PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
Contact: Diane Ainsworth
FOR IMMEDIATE RELEASEMay 20, 1997
HUBBLE SEES CLOUDY SKIES, COLD WEATHER FOR MARS ARRIVAL
New images from the orbiting Hubble Space Telescope suggest
that NASA's two Mars-bound spacecraft -- Mars Pathfinder and Mars
Global Surveyor -- will experience considerably different weather
conditions than those witnessed by the last U.S. spacecraft to
land on Mars 21 years ago.
Astronomers have been using the Hubble Space Telescope to
provide updated planetary weather reports to help plan both Mars
missions. Martian atmospheric conditions will affect the Mars
Pathfinder spacecraft landing and rover rollout on July 4 and the
arrival of the Mars Global Surveyor on September 11.
Images taken barely three weeks apart, on March 10 and March
30, reveal dramatic changes in some local conditions, and show
overall cloudier and colder conditions than Viking encountered
more than two decades ago.
"Because Pathfinder uses the atmosphere to decrease its
velocity for landing, and because the lander and rover are solar
powered, understanding the state of the atmosphere prior to
landing is important," said Dr. Matthew Golombek, Pathfinder
project scientist at NASA's Jet Propulsion Laboratory, Pasadena,
"On July 4, Mars Pathfinder will enter the atmosphere
directly from approach and slow itself behind an aeroshell with a
parachute, small solid rockets and giant airbags. The lander
carries a small rover to explore the surface and investigate the
kinds of materials present on the Martian surface," Golombek
said. "Hubble images of Mars are helping us to adjust our flight
path for landing and effectively plan surface operations."
"This is not the dusty Mars of the Viking days (mid-
1970s to early-1980s) or the habitable oasis of science fiction
stories," said Todd Clancy of the Space Science Institute in
Boulder, CO. "We're finding a Mars that's colder, clearer and
cloudier. Hubble is rapidly changing our view of Mars'
environment. The planet's weather apparently has a flip-side to
Hubble's findings also offer new insights into the
differences and similarities of weather on the other terrestrial
planets. "The planets are similar in many important ways, so the
very major differences between them are interesting from a
viewpoint of better understanding meteorology," said team leader
Phil James of the University of Toledo. "Hubble is allowing us
to look at Mars in ways never before seen."
In September, NASA's Mars Global Surveyor will skim
across the upper Martian atmosphere to slow down by friction and
enter orbit around the red planet. Atmospheric density is a key
factor in precisely executing this complex and delicate
aerobraking maneuver. Hubble is ideal for tracking regional dust
storms which could pose a threat to Surveyor by drastically
changing the planet's air density. Such storms can cause a
tenfold increase in the Martian atmosphere's drag at 96
kilometers (60 miles) above the surface.
Comparing the appearance of Mars to that of earlier
spacecraft observations, Hubble has found some areas of the
Martian surface that have been changed dramatically by wind-blown
dust. The most prominent example is the classic "dark feature"
called Cerberus, which is roughly the size of California (1,250
kilometers by 400 kilometers or 800 miles by 250 miles). This
feature has been seen as a low albedo, or dark region by ground-
based telescopic observers since early in this century, and was
studied in detail by the Mariner 9 and Viking orbiters in the
In Hubble's view, only three dark splotches remain,
probably related to dark sand being carried out of craters by the
wind. The astronomers think that dust storms in the region have
covered the formerly dark surface with bright dust, effectively
erasing Cerberus from the map.
Hubble is ideally suited for long-term study of Mars.
When Mars has been closest to Earth, Hubble has resolved surface
details as small as 40 kilometers (25 miles) across. This allows
astronomers to track subtleties in the shifting cloud patterns
and periodic dust storms. This planet-wide, "weather satellite"
view is complementary to the close-up views which will be
provided by Mars Pathfinder and Mars Global Surveyor.
The Mars Pathfinder and Mars Global Surveyor missions are
managed by the Jet Propulsion Laboratory for NASA's Office of
Space Science, Washington, D.C. The Hubble Space Telescope is
managed by the Space Telescope Science Institute in Baltimore,