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INTERACTIVE 3-D VRMLS Mars Global Surveyor Hubble Space Telescope ALSO:    Message Board: Destination Mars

July 1, 1999
Web posted at: 12:17 p.m. EDT (1617 GMT)

In this story: Big changes since Viking Pathfinder landing site in one image Two volcanic regions featured Hubble captures small impact craters RELATED STORIES, SITES

(CNN) -- Taking advantage of Mars's closest approach to Earth in eight years, astronomers using NASA's Hubble Space Telescope took the space-based observatory's sharpest views yet of the red planet.

NASA released the images this week to commemorate the second anniversary of the Mars Pathfinder landing on July 4, 1997.

The telescope's Wide Field and Planetary Camera 2 snapped the images between April 27 and May 6, when Mars was 87 million kilometers (54 million miles) from Earth.

From this distance the telescope could see Martian features as small as 19 kilometers (12 miles) wide. By comparison, NASA's Mars Global Surveyor currently orbiting the planet to create a global map can resolve surface features as small as 1.5 to 4.5 meters (5-15 feet).

The telescope obtained four images, which, together, show the entire planet. Each view depicts the planet as it completes one quarter of its daily rotation.

The snapshots reveal that substantial changes in the bright and dark markings on Mars have occurred in the 20 years since the Viking spacecraft missions first mapped the planet.

The images show that the Martian surface is dynamic and ever changing. Some regions that were dark 20 years ago are now bright red; some areas that were bright red are now dark.

Winds move sand and dust from region to region, often in spectacular dust storms. Over time, many of the larger bright and dark markings remain stable, but smaller details come and go as they are covered and then uncovered by sand and dust.

One of the images is centered near the location of the Pathfinder landing site. Dark sand dunes that surround the polar cap merge into a large, dark region called Acidalia.

This area, as shown by observations from the Hubble telescope and other spacecraft, is composed of dark, sand-sized grains of pulverized volcanic rock.

Below and to the left of Acidalia are the massive Martian canyon systems of Valles Marineris, some of which form long linear markings that were once thought by some to be canals. Early morning clouds can be seen along the left limb of the planet, and a large cyclonic storm composed of water ice is churning near the polar cap.

The second image is centered on the region of the planet known as Tharsis, home of the largest volcanoes in the solar system.

The bright, ring-like feature just to the left of center is the volcano Olympus Mons, which is more than 550 kilometers (340 miles) across and 27 kilometers (17 miles) high. Thick deposits of fine-grained, windblown dust cover most of this hemisphere.

The colors indicate that the dust is heavily rusted, and millions (or perhaps billions) of years of dust storms have homogenized it. Late afternoon clouds along the right limb of the planet can be seen.

The third image is centered near another volcanic region known as Elysium. This area shows many small, dark markings that have been observed by the Hubble telescope and other spacecraft to change as a result of the movement of sand and dust across the Martian surface.

In the upper left of this image, at high northern latitudes, a large chevron-shaped area of water ice clouds mark a storm front. Along the right limb, a large cloud system has formed around the Olympus Mons volcano.

The lower-right image is centered on the dark feature known as Syrtis Major, first seen telescopically by the astronomer Christiaan Huygens in the 17th century. Many small, dark, circular impact craters can be seen in this region.

To the south of Syrtis is a large circular feature called Hellas. Viking and more recently Mars Global Surveyor have revealed that Hellas is a large and deep impact crater. These Hubble telescope pictures show it is filled with surface frost and water ice clouds. Along the right limb, late afternoon clouds have formed around the volcano Elysium.

Steve Lee of the University of Colorado, Jim Bell of Cornell University, Mike Wolff of the Space Science Institute and NASA technicians took the photos.