Mars Global Surveyor
Mars Orbiter Camera

MOC Aerobraking Orbit Observations - P003-P007

During the past three weeks, the Mars Global Surveyor Orbiter Camera (MOC) has acquired about a dozen moderately high resolution images of Mars to improve our understanding of the exposure and focus control of the camera, in anticipation of mapping operations that will begin in March of next year. Most of the images are of relatively poor quality, as the MGS spacecraft is not yet in the orbit for which the MOC was designed. Specifically, the illumination conditions are poor (the surfaces that MOC is imaging are presently only about one-fourth as bright as they will be during mapping), and the range to the planet when imaging can occur is between three and five times greater than the mapping distance. In addition, information to remove instrument characteristics such as sensitivity variations is just now being assembled, so many of the images have attributes or artifacts, such as bright and dark streaks, caused by these characteristics.

However, as the spacecraft has moved from the low illumination conditions near the evening terminator towards higher sun elevation angles, the images have been improving. Two of the best images are presented here in several versions, along with "context" frames derived from Viking Orbiter images.

Note: The MOC images are made available in order to share with the public the excitement of new discoveries being made via the Mars Global Surveyor spacecraft. The images may be reproduced only if the images are credited to "Malin Space Science Systems/NASA". Release of an image does not constitute a release of scientific data. An image and its caption should not be referenced in the scientific literature. Full data releases to the scientific community are scheduled by the Mars Global Surveyor Project and NASA Planetary Data System. Typically, data will be released after a 6 month calibration and validation period.

Click Here for more information on MGS data release and archiving plans.

Mars Global Surveyor Mars Orbiter Camera Release:       MOC2-11A,-11B,-11C
Mars Global Surveyor Mars Orbiter Camera Image IDs:          559142748.503
                                                                   P005_03

Click on images for full resolution versions

(A) (B)
A: Viking Orbiter Context Image (250 KB) B: MOC Image P005_03 (593 KB)

(C)
Oblique view of P005_03 (132 KB)

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).

Shown above are three pictures:

(A) is excepted 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) shows P005_03 skewed and rotated to the perspective that MOC was viewing at the time the image was taken.

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.

Mars Global Surveyor Mars Orbiter Camera Release:       MOC2-12A,-12B,-12C
                                                                 -12D,-12E
Mars Global Surveyor Mars Orbiter Camera Image IDs:          559303731.605
                                                                   P006_05

Click on images for full resolution versions

(A) (B)
(C)
A: Viking Orbiter Context Image (146 KB) B: MOC Image P006_05 (655 KB)
C: MOC P006_5 (enlargement) (794 KB)

(D)
(E)
D: Oblique view of P006_05 (175 KB)
E: Oblique view of P006_05 (Enlargement)(628 KB)

At 3:08:30 AM on September 21, 1997, the MOC field of view swept across the highland valley network Nirgal 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.

Five images are shown above:

(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) 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) shows P006_05 skewed and rotated to the perspective that MOC was viewing at the time the image was taken.

(E) shows a full-resolution version of a portion of the rotated perspective view.

Nirgal 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.

Launched on November 7, 1996, Mars Global Surveyor entered Mars orbit on Thursday, September 11, 1997. The spacecraft has been using atmospheric drag to reduce the size of its orbit for the past three weeks, and will achieve a circular orbit only 400 km (248 mi) above the surface early next year. Mapping operations begin in March 1998. At that time, MOC narrow angle images will be 5-10 times higher resolution than these pictures.

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.

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