Variation in Light-Toned Deposits in a Martian Trough

This false-color image shows dozens of beds within a light-toned deposit located within a trough in the Noctis Labyrinthus region of Mars. The image comes from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter.

Observations by the same orbiter's Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) suggest a general sulfate mineralogy for the light-toned deposit. However, the beds differ in brightness, color, thickness, and erosional properties, suggesting that many compositions may be present here but are too thin to be resolved. The arrows indicate an upper, dark-toned blocky geological unit that has covered the older, light-toned deposit.

This image covers a swath of ground about 900 meters or yards across at 11.2 degrees south latitude, 261.9 degrees east longitude. It is one product from HiRISE observation PSP_005400_1685, made on Sept. 21, 2007. Other image products from this observation are available at http://hirise.lpl.arizona.edu/PSP_005400_1685.

NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, manages the Mars Reconnaissance Orbiter for the NASA Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, is the prime contractor for the project and built the spacecraft. The University of Arizona, Tucson, operates the HiRISE camera, which was built by Ball Aerospace & Technologies Corp., Boulder, Colo.

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Unexpected Wheel-Test Results

Diagnostic tests were run on Spirit's right-rear wheel and right-front wheel on Sol 2013 (Dec. 12, 2009). The right-rear wheel, which stalled during a drive two weeks earlier, continued to show no motion in the latest tests and exhibited very high resistance in the motor winding. The right-front wheel, which stopped operating on Sol 779 (March 13, 2006), surprised engineers by indicating normal resistance and turning slightly during a resistance test for that wheel.

Small motion is expected during an electrical resistance test for an operating actuator, but the right-front actuator was expected to be non-operational. The right-front wheel was last checked just after its apparent failure in 2006 and at that time indicated an open circuit. Although no clear theory for failure had been established, the failure was generally regarded as permanent. It is important to remember that the Sol 2013 test of the right-front wheel was only a rotor resistance test, and no conclusions can be drawn at this point without further testing.

The plan for Spirit on Sol 2116 (Dec. 15) is to command a drive. This drive will further investigate functionality of the right-front and right-rear wheels. The results are expected Wednesday.

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Global View of Iapetus' Dichotomy

These two global images of Iapetus show the extreme brightness dichotomy on the surface of this peculiar Saturnian moon. The left-hand panel shows the moon's leading hemisphere and the right-hand panel shows the moon's trailing side. While low and mid latitudes of the leading side exhibit a surface almost as dark as charcoal, broad tracts of the trailing side are almost as bright as snow. The dark terrain covers about 40 percent of the surface and is named Cassini Regio. The names of the bright terrain are Roncevaux Terra (north) and Saragossa Terra (south).

On both hemispheres, the dominant landforms are impact craters. The largest known well-preserved basin on Iapetus, called Turgis, has a diameter of about 580 kilometers (360 miles). It lies at 17 degrees north latitude, 28 degrees west longitude at the eastern edge of the dark Cassini Regio and is visible on the right side of the left-hand panel. The prominent basin on the southern trailing side (at the lower left of the right-hand panel) is Engelier. Engelier is located at 41 degrees south latitude, 265 degrees west longitude, and has a diameter of about 504 kilometers (313 miles). Its formation destroyed about half of Gerin, another large basin on Iapetus. Gerin is located at 46 degrees south latitude, 233 degrees west longitude, and has a diameter of about 445 kilometers (276 miles). Tortelosa Montes, a part of the giant equatorial ridge that was discovered in Cassini images on December 25, 2004, is visible in the left panel as a thin line within Cassini Regio, and as a tall prominence at the western limb. It continues onto the trailing side (right side of right panel), where the bright western flanks of the Carcassone Montes appear as dominant bright spots within the western edge of Cassini Regio.

The cause of the extreme brightness dichotomy on Iapetus is likely to be thermal segregation of water ice on a global scale. Thermal effects are usually expected to act latitudinally. That is, polar areas are colder than equatorial terrain in most cases due to the more oblique angle of the solar irradiation. Therefore, an additional process is required to explain the longitudinal difference as well. In one model, dark, reddish dust coming in from space and preferentially deposited on the leading side forms a small, but crucial difference between the leading and trailing hemispheres, which is sufficient to allow the thermal effect to evaporate the water ice on the leading side completely, but only marginally on the trailing side. See PIA11689 to learn more. Iapetus' extremely slow rotation rate (1,904 hours), its distance from the sun, its relatively small size and surface gravity, and its outer position within the regular satellite system of Saturn are also crucial contributing conditions for this mechanism to work as observed.

North on Iapetus is approximately up in the images. Iapetus has a diameter of 1471 kilometers (914 miles).

The right-hand panel, released previously as PIA08384, shows a mosaic of 60 different images, obtained on September 10, 2007.

The left-hand panel is a color composite of three images obtained through infrared, green and ultraviolet spectral filters (centered at 752, 568 and 338 nanometers, respectively) by Cassini's narrow-angle camera on Dec. 27, 2004. The view was acquired at a distance of approximately 717,000 kilometers (446,000 miles) from Iapetus and at a sun-Iapetus-spacecraft, or phase, angle of 22 degrees.

Scale in the original image on the left was about 4 kilometers (2.5 miles) per pixel. For ease of comparison, the scales in both the left and right images were set to 1,400 meters (4,600 feet) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL manages the mission for the Science Mission Directorate at NASA Headquarters in Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.

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Rear Wheel Trouble Continues

Results of diagnostic tests on Spirit's right-rear wheel on Sol 2109 (Dec. 8, 2009) continue to indicate a troubled wheel, which may leave the rover with only four operable wheels.

The Sol 2109 plan included a check of the grind motor of Spirit's rock abrasion tool (RAT) because it shares the same motor controller as the right-rear wheel. It also included rotor resistance tests on the right-rear motor at three temperatures using opposite voltage polarity from earlier tests, backward and forward commanded motion of the right-rear wheel, and a check of rotor resistance on all other operating wheels. The RAT motor appears okay, although a more exhaustive test will be tried later. The right-rear wheel rotor resistance tests continue to show very elevated resistance, although not as high as in previous tests, and exhibiting a curious voltage-dependent effect. No motion of the right-rear wheel occurred during the backward commanded motion. The forward motion was not executed since the initial backward motion did not occur. The rotor resistances on all the other operating wheels are nominal.

The plan ahead, still being developed, will likely include more rotor resistance tests, an attempt to apply higher voltage to the right-rear wheel to see if any movement will occur, and a check of the right-front wheel to confirm its status and to see if it may offer insight into the right-rear wheel's condition. Further ahead, steering tests will be considered to explore an external jam as a possible explanation.

Concurrent with this, the project is exploring whether any meaningful rover motion would be possible with only four operable wheels. Spirit lost the use of its right front wheel in 2006.

Because of the current rover tilt, the environmental conditions and dust accumulation on the solar arrays, Spirit is at risk of inadequate power for surviving through the next southern Mars winter, which reaches solstice on May 13, 2009. Even if extrication is not possible, some limited rover motion may be able to improve rover tilt and increase the chance of winter survival.

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Spring Reveals Saturn's Hexagon Jet Stream

This movie from Cassini, made possible only as Saturn's north pole emerged from winter darkness, shows new details of a jet stream that follows a hexagon-shaped path and has long puzzled scientists.

The hexagon was hidden in darkness during the winter of Saturn's long year, a year that is equal to about 29 Earth years. But as the planet approached its August 2009 equinox and signaled the start of northern spring, the hexagon was revealed to Cassini's cameras. This is the first time the whole hexagonal shape has been mapped out in visible light by Cassini, and these images show unprecedented details of Saturn's high northern latitudes. The hexagon was originally discovered in images taken by Voyager spacecraft in the early 1980s. Since 2006, the Cassini Visual and Infrared Mapping Spectrometer (VIMS) instrument has been observing the hexagon at infrared wavelengths, but at lower spatial resolution than these visible light images.

Three large mosaics were used to create this three-frame movie. The mosaics used dozens of images and the constituent images were projected into polar projections to provide a complete view of the hexagon. The mosaics used in this movie do not show the region directly around the north pole because it had not yet fully emerged from the polar winter night. Seams between the images are visible in the third frame of the movie because the observation geometry in those images made removal of the seams difficult.

The six-sided shape remains a mystery. Scientists think the hexagon is a meandering jet stream at 77 degrees north latitude, but they don't know what controls the path the stream takes. These images also show new phenomena for scientists to decipher, such as waves that can now be seen radiating from the corners of the hexagon where the jet takes its hardest turns. These images confirm the presence of a multi-walled structure in each of the hexagon's six sides, and the structure now can be seen extending to the top of Saturn's cloud layer. The images show that the inside of the hexagon is darker than the outside. The new images also show a large spot inside the hexagon that could be related to a dark spot seen inside the hexagon in 2006 in an image taken by Cassini's VIMS instrument. An earlier Voyager mosaic showed a large spot outside the hexagon. That spot existed at least until 1991 before disappearing into the long winter polar night.

Images from Voyager and from ground-based telescopes suffered from poor viewing perspectives. In late 2006, Cassini's VIMS camera imaged the region in the thermal infrared wavelength, showing the hexagon in false color. Multiple images acquired by the VIMS instrument over a 12-day period showed that the feature is nearly stationary and is likely an unusually strong pole-encircling planetary wave that extends deep into the atmosphere. Scientists had speculated that a large vortex seen outside the hexagon during the Voyager observations exerted forces on the jet stream making it adopt a hexagonal pattern in a manner similar to how jet streams on Earth divert around high-pressure systems. However, in these new images, the vortex is notably absent while the hexagon persists almost 30 years after it was first seen.

The images were taken in visible light with the Cassini spacecraft wide-angle camera on Jan. 3, 2009. The images were obtained at a distance of approximately 764,000 kilometers (475,000 miles) from Saturn. The smallest resolved features at the latitude of the hexagon have a horizontal scale of approximately 100 kilometers.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL manages the mission for the Science Mission Directorate at NASA Headquarters in Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.

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Opportunity's Traverse Map Through Sol 2063

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NASA Offers Media Satellite Interviews Oct. 21 for Ares I-X Launch

NASA's Ares I-X Deputy Mission Manager Jon Cowart is available for satellite interviews from 6 to 9 a.m. EDT on Wednesday, Oct. 21. He will conduct the interviews from the rocket's launch pad at NASA's Kennedy Space Center in Florida.

To interview Cowart, reporters should contact Amber Philman at 321-861-0370 by noon on Oct. 20. NASA Television will broadcast b-roll of the Ares I-X from 5:30 to 6 a.m. at analog satellite AMC-6 at 72 degrees west longitude, transponder 5C, 3800 MHz, vertical polarization, with audio at 6.8 MHz.

The Ares I-X rocket is targeted to launch Tuesday, Oct. 27 on a 28-mile high flight test. The flight test will provide NASA with an early opportunity to test and prove flight characteristics, hardware, facilities and ground operations associated with the Ares I rocket.

In 2007, Cowart became the senior project manager responsible for all modifications to the launch pad, Vehicle Assembly Building, and mobile launcher platform for Ares I-X. In December 2008, he was chosen as the deputy mission manager for Ares I-X. As part of the Mission Management Office, he is responsible for the Ares I-X flight test mission. Cowart graduated from Georgia Tech in 1983 with a bachelor's degree in aerospace engineering and an Air Force commission.

For NASA TV downlink information, schedules and links to streaming video, visit:

http://www.nasa.gov/ntv

To follow the Ares I-X flight test on Twitter, go to:

http://www.twitter.com/NASA_Ares_I_X

For information about Ares I-X, visit:

http://www.nasa.gov/aresIX

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