Io’s Volcanic Surface Captured in Full Motion

Note: animations are online at Keck Observatory

ALBUQUERQUE, New Mexico — The highest resolution infrared global
images ever taken of Jupiter’s volcanic moon, Io, are now available
from the W.M. Keck Observatory and UC Berkeley in a unique animated
movie and 3D Java applet. The images provide a complete survey of
Io’s surface during one full rotation and demonstrate the power of
adaptive optics, enabling astronomers to study phenomena from the
Earth that previously could be studied only from space.

“Adaptive optics technology is now able to produce eightfold
improvements in image quality beyond what has previously been
possible”, said Dr. Frederic H. Chaffee, director of the W. M. Keck
Observatory. “The Io 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, 1800 miles away.”

The Keck II 10-meter mirror telescope, with its adaptive optics
system, provides the highest resolution pictures ever taken from
an Earth-based telescope. The Keck images released today show a
similar level of detail to data taken by the NASA’s Galileo orbiter,
a spacecraft that came within 400,000 miles of Io’s surface. By
contrast, the Keck telescopes on Earth are more than 390 million
miles away (1000 times farther) from Io.

“Observations such as these are the only method by which we can
obtain complete spatial coverage of Io volcanic activity and at
resolutions better than what we find with the global Galileo data
for this wavelength range”, said Dr. David Le Mignant, W.M. Keck
Observatory.

The Io movie was produced from 14 pictures taken with the Keck
infrared camera (NIRC2) placed behind the adaptive optics system.
This camera is capable of producing images with a Strehl ratio of
up to 85 percent. Strehl is a measure of the corrected image and a
Strehl ratio of 100 percent equals a fully corrected, perfect image.
The quality of these images is so high, it’s as if the Keck
telescope were taking pictures from space.

The images of Io were taken at a wavelength of 3.5 microns (L-band)
and were spaced approximately 25 degrees apart in Ionian longitude
such that the entire surface of Io was recorded during a six-night
period in December 2001. The contrast and resolution of the images
were then increased by using a numerical process named Myopic
Iterative Step Preserving Restoration Algorithm (MISTRAL), a
deconvolution, or image enhancement, method developed for planetary
observations by the Office National d’Etudes et de Recherche
Aerospatiales (ONERA). Then, the images were converted to an
animation to show one full rotation of Io as it orbits Jupiter.
Finally, the W.M. Keck Observatory created a Java applet to add
interactive control and synchronous comparisons to pictures taken
at visible wavelengths with the Galileo orbiter.

Infrared wavelengths are important for understanding thermal
emissions associated with Ionian volcanic features. The infrared
wavelength of 2.2 microns (K-band) gives astronomers information
about reflected sunlight modulated by various surface features.
Infrared wavelengths at 3.5 microns (L band) give astronomers
information about thermal volcanic activity with the highest level
of contrast between hot magma and reflected sunlight.

“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. With the Galileo mission
ending, adaptive optics systems will be the only tools available
to study this exotic extra-terrestrial volcanism,” said Dr. Franck
Marchis of UC Berkeley.

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 Dr. David Le Mignant (W.M. Keck Observatory) and Dr.
Franck Marchis (UC Berkeley). Team members include S. Kwok,
P. Amico, R. Campbell, F. Chaffee, A. Conrad, A. Contos,
B. Goodrich, G. Hill, D. Sprayberry, P. Stomski, P. Wizinowich
(W.M. Keck Observatory) and Dr. I. de Pater (UC Berkeley).

This observational study of Io was partially supported by the
France-Berkeley Fund and by the National Science Foundation and
Technology Center for Adaptive Optics, managed by the University
of California at Santa Cruz under cooperative agreement No.
AST-9876783.

The W.M. Keck Observatory, located at the summit of Mauna Kea in
Hawaii, provides astronomers from associated institutions 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 systems,
which provide real-time correction to images affected by
atmospheric turbulences. The NIRC2 instrument was built at
Caltech by a team led by Keith Matthews. Funding for both
telescopes, the NIRC2 instrument, 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).

[NOTE: Images supporting this release are available at
http://www.astro.caltech.edu/mirror/keck/news/io.html ]