* Astronomy

Image credit: NASA/JPL/Cornell

This panoramic image, dubbed "Rub al Khali," was acquired by the Mars Exploration Rover Opportunity on the plains of Meridiani during the period from the rover's 456th to 464th sols on Mars (May 6 to May 14, 2005). Opportunity was about 2 kilometres south of "Endurance Crater" at a place known informally as "Purgatory Dune."

The rover was stuck in the dune's deep fine sand for more than a month. "Rub al Khali" (Arabic translation: "the empty quarter") was chosen as the name for this panorama because it is the name of a similarly barren, desolate part of the Saudi Arabian desert on Earth.

The view spans 360 degrees. It consists of images obtained in 97 individual pointings of the panoramic camera. The camera took images with five camera filters at each pointing. This 22,780-by-6,000-pixel mosaic is an approximately true-colour rendering generated using the images acquired through filters admitting light wavelengths of 750, 530, and 480 nanometres.

Lighting varied during the nine sols it took to acquire this panorama, resulting in some small image seams within the mosaic. These seams have been smoothed in sky parts of the mosaic to better simulate the vista that a person would see if able to view it all at the same time on Mars.

Opportunity's tracks leading back to the north (centre of the panorama) are a reminder of the rover's long trek from Endurance Crater. The deep ruts dug by Opportunity's wheels as it became stuck in the sand appear in the foreground. The crest and trough of the last ripple the rover crossed before getting stuck is visible in the centre. These wind-formed sand features are only about 10 to 15 centimetres tall. The crest of the actual ripple where the rover got stuck can be seen just to the right of centre. The tracks and a few other places on and near ripple crests can be seen in this colour image to be dustier than the undisturbed or "normal" plains soils in Meridiani. Since the time these ruts were made, some of the dust there has been blown away by the wind, reaffirming the dynamic nature of the Martian environment, even in this barren, ocean-like desert of sand.

Browse Image | Medium Image (162 kB) | Large (47.1 MB)

OPPORTUNITY UPDATE: Pushing Away from Purgatory - sol 510-517,
July 11, 2005:

This week Opportunity finished examining "Purgatory Dune" and started driving again. The first few drives were to the north so that possible paths to the south could be imaged and evaluated. The next few steps took the rover east, then southward down a wide trough. A new set of "rules of the road" have been developed and implemented to prevent the rover from getting bogged down again.

The miniature thermal emission spectrometre has also been cleared for regular use, and has returned some useful science products during the last week.

Sol-by-sol summaries:

Sol 510 (June 30, 2005): Opportunity finished characterizing Purgatory ripple with microscopic imager pictures of soil (tracks and undisturbed), and took a first step back. The rover collected several images to document the 2.1-metre drive. Visual odometry confirmed that slip was less than 10 percent during the short traverse.
After the drive, the rover took pictures of the surroundings to evaluate possible safe pathways to the south.

Sol 511: Opportunity backed up 8.5 metres, and again imaged the terrain to the south. The drive used visual odometry and slip checks to stop the rover if it failed to make progress.

Sol 512: The long-term goal for Opportunity is to drive south and slightly east. Before continuing on this path the rover must either go east or west to sidestep Purgatory Dune. Extensive remote sensing with the panoramic camera and navigation camera was done this sol to assist in the decision.

Sol 513: With all imaging needed for driving already acquired, Opportunity spent the sol doing atmospheric observations, dust monitoring, and also imaging of the magnets with the panoramic camera.

Sol 514: The engineering and science team took an Independence Day
Break today, and the rover executed its planned runout science sequence, which included atmospheric observations with the panoramic camera.

Sol 515: Imaging acquired over the weekend showed that the path to the east contained very small ripples (less than 6 centimetres), and led to a wide trough to the south. This sol, rover planners sequenced a 5.5-metre backwards drive over old tracks, then
turned in short segments (less than 20 degrees), and drove east 2.5 metres over one small ripple. Tilt limits, visual odometry failure limits, and cycle limits were employed to prevent the rover from bogging down. The drive succeeded as planned.

Sol 516: An 11-metre drive to the east crossed two small ripples and positioned the rover to enter the trough leading south.
Limits and slip checks were used to ensure that Opportunity would not get stuck.

Sol 517 (July 8, 2005): A new safety check was added to this drive: The drive current limits were lowered from 1 ampere to 0.4 amperes. The standard safety checks were also used on this drive, designed to take Opportunity 4 metres east to the north end of the trough, then 11 metres south through the trough.

Opportunity's total odometry after sol 517 is 5,406.6 metres.

Looking ahead:
Opportunity will continue the drive south, more slowly than before to
ensure a safe path.

Opportunity’s right rear Hazard Camera took this picture on Sol 491 of Meridiani Planum at approximately 13:45:18 Mars local solar time.


Expand

The tracks leading into and away from the sand trap can easily be seen.

Engineers and mission managers for NASA's Mars Exploration Rover mission cheered when images from the Martian surface confirmed Opportunity had successfully escaped from a sand trap.

From about 174 million kilometres away, the rover team at NASA's Jet Propulsion Laboratory, Pasadena, US, had worked diligently for nearly five weeks to extricate the rover. The long-distance roadside assistance was a painstaking operation to free all six wheels of the rover, which were mired up to their rims in the soft sand of a small Martian dune.

"After a nerve-wracking month of hard work, the rover team is both elated and relieved to finally see our wheels sitting on top of the sand instead of half buried in it," - Jeffrey Biesiadecki, a JPL rover mobility engineer.

Traction was difficult in the ripple-shaped dune of windblown dust and sand that Opportunity drove into on April 26. In the weeks following, the rover churned 192 metres worth of wheel rotations before gaining enough traction to actually move one metre. The rover team directed the drives in cautious increments from May 13 through June 4.

"We did careful testing for how to get Opportunity out of the sand. Then we patiently followed the strategy developed from the testing, monitoring every step of the way. We hope to have Opportunity busy with a full schedule of scientific exploration again shortly.” - Jeffrey Biesiadecki.


Expand

Opportunity's next task is to examine the site to provide a better understanding of what makes that ripple different from the dozens of similar ones the rover easily crossed.
"After we analyze this area, we'll be able to plan safer driving in the terrain ahead" - Jim Erickson, JPL's rover project manager.

Both Spirit and Opportunity have worked in harsh Martian conditions much longer than anticipated. They have been studying geology on opposite sides of Mars for more than a year of extended missions since successfully completing their three-month primary missions in April 2004.

"The first thing we're going to do is simply take a hard look at the stuff we were stuck in," - Dr. Steve Squyres of Cornell University, Ithaca, N.Y.
Dr. Steve Squyres is the principal investigator for the Mars rovers' science instruments.
"After that, we will begin a cautious set of moves to get us on our way southward again. South is where we think the best science is, so that's still where we want to go."