Don Savage
Headquarters, Washington, DC      March 21, 1995
(Phone:  202/358-1547)

Tammy Jones
Goddard Space Flight  Center, Greenbelt, MD
(Phone: 301/286-5566)

Ray Villard
Space Telescope Science Institute, Baltimore, MD
(Phone: 410/338-4514)

RELEASE:  95-117

HUBBLE MONITORS WEATHER ON NEIGHBORING PLANETS

       "The weather on Mars: another cool
     and clear day.  Low morning haze will
     give way to a mostly sunny afternoon 
     with high clouds.  The forecast for 
     Venus: hot, overcast, sulfuric acid 
     showers will continue.  Air quality is 
     slightly improved as smog levels subside."

       That kind of weathercast is now possible as NASA's 
Hubble Space Telescope serves as an interplanetary weather 
satellite for studying the climate on Earth's neighboring 
worlds, Mars and Venus.

       To the surprise of researchers, Hubble is showing 
that the Martian climate has changed considerably since the 
unmanned Viking spacecraft visited Mars in the mid-1970s, 
which was the last time astronomers got a close-up look at 
weather on the Red Planet for more than just a few months.  
Hubble images of clouds and spectroscopic detection of an 
ozone abundance in Mars' atmosphere, all indicate that the 
planet is cooler, clearer and drier than a couple of decades 
ago.

       In striking contrast, Hubble's spectroscopic 
observations of Venus show that the atmosphere continues to 
recover from an intense shower of sulfuric "acid rain" 
triggered by the suspected eruption of a volcano in the late 
1970s.  This is similar to what happens on Earth when sulfur 
dioxide emissions from coal power plants are broken apart in 
the atmosphere to make acid rain.  On Venus, this effect 
takes place on a planetary scale.

                     - more -
                      - 2 -

       Although the close-up visits by numerous unmanned 
spacecraft provided brief glimpses of weather on these 
planets, the long-term coverage offered by Hubble has never 
before been possible.  Knowledge about the weather is 
critical to planning future missions to these worlds.  In 
the case of Mars, being able to predict the weather will be 
critical prior to human exploration of the planet.

       Studying conditions on Mars and Venus might also lead 
to a better understanding of Earth's weather system.  
Apparently, processes that occurred early in the solar 
system's history sent terrestrial planets along very 
different evolutionary paths.  The neighboring planets are 
grand natural laboratories for testing computer models that 
will lead to a general theory of the behavior of planetary 
atmospheres.

       The Space Telescope Science Institute 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).

                     - end -

       EDITOR'S NOTE:  A Science Background Fact Sheet to 
accompany this release is available via fax by calling 
202/358-1600.

        Images and video are available to news media 
representatives by calling the Broadcast and Imaging Branch 
at 202/358-1900.   Photo numbers are:

                     Color                   B & W
Venus               HC-95-114               95-H-117
Mars, single face   HC-95- 115              95-H-118
Mars, three faces   HC-95- 113              95-H-116

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