October 28, 1998
The images will be presented on Thursday, October 29, by members of the mission science team at the annual meeting of the Geological Society of America in Toronto, Canada.
The close-up views of Mars' Elysium Basin reveal the first evidence of huge plates of solidified lava, rather than lakebed sediments, that appear to have been broken up and transported across the Martian surface millions of years ago as they floated on top of molten lava. This implies that the area in the planet's northern lowlands was once the site of giant ponds of lava flows hundreds of kilometers across, according to Dr. Alfred S. McEwen of the University of Arizona, Tucson, a member of the Global Surveyor science team.
"NASA Viking mission images of the same region showed a surface of dark plates with intervening bright surfaces that did not quite make sense," McEwen said. "Some scientists thought they could somehow be volcanic, while others thought they might be related to differences in the way that wind had eroded a dried lakebed. With these new images in hand, it is now quite easy to understand the older, lower-resolution Viking images."
McEwen and his co-authors believe that lava erupted near this area and the upper surface became crusted, then cooled and cracked. Some cracks widened and portions of the surface crust became rafts of solid rock that moved in the direction that the molten lava was flowing underneath. Other Viking and Global Surveyor images have shown similar plate-like lava textures in nearby Marte Vallis, implying that some of the lava from Elysium Basin spilled into this valley and flowed thousands of kilometers to the northeast.
"The sparse occurrence of impact craters on these plate-like lava surfaces suggests that the eruptions happened relatively recently in Mars' history," McEwen explained. "These eruptions could be much younger than the youngest of the large Martian volcanoes like Ascraeus Mons and Olympus Mons in the Tharsis region, but they would still have occurred many, many millions of years ago. So these images should not be treated as evidence that Mars is volcanically active today."
Additional close-up views of Martian sand dunes in the north polar region are showing scientists detailed patterns of ongoing movement of sand across the planet for the first time. Drs. Kenneth S. Edgett, staff scientist at Malin Space Science Systems, San Diego, CA, and Michael Malin, Mars Global Surveyor camera principal investigator, report the presence of many fresh dunes that have been active as recently as July or August.
"The north polar cap of Mars is surrounded by a zone of dark dunes," Edgett said. "These were first seen by Mariner 9 as a rippled texture, and by the Viking orbiters as definitive sand dunes. Between late July and mid-September 1998, Mars Global Surveyor's closest passage over the planet took us right over the north polar dune fields four times a day. This provided us with many opportunities to take high-resolution pictures of these mounds."
Martian dunes typically contain granular fragments of rocks and minerals ranging from 0.002 to 0.08 inches (0.06 to 2 millimeters) in size, which puts them in the geologic classification of "sand." The sand appears to have been transported by wind in one of two ways: either by hopping over the ground, a geological process called "saltation," or by rolling along the ground, a process known as "traction."
Some of the dunes appear to be coated with thin, bright frost that was left over from the northern winter season that ended in mid-July, according to Edgett and Malin. This frost is covered with dark streaks emanating from small dark spots that dot the bases of many of the dunes. "The simplest explanation is that gusts of wind have blown the dark sand out across the frost- covered dunes, creating a streak of deposited sand over the frost," Malin said. "Some spots seen in the close-ups have multiple streaks, each one indicating that a different wind gust has moved in a different direction."
The images are available on the Internet at the following locations:
Mars Global Surveyor is part of a sustained program of Mars exploration known as the Mars Surveyor Program. The mission is managed by the Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, CA, for NASA's Office of Space Science, Washington, DC. JPL's industrial partner is Lockheed Martin Astronautics, Denver, CO, which developed and operates the spacecraft.
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
October 12, 1998
The new images are available on the Internet at
http://photojournal.jpl.nasa.gov and at
Taken on April 25, 1998, from a distance of about 900 kilometers (560 miles) above the surface, this wide-angle image of Olympus Mons captures the west side of the volcano on a cool, crisp winter morning. Olympus Mons is by far the tallest volcano in the solar system, rising higher than three Mount Everests and spanning the width of the entire Hawaiian island chain.
The images of Kasei Vallis, a system of giant channels thought to have been carved by catastrophic floods more than a billion years ago, illustrate the complexity of the planet's geologic history. These images were acquired on June 4, 1998, and reveal details of the 6-kilometer-diameter (4-mile) crater as it pokes out from beneath an "island" in the valley. The mesa was created in part by the flood and by its subsequent retreat, which caused small landslides of the scarp that encircles it. A "mote" or trench partly encircles the crater to the west and south. This moat formed were the turbulence of the floodwaters interacting with the crater rim eroded material in front of and alongside the crater.
When Mars Global Surveyor reaches its final mapping orbit in March 1999, the spacecraft's camera will be used to make daily global maps of Martian clouds and weather systems. The wide-angle images will resemble weather satellite pictures of Earth and will help the Mars Global Surveyor science teams plan their observations and test computer-driven prediction models of Martian weather.
July 21, 1998
More than 4,000 km in length, Valles Marineris is the largest canyon system in the solar system. Image caption is appended below.
Mars Global Surveyor Mars Orbiter Camera Mars Orbiter Camera (MOC) High Resolution Images Western Candor Chasma, Valles Marineris Mars Global Surveyor Mars Orbiter Camera Release: MOC2-59a, -59b, -59c, -59d, -59e Mars Global Surveyor Mars Orbiter Camera Image ID: 568534375.8403 P084-03 (C, below); 576779012.23304 P233-04 (D, below); 577575955.25205 P252-05 (E, below). (A) [Image] 270 KByte GIF image (A) The Valles Marineris trough system is more than 4,000 kilometers (2500 miles) in length. Each "Chasma" that makes up the trough system is labeled above (e.g., Ophir is "Ophir Chasma"). White box indicates the location of the context image shown below in (B). Three MOC images within this box are presented in (C), (D), and (E). Picture is a mosaic of Viking Orbiter images from the U.S. Geological Survey. North is up. (B) [Image] 113 KByte GIF image (B) Western Candor Chasma. Small white boxes indicate the approximate locations of each of the MOC images shown below. Each box is labeled with an image number--8403 is the third image from Mars Global Surveyor orbit 84 (shown in (C), below); 23304 is the fourth image from orbit 233 (D, below); and 25205 is the fifth image from orbit 252 (E, below). Picture is a mosaic of Viking Orbiter images from the U.S. Geological Survey. North is up. (C) [Image] 136 KByte GIF image (C) Layers in western Candor Chasma northern wall. MOC image 8403 subframe shown at full resolution of 4.6 meters (15 feet) per pixel. The image shows an area approximately 2.4 by 2.5 kilometers (1.5 x 1.6 miles). North is up, illumination is from the left. Image 8403 was obtained during Mars Global Surveyor's 84th orbit at 10:12 p.m. (PST) on January 6, 1998. (D) [Image] 291 KByte GIF image (D) Layers exposed near the middle of western Candor Chasma. MOC image 23304 subframe shown at 10.7 meters (35 feet) per pixel. Two layered buttes (upper right and lower right) and a layered or stepped mesa (center right) are shown. The image covers an area approximately 5.5 by 5.5 kilometers (3.4 x 3.4 miles). North is approximately up, illumination is from the lower right. Image 23304 was obtained during Mars Global Surveyor's 233rd orbit at 9:23 a.m. (PDT) on April 11, 1998. (E) [Image] 273 KByte GIF image (E) Massive (non-layered) material exposed in central Candor Chasma. MOC image 25205 subframe shown at 11.7 meters (38.4 feet) per pixel resolution. Image shows the southern tip of a massive "interior deposit" that points like a giant tongue from Ophir Chasma (to the north) down into the center of Candor Chasma. The ridged and grooved bright unit is the "interior deposit". South of this ridged unit is a low elevation surface mantled by dark dunes and sand. Image covers an area approximately 5.7 by 5.7 kilometers (3.5 x 3.5 miles). North is approximately up, illumination is from the lower right. Image 25205 was obtained during Mars Global Surveyor's 252nd orbit at 2:45 p.m. (PDT) on April 20, 1998. You may need to adjust the images for the gamma of your monitor to insure proper viewing. Note: This MOC image is made available in order to share with the public the excitement of new discoveries being made via the Mars Global Surveyor spacecraft. The image may be reproduced only if the image is credited to "Malin Space Science Systems/NASA". Release of this image does not constitute a release of scientific data. The 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.
Valles Marineris was first observed in 1972 by the Mariner 9 spacecraft, from which the troughs get their name: Valles--valleys, Marineris--Mariner.
Some hints of layering in both the canyon walls and within some deposits on the canyon floors were seen in Mariner 9 and Viking orbiter images from the 1970s. The Mars Orbiter Camera on board Mars Global Surveyor has been examining these layers at much higher resolution than was available previously.
MOC images led to the realization that there are layers in the walls that go down to great depths. An example of the wall rock layers can be seen in MOC image 8403, shown above (C).
MOC images also reveal amazing layered outcrops on the floors of some of the Valles Marineris canyons. Particularly noteworthy is MOC image 23304 (D, above), which shows extensive, horizontally-bedded layers exposed in buttes and mesas on the floor of western Candor Chasma. These layered rocks might be the same material as is exposed in the chasm walls (as in 8403--C, above), or they might be rocks that formed by deposition (from water, wind, and/or volcanism) long after Candor Chasma opened up.
In addition to layered materials in the walls and on the floors of the Valles Marineris system, MOC images are helping to refine our classification of geologic features that occur within the canyons. For example, MOC image 25205 (E, above), shows the southern tip of a massive, tongue-shaped massif (a mountainous ridge) that was previously identified as a layered deposit. However, this MOC image does not show layering. The material has been sculpted by wind and mass-wasting--downslope movement of debris--but no obvious layers were exposed by these processes.
Valles Marineris is a fascinating region on Mars that holds much potential to reveal information about the early history and evolution of the red planet. The MOC Science Team is continuing to examine the wealth of new data and planning for new Valles Marineris targets once the Mapping Phase of the Mars Global Surveyor mission commences in March 1999.
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.