Universe Today

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

Image credit: NASA/JPL
This image is the first 360 degree view from the Mars Exploration Rover Opportunity’s new position outside “Eagle Crater,” the small crater where the rover landed about two months ago. Scientists are busy analyzing Opportunity’s new view of the plains of Meridiani Planum. The plentiful ripples are a clear indication that wind is the primary geologic process currently in effect on the plains. The rover’s tracks can be seen leading away from Eagle Crater.

At the far left are two depressions – each about a meter (about 3.3 feet) across – that feature bright spots in their centers. One possibility is that the bright material is similar in composition to the rocks in Eagle Crater’s outcrop and the surrounding darker material is what’s referred to as “lag deposit,” or erosional remnants, which are much harder and more difficult to wear away. These twin dimples might be revealing pieces of a larger outcrop that lies beneath. The depression closest to Opportunity is whimsically referred to as “Homeplate” and the one behind it as “First Base.” The rover’s panoramic camera is set to take detailed images of the depressions today, on Opportunity’s 58th sol. The backshell and parachute that helped protect the rover and deliver it safely to the surface of Mars are also visible near the horizon, at the left of the image.

Original Source: NASA/JPL News Release

Image credit: NASA/JPL
NASA’s Opportunity rover has demonstrated some rocks on Mars probably formed as deposits at the bottom of a body of gently flowing saltwater.

“We think Opportunity is parked on what was once the shoreline of a salty sea on Mars,” said Dr. Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for the science payload on Opportunity and its twin Mars Exploration Rover, Spirit.

Clues gathered so far do not tell how long or how long ago liquid water covered the area. To gather more evidence, the rover’s controllers plan to send Opportunity out across a plain toward a thicker exposure of rocks in the wall of a crater.

NASA’s Associate Administrator for Space Science Dr. Ed Weiler said, “This dramatic confirmation of standing water in Mars’ history builds on a progression of discoveries about that most Earthlike of alien planets. This result gives us impetus to expand our ambitious program of exploring Mars to learn whether microbes have ever lived there and, ultimately, whether we can.”

“Bedding patterns in some finely layered rocks indicate the sand-sized grains of sediment that eventually bonded together were shaped into ripples by water at least five centimeters (two inches) deep, possibly much deeper, and flowing at a speed of 10 to 50 centimeters (four to 20 inches) per second,” said Dr. John Grotzinger, rover science-team member from the Massachusetts Institute of Technology, Cambridge, Mass.

In telltale patterns, called crossbedding and festooning, some layers within a rock lie at angles to the main layers. Festooned layers have smile-shaped curves produced by shifting of the loose sediments’ rippled shapes under a current of water.

“Ripples that formed in wind look different than ripples formed in water,” Grotzinger said. “Some patterns seen in the outcrop that Opportunity has been examining might have resulted from wind, but others are reliable evidence of water flow,” he said.

According to Grotzinger, the environment at the time the rocks were forming could have been a salt flat, or playa, sometimes covered by shallow water and sometimes dry. Such environments on Earth, either at the edge of oceans or in desert basins, can have currents of water that produce the type of ripples seen in the Mars rocks.

A second line of evidence, findings of chlorine and bromine in the rocks, also suggests this type of environment. Rover scientists presented some of that news three weeks ago as evidence the rocks had at least soaked in mineral-rich water, possibly underground water, after they formed. Increased assurance of the bromine findings strengthens the case rock-
forming particles precipitated from surface water as salt concentrations climbed past saturation while water was evaporating.

Dr. James Garvin, lead scientist for Mars and lunar exploration at NASA Headquarters, Washington, said, “Many features on the surface of Mars that orbiting spacecraft have revealed to us in the past three decades look like signs of liquid water, but we have never before had this definitive class of evidence from the martian rocks themselves. We planned the Mars Exploration Rover Project to look for evidence like this, and it is succeeding better than we had any right to hope. Someday we must collect these rocks and bring them back to terrestrial laboratories to read their records for clues to the biological potential of Mars.”

Squyres said, “The particular type of rock Opportunity is finding, with evaporite sediments from standing water, offers excellent capability for preserving evidence of any biochemical or biological material that may have been in the water.”

Engineers at NASA’s Jet Propulsion Laboratory (JPL), Pasadena, Calif., expect Opportunity and Spirit to operate several months longer than the initial rover’s three-month prime missions on Mars. To analyze hints of crossbedding, mission controllers programmed Opportunity to move its robotic arm more than 200 times in one day, taking 152 microscope pictures of layering in a rock called “Last Chance.”

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. For images and information about the project on the Internet, visit:

http://www.nasa.gov

http://marsrovers.jpl.nasa.gov

http://athena.cornell.edu

Original Source: NASA News Release