Credit: NASA, J. Bell (Cornell U.) and M. Wolff (SSI)

This view of Mars, the sharpest photo ever taken from Earth, reveals small craters and other surface markings only about a dozen miles (a few tens of kilometers) across. (The spatial scale is 5 miles, or 8 kilometers per pixel). The Advanced Camera for Surveys (ACS) aboard NASA's Hubble Space Telescope snapped this image on Aug. 24, just a few days before the red planet's historic "close encounter" with Earth.

Among the Martian surface features are: numerous craters; several large volcanoes of the great Tharsis plateau along the upper left limb; and a large multi-ring impact basin, called Hellas, near image center. These kinds of features from past and present NASA spacecraft that have orbited Mars are also being studied in detail. But they have never before been seen from Earth with this kind of clarity.

Subtle outliers of bright, whitish carbon dioxide ice (dry ice) can be seen in the neighborhood of the subliming white south polar cap at lower left, near the bottom of the image. The bright reddish meandering lines seen within the dark regions near the center of the image are caused by sunlight reflecting off the sloping walls of a giant canyon system called Valles Marineris, which cuts across more than 2,000 miles of the planet's surface.

The ACS's color capabilities can also be used to reveal other interesting details. For example, there is a reddish tinge to part of the south polar cap, suggesting that there are either dust clouds over the cap or that the ices are mixed with dusty surface materials. Dust clouds over the cap would not be surprising, as the dry ice is actively subliming near the time of the southern summer solstice, causing high winds and dynamic weather patterns.

This color image also reveals interesting weather phenomena at the highest northern latitudes. Hubble resolves a variety of clouds over the dark region in the upper right. This region is called Acidalia Planitia, and it is known to be the location of frequent cloud activity. The color image shows that there are both dust clouds (reddish/yellow) and ice clouds (blueish/white) over Acidalia. There is even some evidence of wave structures or other large-scale organized meteorological activity. If these are storms or storm fronts, they may be associated with the large amount of carbon dioxide condensation that is happening in the northern winter polar regions, where the north polar cap has started forming during the long polar night.

The color data show very subtle blueish clouds and hazes along both the morning (left) and evening (right) limbs of the planet. Like the north polar region, these are the places where the atmosphere is coldest, allowing the tiny amounts of water vapor in the Martian atmosphere to condense as clouds. Mars is not very cloudy, though, as compared with other times of the Martian year--like the southern fall and winter seasons imaged by Hubble during close approaches in the 1990s.

The black diagonal "finger" of missing data at about the eight o'clock position is a part of the ACS camera's coronograph, which is designed to block light from bright stars so that fainter objects near the stars can be studied. In this case, Mars loomed so large in the ACS High Resolution Camera's field of view that the coronograph finger blocked part of the scene. Multiple sets of images taken at different rotational aspects should allow scientists to eventually fill in this missing data, once the remaining sets of Hubble Mars observations for 2003 are obtained and processed.

Taken with the high-resolution camera, the color-composite image was constructed from separate images taken through separate red, green, and blue filters (658 nm, 502 nm, and 410 nm, respectively). Images have been processed to bring out the maximum amount of detail inherent in the data.

The Space Telescope Science Institute (STScI) is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), for NASA, under contract with the Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA).