EMBARGOED UNTIL:  9:00 A.M. February 25, 1999

PHOTO NO.: STScI-PRC99-07


MARTIAN COLORS PROVIDE CLUES ABOUT MARTIAN WATER

NASA Hubble Space Telescope images of Mars detail a rich geologic
history and provide further evidence for water-bearing minerals on the
planet's surface.

These pictures showcase the planet in both visible and infrared light.
In the image on the left, taken in visible light by the Wide Field and
Planetary Camera 2, Mars appears in natural color or as we would see it
close-up. The multicolor picture on the right was taken in infrared
light by the Near Infrared Camera and Multi-Object Spectrometer.
Infrared light is invisible to the eye. Therefore, astronomers have
assigned false colors to highlight important features that cannot be
seen in visible light.

Left: This "true-color" picture shows that Mars is clearly more
earth-toned than usually depicted in other images of the planet.

The slightly bluer shade along the edges of the disk is due to
atmospheric hazes and wispy water ice clouds (like cirrus clouds) in the
early morning and late evening Martian sky. Mars Pathfinder also imaged
clouds like these in 1997. The north polar cap, the bright region at the
top of the image, is not actually white, but yellowish-pink. This color
indicates the presence of small iron-bearing dust particles. These
particles are covering or are suspended in the air above the blue-white
water ice and carbon dioxide ice, which make up the polar cap.

Accurate knowledge of the true color of Mars not only provides artistic
and aesthetic beauty, but also provides insight into the composition and
mineralogy of Mars by allowing detailed comparisons to the color
properties, and thus mineralogy and composition, of rocks and minerals
on Earth. These and previous observations reveal that the classical
"bright regions" of Mars are composed of a heavy dose of oxidized
(rusted) iron minerals.

The mineral hematite (alpha-Fe2O3), which often forms on Earth via the
sustained action of water and heat on rocks, has been identified from
color imaging and spectroscopy data. These data reveal that hematite is
found mostly in extremely fine-grained particles, like those formed in
some volcanic or underwater regions on Earth. Some scientists believe
that the planet contains other iron oxides, such as goethite
(alpha-FeOOH) and maghemite (gamma-Fe2O3). Their belief is based on the
planet's color properties at visible and infrared wavelengths as well as
other direct measurements by the Viking and Pathfinder landers.
Confirmation of the presence of these minerals would imply the
possibility of different, perhaps much more Earth-like, past Martian
climate periods.

The classical "dark regions" appear generally less heavily oxidized and
composed of more primitive, darker minerals like pyroxene, erupted long
ago from Martian volcanoes.  Like any world with a complex geology and
diverse past, though, there are local differences in color and
composition that do not follow these general global trends. One great
advantage of imaging Mars with the Hubble telescope is that small-scale
variations can be accurately detected and interpreted for the first
time. In fact, the smallest features visible in this image are only
about 14 miles (22 km) wide.

The image was generated from three separate Hubble telescope images
acquired at wavelengths of 410, 502, and 673 nanometers in March 1997.

Right: Although an armada of spacecraft has photographed Mars, none has
had the near-infrared capabilities of the Hubble telescope.

Astronomers used the infrared camera to search for evidence of water.
This multicolor, composite image shows the variations in the abundance
and distribution of certain water-bearing minerals on the same part of
the planet as the picture on the left.

Astronomers were looking for evidence of a link between a putative
warmer, wetter past and the cold, dry conditions on the planet today.
They found one possible link in the region around the Mars Pathfinder
landing area, at the southern end of the large reddish region known as
Mare Acidalium. This was the site of massive flooding early in Martian
history. While it has been known for decades that small amounts of
water-bearing minerals exist on the planet's surface, the reddish
regions in this image indicate areas of enhanced concentrations of these
as-yet-unidentified deposits, perhaps related to the water-rich history
of this part of Mars. The regions containing larger concentrations of
water-bearing minerals appear related to differences in the local
geology on Mars, but not to regional elevation or temperature.

Astronomers are interested in how water has influenced the creation of
rocks and minerals found on Mars today, as well as the distribution and
abundance of ice and subsurface liquid water. They are studying not only
the Hubble telescope data, but other information collected by the Mars
Global Surveyor orbiter, set to begin mapping the planet in March 1999,
and the Mars Climate Orbiter, which will begin observing weather
conditions in early 2000. These missions include instruments with
far-infrared capabilities, which may provide more clues about Martian
water-bearing minerals.

This composite image was taken in July 1997. Red corresponds to the
strength of an absorption band detected near 1450 nanometers; green to
the brightness of the surface in the near-infrared; and blue to
topographic elevation, determined from Viking Orbiter data.

Researchers: Jim Bell (Cornell University), Justin Maki (NASA Jet
Propulsion Laboratory or JPL), and Mike Wolff (Space Sciences
Institute), with acknowledgements to Robert Comstock (Central Washington
University), Phil James (University of Toledo), and Dave Crisp (JPL) for
image processing and acquisition assistance.

Photo Credit:  Jim Bell (Cornell University), Justin Maki (JPL), and
Mike Wolff (Space Sciences Institute) and NASA

NOTE TO EDITORS:  Image files and photo caption are available on the
Internet at:
http://oposite.stsci.edu/pubinfo/pr/1999/07 or via links in
http://oposite.stsci.edu/pubinfo/latest.html and
http://oposite.stsci.edu/pubinfo/pictures.html

Higher resolution digital versions of (300 dpi JPEG and TIFF) of the
release photo are available at:
http://oposite.stsci.edu/pr/1999/07/extra-photos.html