HiRISE photographs avalanches on Mars
Mon Mar 3, 2008 at 19:15 UTC
The High Resolution Imaging Experiment (HiRISE) on NASA's Mars Reconnaissance Orbiter has taken the first ever image of active avalanches near the Red Planet's north pole. The image shows tan clouds billowing away from the foot of a towering slope, where ice and dust have just cascaded down.
The image was taken Feb. 19. It is one of approximately 2,400 HiRISE images being released today.
Ingrid Daubar Spitale of the University of Arizona, Tucson, who works on targeting the camera and has studied hundreds of HiRISE images, was the first person to notice the avalanches. "It really surprised me," she said. "It's great to see something so dynamic on Mars. A lot of what we see there hasn't changed for millions of years."
The camera is looking repeatedly at selected places on Mars to track seasonal changes. However, the main target of the Feb. 19 image was not the steep slope.
"We were checking for springtime changes in the carbon-dioxide frost covering a dune field, and finding the avalanches was completely serendipitous," said Candice Hansen, deputy principal investigator for HiRISE, at NASA's Jet Propulsion Laboratory, Pasadena, Calif.
The full image reveals features as small as a desk in a strip of terrain 6 kilometers (3.7 miles) wide and more than 10 times that long, at 84° north latitude. Reddish layers known to be rich in water ice make up the face of a steep slope more than 700 meters (2,300 feet) tall, running the length of the image.
"We don't know what set off these landslides," said Patrick Russell of the University of Berne, Switzerland, a HiRISE team collaborator. "We plan to take more images of the site through the changing Martian seasons to see if this kind of avalanche happens all year or is restricted to early spring."
Credit: NASA/JPL-Caltech/University of Arizona.
High resolution image.
Amazingly, this image has captured at least four Martian avalanches, or debris falls, in action. It was taken on February 19, 2008, by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter.
The image to the left shows the context of where these avalanches occurred, with white boxes indicating the locations of the more detailed image portions shown to the right. All images are false color. Material, likely including fine-grained ice and dust and possibly including large blocks, has detached from a towering cliff and cascaded to the gentler slopes below. The occurrence of the avalanches is spectacularly revealed by the accompanying clouds of fine material that continue to settle out of the air. The largest cloud (upper images) traces the path of the debris as it fell down the slope, hit the lower slope, and continues downhill, forming a billowing cloud front. This cloud is about 180 meters (590 feet) across and extends about 190 meters (625 feet) from the base of the steep cliff. Shadows to the lower left of each cloud illustrate further that these are three dimensional features hanging in the air in front of the cliff face, and not markings on the ground. Sunlight is from the upper right.
Cameras orbiting Mars have taken thousands of images that have enabled scientists to put together pieces of Mars' geologic history. However, most of them reveal landscapes that haven't changed much in millions of years. Some images taken at different times of year do show seasonal changes from one image to the next, however, it is extremely rare to catch such a dramatic event in action. (Another, unrelated, active process that has been captured by Mars cameras are dust devils.) Observing currently active processes is often a useful tool in unlocking puzzles of the past for scientists studying the Earth. Working from primarily still images, it is harder for scientists studying Mars to rely on this tool. The HiRISE image of avalanching debris is a very rare opportunity to directly do so.
The scarp in this image is on the edge of the dome of layered deposits centered on Mars' north pole. From top to bottom this impressive cliff is over 700 meters (2300 feet) tall and reaches slopes over 60°. The top part of the scarp, to the left of the images, is still covered with bright (white) carbon dioxide frost which is disappearing from the polar regions as spring progresses. The upper mid-toned (pinkish-brownish) section is composed of layers (difficult to see here) that are mostly ice with varying amounts of dust. The darkest deposits below form more gentle slopes, less than 20°, and are mainly composed of two materials: mid-toned layers, possibly ice-rich, that form small shelves, and more mobile, wide-spread, sand-sized dark material. The wavy forms on the flatter areas to the right are dunes.
The upper, steepest section, which appears highly fractured due to blocks pulling away from the wall, is the likely source zone for the falls. The precise trigger mechanism is not yet known, although the disappearance of the carbon dioxide frost, the expansion and contraction of the ice in response to temperature differences, a nearby Mars-quake or meteorite impact, and vibrations caused by the first fall in the area, are all possible contributors.
By comparing images taken before the fall (such as HiRISE image PSP_007140_2640) and after the fall, we may be able to see where material has disappeared from the steep scarp and where it has appeared on the gentler slopes below, possibly as larger blocks, diffuse streaks, or other debris deposits. By imaging this scarp throughout the polar summer, we may be able to determine how much material falls over a given time period. These observations would help determine how much, and at what rate, ice is being eroded from the cliff. Understanding the processes and rates of erosion will help determine how the polar landscape has evolved, and help reveal how volatiles, such as water and carbon dioxide ices and gases, move around Mars. The precise composition of the ice-dust mixture making up layers in the upper, steepest section of scarp is not known. However, detailed measurements of the volume of material removed, the configuration of the source area, and the steepness of the slope can be used to estimate physical properties of the material that may relate to composition.
The complete image, HiRISE PSP_007338_2640, is centered at 83.7° latitude, 235.8° east longitude. The image was taken at a local Mars time of 1:05 PM and the scene is illuminated from the west with a solar incidence angle of 70°, thus the sun was about 20° above the horizon. At a solar longitude of 34.0°, the season on Mars is northern spring.
Observation Geometry
Image PSP_007140_2640 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on 03-Feb-2008. The complete image is centered at 83.7° latitude, 235.7° East longitude. The range to the target site was 319.1 km (199.4 miles). At this distance the image scale is 31.9 cm/pixel (with 1 x 1 binning) so objects ~96 cm across are resolved. The image shown here has been map-projected to 25 cm/pixel . The image was taken at a local Mars time of 12:33 PM and the scene is illuminated from the west with a solar incidence angle of 73°, thus the sun was about 17° above the horizon. At a solar longitude of 26.9°, the season on Mars is Northern Spring.
Credit: NASA/JPL-Caltech/University of Arizona.
High resolution image.
The High Resolution Imaging Science Experiment (HiRISE) camera would make a great backyard telescope for viewing Mars, and we can also use it at Mars to view other planets. This is an image of Earth and the moon, acquired on October 3, 2007, by the HiRISE camera on NASA's Mars Reconnaissance Orbiter.
At the time the image was taken, Earth was 142 million kilometers (88 million miles) from Mars, giving the HiRISE image a scale of 142 kilometers (88 miles) per pixel, an Earth diameter of about 90 pixels and a moon diameter of 24 pixels. The phase angle is 98°, which means that less than half of the disk of the Earth and the disk of the moon have direct illumination. We could image Earth and moon at full disk illumination only when they are on the opposite side of the sun from Mars, but then the range would be much greater and the image would show less detail.
On the Earth image we can make out the west coast outline of South America at lower right, although the clouds are the dominant features. These clouds are so bright, compared with the moon, that they are saturated in the HiRISE images. In fact the red-filter image was almost completely saturated, the Blue-Green image had significant saturation, and the brightest clouds were saturated in the infrared image. This color image required a fair amount of processing to make a nice-looking release. The moon image is unsaturated but brightened relative to Earth for this composite. The lunar images are useful for calibration of the camera.
More ice than dust probably makes up the material that fell from the upper portion of the scarp. Imaging of the site during coming months will track any changes in the new deposit at the base of the slope. That will help researchers estimate what proportion is ice.
"If blocks of ice broke loose and fell, we expect the water in them will be changing from solid to gas," Russell said. "We'll be watching to see if blocks and other debris shrink in size. What we learn could give us a better understanding of one part of the water cycle on Mars."
Another notable HiRISE image released today shows a blue crescent Earth and its moon, as seen by the Mars Reconnaissance Orbiter. The west coast of South America is visible in the photo. Still other images allow viewers to explore a wide variety of Martian terrains, such as dramatic canyons and rhythmic patterns of sand dunes.
The camera is one of six science instruments on the orbiter. The spacecraft reached Mars in March 2006 and has returned more data than all other current and past missions to Mars combined.
"Our Mars program is the envy of the world," said Alan Stern, associate administrator of NASA's Science Mission Directorate, Washington. "We plan to launch a total of five more missions in the next decade, beginning with the Mars Science Lab rover next year and a Mars Aeronomy Scout mission in 2011."
| Source: Jet Propulsion Laboratory | |
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