Cassini Image: The Veils of Titan

http://saturn.jpl.nasa.gov/cgibin/gs...jpg&type=image

The Veils of Titan
May 06, 2004

Full-Res: PIA05390
http://photojournal.jpl.nasa.gov/catalog/PIA05390

The veils of Saturn's most mysterious moon have begun to lift in
Cassini's
eagerly awaited first glimpse of the surface of Titan, a world where
scientists believe organic matter rains from hazy skies and seas of
liquid hydrocarbons dot a frigid surface.

Surface features previously observed only from Earth-based telescopes
are
now visible in images of Titan taken in mid-April by Cassini through
one
of the narrow angle camera's spectral filters specifically designed to
penetrate the thick atmosphere. The image scale is 230 kilometers
(143 miles) per pixel, and it rivals the best Earth-based images.

The two images displayed here show Titan from a vantage point 17
degrees
below its equator, yielding a view from 50 degrees north latitude all
the
way to its south pole. The image on the left was taken four days after
the
image on the right. Titan rotated 90 degrees in that time. The two
images
combined cover a region extending halfway around the moon. The
observed
brightness variations suggest a diverse surface, with variations in
average
reflectivity on scales of a couple hundred kilometers.

The images were taken through a narrow filter centered at 938
nanometers, a
spectral region in which the only obstacle to light is the
carbon-based,
organic haze. Despite the rather long 38-second exposure times, there
is
no noticeable smear due to spacecraft motion. The images have been
magnified 10 times and enhanced in contrast to bring out details. No
further processing to remove the effects of the overlying atmosphere
has
been performed.

The superimposed grid over the images illustrates the orientation of
Titan
-- north is up and rotated 25 degrees to the left -- as well as the
geographical regions of the satellite that are illuminated and
visible.
The yellow curve marks the position of the boundary between day and
night
on Titan. The enhanced image contrast makes the region within 20
degrees
of this day and night division darker than usual. The Sun illuminates
Titan
from the right at a phase angle of 66 degrees. Because the Sun is in
the
southern hemisphere as seen from Titan, the north pole is canted
relative
to the boundary between day and night by 25 degrees.

Also shown here is a map of relative surface brightness variations on
Titan
as measured in images taken in the 1080-nanometer spectral region in
1997
and 1998 by the Near Infrared Camera and Multi-Object Spectrometer on
NASA?s Hubble Space Telescope. These images have scales of 300
kilometers
(186 miles) per pixel. The map colors indicate different surface
reflectivities. From darkest to brightest, the color progression is:
deep
blue (darkest), light blue, green, yellow, red and deep red
(brightest).
The large, continent-sized, red feature extending from 60 degrees to
150
degrees west longitude is called Xanadu. It is unclear whether Xanadu
is a
mountain range, giant basin, smooth plain, or a combination of all
three.
It may be dotted with hydrocarbon lakes but that is also unknown. All
that
is presently known is that in Earth-based images, it is the brightest
region
on Titan.

A comparison between the Cassini images and the Hubble map indicates
that
Xanadu is visible as a bright region in the Cassini image on the
right. The
dark blue northwest-southeast trending feature from 210 degrees to 250
degrees
west longitude, and the bright yellow/green region to the east (right)
and
southeast of it at minus 50 degrees latitude and 180 to 230 degrees
west
longitude on the Hubble map, can both be seen in the image on the
left.

It is noteworthy that the surface is visible to Cassini from its
present
approach viewing geometry, which is not the most favourable for
surface
viewing. These early Cassini observations are promising for upcoming
imaging sequences of Titan in which the resolution improves by a
factor of
five over the next two months. These results are encouraging for
future,
in-orbit observations of Titan that will be acquired from lower, more
favorable phase angles.

The first opportunity to view small-scale features (2 kilometers or
1.2 miles)
on the surface comes during a 350,000 kilometer (217,500 mile) flyby
over
Titan's south pole on July 2, 2004, only 30 hours after Cassini's
insertion
into orbit around the ringed planet.

The Cassini-Huygens mission is a cooperative project of NASA, the
European
Space Agency and the Italian Space Agency. The Jet Propulsion
Laboratory, a
division of the California Institute of Technology in Pasadena,
manages the
Cassini-Huygens mission for NASA's Office of Space Science,
Washington, D.C.
The Cassini orbiter and its two onboard cameras, were designed,
developed and
assembled at JPL. The imaging team is based at the Space Science
Institute,
Boulder, Colo.

For more information about the Cassini-Huygens mission visit,

http://saturn.jpl.nasa.gov

and the Cassini imaging team home page,

http://ciclops.org .

Image Credit:
NASA/JPL/Space Science Institute