Two views of Iapetus
Saturn's odd, two-toned, walnut-shaped moon, Iapetus,
has a ridge of surprisingly large mountains
— the so-called "belly-band" — that lies directly on top
of the equator. The moon also has a distinct difference in the brightness of
its leading and trailing hemispheres, one as bright as snow and the other dark
as tar. The ultraviolet-light image taken with UVIS (left) was taken during
a flyby in December 2004. A visible light image taken on the same date is shown
on the right for reference. The ultraviolet image indicates water
ice abundance across the surface: the bright north polar terrain (shown in red)
is the iciest region in this view. Away from the pole, as the color shifts to
blue, less water ice is present in the surface. The darkest terrain, which includes
very little water ice, is shown in light blue. The dark sky background viewed
during the observation is shown as purple in this color scheme.
will make its only close flyby of Iapetus on Sept. 10, 2007,
at about 1,640 kilometers (1,000 miles) from the surface which
will be 100 times closer than Cassini's 2004 encounter, and will
be the last time the spacecraft will aim its instruments at this
moon. The irregular shape, the mountain ridge and Iapetus' brightness
contrast are among the key mysteries scientists are trying to
NASA/JPL/University of Colorado/Space Science Institute (PIA09970)
|Hyperion's Icy Surface - July 4, 2007
In this ultraviolet image of Hyperion, produced using data taken
with UVIS during the September 2005 close flyby, brightness contrasts
are due to both topographic and compositional variations across
the surface. The brightest regions are exposed water ice in the
rim of the crater that dominates the hemisphere in view.
This new ultraviolet map (left) is shown next to a previously
released image (right) taken by the Imaging Science Subsystem.
Credit: NASA/JPL/University of Colorado/Space Science Institute
Mapping Clumps in Saturn's Rings - May 22, 2007
This false-color image of Saturn's main rings was made by
combining data from multiple star occultations using the Cassini
ultraviolet imaging spectrograph (UVIS).
During occultations, scientists observe the brightness of
a star as the rings pass in front of the star. This provides
a measurement of the amount of ring material between the spacecraft
and the star.
Cassini has given scientists the most detailed view yet of
Saturn's densely packed B ring. Cassini found that this part
of the rings is densely packed with clumps, called self-gravity
wakes, separated by nearly empty gaps. These clumps in Saturn's
B ring are neatly organized and constantly colliding, which
The clumps in Saturn's B ring, 30 to 50 meters (100 to 160
feet) across, are too small to be seen directly. However, scientists
can map the distribution, shape and orientation of the clumps.
Colors in this image indicate the orientation of clumps, and
brightness indicates the density of ring particles. The formation
of wakes is strongest in the bluer regions, where ring particles
clump together in tilted wakes. Particles in the central yellow
regions are too densely packed for any starlight to pass through.
Credit: NASA/JPL/ University of Colorado (PIA09210)
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 mission for NASA's Science Mission Directorate, Washington,
D.C. The Cassini orbiter was designed, developed and assembled
at JPL. The ultraviolet imaging spectrograph was designed
and built at, and the team is based at the University of
Amanda Hendrix: Rhea imaged in front of the
rings of Saturn
Rhea is imaged at UV wavelengths, with Saturn's rings in the
background, in these images from November 18, 2005. The two
images show the same geometry but use varying color schemes
to accentuate different wavelengths. The top image is a 3-color
UV image, where red represents Lyman-alpha (1216 Angstroms),
characterizing the background hydrogen. Blue and green represent
longer-wavelength FUV light, displaying reflected solar light
from the water-ice-rich surface. The lower (rainbow) image
highlights the reflected solar component, with increased brightness
near the sub-solar region in the south. A bright, fresh crater
on the right limb also is relatively reflective.
|NEW CASSINI IMAGES SHOW "NORTHERN LIGHTS" OF
New images of Saturn obtained by UVIS on June 21, 2005 show
auroral emissions at its poles similar to Earth's Northern
The two UV images, invisible to the human eye, are the first from the
Cassini-Huygens mission to capture the entire "oval" of the
auroral emissions at Saturn's south pole. They also show similar emissions
at Saturn's north pole, according to Larry Esposito, principal investigator
and Wayne Pryor.
In the false-color images, blue represents aurora emissions from hydrogen
gas excited by electron bombardment, while red-orange represents reflected
sunlight. The images show that the aurora lights at the polar regions
respond rapidly to changes in the solar wind, said the researchers. Previous
images have been taken closer to the equator, making it difficult to
see the polar regions.
Major changes in the emissions inside the Saturn south-pole aurora are
evident by comparing the two images, which were taken about one hour
apart, they said. The brightest spot in the left aurora fades, and a
bright spot appears in the middle of the aurora in the second image.
Made by slowly scanning the UVIS instrument across the planet, the images
also contain more than 2,000 wavelengths of spectral information within
each picture element. We will use the wavelength information to study
Saturn's auroras, gases, and hazes and their changing distributions.
Northern Lights - Aurora Borealis Information
| UVIS Detects and
atmosphere around Enceladus
Uploaded August 3, 2005
The Cassini Ultraviolet Imaging Spectrograph
(UVIS) has made the first direct detection of an atmosphere
around Saturn's moon Enceladus, first suggested by Cassini
magnetometer measurements. The UVIS observed the star Gamma
Orionis as Enceladus crossed in front of the star. The light
of the star dimmed as it was obscured by the atmosphere before
being blocked entirely by Enceladus. The spectrum of the starlight
changed as it passed through the atmosphere and indicates the
presence of water vapor in the atmosphere. UVIS results suggest
that the density of Enceladus's atmosphere is not globally
uniform and may be consistent with a greater amount of atmospheric
gas near the south polar region. The presence of water vapor
is more consistent with warm water ice than with sputtering
See full Press
Release on the JPL site
See story on
Planetary Society Site
| Two Images of
Saturn's 1) Non-organized Aurora; 2) Lyman-Alpha Absorption;
and 3) Haze Layer
Released March 10, 2005
Images from two Titan fly-bys are presented,
T-B (December 13, 2004) and T-3 (February 15, 2005). Both images
are of Titan.s atmosphere and show similar features, but with
minor differences. The four panels show Titan in different
ultraviolet wavelengths. The first panel, in the upper left,
is Titan in the Lyman-alpha (121.6 nanometers). The solid surface
of Titan is indicated by the white line. Lyman-alpha radiation,
from interstellar and solar hydrogen, is absorbed by the methane
in Titans atmosphere, as indicated by the dark region extending
from Titan's surface. The second frame, in the upper right,
is formed from the wavelength range that includes the Lyman-Birge-Hopfield
(LBH) band system of molecular Nitrogen. These emissions are
similar to Earth's aurora, but since Titan has no intrinsic
magnetic field to focus the precipitating electrons at the
poles, the 'non-organized aurora' extends over the entire moon.
The frame in the lower left is composed of incoming solar radiation
that is scattered by the haze in Titan's atmosphere. It appears
as a thin band as there is insufficient haze higher in the
atmosphere to scatter the light, and too much lower where it
absorbs all the light. The height of these haze layers agrees
with measurements made by UVIS during stellar occultations
in December and observations by the ISS. The final frame, in
the lower right, is a combination of the other three frames,
showing the spatial relation between the upper levels of Titan's
haze (blue), the extent of the thick methane atmosphere (red),
and the extent of the 'non-organized aurora' (green).
T-B (December 13, 2004)
T-3 (February 15, 2005)
Movie: Changes in the Saturn
Magneosphere's atomic oxygen emission during Saturn approach, December
2003 - June 2004. (click on image)
Note: A series of four images will loop three
Density Waves in Saturn's A Ring
Released November 9, 2004 - This false color image of two
density waves in Saturn's A ring was made from the stellar
occultation observed by Cassini's ultraviolet imaging spectrograph
when the spacecraft was 6.8 million kilometers (4.2 million
miles) from Saturn.
Bright areas indicate the denser regions of the rings. The bright
bands in the left part of the image are the "peaks" of
a density wave caused by gravitational stirring of the rings
by Saturn's moon, Janus. A smaller density wave in the right
half of the image is produced by the moon Pandora. The ultraviolet
imaging spectrograph observed the brightness of the star Xi Ceti
as the rings passed in front of it, and the flickering of the
starlight was converted into the ring density depicted by the
image. The image represents a distance of about 724 kilometers
(450 miles), and the smallest features are about one-half mile
Water Ice in the Rings:
The UV spectrum allows us to measure the composition of the
rings. These are color-enhanced images of the rings from the
UVIS observations during the Saturn orbit insertion event—when
Cassini entered Saturn's orbit after a nearly seven year journey—on
June 30th, 2004 (MST). The turquoise represents more water
ice in the rings. The red represents the most transparent (optically
thinnest) area in the rings.
Click on images to enlarge.
From the inside out,
the "Cassini division" in faint red at left is followed
by the A ring in its entirety. The A ring begins with a "dirty" interior
of red followed by a general pattern of more turquoise further
away from the planet, which indicates material made with more
ice. The red band roughly three-fourths of the way outward in
the A ring is known as the Encke gap.
This image shows the
outer C and inner B rings respectively from left to right, with
the inner B ring beginning a little more than halfway across
the image. The general pattern is from "dirty" red
particles to the denser ice shown in turquoise as the ringlets
Water Frost on Phoebe
Posted June 23, 2004 — On the right side of the graphic, an
ultraviolet image of Saturn's moon Phoebe, taken at a distance of 31,000
km, shows an irregular surface and bright crater region (white area).
The ultraviolet spectra confirm water frost on Phoebe's surface. The
image was taken by Cassini's ultraviolet imaging spectrograph during
the spacecraft's closest approach to Phoebe, on June 11, 2004. The
large crater shows clearly in the image on the left.
Click to Enlarge
Click on graphic for enlarged view
Cassini UVIS Observation of the
Saturn System in emission of the atomic hydrogen resonance line
The figure shows the distribution of atomic hydrogen emission in the Saturn
system obtained using the UVIS FUV imaging spectrometer experiment. The observations
provide the first spectral image from the Cassini Observatory Period. The
data was accumulated December 25, 2003 through January 6, 2004, at an average
range of 85 Mkm from Saturn. The image definitively establishes the distribution
of atomic hydrogen in the magnetosphere as a vast mass distributed asymmetrically
in local time. The (false) view shown in the image is from above the South
Pole with local west to the right. The sub-spacecraft point on Saturn was
20° S latitude and 62° solar phase angle. The sunlit atmosphere is
on the right side of the figure. The primary properties of the distribution
evident in the image are the extremely broad distribution in the orbital
plane measurable to at least 45 Saturn radii from planet to center (Rs),
and the extreme extent in latitude evidently significantly beyond 8 Rs above
and below the poles. The distributional asymmetry and increasing abundance
toward the planet is indicative of a source of energetic hydrogen at the
top of the Saturn atmosphere. The abundance shows a sharp shelf on the western
side at 25 Rs approximately at the location of the solar wind bow shock.
This may be an indication of a cold out-flowing hydrogen component from Titan.
In this view, there is no sign of the presence of an orbiting torus of hydrogen
gas. A complete determination of distribution will require observations from
different lines of sight, to be obtained later in the Saturn Tour. The signal
shows a peak at the south pole of the planet, generated by auroral precipitation.
A secondary peak appears from the dayglow in the sunlit atmosphere. The emission
from the magnetosphere is caused by fluorescence of solar radiation. The
pixel spatial resolution is 1.4 Rs in the east-west direction, and 2. Rs
(interpolated) in the north-south direction.
1 October 2000, the NASA/ESA Cassini spacecraft on its way to Saturn started observations of the planet Jupiter. The
first data from the Ultraviolet Imaging Spectrograph (UVIS) clearly showed the planet's aurora and a glowing ring of
gas ejected from Jupiter's moon Io. This donut of atoms is known as the Io torus.
The UVIS images show multiple overlapping exposures of this torus, each in the characteristic light emitted by sulfur and oxygen
atoms. All of these emissions are invisible to the naked eye and can only be seen in the ultraviolet light that
the CU telescopes detect. We see the entire donut of glowing gas in all its invisible colors.
One Day in the Life of Jupiter's Io Torus.
The above image is the sum of extreme ultraviolet images taken on Tuesday, 14 November 2000, when Cassini was 27 million
miles (or 618 Jupite radii) from Jupiter. The Cassini spacecraft stared at Jupiter for an entire rotation of its atmosphere, that is, one Jupiter "day." Each
vertical line shows one type of ionized atom in the Io plasma torus. Shorter wavelengths are on the left and longer on the right. The
strongest signals (white) are seen in emissions from ionized oxygen and sulfur atoms. The Jupiter auroral emissions
from molecular hydrogen form a central horizontal band on the right; they are dense enough to appear as a structured continuum.
Here to play a movie of the Io torus as observed on 11 November 2000. Because the atoms giving off the light are trapped by Jupiter's
tilted magnetic field, the torus wobbles back and forth during the course of a Jupiter day.
Here to play a movie summing observations of the Io torus during five Jupiter days (10-14 November 2000).
[NOTE: QuickTime 4 is needed to play these movies. Click
Here for your free QuickTime Player].
In the first two months of observing Jupiter, we saw the Jupiter system significantly larger, with clear brightness
variations. The aurora brightness changed daily. A brightness asymmetry was also persistent in our pictures: the sunset
(top) portion of the torus was brighter than the sunrise (bottom) portion.
Through March 22, UVIS continued to observe Jupiter, the Io torus, and Jupiter's moons and aurora as the Cassini spacecraft sped
toward Saturn. It will arrive at Saturn on 1 July 2004, drop a European-built probe to land on Saturn's moon
Titan, and observe Saturn and its moons and rings from orbit for at least 4 years.
The Cassini Ultraviolet Imaging Spectrograph Investigation, accepted for publication in Space
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 mission for NASA's Science
Mission Directorate, Washington, D.C. The Cassini orbiter was designed,
developed and assembled at JPL. The ultraviolet imaging spectrograph
was designed and built at, and the team is based at the University
of Colorado, Boulder.