A Closer Encounter With Mars

NASA is releasing these images to commemorate the second anniversary of the Mars Pathfinder landing. The lander and its rover, Sojourner, touched downon the Red Planet's rolling hills on July 4, 1997, embarking on anhistoric three-month mission to gather information on the planet'satmosphere, climate, and geology.

The telescope's Wide Field and Planetary Camera 2 snapped these imagesbetween April 27 and May 6, when Mars was 54 million miles (87 millionkilometers) from Earth. From this distance the telescope could seeMartian features as small as 12 miles (19 kilometers) wide.

The telescope obtained four images, which, together, show the entireplanet. Each view depicts the planet as it completes one quarter of itsdaily rotation. In these views the north polar cap is tilted toward theEarth and is visible prominently at the top of each picture. The imageswere taken in the middle of the Martian northern summer, when the polarcap had shrunk to its smallest size. During this season the Sun shinescontinuously on the polar cap. Previous telescopic and spacecraftobservations have shown that this summertime "residual" polar cap iscomposed of water ice, just like Earth's polar caps.

These Hubble telescope snapshots reveal that substantial changes in thebright and dark markings on Mars have occurred in the 20 years since the NASA Viking spacecraft missions first mapped the planet. The Martiansurface is dynamic and ever changing. Some regions that were dark 20years ago are now bright red; some areas that were bright red are nowdark. Winds move sand and dust from region to region, often inspectacular dust storms. Over long timescales many of the larger brightand dark markings remain stable, but smaller details come and go as they are covered and then uncovered by sand and dust.

The upper-left image is centered near the location of the Pathfinderlanding site. Dark sand dunes that surround the polar cap merge into alarge, dark region called Acidalia. This area, as shown by images fromthe Hubble telescope and other spacecraft, is composed of dark,sand-sized grains of pulverized volcanic rock. Below and to the left ofAcidalia are the massive Martian canyon systems of Valles Marineris,some of which form long linear markings that were once thought by someto be canals. Early morning clouds can be seen along the left limb ofthe planet, and a large cyclonic storm composed of water ice is churning near the polar cap.

The upper-right image is centered on the region of the planet known asTharsis, home of the largest volcanoes in the solar system. The bright,ring-like feature just to the left of center is the volcano OlympusMons, which is more than 340 miles (550 kilometers) across and 17 miles(27 kilometers) high. Thick deposits of fine-grained, windblown dustcover most of this hemisphere. The colors indicate that the dust isheavily oxidized ("rusted"), and millions (or perhaps billions) of years of dust storms have homogenized its composition. Prominent lateafternoon clouds along the right limb of the planet can be seen.

The lower-left image is centered near another volcanic region known asElysium. This area shows many small, dark markings that have beenobserved by the Hubble telescope and other spacecraft to change as aresult of the movement of sand and dust across the Martian surface. Inthe upper left of this image, at high northern latitudes, a largechevron-shaped area of water ice clouds mark a storm front. Along theright limb, a large cloud system has formed around the Olympus Monsvolcano.

The lower-right image is centered on the dark feature known as SyrtisMajor, first seen telescopically by the astronomer Christiaan Huygens in the 17th century. Many small, dark, circular impact craters can be seenin this region, attesting to the Hubble telescope's ability to revealfine detail on the planet's surface. To the south of Syrtis is a largecircular feature called Hellas. Viking and more recently Mars GlobalSurveyor have revealed that Hellas is a large and deep impact crater.These Hubble telescope pictures show it to be filled with surface frostand water ice clouds. Along the right limb, late afternoon clouds haveformed around the volcano Elysium.

Shown here are color composites generated from data using three filters: blue (410 nanometers), green (502 nanometers), and red (673 nanometers).

A total of 12 color filters, spanning ultraviolet to near-infraredwavelengths, were used in the observation.

Photo credits: Steve Lee (University of Colorado), Jim Bell (CornellUniversity), Mike Wolff (Space Science Institute), and NASA

Other researchers involved in the collection and analysis of theseHubble telescope data are R. Todd Clancy (Space Science Institute),Philip James (University of Toledo), and Michael Ravine (Malin SpaceScience Systems, Inc.).

The Space Telescope Science Institute is operated by the Association ofUniversities for Research in Astronomy, Inc. for NASA, under contractwith NASA's Goddard Space Flight Center, Greenbelt, MD. The Hubble Space

Telescope is a project of international cooperation between NASA and the European Space Agency.

- end -

NOTE TO EDITORS:

For additional information, please contact Jim Bell atjimbo@marswatch.tn.cornell.edu.

Image files are available on the Internet at:http://oposite.stsci.edu/pubinfo/pr/1999/27 or via links inhttp://oposite.stsci.edu/pubinfo/latest.html andhttp://oposite.stsci.edu/pubinfo/pictures.html

Higher resolution digital versions (300 dpi JPEG and TIFF) of therelease photo are available at:http://oposite.stsci.edu/pubinfo/pr/1999/27/pr-photos.html