          UA SCIENTIST & TEAM DISCOVER 

          SURFACE FEATURES COVER TITAN

          

          (Science contacts:  Peter H. Smith, (602) 621-2725;

                               Mark Lemmon, (602) 621-1485;

                               UA Lunar and Planetary Laboratory)     

          

               

               Scientists for the first time have made images of the

          surface of Saturn's giant, haze-shrouded moon, Titan. They

          mapped light and dark features over the surface of the

          satellite during nearly a complete 16-day rotation.  One

          prominent bright area they discovered  is a surface feature

          2,500 miles across, about the size of the continent of

          Australia.  

          

               Titan, larger than Mercury and slightly smaller than

          Mars, is the only body in the solar system, other than Earth,

          that may have oceans and rainfall on its surface,  albeit 

          oceans and rain of ethane-methane rather than water. 

          Scientists suspect that Titan's present environment --

          although colder than minus 289 degrees Fahrenheit, so cold

          that water ice would be as hard as granite -- might be

          similar to that on Earth billions of years ago, before life

          began pumping oxygen into the atmosphere.

          

               Peter H. Smith of the University of Arizona Lunar

          and Planetary Laboratory and his team took the images

          with the Hubble Space Telescope during 14 observing runs

          between Oct. 4 - 18.   Smith announced the team's first

          results last week at the 26th annual meeting of the

          American Astronomical Society Division for Planetary

          Sciences in Bethesda, Md.   Co-investigators on the team

          are Mark Lemmon, a doctoral candidate with the UA Lunar

          and Planetary Laboratory; John Caldwell of York University,

          Canada; Larry Sromovsky of the University of Wisconsin;

          and Michael Allison of the Goddard Institute for Space

          Studies, New York City.

          

                Titan's atmosphere, about four times as dense as

          Earth's atmosphere, is primarily nitrogen laced with such

          poisonous substances as methane and ethane.  This thick,

          orange, hydrocarbon haze was impenetrable to cameras

          aboard the Pioneer and Voyager spacecraft that flew by the

          Saturn system in the late 1970s and early 1980s.  The haze

          is formed as methane in the atmosphere is destoyed by

          sunlight.  The hydrocarbons produced by this methane

          destruction form a smog similar to that found over large

          cities, but is much thicker.  

          

               Smith's group used the Hubble Space Telescope's

          WideField/Planetary Camera 2  at near-infrared wavelengths

          (between .85 and 1.05 microns).  Titan's  haze is

          transparent enough in this wavelength range to allow

          mapping of surface features according to their reflectivity.

          Only Titan's polar regions could not be mapped this way,

          due to the telescope's viewing angle of the poles and the

          thick haze near the edge of the disk.  Their image-

          resolution (that is, the smallest distance seen in detail) with

          the WFPC2 at the near-infrared wavelength is 360 miles.

          The 14 images  processed and compiled into the Titan

          surface map were  as "noise" free, or as free of signal

          interference, as the space telescope allows, Smith said.

          

               Titan makes one complete orbit around Saturn in 16

          days, roughly the duration of the imaging project. 

          Scientists have suspected that Titan's rotation also takes 16

          days, so that the same hemisphere of  Titan always faces

          Saturn,  just as the same hemisphere of the Earth's moon

          always faces the Earth.  Recent observations by Lemmon

          and colleagues at the University of Arizona confirm this is

          true. 

          

               It's too soon to conclude much about what the dark

          and bright areas in the Hubble Space Telescope images are

          -- continents, oceans, impact craters or other features,

          Smith said.  Scientists have long suspected that Titan's

          surface was covered with a global ehtane-methane ocean. 

          The new images show that there is at least some solid

          surface.

          

               Smith's team made a total 50 images of Titan last

          month in their program, a project to search for small scale

          features in Titan's lower atmosphere and surface.  They

          have yet to analyze images for information about Titan's

          clouds and winds.  That analysis could help explain if the

          bright areas are major impact craters in the frozen water

          ice-and-rock or higher-altitude features.

          

                 The images are important information for the

          Cassini mission, which is to launch a robotic spacecraft on

          a 7-year journey to Saturn in October 1997.  About three

          weeks before Cassini's first flyby of Titan, the spacecraft is

          to release the European Space Agency's Huygens Probe to

          parachute to Titan's surface.  Images like Smith's team has

          taken of Titan can be used to identify choice landing spots -

          - and help engineers and scientists understand how Titan's

          winds will blow the parachute through the satellite's

          atmosphere.  

          

               UA scientists play major roles in the Cassini mission: 

          Carolyn C. Porco, an associate professor at the Lunar and

          Planetary Laboratory, leads the 14-member Cassini Imaging

          Team.  Jonathan I. Lunine, also an associate professor at

          the lab, is the only American selected by the European

          Space Agency to be on the three-member Huygens Probe

          interdisciplinary science team.  Smith is a member of

          research professor Martin G. Tomasko's international team

          of scientists who will image the surface of Titan in visible

          light and in color with the Descent Imager/Spectral

          Radiometer, one of five instruments in the Huygens Probe's

          French, German, Italian and U.S. experiment payload.

          Senior research associate Lyn R. Doose is also on

          Tomasko's team.  Lunine and LPL professor Donald M.

          Hunten are members of the science team for another U.S.

          instrument on that payload, the gas chromatograph mass

          spectrometer.  Hunten was on the original Cassini mission

          science definition team back in 1983.

               

                                   ----   

          

          PHOTO CAPTION:  Four global projections of the HST

          Titan data, separated in longitude by 90 degrees.  Upper

          left:  hemisphere facing Saturn.  Upper right: leading

          hemisphere (brightest region). Lower left:  the hemisphere

          which never faces Saturn. Lower right: trailing hemisphere. 

          Not that these assignments assume that the rotation is

          synchronous.  The imaging team says its data strongly

          support this assumption -- a longer time baseline is needed

          for proof.  The surface near the poles is never visible to an

          observer in Titan's equatorial plane because of the large

          optical path.

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