Mars Reconnaissance Orbiter read layered clues to changes on Mars
Wed Dec 13, 2006 at 21:24 UTC
Layers on Mars are yielding history lessons revealed by instruments flying overhead and rolling across the surface.
Some of the first radar and imaging results from NASA's newest Mars spacecraft, the Mars Reconnaissance Orbiter, show details in layers of ice-rich deposits near the poles. Observed variations in the layers' thickness and composition will yield information about recent climate cycles on the red planet.
NASA's Mars Exploration Rover Opportunity has photographed patterns in the layering of crater-wall cliffs that are the clearest evidence of ancient sand dunes the rover has seen since arriving at Mars nearly three years ago. The science team for Opportunity's twin, Spirit, is using new orbital images of the rover's surroundings to interpret how some rocks with minerals altered by water fit into the area's complex layered structure.
"The combination of instruments on Mars Reconnaissance Orbiter is such a great advantage," said Dr. Jack Mustard of Brown University, Providence, R.I. He is deputy principal investigator for the Compact Reconnaissance Imaging Spectrometer for Mars, a mineral-identifying instrument on Mars Reconnaissance Orbiter. Researchers are using mineral information from analyses of spectrometer observations, combined with images from the orbiter's High Resolution Imaging Science Experiment, to seek the source of the mineral gypsum in dunes near the Martian north pole and clay minerals elsewhere. Gypsum and clay minerals are indicators of formerly wet conditions.
Other new images from that camera show mysterious pitting in the layered terrain near the north pole. Nearby, a steep slope exposing the layers appears to be shedding blocks of icy material that disappear instead of accumulating at the bottom of the slope.
"Observations of the polar layered deposits are telling us about the material properties there," said Dr. Ken Herkenhoff of the U.S. Geological Survey, Flagstaff, Ariz. "These deposits record relatively recent climate variations on Mars, like recent ice ages on Earth."
Image Credit: NASA/JPL-Caltech/ASI/University of Rome/Washington Universtiy in St. Louis
High resolution image
A radargram from the Shallow Subsurface Radar instrument (SHARAD) on NASA's Mars Reconnaissance Orbiter reveals detailed structure in the polar layered deposits of Mars' south pole.
The horizontal scale of the radargram is distance along the orbiter's ground track, about 650 kilometers (400 miles) from about 74 degrees south latitude on the left to about 85 degrees south latitude at right. The vertical scale is time delay of radar signals reflected back to the spacecraft from the surface and subsurface. For reference, the white double-headed arrow indicates a distance of about 800 meters (2,600 feet) between one of the strongest subsurface reflectors and ground level, based on an assumed velocity of the radar waves in the subsurface. This reflector marks the base of the polar layered deposits. The color scale varies from black for weak reflections to white for strong reflections.
The sounding radar collected the data presented here during orbit 1360 of the mission, on Nov. 10, 2006.
Image Credit: NASA/JPL-Caltech/ASI/University of Rome/Washington Universtiy in St. Louis
High resolution image (1.7 MB)
A radargram from the Shallow Subsurface Radar instrument (SHARAD) on NASA's Mars Reconnaissance Orbiter is shown in the upper-right panel and reveals detailed structure in the polar layered deposits of the south pole of Mars.
The sounding radar collected the data presented here during orbit 1334 of the mission, on Nov. 8, 2006.
The horizontal scale in the radargram is distance along the ground track. It can be referenced to the ground track map shown in the lower right. The radar traversed from about 75 to 85 degrees south latitude, or about 590 kilometers (370 miles). The ground track map shows elevation measured by the Mars Orbiter Laser Altimeter on NASA's Mars Global Surveyor orbiter. Green indicates low elevation; reddish-white indicates higher elevation. The traverse proceeds up onto a plateau formed by the layers.
The vertical scale on the radargram is time delay of the radar signals reflected back to Mars Reconnaissance Orbiter from the surface and subsurface. For reference, using an assumed velocity of the radar waves in the subsurface, time is converted to depth below the surface at one place: about 1,500 meters (5,000 feet) to one of the deeper subsurface reflectors. The color scale varies from black for weak reflections to white for strong reflections.
The middle panel shows mapping of the major subsurface reflectors, some of which can be traced for a distance of 100 kilometers (60 miles) or more. The layers are not all horizontal and the reflectors are not always parallel to one another. Some of this is due to variations in surface elevation, which produce differing velocity path lengths for different reflector depths. However, some of this behavior is due to spatial variations in the deposition and removal of material in the layered deposits, a result of the recent climate history of Mars.
Image Credit: NASA/JPL-Caltech/ASI/University of Rome/Washington Universtiy in St. Louis
High resolution image
A radargram from the Shallow Subsurface Radar instrument (SHARAD) on NASA's Mars Reconnaissance Orbiter reveals detailed structure in the polar layered deposits of Mars' south pole.
The horizontal scale of the radargram is distance along the orbiter's ground track, about 650 kilometers (400 miles) from about 74 degrees south latitude on the left to about 85 degrees south latitude at right. The vertical scale is time delay of radar signals reflected back to the spacecraft from the surface and subsurface. For reference, the white double-headed arrow indicates a distance of about 800 meters (2,600 feet) between one of the strongest subsurface reflectors and ground level, based on an assumed velocity of the radar waves in the subsurface. This reflector marks the base of the polar layered deposits. The color scale varies from black for weak reflections to white for strong reflections.
The sounding radar collected the data presented here during orbit 1360 of the mission, on Nov. 10, 2006.
Image Credit: NASA/JPL-Caltech/ASI/University of Rome/Washington Universtiy in St. Louis
High resolution image (1.2 MB)
A radargram from the Shallow Subsurface Radar instrument (SHARAD) on NASA's Mars Reconnaissance Orbiter is shown in the upper-right panel and reveals detailed structure in the polar layered deposits of the south pole of Mars.
The sounding radar collected the data presented here during orbit 1360 of the mission, on Nov. 10, 2006.
The horizontal scale in the radargram is distance along the ground track. It can be referenced to the ground track map shown in the lower right. The radar traversed from about 74 degrees to 85 degrees south latitude, or about 650 kilometers (400 miles). The ground track map shows elevation measured by the Mars Orbiter Laser Altimeter on NASA's Mars Global Surveyor orbiter. Green indicates low elevation; reddish-white indicates higher elevation. The traverse proceeds up onto a plateau formed by the layers.
The vertical scale on the radargram is time delay of the radar signals reflected back to Mars Reconnaissance Orbiter from the surface and subsurface. For reference, using an assumed velocity of the radar waves in the subsurface, time is converted to depth below the surface at one place: about 800 meters (2,600 feet) to one of the strongest subsurface reflectors. This reflector marks the base of the polar layered deposits. The color scale varies from black for weak reflections to white for strong reflections.
The middle panel shows mapping of the major subsurface reflectors, some of which can be traced for a distance of 100 kilometers (60 miles) or more. The layering manifests the recent climate history of Mars, recorded by the deposition and removal of ice and dust.
Image Credit: NASA/JPL-Caltech/ASI/University of Rome/Washington Universtiy in St. Louis
High resolution image
A radargram from the Shallow Subsurface Radar instrument (SHARAD) on NASA's Mars Reconnaissance Orbiter is shown in the upper-right panel and reveals detailed structure in the polar layered deposits of the south pole of Mars.
The sounding radar collected the data presented here during orbit 1334 of the mission, on Nov. 8, 2006.
The horizontal scale in the radargram is distance along the ground track. It can be referenced to the ground track map shown in the lower right. The radar traversed from about 75 to 85 degrees south latitude, or about 590 kilometers (370 miles). The ground track map shows elevation measured by the Mars Orbiter Laser Altimeter on NASA's Mars Global Surveyor orbiter. Green indicates low elevation; reddish-white indicates higher elevation. The traverse proceeds up onto a plateau formed by the layers.
The vertical scale on the radargram is time delay of the radar signals reflected back to Mars Reconnaissance Orbiter from the surface and subsurface. For reference, using an assumed velocity of the radar waves in the subsurface, time is converted to depth below the surface at one place: about 1,500 meters (5,000 feet) to one of the deeper subsurface reflectors. The color scale varies from black for weak reflections to white for strong reflections.
The middle panel shows mapping of the major subsurface reflectors, some of which can be traced for a distance of 100 kilometers (60 miles) or more. The layers are not all horizontal and the reflectors are not always parallel to one another. Some of this is due to variations in surface elevation, which produce differing velocity path lengths for different reflector depths. However, some of this behavior is due to spatial variations in the deposition and removal of material in the layered deposits, a result of the recent climate history of Mars.
Image Credit: NASA/JPL-Caltech/ASI/University of Rome/Washington Universtiy in St. Louis
High resolution image
A radargram from the Shallow Subsurface Radar instrument (SHARAD) on NASA's Mars Reconnaissance Orbiter is shown in the upper-right panel and reveals detailed structure in the polar layered deposits of the north pole of Mars (with blowups shown in the upper-left panels). The sounding radar collected the data presented here during orbit 1512 of the mission, on Nov. 22, 2006.
The horizontal scale in the radargram is distance along the ground track. It can be referenced to the ground track map shown in the lower right. The radar traversed from about 83.5 degrees to 80.5 degrees north latitude, or about 180 kilometers (110 miles). The ground track map shows elevation measured by the Mars Orbiter Laser Altimeter on NASA's Mars Global Surveyor orbiter. Green indicates low elevation; reddish-white indicates higher elevation. The traverse is from the high elevation of the plateau formed by the layers to the lowlands below.
The vertical scale on the radargram is time delay of the radar signals reflected back to Mars Reconnaissance Orbiter from the surface and subsurface. For reference, using an assumed velocity of the radar waves in the subsurface, time is converted to depth below the surface in two places: about 600 meters (2,000 feet) to the lowest of an upper series of bright reflectors and about 2,000 meters (6,500 feet) to the base of the polar layered deposits. The color scale of the radargram varies from black for weak reflections to bright yellow for strong reflections.
The lower-left panel is a image from the Mars Orbiter Camera on Mars Global Surveyor showing exposed polar layering in the walls of a canyon near the north pole. The layering is divided into a finely structured upper unit (labeled "Upper PLD") and less-well-defined stratigraphy in the lower unit (labeled "Lower PLD"). The radargram clearly reveals the complexity of the layering in the upper unit, additional reflections from the lower unit, and the base of the entire stack of layered deposits. The layering manifests the recent climate history of Mars, recorded by the deposition and removal of ice and dust.
The Shallow Subsurface Radar instrument on Mars Reconnaissance Orbiter has begun probing through similar layered deposits at Mars' south pole. "The radar is penetrating through the entire thickness of these deposits and revealing the fine-scale internal layering," said Dr. Roger Phillips of Washington University, St. Louis, the deputy team leader for that instrument.
Far from the poles, Opportunity is navigating the scalloped rim of Victoria crater about half a mile in diameter, stopping at promontories along the way to look at cliff walls of adjacent promontories. The top part of the stack of layers exposed in the cliffs appears to be rocky rubble thrown outward by the impact that dug the crater. "We see an abrupt transition between the jumbled-up material and intact layers below it that are still in place from before the impact," said Dr. Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for the rovers. Some of the intact layering resembles fossilized dunes in the U.S. Southwest.
Spirit recently found water-altered minerals in disturbed soils and granular rocks near where the rover spent the Martian winter. An image of the region from Mars Reconnaissance Orbiter is aiding interpretation of how different parts of the terrain, such as a bright platform nicknamed "Home Plate," are related to others. "It appears likely that these rocks came from one or more volcanic explosions that produced 'Home Plate,'" said Dr. Ray Arvidson, also of Washington University, deputy principal investigator for the rovers.
Dr. John Callas of NASA's Jet Propulsion Laboratory, Pasadena, Calif., project manager for the rovers, said, "The biggest news about the health of the rovers is that it is essentially unchanged from nine months ago. Each rover has operated more than 1,000 Martian days on the surface of Mars. They are well past their original design life of 90 Martian days, and there is always the possibility that a critical component on either rover could stop functioning at any time, so we operate the rovers with that in mind and value each additional day they continue to work."
Jet Propulsion Laboratory News Release
