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