The images were assembled by University of California,
Berkeley, postdoctoral fellow Franck Marchis and converted
into an animated movie by a team at the W.M. Keck Observatory.
The movie shows Io during one full rotation, a period of
about one and three-quarters days.
"These new observations give important clues about the
temperature and composition of Io's volcanic structures
such as lava lakes, fire fountains, calderas and lava tubes,"
Marchis said. "With the Galileo mission ending, adaptive
optics systems will be the only tools available to study
this exotic extra-terrestrial volcanism."
"The volcanoes on the surface are always changing, so this
is an ideal way to continue to monitor Io's activity," added
colleague Imke de Pater, professor of astronomy at UC Berkeley.
She and Marchis regularly collect data on Io at several
different wavelengths to determine the temperature distribution
in Io's volcanoes and gather information about how the volcanoes
evolve and vary over time.
Constant monitoring can turn up surprises, such as the
enormous eruption in February 2001 of a relatively quiet
volcano, Surt, that de Pater and Marchis say was the most
energetic volcanic eruption ever seen in our solar system.
It was so bright that it outshone most of the moon's surface,
she said. Surt's last previous eruption was in 1996.
The success of Keck's adaptive optics system, consisting
of a wavefront sensor to detect the distortions caused by
atmospheric turbulence - stellar twinkling - and a deformable
mirror that adjusts several hundred times a second to remove
the distortion, proves its value for studying solar system
objects from Earth that, until now, have been hidden to
all but satellites and probes.
"Adaptive optics technology is now able to produce eight-fold
improvements in image quality beyond what has previously
been possible," said Frederic H. Chaffee, PhD, director
of the Observatory. "The Ionian images released today show
features on its surface as small as 60 to 120 miles across.
This is equivalent to being able to distinguish the two
headlights of a single car in St. Louis while looking at
them from Los Angeles, 1,800 miles away."
The movie of Io's full surface was produced from 14 pictures
taken with Keck's Near InfraRed Camera Two (NIRC2) placed
behind the adaptive optics system. The telescope is able
to get rid of the atmospheric distortion, producing high-quality
images as if the 10-meter Keck telescope were in space.
Marchis was able to boost detail in the pictures by using
an image enhancement process developed by the French Office
National d'Etudes et de Recherche Aerospatiales to enhance
planetary observations. Called MISTRAL (Myopic Iterative
Step Preserving Restoration Algorithm), the method improved
the contrast and resolution. The images were then converted
by a Keck team to an animation and a Java applet, which
gives interactive control with simultaneous comparisons
to close-up pictures taken at visible wavelengths by the
Though the movie images of Io were taken at a wavelength
of 3.5 microns (L-band), NIRC2 also obtained images at two
other wavelengths. Observations at the 2.2 micron infrared
wavelength (K -band) give astronomers information about
reflected sunlight modulated by various surface features.
The 3.5 micron infrared band (L-band) gives astronomers
information about thermal volcanic activity with the highest
level of contrast between hot magma and reflected sunlight.
The movie of Io's surface previewed this week is only the
starting point for UC Berkeley studies, de Pater emphasized.
She and Marchis will combine all the NIRC2 data to determine
the temperatures of Io's many volcanoes and infer the type
of activity at each.
Io's surface is pockmarked with volcanoes of varying activity,
interspersed with terrain covered by sulfur dioxide "frost"
at a temperature of about 120 Kelvin (-153ºC or -218ºF).
The project to image the surface of Io and demonstrate
the imaging performance of the Keck adaptive optics with
NIRC2 is being led jointly by Marchis and David Le Mignant,
PhD, of the observatory. Other Keck team members include
P. Amico, R. Campbell, A. Conrad, A. Contos, B. Goodrich,
G. Hill, S. Kwok, D. Sprayberry, P. Stomski and P. Wizinowich.
This observational study of Io was partially supported by
the France-Berkeley Fund and by UC Santa Cruz's Center for
Adaptive Optics, a National Science Foundation-funded Science
and Technology Center.
The observatory, located at the summit of Mauna Kea, provides
astronomers access to two 10-meter optical telescopes, the
world's largest. Each telescope features a revolutionary
primary mirror composed of 36 hexagonal segments that work
in concert as a single piece of reflective glass to provide
unprecedented power and precision. Both Keck telescopes
are equipped with adaptive optics. Funding for the telescopes
and the Keck II adaptive optics system was provided by the
W.M. Keck Foundation.
The observatory is operated by the California Association
for Research in Astronomy, a partnership of the California
Institute of Technology, the University of California, and
the National Aeronautics and Space Administration (NASA).