Category: Saturn

Despite the views of Titan?s surface that Cassini is able to provide, the moon remains inscrutable to the human eye. In true color images that are taken in the visible wavelengths, Titan?s photochemical smog, rich in organic material, gives the moon a smooth featureless orange glow.

The Cassini orbiter carries specially-designed spectral filters that can pierce Titan?s veil. Its piggybacked Huygens probe will descend through the atmosphere in early 2005, giving an up-close-and-personal look at this mysterious orange moon.

Images taken with the narrow angle camera using red, green and blue spectral filters were combined to create this color view. The images were obtained at a Sun-Titan-spacecraft, or phase, angle of 67 degrees and from a distance of approximately 13.1 million kilometers (8.2 million miles) on June 10, 2004. Image scale is approximately 79 kilometers (49 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 Cassini-Huygens mission for NASA’s Office of Space Science, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colorado.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Original Source: CICLOPS News Release

On approach to Saturn, data obtained by the Cassini spacecraft are already posing a puzzling question: How long is the day on Saturn?

Cassini took readings of the day-length indicator regarded as most reliable, the rhythm of natural radio signals from the planet. The results give 10 hours, 45 minutes, 45 seconds (plus or minus 36 seconds) as the length of time it takes Saturn to complete each rotation. Here’s the puzzle: That is about 6 minutes, or one percent, longer than the radio rotational period measured by the Voyager 1 and Voyager 2 spacecraft, which flew by Saturn in 1980 and 1981.

Cassini scientists are not questioning Voyager’s careful measurements. And they definitely do not think the whole planet of Saturn is actually rotating that much slower than it did two decades ago. Instead, they are looking for an explanation based on some variability in how the rotation deep inside Saturn drives the radio pulse.

The radio sounds of Saturn’s rotation, which are also the first sounds from Saturn studied by Cassini, are like a heartbeat and can be heard by visiting http://www.jpl.nasa.gov/videos/cassini/0604/ and http://www-pw.physics.uiowa.edu/space-audio

“The rotational modulation of radio emissions from distant astronomical objects has long been used to provide very accurate measurements of their rotation period,” said Dr. Don Gurnett, principal investigator for the Cassini Radio and Plasma Wave Science instrument, University of Iowa, Iowa City. “The technique is particularly useful for the giant gas planets, such as Jupiter and Saturn, which have no surfaces and are covered by clouds that make direct visual measurements impossible.”

The first hint of something strange about that type of measurement at Saturn was in 1997, when a researcher from Observatoire de Paris reported that Saturn’s radio rotation period differed substantially from Voyager.

Dr. Michael D. Desch, Cassini Radio Plasma Wave Science team member, and scientist at NASA?s Goddard Space Flight Center in Greenbelt, Md., has analyzed Saturn radio data collected by Cassini from April 29, 2003, to June 10, 2004. “We all agree that the radio rotation period of Saturn is longer today than it was in during the Voyager flyby in 1980,” he said.

Gurnett said, “Although Saturn’s radio rotation period has clearly shifted substantially since the Voyager measurements, I don?t think any of us could conceive of any process that would cause the rotation of the entire planet to actually slow down. So it appears that there is some kind of slippage between the deep interior of the planet and the magnetic field, which controls the charged particles responsible for the radio emission.” He suggests the solution may be tied to the fact that Saturn’s rotational axis is nearly identical to its magnetic axis. Jupiter, with a more substantial difference between its magnetic axis and its rotational axis, shows no comparable irregularities in its radio rotation period.

“This finding is very significant. It demonstrates that the idea of a rigidly rotating magnetic field is wrong,” said Dr. Alex Dessler, a senior research scientist at the University of Arizona, Tucson. In that way, the magnetic fields of gas giant planets may resemble that of the Sun. The Sun?s magnetic field does not rotate uniformly. Instead, its rotation period varies with latitude. “Saturn’s magnetic field has more in common with the Sun than the Earth. The measurement can be interpreted as showing that the part of Saturn?s magnetic field that controls the radio emissions has moved to a higher latitude during the last two decades,” said Dressler.

“I think we will be able to unravel the puzzle, but it’s going to take some time,” said Gurnett. ?With Cassini in orbit around Saturn for four years or more, we will be in an excellent position to monitor long-term variations in the radio period, as well as investigate the rotational period using other techniques.”

Cassini, carrying 12 scientific instruments, is just two days from its planetary rendezvous with Saturn. On June 30 it will become the first spacecraft to orbit Saturn, when it begins a four-year study of the planet, its rings and its 31 known moons. The spacecraft recently flew past Saturn?s cratered moon Phoebe, where it captured spectacular images as well as data on its mass and composition.

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. JPL designed, developed and assembled the Cassini orbiter.

For the latest images and more information about the Cassini-Huygens mission, visit http://www.nasa.gov/cassini .

Original Source: NASA/JPL News Release

The Cassini spacecraft has beamed back a new, more detailed image of smog-enshrouded Titan.

This view represents an improvement in resolution of nearly a factor of three over the previous Cassini image release about Titan. The observed brightness variations are real on scales of a hundred kilometers or less.

The image was obtained in the near-infrared (centered at 938 nanometers) through a polarizing filter. The combination was designed to reduce the obscuration by atmospheric haze. The haze is more transparant at 938 nm than it is at shorter wavelengths and light of 938 nm wavelength is not absorbed by methane gas in Titan’s atmosphere. Light at this wavelength consequently samples the surface, and the polarizer blocks out light scattered mainly by the haze. This is similar to the way a polarizer, put on the front of a lens of a hand-held camera, makes distant objects more clear on the Earth.

The superimposed coordinate system grid in the accompanying image at right illustrates the geographical regions of the moon that are illuminated and visible, as well as the orientation of Titan ? north is up and rotated 25 degrees to the left. The yellow curve marks the position of the boundary between day and night on Titan.

This image shows about one quarter of Titan’s surface, from 0 to 70 degrees West longitude, and just barely overlaps part of the surface shown in the previous Titan image release. Most of the visible surface in this image has not yet been shown in any Cassini image release.

The image was obtained with the narrow angle camera on June 14, 2004, at a phase, or Sun-Titan-spacecraft, angle of 61 degrees and at a distance of 10.4 million kilometers (6.5 million miles) from Titan. The image scale is 62 kilometers (39 miles) per pixel. The image was magnified by a factor of two using a linear interpolation scheme. No further processing to remove the effects of the overlying atmosphere has been performed.

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 imaging team is based at the Space Science Institute, Boulder, Colorado.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Like a woolly mammoth trapped in Arctic ice, Saturn’s small moon Phoebe may be a frozen artifact of a bygone era, some four billion years ago. The finding is suggested by new data from the Cassini spacecraft.

Cassini scientists reviewed data from the spacecraft’s June 11, 2004, flyby of the diminutive moon. They concluded Phoebe is likely a primordial mixture of ice, rock and carbon-containing compounds similar in many ways to material seen in Pluto and Neptune’s moon Triton. Scientists believe bodies like Phoebe were plentiful in the outer reaches of the solar system about four and a half billion years ago.

These icy planetesimals (small bodies) formed the building blocks of the outer solar system and some were incorporated into the giant planets Jupiter, Saturn, Uranus and Neptune. During this process, gravitational interactions ejected much of this material to distant orbits, joining a native population of similar bodies to form the Kuiper Belt.

“Phoebe apparently stayed behind, trapped in orbit about the young Saturn, waiting eons for its secrets to be revealed during its rendezvous with the Cassini spacecraft,” said Dr. Torrence Johnson, Cassini imaging team member at NASA’s Jet Propulsion Laboratory, Pasadena, Calif.

“All our evidence leads us to conclude, Phoebe’s surface is made of water ice, water-bearing minerals, carbon dioxide, possible clays and primitive organic chemicals in patches at different locations on the surface,” said Dr. Roger N. Clark, team member for the visual and infrared mapping spectrometer, U.S. Geological Survey in Denver. “We also see spectral signatures of materials we have not yet identified.” Cassini’s observations gave scientists the first detailed look at one of these primitive icy planetesimals.

Phoebe’s mass was determined from precise tracking of the spacecraft and optical navigation, combined with an accurate volume estimate from images. The measurements yield a density of about 1.6 grams per cubic centimeter (100 pounds per cubic foot), much lighter than most rocks, but heavier than pure ice at approximately 0.93 grams per cubic centimeter (58 pounds per cubic foot). This suggests a composition of ice and rock similar to Pluto and Triton.

Spectral measurements, light intensity as a function of color or wavelength, confirmed the presence of water ice previously detected by Earth-based telescopes. The measurements provided evidence for hydrated minerals on Phoebe’s surface, and detected carbon dioxide and solid hydrocarbons similar to those found in primitive meteorites.

“One intriguing result is the discovery of possible chemical similarities between the materials on Phoebe and those seen on comets,” said Dr. Robert H. Brown, team leader for the visible and infrared mapping spectrometer, University of Arizona, Tucson. Evidence that Phoebe might be chemically kin to comets strengthens the case that it is similar to Kuiper Belt Objects.

Measurements taken by the composite infrared spectrometer were used to generate temperature maps. The maps show the surface of Phoebe is very cold, only about 110 degrees above absolute zero (minus 163 degrees Celsius, or minus 261 degrees Fahrenheit). Even colder nighttime temperatures suggest a fluffy, porous surface layer.

“One of the first results from this map is the surface of Phoebe has been badly chewed up, probably by meteorite impacts,” said Dr. John Pearl, a Cassini co-investigator for the composite infrared spectrometer, at NASA’s Goddard Space Flight Center, Greenbelt, Md. “We are discovering Phoebe is a very complex object, with large variations in topography.”

Cassini also made radar observations of Phoebe’s enigmatic surface, making it the first spacecraft radar observations of an outer-planet moon. The results are consistent with the dirty, rocky, icy surface suggested by other observations.

“We have conducted our first analysis of an outer solar system resident akin to Kuiper Belt Objects,” said Dr. Dennis Matson, project scientist of the Cassini-Huygens mission at JPL. “In two short weeks, we have added more to what we know about Phoebe than we had learned about it since it was discovered 100 years ago. We did this by having multiple instruments conducting investigations all at one time during our flyby.”

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL manages the mission for NASA’s Office of Space Science, Washington. For the latest images and more information about the mission on the Internet, visit http://www.nasa.gov and http://saturn.jpl.nasa.gov .

Original Source: NASA/JPL News Release

Image credit: NASA/JPL/Space Science Institute
This Cassini image hints at the split personality of Saturn?s 1436 kilometer (892 mile)-wide moon Iapetus. The Voyager spacecraft first imaged this curious yin/yang moon, with its light and dark hemispheres. The dark hemisphere is the side of Iapetus that leads in its orbit. In this view, both light and dark areas are visible.

The image was taken in visible light with the narrow angle camera on May 23, 2004, from a distance of 20.2 million kilometers (12.5 million miles) from Iapetus. The image scale is 12 kilometers (75 miles) per pixel. The image was magnified to aid visibility.

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 imaging team is based at the Space Science Institute, Boulder, Colorado.

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
Saturn?s bright equatorial band displays an exquisite swirl near the planet?s eastern limb. This image was taken with the narrow angle camera on May 18, 2004, from a distance of 23.4 million kilometers (14.5 million miles) from Saturn through a filter sensitive to absorption and scattering of sunlight by methane gas in the infrared (centered at 889 nanometers). The image scale is 139 kilometers (86 miles) per pixel. No contrast enhancement has been performed on this image.

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 imaging team is based at the Space Science Institute, Boulder, Colorado.

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
Cassini continues its vigil as Saturn?s atmosphere churns and morphs through time. Four large, dark spots, or storms, form a symmetrical pattern in the mid-southern latitudes as these features squeeze past each other. Further observations will show whether these storms merge or spawn new spots of their own. North of the features, some latitudinal bands exhibit a bumpy or scalloped pattern, probably indicative of planet-scale wave motions in the atmosphere.

The image was taken with the narrow angle camera on May 15, 2004, from a distance of 24.7 million kilometers (15.3 million miles) from Saturn through a filter centered at 750 nanometers. The image scale is 147 kilometers (91 miles) per pixel. Contrast in the image was enhanced to aid visibility.

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 imaging team is based at the Space Science Institute, Boulder, Colorado.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Original Source: CICLOPS News Release

Image credit: NASA/JPL/Space Science Institute
Cassini?s finely-tuned vision reveals hazes high in the skies over Titan in this narrow angle camera image from May 22, 2004. Here the northern hemisphere is notably brighter than the southern hemisphere. This trait was noticed in images returned by the Voyager spacecraft, but the effect is presently reversed, North to South, as Titan is currently experiencing opposite seasons from those during the Voyager epoch 23 years ago.

The image was taken from a distance of 21.7 million kilometers (13.5 million miles) from Saturn through a filter sensitive to strong absorption by methane gas (centered at 889 nanometers). The image scale is 129 kilometers (80 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 Cassini-Huygens mission for NASA’s Office of Space Science, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colorado.

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
Images collected during the Cassini-Huygens close fly-by of Saturn’s moon Phoebe give strong evidence that the tiny moon may be rich in ice and covered by a thin layer of darker material.

Its surface is heavily battered, with large and small craters. It might be an ancient remnant of the formation of the Solar System.

On Friday 11 June, at 21:56 CET, the Cassini-Huygens spacecraft flew by Saturn’s outermost moon Phoebe, coming within approximately 2070 kilometres of the satellite’s surface. All eleven on-board instruments scheduled to be active at that time worked flawlessly and acquired data.

The first high-resolution images show a scarred surface, covered with craters of all sizes and large variation of brightness across the surface.

Phoebe is a peculiar moon amongst the 31 known satellites orbiting Saturn. Most of Saturn’s moons are bright but Phoebe is very dark and reflects only 6% of the Sun’s light. Another difference is that Phoebe revolves around the planet on a rather elongated orbit and in a direction opposite to that of the other large moons (a motion known as ‘retrograde’ orbit).

All these hints suggested that Phoebe, rather than forming together with Saturn, was captured at a later stage. Scientists, however, do not know whether Phoebe was originally an asteroid or an object coming from the ‘Kuiper Belt’.

The stunning images obtained by Cassini’s high-resolution camera now seem to indicate that it contains ice-rich material and is covered by a thin layer of dark material, probably 300-500 metres thick.

Scientists base this hypothesis on the observation of bright streaks in the rims of the largest craters, bright rays radiating from smaller craters, grooves running continuously across the surface of the moon and, most importantly, the presence of layers of dark material at the top of crater walls.

“The imaging team is in hot debate at the moment on the interpretations of our findings,” said Dr Carolyn Porco, Cassini imaging team leader at the Space Science Institute in Boulder, USA.

“Based on our images, some of us are leaning towards the view that has been promoted recently, that Phoebe is probably ice-rich and may be an object originating in the outer solar system, more related to comets and Kuiper Belt objects than to asteroids.”

The high-resolution images of Phoebe show a world of dramatic landforms, with landslides and linear structures such as grooves, ridges and chains of pits. Craters are ubiquitous, with many smaller than one kilometre.

“This means, besides the big ones, lots of projectiles smaller than 100 metres must have hit Phoebe,” said Prof. Gerhard Neukum, Freie Universitaet Berlin, Germany, and a member of the imaging team. Whether these projectiles came from outside or within the Saturn system is debatable.

There is a suspicion that Phoebe, the largest of Saturn’s outer moons, might be parent to the other, much smaller retrograde outer moons that orbit Saturn. They could have resulted from the impact ejecta that formed the many craters on Phoebe.

Besides these stunning images, the instruments on board Cassini collected a wealth of other data, which will allow scientists to study the surface structures, determine the mass and composition of Phoebe and create a global map of it.

“If these additional data confirm that Phoebe is mostly ice, covered by layers of dust, this could mean that we are looking at a ‘leftover’ from the formation of the Solar System about 4600 million years ago,” said Dr Jean-Pierre Lebreton, ESA Huygens Project Scientist.

Phoebe might indeed be an icy wanderer from the distant outer reaches of the Solar System, which, like a comet, was dislodged from the Kuiper Belt and captured by Saturn when the planet was forming.

Whilst studying the nature of Phoebe may give scientists clues on the origin of the building blocks of the Solar System, more data are needed to reconstruct the history of our own neighbourhood in space.

With that aim, ESA’s Rosetta mission is on its way to study one of these primitive objects, Comet 67P/Churyumov-Gerasimenko, from close quarters for over a year and land a probe on it.

The fly-by of Phoebe on 11 June was the only one that Cassini-Huygens will perform with this mysterious moon. The mission will now take the spacecraft to its closest approach to Saturn on 1 July, when it will enter into orbit around the planet.

From there, it will conduct 76 orbits of Saturn over four years and execute 52 close encounters with seven other Saturnian moons. Of these, 45 will be with the largest and most interesting one, Titan. On 25 December, Cassini will release the Huygens probe, which will descend through Titan’s thick atmosphere to investigate its composition and complex organic chemistry.

Original Source: ESA News Release

Image credit: NASA/JPL/Space Science Institute
This eye-popping high-resolution image of Phoebe’s pitted surface taken very near closest approach shows a 13-kilometer (8-mile) diameter crater with a debris-covered floor. Part of another crater of similar size is visible at left, as is part of a larger crater at top and many scattered smaller craters. The radial streaks in the crater are due to downslope movements of loose fragments from impact ejecta. Also seen are boulders ranging from about 50 to 300 meters (160 to 990 feet) in diameter. The building-sized rocks may have been excavated by large impacts, perhaps from some other region of Phoebe rather than the craters seen here. There is no visible evidence for layering of ice and regolith or a hardened crust in this region, as on other parts of this moon.

Some of the relatively bright spots are from small impacts that excavated bright material from beneath the dark surface. Images like this provide information about impact and regolith processes on Phoebe.

This image was obtained at a phase, or Sun-Phoebe-spacecraft, angle of 78 degrees, and from a distance of 11,918 kilometers (7,407 miles). The image scale is approximately 18.5 meters (60.5 feet) per pixel. The illumination is from the right. No enhancement was performed on this image.

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 imaging team is based at the Space Science Institute, Boulder, Colorado.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Original Source: CICLOPS News Release