Opportunity has been studying the so-called "bathtub ring," a light band of rock that appears to circle Victoria Crater partway below the surface. Scientists think the band may be the remains of the original surface of Meridiani Planum before a meteor blasted out the crater. The ring itself appears to have three layers, originally dubbed "alpha," "beta" and "gamma" after the first three letters of the Greek alphabet, but now renamed "Steno," "Smith" and "Lyell," in honor of pioneering geologists of the 17th and 18th centuries.

Opportunity is to complete studies of Steno after grinding a hole into the rock surface with the rock abrasion tool and acquire a final set of observations that include measurements with the Moessbauer spectrometer.

The two spectrometers on Opportunity provide different kinds of information. The alpha-particle X-ray spectrometer is a general-purpose spectrometer that helps determine the chemical composition of the rocks. The Moessbauer spectrometer is specifically designed to study iron-bearing minerals, which are abundant on Mars and give the planet its red-orange color. Both spectrometers rely on radioactive energy sources but the one in the Moessbauer spectrometer has a shorter half-life. That means it gets weaker faster. As a result, Moessbauer integrations now take longer, typically as many as 60 hours to acquire useful data. The rover acquires the observations over several sols.

To conserve battery power, which relies on sunlight as a source of energy, Opportunity sleeps at night. Opportunity happens to have a heater stuck in the "on" position that draws additional power. Mechanical thermostats added to the mission just before it was launched in 2003 prevent the heater from running during the daytime. But the heater continues to draw power at night.

Scientists plan to move Opportunity to a second spot on Steno for continued investigation. Before moving, Opportunity must stow the robotic arm. If the stow is successful, plans call for the rover to back uphill and aim high to compensate for potential slip on the steep slope of Victoria Crater before driving forward.

Plans also call for the rover to measure atmospheric argon. Argon is a trace gas in the Martian atmosphere, comprising about 1.6 percent (the bulk of the Martian atmosphere is carbon dioxide, the same gas that gives soft drinks their fizz). Argon is one of the noble gases, so named because they don't react chemically with other substances. It is always a gas. Water, on the other hand, can be a gas (water vapor), a liquid (cloud, mists, and rain), or a solid (ice, snow, sleet, and hail). Water can also bind physically or chemically to other substances in the air, such as dusts and soots, smog, and acid rain.

Because argon is always in one physical state (a gas) that is unadulterated by other substances, it can be used as a barometer. When atmospheric pressure is high, there's more argon in the field of view. When it's low, there's less argon. Measurements of the gas with the alpha-particle X-ray spectrometer track changes in Mar's atmospheric pressure as a result of changes in global energy flows, dust storms, and Mars' position relative to the Sun.

On sol 1320 (Oct. 11, 2007), Opportunity is scheduled to take a series of nine microscopic images within a minute or two at exactly the same spot. By adding the pixels (picture elements), engineers can reduce the amount of "noise" -- random, microscopic overexposures or underexposures -- within the image. Such noise is a constant in nature. By combining the pixels, engineers can average out the noise to reveal details and fine texture that would otherwise be obscured.

Sol-by-sol summary:

In addition to daily observations that included measurements of atmospheric dust with the panoramic and navigation cameras, surveys of the sky and ground with the miniature thermal emission spectrometer, and transfers of data to Earth via the Odyssey orbiter, Opportunity completed the following activities:

Sol 1316 (Oct. 6, 2007): Opportunity acquired stereo microscopic images of Steno, studied the rock's composition with the alpha-particle X-ray spectrometer, and checked for drift (changes with time) in the miniature thermal emission spectrometer.

Sol 1317: Opportunity acquired data from Steno using the Moessbauer spectrometer, went into a mini-deep sleep, and checked for drift in the miniature thermal emission spectrometer.

Sol 1318: Opportunity restarted the Moessbauer spectrometer for continued observation of Steno for 24 hours. The rover took thumbnail images of the sky and a mosaic of images of a target known as "Dolomieu" using the panoramic camera. The rover checked for drift in the miniature thermal emission spectrometer.

Sol 1319: Plans called for Opportunity to restart the Moessbauer spectrometer for 11 hours of observation of Steno and acquire images with the panoramic camera as well as check for drift in the miniature thermal emission spectrometer. The rover was to wake up at 11:20 p.m. local Mars time to turn off the Moessbauer spectrometer before returning to a mini-deep sleep. The following morning, Opportunity was to take thumbnail images of the sky with the panoramic camera and scan the sky for clouds with the navigation camera.

Sol 1320: Plans called for Opportunity to take microscopic images of a hole ground into the surface of Steno with the rock abrasion tool and spend 23 hours observing the same surface with the Moessbauer spectrometer. Opportunity was also slated to acquire full-color images, using all 13 filters of the panoramic camera, of a target known as "Arduino" and survey the horizon and take thumbnail images of the sky with the panoramic camera.

Sol 1321 (Oct. 12, 2007): Plans called for Opportunity to stow the robotic arm, bump backward a short distance, take images with the hazard avoidance camera along the way as well as navigation camera images after the drive, and acquire panoramic camera images of the work volume reachable by the robotic arm. The rover was to acquire post-drive images with the navigation camera, unstow the robotic arm, measure atmospheric argon with the alpha-particle X-ray spectrometer, monitor dust on the rover mast, and check for drift in the miniature thermal emission spectrometer.

Odometry: As of sol 1321 (Oct. 12, 2007), Opportunity's total odometry remained at 11,572.94 meters (7.19 miles).

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