.
However, after each aerobraking pass, the spacecraft must change its orientation from the aerobraking attitude to ANS. The spacecraft team has designed this transition, called the roll-out maneuver, to rotate the spacecraft around the axis that allows images to be scanned and move the camera axis across the planet. So, once each orbit, there will be an opportunity to take a picture of the planet.
Several factors could reduce the quality of these pictures. First, early in the aerobraking period, the ground beneath the spacecraft is so dark (the orbit is at 5:30 PM local solar time) that the cameras will not be able to see much. This problem has been mitigated somewhat by pointing the camera axis towards the illuminated portion of the planet, but the overall effectiveness of this approach is not known. Second, the focus of the cameras (both the high and low resolution) is sensitive to temperature. Since the temperature of the cameras will vary depending on position in each orbit, and slowly from orbit to orbit, some adjustment for focus will have to be attempted. Unfortunately, without bright stars as a test of focus, this attempt will be subject to considerable uncertainty. Finally, because the timing of each imaging opportunity will only be known to a few minutes accuracy, it is not possible to predict in advance what will be seen in each picture. This could lead to improper exposures (independent of the illumination conditions) that result from intrinsic brightness variations of the ground.
Imaging opportunities end when the spacecraft begins to go behind the
planet relative to the sun on each orbit. This is because the spacecraft
will then be using battery power to sustain its vital functions for those
portions of the orbit, and the science instruments will have to be turned
off. This will occur in late November or early December 1997.
A: JPEG = 242 KBytes MOC Image P024_01 and 02 October 20, 1997 Click on image for full resolution
|
Olympus Mons
As has been noted in other MOC releases, Olympus Mons is the largest of the major Tharsis volcanoes, rising 25 km (15.5 miles) and stretching over nearly 550 km (340 miles) east-west. The summit caldera, a composite of as many as seven roughly circular collapse depressions, is 66 by 83 km (41 by 52 miles) across. Also seen in this image are water-ice clouds that accumulate around and above the volcano during the late afternoon (at the time the image was acquired, the summit was at 5:30 PM local solar time). Through Monday, October 28, the MOC had acquired a total of 132 images, most of which were at low sun elevation angles. Of these images, 74 were taken with the high resolution narrow angle camera and 58 with the low resolution wide angle cameras. Twenty-eight narrow angle and 24 wide angle images were taken after the suspension of aerobraking. These images, including the one shown above, are among the best returned so far. |
A: Viking Orbiter Context Image
|
Valles Marineris
MOC images P013_01 and P013_02 were acquired with the low resolution red and blue wide angle cameras at 2:14 PM PDT on October 3, 1997, about 11 minutes after Mars Global Surveyor passed close to the planet for the thirteenth time. To make a color image, a third component (green) was synthesized from the red and blue images. During the imaging period, the spacecraft was canted towards the sun-lit hemisphere by 25°, and the MOC was obliquely viewing features from about 600 to 1000 km (360 to 600 miles) away. The resolution at those distances was between 350 and 600 meters (0.25 to 0.37 miles) per picture element. The image covers an area from 73° to 86° W longitude and 5° N to to 10° S). In both of the two images shown above, north is to the top. In the MOC image, the camera was viewing towards the west.
(B) is the composite of MOC frames P013_01 and P013_02. Because the MOC acquires its images one line at a time, the cant angle towards the sun-lit portion of the planet, the spacecraft orbital velocity, and the spacecraft rotational velocity combine to distort the image slightly. However, the wide angle cameras provide a fairly realistic portrayal of what one would see looking out across Mars from the Orbiter. Notable in this image are the late afternoon clouds and hazes that are concentrated within the canyon system. |
A: Viking Orbiter Context Image (250 KB)
|
Labyrinthus Noctis is near the
crest of a large (many thousands of kilometers) updoming of the Martian
crust, and the 2000 meter (6500 foot) deep canyons visible in these pictures
are bounded by faults. Debris shed from the steep slopes has moved down
into after the canyons opened. Small dunes are seen in the lowest area,
beneath the high cliffs.
MOC image P005_03 was acquired at 6:25 AM PDT on September 19, 1997, about 11 minutes after Mars Global Surveyor passed close to the planet for the fifth time. During the imaging period, the spacecraft was canted towards the sun-lit hemisphere by 25°, and the MOC was obliquely viewing features about 1600 km (1000 miles) away. The resolution at that distance was about 6 meters (20 feet) per picture element (pixels), but in order to improve the number of gray levels, the pixels were summed in both the cross-track and along-track directions, yielding final resolution of about 12 meters (40 feet) per pixel. The MOC image covers an area about 12 km X 12 km (7.5 X 7.5 miles). (A) is excerpted from the U.S. Geological Survey's Mars Digital Image Mosaic, showing the Labyrinthus Noctis area west of the Valles Marineris. This image is about 175 km (109 miles) square. The outline of the MOC high resolution (Narrow Angle ) camera image is centered at 4.6°S, 102.6°W. (B) is the MOC frame P005_03. Because the MOC acquires its images one line at a time, the cant angle towards the sun-lit portion of the planet, the spacecraft orbital velocity, and the spacecraft rotational velocity combined to distort the image slightly. |
C: Oblique view of P005_03 (132 KB) |
(C) shows P005_03 skewed and rotated to the perspective that MOC was viewing at the time the image was taken. |
A: Viking Orbiter Context Image (146 KB)
|
Nigral Vallis is one of a number
of canyons called valley networks or runoff channels. Much
of the debate concerning the origin of these valleys centers on whether
they were formed by water flowing across the surface, or by collapse and
upslope erosion associated with groundwater processes. At the resolution
of this image, it is just barely possible to discern an interwoven pattern
of lines on the highland surrounding the valley, but it is not possible
to tell whether this is a pattern of surficial debris (sand or dust), as
might be expected with the amount of crater burial seen, or a pattern of
drainage channels. With 4X better resolution from its mapping orbit, MOC
should easily be able to tell the difference between these two possibilities.
At 3:08:30 AM on September 21, 1997, the MOC field of view swept across the highland valley network Nigral Vallis at 28.5°S, 41.6 W. Although the MGS spacecraft was at an altitude of about 400 km (250 miles), the MOC was pointed obliquely across the planet at about 35°, so the distance to Nirgal Vallis was closer to 800 km (500 miles). At that range and viewing angle, the MOC field of view was about 16 km (10 miles) wide, and the resolution was about 9 meters (30 feet) per pixel. The acquired image is 36 km (23 miles) long. (A) is an excerpt from the USGS MDIM, roughly 180 km (112 mile) square. The small box outlines the MOC image acquisition. (B) is MOC frame P006_05, shown here at reduced resolution because the full image is almost 7 MBytes in size. Because the MOC acquires its images one line at a time, the cant angle towards the sun-lit portion of the planet, the spacecraft orbital velocity, and the spacecraft rotational velocity combined to significantly distort the image. However, even in this reduced resolution version, dunes can be seen in the canyon and in areas on the upland surface around the canyon. |
C: MOC P006_5 (enlargement) (794 KB) |
(C) shows a portion of P006_05 at the full resolution of the data. This view shows the dunes more clearly, and also illustrates better the distortion introduced by the method of data acquisition. |
D: Oblique view of P006_05 (175 KB) |
(D) shows P006_05 skewed and rotated to the perspective that MOC was viewing at the time the image was taken. |
E: Oblique view of P006_05 (628 KB) |
(E) shows a full-resolution version of a portion of the rotated perspective view. |
