PUT ON A HAPPY FACE The "Happy Face Crater" - officially named Galle Crater - puts a humorous spin on the "Face on Mars" controversy. This image was provided by the Mars Global Surveyor orbiter.

GRAND CANYON This is a composite of Viking orbiter images that shows the Valles Marineris canyon system. The entire system measures more than 1,875 miles long and has an average depth of 5 miles.

THE FACE OF MARS The Hubble Space Telescope focuses on the full disk of Mars, with a head-on view of a dark feature known as Syrtis Major. Hubble astronomers could make out features as small as 12 miles wide.

RED ROVER A mosaic of eight pictures shows the Pathfinder probe"s Sojourner rover just after it rolled off its ramp. At lower right you can see one of the airbags that cushioned Pathfinder"s landing on July 4, 1997.

TWIN PEAKS AT THEIR PEAK The Pathfinder probe focuses on Twin Peaks, two hills of modest height on the Martian horizon. Each peak rises about 100 feet above the surrounding rock-littered terrain.

A monster of a mountain Mars" highest mountain, an inactive volcano dubbed Olympus Mons, rises as high as three Everests and covers roughly the same area as the state of Arizona. Mars Global Surveyor took this wide-angle view.

FROM MARS WITH LOVE This valentine from Mars, as seen by Mars Global Surveyor, is actually a pit formed by a collapse within a straight-walled trough known in geological terms as a graben. The pit spans 1.4 miles at its widest point.

SANDY SWIRLS An image taken by Mars Global Surveyor shows a section of the northern sand dunes on Mars" surface. The dunes, composed of dark sand grains, encircle the north polar cap.

BLUE HORIZON A Martian sunset reverses the colors you"d expect on Earth: Most of the sky is colored by reddish dust hanging in the atmosphere, but the scattering of light creates a blue halo around the sun itself.