Universe Today

Image credit: NASA/JPL
NASA’s Spirit will begin trekking toward hills on its eastern horizon in the next few days, entering a new phase of the rover’s exploration of Mars just before its prime three-month mission ends and its extended mission begins, rover team members said today.

The range of peaks named “Columbia Hills” is an island of older rock surrounded by a younger volcanic layer which surfaces the plain that Spirit has been crossing, said Dr. Ray Arvidson of Washington University, St. Louis. He is deputy principal investigator for the science payload on both Spirit and its twin rover, Opportunity.

Older rocks may hold evidence of an ancient body of water thought to have once filled Gusev Crater. Spirit landed inside that 150-kilometer-wide (95-mile-wide) crater 12 weeks ago, and the rover’s main task is to find geological clues about whether the region ever had a wet environment. Spirit has spent much of its time since landing driving toward a 200-meter-wide (660-foot-wide) crater nicknamed “Bonneville.” Rover scientists had anticipated that the impact that excavated Bonneville might have ejected rocks old enough to hold clues about whether Gusev held water.

“The ejecta from Bonneville didn’t get excavated from deep enough to get below the volcanic layer,” Arvidson said. So, after finishing an examination of a light-colored rock on the crater’s rim, Spirit will head for the hills.

NASA’s Jet Propulsion Laboratory, Pasadena, Calif., built each of the two Mars Exploration Rovers for a prime mission of 90 martian days of operation. Both rovers are healthy and could operate for several additional months, said JPL’s Matt Wallace, mission manager. A martian day, or sol, lasts about 40 minutes longer than an Earth day, and Spirit’s 82nd sol began on Friday. “Spirit will start driving toward the hills on sol 84 or a little after that,” Wallace said.

Scientists have examined the terrain between Bonneville Crater and Columbia Hills in photographs taken from orbit by NASA’s Mars Global Surveyor and found several features to inspect along the route. These include some small craters and a dark streak apparently left by a whirlwind that removed dust.

Science team member Dr. Larry Crumpler of New Mexico Museum of Natural History, Albuquerque, said, “It won’t be a continuous drive, like a bad road trip. We’ll actually get out and do some touristy things along the way.”

With stops for “traverse science” along the way, the trip of about 2.3 kilometers (1.3 miles) to the near edge of Columbia Hills will probably take 60 to 90 sols, Arvidson said.

Beginning next week and continuing into the extended mission, Spirit’s controllers will switch from working on Mars time – with schedules set to coincide with day or night at Gusev crater – to an Earth time schedule easier to maintain for the long haul. The Opportunity team will shift the following week, Wallace said.

Opportunity is also at the start of a trek. This week, it climbed out of the small impact crater informally named “Eagle Crater” that it had been examining since it landed nine weeks ago. Rocks in an outcrop within the crater have provided evidence that the site was once under flowing water. In coming weeks, Opportunity will drive about 750 meters (nearly half a mile) to a crater nicknamed “Endurance,” where scientists hope to find and examine a thicker set of bedrock layers to learn more about the duration of the region’s wet history.

Before leaving Eagle Crater, Opportunity inspected the soil at five sites in the opposite half of the crater from the outcrop. The target patches show a diversity of particle sizes and shapes on the surface. “We’re seeing the effects of differences in wind speed,” said Bethany Ehlmann, a science team collaborator from the University of Washington, St. Louis. In some patches more than others, winds have removed small particles and left large particles behind, she said.

Spherical gray particles that have been fancifully called blueberries are plentiful in some soil patches higher on the inner slope of the crater than near the center of the crater. A reading by Opportunity’s Moessbauer spectrometer on one of the higher patches found the highest concentration of hematite seen so far in the mission, reported Dr. Goestar Klingelhoefer of the University of Mainz, Germany. He is the lead scientist for that instrument, which is used for identifying iron-containing minerals. The type of hematite Opportunity has been finding usually forms on Earth under wet environmental conditions. JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover project for NASA’s Office of Space Science, Washington, D.C. Images and additional information about the project are available from JPL at http://marsrovers.jpl.nasa.gov and from Cornell University, Ithaca, N.Y., at http://athena.cornell.edu .

Original Source: NASA/JPL News Release

Image credit: UA
The spiral troughs of Mars’ polar ice caps have been called the most enigmatic landforms in the solar system. The deep canyons spiraling out from Red Planet?s North and South poles cover hundreds of miles. No other planet has such structures.

A new model of trough formation suggests that heating and cooling alone are sufficient to form the unusual patterns. Previous explanations had focused on alternate melting and refreezing cycles but also required wind or shifting ice caps.

“I applied specific parameters that were appropriate to Mars and out of that came spirals that were not just spirals, but spirals that had exactly the shape we see on Mars.” said Jon Pelletier, an assistant professor of geosciences at the University of Arizona in Tucson. “They had the right spacing, they had the right curvature, they had the right relationship to one another.”

His report, “How do spiral troughs form on Mars?,” is published in the April issue of the journal Geology. One of his computer simulations of the troughs graces the cover.

How the icy canyons formed in a spiral has puzzled scientists since the pattern was first spotted by the Viking spacecraft in 1976.

Pelletier, a geomorphologist who studies landforms on Earth such as sand dunes and river channels, has a fondness for natural patterns that are regularly spaced.

Spirals fit the bill, and while perusing a book on mathematical patterns in biology, he was struck by the spiral shape formed by slime molds. He wondered whether the mathematical equation that described how the slime mold grew could also be applied to geological processes.

“There’s a recipe for getting spirals to form,” he said. So he tried it out, using information that described the situation on Mars.

Temperatures on Mars are below freezing most of the year. During very brief periods during the summer, temperatures on the polar ice caps get just high enough to let the ice melt a bit, Pelletier said.

He proposes that during that time, cracks or nicks in the ice’s surface that present a steep side toward the sun might melt a bit, deepening and widening the crack. Heat from the sun also diffuses through the ice.

Much as ice cubes evaporate inside a freezer, on Mars, the melting ice vaporizes rather than becoming liquid water.

The water vapor, when it hits the cold, shady side of the little canyon, condenses and refreezes. So the canyon expands and deepens because one side is heated occasionally while the other side always remains cold.

“The ambient temperatures on Mars are just right to create this form. And that’s not true anywhere else in the solar system,” he said. “The spirals are created because melting is focused in a particular place.”

Pelletier said the differential melting and refreezing is the key to the formation of Mars’ spiral troughs.

So he put mathematical descriptions of the heating and cooling cycles into the spiral-generating equation and ran computer simulations to predict what would occur over thousands of such cycles. He did not include wind or movement of polar ice caps in his model.

The computer made patterns that match what’s seen on Mars, even down to the imperfections in the spirals.

“The model I have predicts the spacing between these things, how they’re curved, and how they evolve over time to create spiral feature,” he said.

“A lot of planetary sciences is about making educated guesses about the imagery that we see. We can’t go there, we can’t do do field experiments,” he said. “The development of numerical models provides strong suggestions as to what’s essential to create the form that we see,” and allows scientists to test their assumptions, he said.

Original Source: UA News Release