Category: Saturn

Saturn’s moon Rhea. Image credit: NASA/JPL/SSI Click to enlarge
Saturn’s moon Rhea is an alien ice world, but in this frame-filling view it is vaguely familiar. Here, Rhea’s cratered surface looks in some ways similar to our own Moon, or the planet Mercury. But make no mistake – Rhea’s icy exterior would quickly melt if this moon were brought as close to the Sun as Mercury. Rhea is 1,528 kilometers (949 miles) across.

Instead, Rhea preserves a record of impacts at its post in the outer solar system. The large impact crater at center left (near the terminator or boundary between day and night), called Izanagi, is just one of the numerous large impact basins on Rhea.

This view shows principally Rhea’s southern polar region, centered on 58 degrees South, 265 degrees West.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Aug. 1, 2005, at a distance of approximately 255,000 kilometers (158,000 miles) from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of 62 degrees. Image scale is 2 kilometers (1.2 miles) per pixel.

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 and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Infrared mapping of Saturn’s clouds by Cassini. Image credit: NASA/JPL/SSI Click to enlarge
Cassini scientists have discovered an unexpected menagerie of clouds lurking in the depths of Saturn’s complicated atmosphere.

“Unlike the hazy, broad, global bands of clouds regularly seen in Saturn’s upper atmosphere, many of the deeper clouds appear to be isolated, localized features,” said Dr. Kevin H. Baines, a member of the visual and infrared mapping spectrometer team from NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “They come in a large variety of sizes and shapes, including circular and oval shapes, donut shapes, and swirls.”

These clouds are deep in the atmosphere, about 30 kilometers (19 miles) underneath the upper clouds usually seen on Saturn. They also behave differently from those in the upper atmosphere and are made of different materials. They are made of either ammonium hydrosulfide or water, but not ammonia — generally thought to comprise the upper clouds.

Scientists are using the motions of these clouds to understand the dynamic weather of Saturn’s deep atmosphere and get a three-dimensional global circulation picture of Saturn. They have mapped low-altitude winds over nearly the entire planet. Comparing these winds to the winds at higher altitudes has led them to conclude that substantial wind shears exist at Saturn’s equator. These shears are similar to wind shear observed by Galileo at Jupiter, indicating that similar processes occur on both planets. The new wind speeds measured by the mapping spectrometer shows that winds blow about 275 kilometers per hour (170 miles per hour) faster deeper down than in the upper atmosphere.

Besides the donut-shaped and other localized cloud systems, dozens of planet girdling lanes of clouds also appear in the new images. Such lanes — known as “zones”– are commonly seen in the upper clouds of Saturn and the other large planets. However, these deeper-level lanes are surprisingly narrow and more plentiful than seen elsewhere, including the upper clouds of Saturn. They also have a much more thread-like structure than normally seen in Jupiter or Saturn’s upper atmosphere, with many of the thread-like structures and swirls connected to discrete cloud “cells,” which look like convective cells on Earth.

The visual and infrared mapping spectrometer took high-resolution, near-infrared images of the deep clouds during four close passes of Saturn between February and July of this year. The images were at a wavelength seven times greater than visible to the human eye and five times greater than available to the Cassini visual camera.

The scientists used a new technique that allowed them to image the deep clouds silhouetted against the background radiation of heat generated by the planet’s interior. Until now, imaging clouds in the depths of Saturn has not been practical since upper-level hazes and clouds obscure the view.

“Instead of using sunlight as the source of radiation for imaging the deep clouds residing underneath the obscuring layer of upper-level clouds, we developed a new technique that uses Saturn’s own thermal heat as a source of light,” said Baines. “It’s like looking down at a well-lit city from an aircraft at night, and seeing the black areas against the city lights, which tells you there is a cloud there blocking the light. Saturn emits its own radiant glow, which looks much like the glow of city lights at night.”

Tracking these thermally-backlit clouds for several days enabled the determination of wind speeds at the deepest levels ever measured on Saturn.

“Understanding cloud development in the depths of Saturn will sharpen our understanding of global circulation throughout Saturn and of the major planets,” said Baines.

These findings were presented in a news briefing at the 37th Annual Meeting of the Division for Planetary Sciences meeting held this week in Cambridge, England.

More information on the Cassini-Huygens mission is available at http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini .

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The visual and infrared mapping spectrometer team is based at the University of Arizona.

Original Source: NASA/JPL/SSI News Release

Saturn Rings. Image credit: NASA/JPL/SSI Click to enlarge
Cassini scientists today (5th September 2005) announced a host of fantastic new results from the spacecraft’s first season of prime ring viewing, including some unexpected findings on Saturn’s rings. These include new structures in Saturn’s diffuse rings, clumps and knots in the F ring – some of which may be small moons – and a completely unexpected spiral ring around the planet in the vicinity of the F ring.

The findings are illustrated in processed images and movies being released today and found at http://ciclops.org, http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini.

First in the line of new discoveries is that parts of the D ring (Saturn’s innermost ring) have relocated and dimmed. Images show one of the major discrete ring structures in the D ring has changed in brightness and moved inward towards Saturn by as much as 200 kilometres (124 miles). A change over the 25 years since the NASA Voyager spacecraft flybys indicates very short evolutionary lifetimes in the D ring and is of great interest to ring scientists who have been hoping that Cassini would yield information about ring ages and lifetimes.

Dr. Matt Hedman, an imaging team associate at Cornell University, Ithaca, N.Y. said, “I think our Cassini images of the D ring are providing new information about the dynamics and lifetimes of ring particles in a new regime, very close to the planet.”

The delicate G ring encircles the planet at about 170,000 kilometres (106,000 miles) from Saturn’s centre. Cassini scientists have now found a discontinuous bright ring segment, or ‘arc’, in this ring that bear at least a fleeting similarity to those imaged around Neptune in 1989 by NASA’s Voyager 2 spacecraft. Scientists think that long-lived arcs may be created or maintained by a nearby hidden moon. Another thought is that they formed as a result of a meteoroid impact.

Saturn’s tenuous D and G rings contain very little material, and the tiny, icy particles are the size of dust or smoke.

In examining the intriguing, knotted F ring, imaging team scientists have also discovered that the ghostly ringlets flanking the ring’s core are arranged into a spiral structure wound like a spring around the planet. Other spiralling structures seen in the main rings of Saturn, the density and bending waves, are initiated by the gravitational influence of an orbiting moon.

Density and bending waves move across the rings because of the way that relatively massive ring particles exert a gravitational influence on each other and can all move together. In contrast, the spiral structure contains very little mass and appears to originate from material somehow episodically ejected from the core of the F ring and then sheared out due to the different orbital speeds followed by the constituent particles.

“It is a big surprise to see a spiral arm in Saturn’s rings,” said Dr. Sebastien Charnoz, imaging team associate at the University of Paris. “It is very possible that the spiral is a consequence of moons crossing the F ring and spreading particles around, and may be telling us that the F ring might be a very unstable or even an ephemeral structure.”

In the same region, scientists continue to spot small, clump-like features that may be loosely-bound clumps of material or tiny moonlets. Some of them have been sighted for the better part of a year. The solid-or-not nature of these mysterious F ring objects may be determined by repeated sightings: moons will persist, while clumps are expected to dissipate with time.

“We have long suspected that small moons were hiding among the F ring’s strands and producing some of the structures that we see,” said Imaging Team Member Professor Carl Murray of Queen Mary, University of London. “But now the problem is that we are detecting objects that may be either solid moons controlling the ring, or just loose clumps of particles within the ring, and it’s hard to tell the difference. It is like trying to distinguish sheep dogs from sheep in a very large flock.”

A puzzling characteristic of at least two of the clumps/moons is that they appear to cross the F ring periodically. One of them, an object that was discovered last year (S/2004 S6), may be responsible for forming the spiral.

“If the orbit that we have computed for S/2004 S6 is correct, then it must periodically plow through the core of the F ring,” said Dr. Joseph Spitale, an imaging team associate at the Space Science Institute in Boulder, Colo. “The details of that interaction are not understood, but there probably are observable consequences, and maybe the F ring spiral is one of them.”

These ring results were acquired over the summer as Cassini was in a prime ring-viewing period where the spacecraft’s orbit was raised to look down on the rings. The discoveries began almost immediately, with the discovery in May of a tiny moonlet orbiting within the narrow Keeler Gap in Saturn’s outer A ring.

These and other results were presented in a press briefing at the 37th Annual Meeting of the Division for Planetary Sciences meeting held this week in Cambridge, England.

Original Source: PPARC News Release

Moon Pandora from outside Saturn’s F ring. Image credit: NASA/JPL/SSI Click to enlarge
From just outside the faint edge of Saturn’s F ring, the moon Pandora keeps watch over her fine grained flock. The outer flanks of the F ring region are populated by ice particles approaching the size of the particles comprising smoke. As a shepherd moon, Pandora helps her cohort Prometheus confine and shape the main F ring. Pandora is 84 kilometers (52 miles) across.
Prometheus is 102 kilometers (63 miles) wide and orbits interior to the F ring.

The small knot seen attached to the core is one of several that Cassini scientists are eyeing as they attempt to distinguish embedded moons from transient clumps of material.

The image was taken with the Cassini spacecraft narrow-angle camera on Aug. 2, 2005, using a filter sensitive to wavelengths of infrared light centered at 930 nanometers at a distance of approximately 610,000 kilometers (379,000 miles) from Pandora and at a Sun-Pandora-spacecraft, or phase, angle of 146 degrees. Image scale is 4 kilometers (2 miles) per pixel.

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 and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Saturn’s rings from their unlit side. Image credit: NASA/JPL/SSI Click to enlarge
This magnificent view looks down upon, and partially through, Saturn’s rings from their unlit side.
The densest part of the rings occults the bright globe of Saturn. Scientists can use observations like this to determine precisely the concentration of ring particles.

When the bright source is the signals coming from the spacecraft, the technique is called a ‘radio occultation.’ In a radio occultation measurement, a signal is beamed toward Earth from Cassini’s 4-meter-wide (13-foot) high-gain antenna. Researchers on Earth receive the signal as the spacecraft passes behind the rings. The reduction in Cassini’s radio signal tells researchers how densely packed the ring particles are. Scientists can also learn about the size distributions of the particles from occultations.

As an added (but tiny) bonus, Saturn’s moon Atlas (32 kilometers, or 20 miles across) is visible as a dark speck against the planet, just outside the A ring.

The image was taken in visible red light with the Cassini spacecraft wide-angle camera on Aug. 2, 2005, at a distance of approximately 617,000 kilometers (383,000 miles) from Saturn. The image scale is 37 kilometers (23 miles) per pixel.

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 and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Saturn’s rings. Image credit: NASA/JPL/SSI Click to enlarge
The extreme contrast in this view of the unlit side of Saturn’s rings is intentional. Contrast-enhanced views like this are used to look for spokes (the transient, ghostly lanes of dust seen in NASA Voyager and Hubble Space Telescope images), but so far, none have been seen by Cassini.

The apparent absence of spokes is thought to be related to the Sun’s elevation angle above the ringplane, which currently is rather high. As summer wanes in the southern hemisphere, the Sun’s angle will drop, and spoke viewing is expected to become more favorable.

In unlit-side views, the denser ring regions (and empty gaps) appear dark, while less populated and dustier ring regions appear bright.

The image was taken in visible light with the Cassini spacecraft wide-angle camera on Aug. 3, 2005, at a distance of approximately 781,000 kilometers (485,000 miles) from Saturn. The image scale is 43 kilometers (27 miles) per pixel.

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 and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Infrared mapping spectrometer image of Enceladus. Image credit: NASA/JPL/University of Arizona Click to enlarge
The Cassini spacecraft has discovered the long, cracked features dubbed “tiger stripes” on Saturn’s icy moon Enceladus are very young — between 10 and 1,000 years young.

These findings support previous results showing the moon’s southern pole is active. The pole had episodes of geologic activity as recently as 10 years ago. These cracked features are approximately 130 kilometers long (80 miles), spaced about 40 kilometers (25 miles) apart and run roughly parallel to one another.

The cracks act like vents. They spew vapor and fine ice water particles that have become ice crystals. This crystallization process can be dated, which helped scientists pin down the age of the features.

“There appears to be a continual supply of fresh, crystalline ice at the tiger stripes, which could have been very recently resurfaced,” said Dr. Bonnie Buratti. She is a team member of the Cassini visual and infrared mapping spectrometer at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “Enceladus is constantly evolving and getting a makeover.”

This finding is especially exciting because ground-based observers have seen tiny Enceladus brighten as its south pole was visible from Earth. Cassini allows scientists to see close up that the brightening is caused by geologic activity. When NASA’s Voyager 2 spacecraft flew over the moon’s north pole in 1981, it did not observe the tiger stripes.

Cassini’s visual and infrared mapping spectrometer shows water ice exists in two forms on Enceladus: in pristine, crystalline ice and radiation-damaged amorphous ice.

When ice comes out of the “hot” cracks, or “tiger stripes,” at the south pole, it forms as fresh, crystalline ice. As the ice near the poles remains cold and undisturbed, it ages and converts to amorphous ice. Since this process is believed to take place over decades or less, the tiger stripes must be very young.

“One of the most fascinating aspects of Enceladus is that it is so very small as icy moons go, but so very geophysically active. It’s hard for a body as small as Enceladus to hold onto the heat necessary to drive such large-scale geophysical phenomena, but it has done just that,” said Dr. Bob Brown. Brown is a team leader for the visual and infrared mapping spectrometer at the University of Arizona, Tucson. “Enceladus and its incredible geology is a marvelous puzzle for us to figure out.”

Adding to the already mounting evidence for an active body is the correlation of results from multiple instruments. Cassini’s cameras provided detailed images of the south polar cap, in which the tiger stripe fractures were found to be among the hottest features.

The timing of the craft’s ion and neutral mass spectrometer and the cosmic dust analyzer observations seems to indicate the vapor and fine material are originating from the “hot” polar cap region. These data also indicate the production of water vapor and ejection of fine material are connected, as they are in a comet. This suggests that vapor and dust-sized icy material are coming from the tiger stripes.

Enceladus is on a short list of bodies in our solar system where scientists have found internal activity. The others are the volcanoes on Jupiter’s moon Io and geysers on Neptune’s moon Triton.

Data for these measurements were taken during Cassini’s closest flyby on July 14, 2005. The spacecraft came within 175 kilometers (109 miles) of the surface of Enceladus. Enceladus is 500 kilometers (314 miles) across and has the most reflective surface in the solar system.

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.

For information about the Cassini-Huygens mission on the Web, visit http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov . For information about NASA and agency programs on the Web, visit http://www.nasa.gov/home/index.html .

Original Source: NASA News Release

Saturn’s moon Enceladus. Image credit: NASA/JPL/SSI Click to enlarge
Saturn’s moon Enceladus is only 505 kilometers (314 miles) across, small enough to fit within the length of the United Kingdom, as illustrated here. The intriguing icy moon also could fit comfortably within the states of Arizona or Colorado.

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 and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Moon Pan behind ring A. Image credit: NASA/JPL/SSI Click to enlarge
Cassini turns its gaze toward Saturn’s outer A ring to find the moon Pan coasting behind one of the thin ringlets which it shares with the Encke Gap. Pan is 26 kilometers (16 miles) across.
Understanding the influence of Saturn’s moons on its immense ring system is one of the goals of the Cassini mission. The study of the icy rings includes the delicate and smoky-looking F ring, seen here toward the upper right. The F ring exhibits bright kinks and multiple strands here.

Arching across the center of the scene, the outermost section of the A ring is notably brighter than the ring material interior to it.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Aug. 13, 2005, at a distance of approximately 2.3 million kilometers (1.5 million miles) from Saturn. The image scale is 14 kilometers (9 miles) per pixel on Pan.

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 and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Natural color view of Titan. Image credit: NASA/JPL/SSI Click to enlarge
As Cassini approached Titan on Aug. 21, 2005, it captured this natural color view of the moon’s orange, global smog. Titan’s hazy atmosphere was frustrating to NASA Voyager scientists during the first tantalizing Titan flybys 25 years ago, but now Titan’s surface is being revealed by Cassini with startling clarity (see Titan Mosaic — East of Xanadu ).
Images taken with the wide-angle camera using red, green and blue spectral filters were combined to create this color view. The images were acquired at a distance of approximately 213,000 kilometers (132,000 miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 55 degrees. Resolution in the image is about 13 kilometers (8 miles) per pixel.

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 and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Original Source: NASA/JPL/SSI News Release