Volcanic activity on the Red Planet

Associated Press Arizona Daily Wildcat This is a Mars Orbiter Camera (MOC) undated image of a 10 km by 12 km area within Coprates Chasma a ridge with a flat upper surface in the center of the 6000-km-long Valles Marineris. Mars may still have some fire left in its belly, say researchers who studied new images radioed back by a Mars-orbiting satellite. In one of two studies published in the journal Nature, researchers reported evidence that more than 3.5 billion years ago, Mars' volcanoes filled one canyon alone with enough molten rock to bury the entire United States beneath a fiery lake four miles deep. Low-resolution Viking color images were used to "colorize" the grayscale MOC image.

That amount is 10 times more volcanic activity than previously believed.

Alfred McEwen, director of the Planetary Image Research Lab at the University of Arizona's Lunar and Planetary Laboratory, has used the Surveyor's cameras to study extensive lava flows on the planet's surface. The largest currents measure hundreds of miles long.

The results that McEwen and his teammates received were published in the Feb. 18 issue of Nature Magazine.

Such a high rate of volcanism "helps the plausibility of a thick atmosphere" during the first billion years of Mars' history, he said.

While scientists have long believed that there was water on the planet's surface, they did not understand how Mars could have retained the thick atmosphere necessary to stop it from evaporating.

Mars has a thin atmosphere of carbon dioxide. Even if it had originally been more abundant, the atmosphere would have been dissipated by the liquid water on the surface. The water bonds with carbon dioxide and makes it precipitate in the form of carbonates, which consist of a carbon atom and three oxygen atoms.

As this occurs, the atmosphere thins. During the period of high volcanic activity, the spewing of carbon dioxide from beneath the Martian surface would replace the lost gas, McEwen said.

McEwen has been concentrating his efforts on the Valles Marineris, a 2,500 mile-long canyon containing numerous lava flows.

Layers of igneous rock on the canyon walls show that there were repeated deposits of lava during a long period of time, said Peter Lanagan, a graduate student focusing on planetary sciences.

"We originally thought it was water-lain sediments," he said.

Spectroscopic analysis, a method of determining the chemical makeup of a substance from a distance, showed that the rock layers were volcanic.

Lanagan is using the Surveyor's laser altimeter to make a topographic map of the lava flows. The altimeter works on the same principle as sonar - while sonar bounces sound waves off an object to determine its distance, the altimeter uses a laser.

The astronomers are unsure how the lava could have spread over hundreds of miles without cooling. Lanagan suggests that these rivers of molten rock could have been covered by a huge sheet of partially-cooled crust. The crust would have acted as insulation and kept the lava underneath from hardening.

Most of the volcanic activity occurred during the first billion years after Mars was formed, a period from 3.5 to 4.5 billion years ago. But some eruptions were as recent as ten million years ago, said Ross Beyer, a graduate student focusing on planetary sciences.

Astronomers date the volcanic eruptions by counting the number of craters on the surface of the lava flow.

During the early years of the solar system, interplanetary space was swarming with meteors. The impacts pocked the surface of Mars and the other planets, including our own moon.

The older a lava flow, the more time it had to be scarred by meteors.

"If you put a piece of paper out in the rain for a little while, it will get a few drops on it," Beyer said. "If you leave it out for longer, it will get totally saturated."

The exact dates of moon rocks retrieved during the Apollo missions are compared with the density of craters where they were found. Areas of similar crater densities on Mars are assumed to be of roughly the same age, he said.

Check out NASA's Mars Exploration page for more infromation on the Pathfinder project.