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June 18, 1999
Web posted at: 2:28 p.m. EDT (1828 GMT)

In this story: Volcanoes in the clouds Buttes and mesas RELATED STORIES, SITES

PASADENA (CNN) -- First, Mars seemed to greet NASA's mapping orbiter with a smile. Now, it seems as if the red planet has sent a valentine in one of the latest pictures from the spacecraft's camera.

The image, which shows what appears to be a heart-shaped pile of gray dust, actually reveals a pit formed by collapse within a straight-walled trough known as a graben. Graben are formed along fault lines by expansion of the bedrock terrain.

The pit is about 1.4 miles across at its widest. The scientists in charge of the camera on the Mars Global Surveyor wanted to study the pit to examine the relationship between a lava flow, the graben and pits that disrupted and cut across the flow. All three are on the east flank of the Alba Patera volcano in a Martian region called northern Tharsis.

A related image shows the cracked and pitted floor of a crater in the northern plains partly filled with what probably is sediment. The image covers an area less than a mile wide, with each picture element representing 6 feet of the Martian surface.

Another of the photos, all of which were released Thursday by NASA's Jet Propulsion Laboratory, which manages the Mars mapping mission, shows cloud-shrouded volcanoes photographed on a single Martian afternoon. A feature called the Olympus Mons dominates the upper left corner. It is one of the largest known volcanoes and is nearly 340 miles wide.

The 'happy face' crater

Mars is home to some large, windblown dunes, as evidenced by another image in the June photo set. The dunes shown in that image rise to almost 275 feet at their crests.

Unlike dunes on Earth, the larger dunes of Mars are composed of dark, rather than light grains. This is probably due to their makeup. For example, beaches on the island of Oahu in Hawaii are light colored because they consist of ground-up seashells, while beaches in the southern shores of the island of Hawaii (the "Big Island" in the Hawaiian island chain) are dark because they consist of sand derived from dark lava rock.

The dunes in this picture are on the floor of an old, 45-mile diameter crater located northeast of a region called Syrtis Major. The image covers an area about 1.6 miles wide.

Finally, the photo set shows a "Martian Monument Valley" with eroded buttes and mesas carved from layered bedrock, resembling the stunning structures found at the U.S. attraction on the border of Arizona and Utah. The image covers an area about two miles.

On the first day of the mapping for the mission, in March 1999, the Global Surveyor camera snapped a shot of a crater resembling a smiling face, found in a region called Argyre Planitia. The Galle Crater is about 134 miles across.

Malin Space Science Systems and the California Institute of Technology built the cameras on Mars Global Surveyor using spare hardware from the Mars Observer mission, which is thought to have blown up just before reaching Mars in 1993. MSSS operates the camera from its facilities in San Diego.