UA SCIENTIST & TEAM DISCOVER
SURFACE FEATURES COVER TITAN
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
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
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
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
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.