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Postcards from the Grander Canyon

September 26, 2004

As the largest feature of its kind in the solar system, the martian canyon, Valles Marineris, stretches an equivalent terrestrial distance from New York to Los Angeles. But getting a robotic explorer down into the canyon floor challenges even the most intrepid of navigators.

Astrobiology Magazine — If the martian canyon, Valles Marineris, were on Earth, it would stretch from New York to Los Angeles. It is the largest canyon in the solar system (more than 4,000 kilometers (2,500 miles) long with 5 to 10 kilometers (3 to 6 miles) relief from floors to tops of surrounding plateaus).

The image (below) from the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) shows a thick, massive outcrop of light-toned rock exposed within eastern Candor Chasma, part of the vast Valles Marineris trough system.

Dark, windblown sand has banked against the lower outcrop slopes. Outcrops such as this in the Valles Marineris chasms have been known since Mariner 9 images were obtained in 1972. However, the debate as to whether these represent sedimentary or igneous rocks has not been settled within the Mars science community.

In either case, they have the physical properties of sedimentary rock (that is, they are formed of fine-grained materials), but some igneous rocks made up of volcanic ash may also exhibit these properties.

During its mapping operations, the Global Surveyor spacecraft circles Mars once every 118 minutes at an average altitude of 378 kilometers (235 miles). After mapping finishes, the spacecraft also functions as a communications satellite to relay data back to Earth from surface landers such as the Mars Exploration rovers now on opposite sides of the red planet.

Looking down on such a six-mile deep crevass presents a spectacular landscape, even when seen from high overhead in orbit. Such oblique views, resembling how a person looking out a window might view across the broad Martian horizon, have a special appeal, according to Dr. Bill Hartmann, a member of the imaging team that works with the Mars Global Surveyor.”

There are a number of regions I’d like to see photographed in that ‘human’ oblique view angle, the way we are used to seeing the land from our airplane windows. I think that they inspire a broader, more holistic view that lets us see Mars in the context of our terrestrial experience (not as an alien “target”), and that in turn inspires new thinking, a new sense of relationships, and new questions.”

“I’d love to see obliques looking down Valles Marineris , across some of the big frosty craters, across some of the lava flows, down big riverbed channels like Ares Vallis and Ma’adim Vallis, and so on”, concluded Hartmann.

To the west of Candor, one finds more intricate chasms that span the equatorial regions. The Odyssey spacecraft has taken some great pictures of Valles Marineris (left), including Ius Chasma in the west, and Coprates Chasma to the east.

The hill formation on the bottom half of the image separates Ophir (northern) and Candor (southern) Chasmas. The top half of the image shows an interesting wind etched rock formation in Ophir Chasma.

While also linking into the solar system’s first satellite constellation that relays surface pictures from Mars, Odyssey is used to determine the distribution of minerals, particularly those that can only form in the presence of water.

It will be difficult to get an eventual lander into such rugged terrain. As James Kasting of Penn State points out: “We want to understand the surface of Mars like we understand the surface of the Earth. We’ll learn something by robotic missions, we’re learning lots right now from the current missions, but we won’t understand Mars like we understand the Earth until we get teams of geologists up there with rock hammers, clambering down Valis Marineris and looking at the whole stratigraphic sequence that is very difficult to get to robotically.”

Planet at a Glance

– Highest point is Olympus Mons, a huge shield volcano about 26 kilometers (16 miles) high and 600 kilometers (370 miles) across; has about the same area as Arizona

– Canyon system of Valles Marineris is largest and deepest known in solar system; extends more than 4,000 kilometers (2,500 miles) and has 5 to 10 kilometers (3 to 6 miles) relief from floors to tops of surrounding plateaus

– “Canals” observed by Giovanni Schiaparelli and Percival Lowell about 100 years ago were a visual illusion in which dark areas appeared connected by lines.

– The Mariner 9 and Viking missions of the 1970s, however, established that Mars has channels possibly cut by ancient rivers Moons

– Two irregularly shaped moons, each only a few kilometers wide

– Larger moon named Phobos (“fear”); smaller is Deimos (“terror”), named for attributes personified in Greek mythology as sons of the god of war

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