The Starbase One Astronomy & Space Collection/STARBASE_ONE.ISO/hst/titanst1.txt

Text File | 1996-01-12 | 8KB | 150 lines

          From Lori Stiles, [phone]
          University of Arizona, News Services
          -- Sent Nov. 8, 1994 --


          UA SCIENTIST & TEAM DISCOVER
          SURFACE FEATURES COVER TITAN

          (Science contacts:  Peter H. Smith, [phone];
                               Mark Lemmon, [phone];
                               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.

                                   ----

          EDITOR'S NOTE:  The HST images of Titan's surface are
          currently available as .GIF files.  Hardcopies are available
          from UA News Services, tel: [phone], and are to be
          available soon from the Space Telescope Science Institute
          in Baltimore, [phone]. Animation also may be
          available.

                         ---

          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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