Category: Saturn

Intriguing features resembling drapes and kinks are visible in this Cassini view of Saturn’s thin F ring. Several distinct ringlets are present, in addition to the bright, knotted core of the ring.

The obvious structure in the ring and its strands has been caused by Prometheus, the inner F ring shepherd moon that recently swept past this region. (Prometheus is about 10 degrees ahead of the F ring material in this image). These types of features were first seen in images taken just after Cassini entered into orbit around Saturn. The gravitational interaction of Prometheus (102 kilometers, or 63 miles across) on the ring pulls material out the ring once every orbit (every 14.7 hours) as the moon gets close to the ring and its strands.

The image was taken with the Cassini spacecraft narrow-angle camera on Jan. 19, 2005, at a distance of approximately 1.9 million kilometers (1.2 million miles) from Saturn through a filter sensitive to polarized visible light. Resolution in the original image was 11 kilometers (7 miles) per pixel. The image was contrast-enhanced and magnified by a factor of two 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 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 team is based at the Space Science Institute, Boulder, Colo.

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

Original Source: NASA/JPL/SSI News Release

When the European Space Agency’s Huygens probe visited Saturn’s moon Titan last month, the probe parachuted through humid clouds. It photographed river channels and beaches and things that look like islands. Finally, descending through swirling fog, Huygens landed in mud.

To make a long story short, Titan is wet.

Christian Huygens wouldn’t have been a bit surprised. In 1698, three hundred years before the Huygens probe left Earth, the Dutch astronomer wrote these words:

“Since ’tis certain that Earth and Jupiter have their Water and Clouds, there is no reason why the other Planets should be without them. I can’t say that they are exactly of the same nature with our Water; but that they should be liquid their use requires, as their beauty does that they be clear. This Water of ours, in Jupiter or Saturn, would be frozen up instantly by reason of the vast distance of the Sun. Every Planet therefore must have its own Waters of such a temper not liable to Frost.”

Huygens discovered Titan in 1655, which is why the probe is named after him. In those days, Titan was just a pinprick of light in a telescope. Huygens could not see Titan’s clouds, pregnant with rain, or Titan’s hillsides, sculpted by rushing liquids, but he had a fine imagination.

Titan’s “water” is liquid methane, CH4, better known on Earth as natural gas. Regular Earth-water, H2O, would be frozen solid on Titan where the surface temperature is 290o F below zero. Methane, on the other hand, is a flowing liquid, of “a temper not liable to Frost.”

Jonathan Lunine, a professor at the University of Arizona, is a member of the Huygens mission science team. He and his colleagues believe that Huygens landed in the Titan-equivalent of Arizona, a mostly-dry area with brief but intense wet seasons.

“The river channels near the Huygens probe look empty now,” says Lunine, but liquids have been there recently, he believes. Little rocks strewn around the landing site are compelling: they’re smooth and round like river rocks on Earth, and “they sit in little depressions dug, apparently, by rushing fluids.”

The source of all this wetness might be rain. Titan’s atmosphere is “humid,” meaning rich in methane. No one knows how often it rains, “but when it does,” says Lunine, “the amount of vapor in the atmosphere is many times that in Earth’s atmosphere, so you could get very intense showers.”

And maybe rainbows, too. “The ingredients you need for a rainbow are sunlight and raindrops. Titan has both,” says atmospheric optics expert Les Cowley.

On Earth, rainbows form when sunlight bounces in and out of transparent water droplets. Each droplet acts like a prism, spreading light into the familiar spectrum of colors. On Titan, rainbows would form when sunlight bounces in and out of methane droplets, which, like water droplets, are transparent.

“Their beauty [requires] that they be clear….”

“A methane rainbow would be larger than a water rainbow,” notes Cowley, “with a primary radius of at least 49o for methane vs 42.5o for water. This is because the index of refraction of liquid methane (1.29) differs from that of water (1.33).” The order of colors, however, would be the same: blue on the inside and red on the outside, with an overall hint of orange caused by Titan’s orange sky.

One problem: Rainbows need direct sunlight, but Titan’s skies are very hazy. “Visible rainbows on Titan might be rare,” says Cowley. On the other hand, infrared rainbows might be common.

Atmospheric scientist Bob West of NASA’s Jet Propulsion Laboratory explains: “Titan’s atmosphere is mostly clear at infrared wavelengths. That’s why the Cassini spacecraft uses an infrared camera to photograph Titan.” Infrared sunbeams would have little trouble penetrating the murky air and making rainbows. The best way to see them: infrared “night vision” goggles.

All this talk of rain and rainbows and mud makes liquid methane sound a lot like ordinary water. It’s not. Consider the following:

The density of liquid methane is only about half the density of water. This is something, say, a boat builder on Titan would need to take into account. Boats float when they’re less dense than the liquid beneath them. A Titan-boat would need to be extra lightweight to float in a liquid methane sea. (It’s not as crazy as it sounds. Future explorers will want to visit Titan and boats could be a good way to get around.)

Liquid methane also has low viscosity (or “gooiness”) and low surface tension. See the table below. Surface tension is what gives water its rubbery skin and, on Earth, lets water bugs skitter across ponds. A water bug on Titan would promptly sink into a pond of flimsy methane. On the bright side, Titan’s low gravity, only one-seventh Earth gravity, might allow the creature climb back out again.

Back to boats: Propellers turning in methane would need to be extra-wide to “grab” enough of the thin fluid for propulsion. They’d also have to be made of special materials resistant to cracking at cryogenic temperatures.

And watch out for those waves! European scientists John Zarnecki and Nadeem Ghafoor have calculated what methane waves on Titan might be like: seven times taller than typical Earth-waves (mainly because of Titan’s low gravity) and three times slower, “giving surfers a wild ride,” says Ghafoor.

Last but not least, liquid methane is flammable. Titan doesn’t catch fire because the atmosphere contains so little oxygen–a key ingredient for combustion. If explorers visit Titan one day they’ll have to be careful with their oxygen tanks and resist the urge to douse fires with “water.”

Infrared rainbows, towering waves, seas beckoning to sailors. Huygens saw none of these things before it plopped down in the mud. Do they really exist?

“…there is no reason why the other Planets should be without them.”

Original Source: Science@NASA

Using an innovative camera on NASA’s Cassini spacecraft, scientists have captured images of a radiation belt inside the rings of Saturn and have the clearest picture yet of the planet’s giant magnetosphere, according to a mid-year report of the spacecraft published today in the journal Science.

The Cassini spacecraft entered Saturn’s orbit in July 2004, kicking off a four-year study of the sixth planet from the sun. Among the 12 science instruments on the spacecraft is the Magnetospheric Imaging Instrument (MIMI) — developed by the Johns Hopkins University Applied Physics Laboratory (APL) — which scientists are using to study the energetic charged particle environment at Saturn and obtain images of the ringed planet’s magnetosphere.

“Every time we fly a new instrument in space, it reveals new vistas of whatever object we happen to be studying,” says Dr. Stamatios (Tom) Krimigis, principal investigator for the MIMI experiment, of APL.

This time, says Krimigis, the MIMI instrument has enabled scientists to “visualize the invisible” — to “see” the plasma and radiation belts in Saturn’s environment in an image; to discover that the belts are more intense on the night-side of the planet; that there is an unexpected radiation belt inward of the “D” ring, the fourth major ring closest to the tenuous upper atmosphere of the planet; and that there is a virtual soup of ions that derive from the dissociation of water, most likely due to radiation impacting the rings.

These images were captured during Saturn orbit insertion with MIMI’s Ion and Neutral Camera (INCA), which measures the three-dimensional distribution, velocities and rough composition of magnetospheric and interplanetary ions for regions in which the energetic ion fluxes are very low. It also provides a global view of the energetic neutral emission of hot plasmas in the Saturnian magnetosphere, measuring the composition and velocities of those energetic neutrals for each image pixel.

“By detecting various energetic particles and discriminating among them according to energy and mass, the camera is able to obtain remote images of the global distribution of these particles,” says Dr. Donald Mitchell of APL, who leads the camera science team.

“Using INCA, we also discovered a radiation belt in a place where no spacecraft can go — inside the planet’s rings,” says APL’s Dr. Ed Roelof, a coinvestigator on the MIMI team. “We never knew this belt existed, but we saw it and were able to determine some of its properties and characteristics.”

The properties of the main radiation belts are perhaps among the more significant of the findings, says Dr. Doug Hamilton of the University of Maryland , College Park, who led the instrument team measuring the composition. “It’s comprised mostly of oxygen and water products,” he says. “That is most likely the result of the bombardment of the planet’s rings and the icy moons by the radiation trapped in Saturn’s magnetic field. And by this bombardment, the water is released and it becomes charged.”

According to Krimigis, the ability to visualize a planet’s magnetosphere will enable scientists to better monitor space weather. “This will benefit science and, in the case of Earth, may lead to space weather forecasts that will give advance warning of electromagnetic storms, which in the past have disrupted communications and crippled electrical power grids.”

In addition to Krimigis, Mitchell and Roelof, research team members at APL and co-authors on the Science paper, “Dynamics of Saturn’s Magnetosphere from MIMI During Cassini’s Orbital Insertion,” include Stefano Livi, Barry Mauk, Christopher Paranicas, Pontus Brandt, Andrew Cheng, Teck Choo, John Hayes, Stephen Jaskulek, Edwin Keath, Martha Kusterer, David LaVallee, Richard McEntire, Joachim Saur, Franklin Turner and Donald Williams.

The Cassini-Huygens mission is a cooperative project of NASA, ESA and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA. The MIMI team includes investigators and expertise from APL; the University of Maryland, College Park; University of Kansas, Lawrence; University of Arizona, Tucson; Bell Laboratories, Murray Hill, N.J.; the Max Planck Institute for Solar System Research, Lindau, Germany; and the Centre d’Etude Spatiale des Rayonnements in Toulouse, France.

Original Source: JHU News Release

Image credit: Hubble
Data from the Cassini-Huygens satellite showing oxygen ions in the atmosphere around Saturn’s rings suggests once again that molecular oxygen alone isn’t a reliable indicator of whether a planet can support life.

That and other data are outlined in two papers in the Feb. 25 issue of the journal Science co-authored by University of Michigan engineering professors Tamas Gombosi, J. Hunter Waite and Kenneth Hansen; and T.E. Cravens from the University of Kansas. The papers belong to a series of publications on data collected by Cassini as it passed through the rings of Saturn on July 1.

Molecular oxygen forms when two oxygen atoms bond together and is known in chemical shorthand as O2. On Earth, it is a continual byproduct of plant respiration, and animals need this oxygen for life. But in Saturn’s atmosphere, molecular oxygen was created without life present, through a chemical reaction with the sun’s radiation and icy particles that comprise Saturn’s rings.

“That means you don’t need biology to produce an O2 atmosphere,” Waite said. “If we want indicators to use in the search for life on other planets, we need to know what to look for. But oxygen alone isn’t it.”

Because Saturn’s rings are made of water ice, one would expect to find atoms derived from water, such as atomic oxygen (one atom) rather than O2, Waite said. However, the paper, called “Oxygen Ions Observed Near Saturn’s A Ring,” suggests the formation of molecular oxygen atmospheres happens more often in the outer solar system than expected. There is earlier evidence of molecular oxygen atmospheres elsewhere in the solar system?for instance above the icy Galilean moons of Jupiter?he said.

Four U-M College of Engineering faculty members are involved in the Cassini mission to explore Saturn’s rings and some of its moons. Waite leads the team operating the ion and neutral mass spectrometer, the instrument that detected and measured the molecular oxygen ions. Other team members are J.G. Luhmann of the University of California, Berkeley; R.V. Yelle, of the University of Arizona, Tuscon; W.T. Kasprzak, of the Goddard Space Flight Center; R.L. McNutt of Johns Hopkins University; and W.H. Ip, of the National Central University, Taiwan.

A second, viewpoint paper called, “Saturn’s Variable Magnetosphere,” by Hansen and Gombosi, who is chair of the College of Engineering’s department of Atmospheric, Oceanic and Space Sciences, reviews key findings from the other Cassini teams, including new information that contradicts data gathered 25 years ago, when the space craft Voyager passed by the planet.

Original Source: UMICH News Release

A large, bright and complex convective storm that appeared in Saturn’s southern hemisphere in mid-September 2004 was the key in solving a long-standing mystery about the ringed planet.

Saturn’s atmosphere and its rings are shown here in a false color composite made from Cassini images taken in near infrared light through filters that sense different amounts of methane gas. Portions of the atmosphere with a large abundance of methane above the clouds are red, indicating clouds that are deep in the atmosphere. Grey indicates high clouds, and brown indicates clouds at intermediate altitudes. The rings are bright blue because there is no methane gas between the ring particles and the camera.

The complex feature with arms and secondary extensions just above and to the right of center is called the Dragon Storm. It lies in a region of the southern hemisphere referred to as “storm alley” by imaging scientists because of the high level of storm activity observed there by Cassini in the last year.

The Dragon Storm was a powerful source of radio emissions during July and September of 2004. The radio waves from the storm resemble the short bursts of static generated by lightning on Earth. Cassini detected the bursts only when the storm was rising over the horizon on the night side of the planet as seen from the spacecraft; the bursts stopped when the storm moved into sunlight. This on/off pattern repeated for many Saturn rotations over a period of several weeks, and it was the clock-like repeatability that indicated the storm and the radio bursts are related. Scientists have concluded that the Dragon Storm is a giant thunderstorm whose precipitation generates electricity as it does on Earth. The storm may be deriving its energy from Saturn’s deep atmosphere.

One mystery is why the radio bursts start while the Dragon Storm is below the horizon on the night side and end when the storm is on the day side, still in full view of the Cassini spacecraft. A possible explanation is that the lightning source lies to the east of the visible cloud, perhaps because it is deeper where the currents are eastward relative to those at cloud top levels. If this were the case, the lightning source would come up over the night side horizon and would sink down below the day side horizon before the visible cloud. This would explain the timing of the visible storm relative to the radio bursts.

The Dragon Storm is of great interest for another reason. In examining images taken of Saturn’s atmosphere over many months, imaging scientists found that the Dragon Storm arose in the same part of Saturn’s atmosphere that had earlier produced large bright convective storms. In other words, the Dragon Storm appears to be a long-lived storm deep in the atmosphere that periodically flares up to produce dramatic bright white plumes which subside over time. One earlier sighting, in July 2004, was also associated with strong radio bursts. And another, observed in March 2004 and captured in a movie created from images of the atmosphere (http://photojournal.jpl.nasa.gov/catalog/PIA06082 and http://photojournal.jpl.nasa.gov/catalog/PIA06083) spawned three little dark oval storms that broke off from the arms of the main storm. Two of these subsequently merged with each other; the current to the north carried the third one off to the west, and Cassini lost track of it. Small dark storms like these generally get stretched out until they merge with the opposing currents to the north and south.

These little storms are the food that sustains the larger atmospheric features, including the larger ovals and the eastward and westward currents. If the little storms come from the giant thunderstorms, then together they form a food chain that harvests the energy of the deep atmosphere and helps maintain the powerful currents.

Cassini has many more chances to observe future flare-ups of the Dragon Storm, and others like it over the course of the mission. It is likely that scientists will come to solve the mystery of the radio bursts and observe storm creation and merging in the next 2 or 3 years.

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 team is based at the Space Science Institute, Boulder, Colo.

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

Original Source: NASA/JPL/SSI

On January 14, 2005, the ESA Huygens probe arrived at Saturn’s largest satellite, Titan. After a faultless descent through the dense atmosphere, it touched down on the icy surface of this strange world from where it continued to transmit precious data back to the Earth.

Several of the world’s large ground-based telescopes were also active during this exciting event, observing Titan before and near the Huygens encounter, within the framework of a dedicated campaign coordinated by the members of the Huygens Project Scientist Team. Indeed, large astronomical telescopes with state-of-the art adaptive optics systems allow scientists to image Titan’s disc in quite some detail. Moreover, ground-based observations are not restricted to the limited period of the fly-by of Cassini and landing of Huygens. They hence complement ideally the data gathered by this NASA/ESA mission, further optimising the overall scientific return.

A group of astronomers [1] observed Titan with ESO’s Very Large Telescope (VLT) at the Paranal Observatory (Chile) during the nights from 14 to 16 January, by means of the adaptive optics NAOS/CONICA instrument mounted on the 8.2-m Yepun telescope [2]. The observations were carried out in several modes, resulting in a series of fine images and detailed spectra of this mysterious moon. They complement earlier VLT observations of Titan, cf. ESO Press Photos 08/04 and ESO Press Release 09/04.

The new images show Titan’s atmosphere and surface at various near-infrared spectral bands. The surface of Titan’s trailing side is visible in images taken through narrow-band filters at wavelengths 1.28, 1.6 and 2.0 microns. They correspond to the so-called “methane windows” which allow to peer all the way through the lower Titan atmosphere to the surface. On the other hand, Titan’s atmosphere is visible through filters centred in the wings of these methane bands, e.g. at 2.12 and 2.17 microns.

Eric Gendron of the Paris Observatory in France and leader of the team, is extremely pleased: “We believe that some of these images are the highest-contrast images of Titan ever taken with any ground-based or earth-orbiting telescope.”

The excellent images of Titan’s surface show the location of the Huygens landing site in much detail. In particular, those centred at wavelength 1.6 micron and obtained with the Simultaneous Differential Imager (SDI) on NACO [4] provide the highest contrast and best views. This is firstly because the filters match the 1.6 micron methane window most accurately. Secondly, it is possible to get an even clearer view of the surface by subtracting accurately the simultaneously recorded images of the atmospheric haze, taken at wavelength 1.625 micron.

The images show the great complexity of Titan’s trailing side, which was earlier thought to be very dark. However, it is now obvious that bright and dark regions cover the field of these images.

The best resolution achieved on the surface features is about 0.039 arcsec, corresponding to 200 km on Titan. ESO PR Photo 04c/04 illustrates the striking agreement between the NACO/SDI image taken with the VLT from the ground and the ISS/Cassini map.

The images of Titan’s atmosphere at 2.12 microns show a still-bright south pole with an additional atmospheric bright feature, which may be clouds or some other meteorological phenomena. The astronomers have followed it since 2002 with NACO and notice that it seems to be fading with time. At 2.17 microns, this feature is not visible and the north-south asymmetry – also known as “Titan’s smile” – is clearly in favour in the north. The two filters probe different altitude levels and the images thus provide information about the extent and evolution of the north-south asymmetry.

Because the astronomers have also obtained spectroscopic data at different wavelengths, they will be able to recover useful information on the surface composition.

The Cassini/VIMS instrument explores Titan’s surface in the infrared range and, being so close to this moon, it obtains spectra with a much better spatial resolution than what is possible with Earth-based telescopes. However, with NACO at the VLT, the astronomers have the advantage of observing Titan with considerably higher spectral resolution, and thus to gain more detailed spectral information about the composition, etc. The observations therefore complement each other.

Once the composition of the surface at the location of the Huygens landing is known from the detailed analysis of the in-situ measurements, it should become possible to learn the nature of the surface features elsewhere on Titan by combining the Huygens results with more extended cartography from Cassini as well as from VLT observations to come.

Original Source: ESO News Release

Cassini-Huygens supplied new evidence about why Titan has an atmosphere, making it unique among all solar system moons, a University of Arizona planetary scientist says.

Scientists can infer from Cassini-Huygens results that Titan has ammonia, said Jonathan I. Lunine, an interdisciplinary scientist for the European Space Agency’s Huygens probe that landed on Titan last month.

“I think what’s clear from the data is that Titan has accreted or acquired significant amounts of ammonia, as well as water,” Lunine said. “If ammonia is present, it may be responsible for resurfacing significant parts of Titan.”

He predicts that Cassini instruments will find that Titan has a liquid ammonia-and-water layer beneath its hard, water-ice surface. Cassini will see — Cassini radar has likely already seen — places where liquid ammonia-and-water slurry erupted from extremely cold volcanoes and flowed across Titan’s landscape. Ammonia in the thick mixture released in this way, called “cryovolcanism,” could be the source of molecular nitrogen, the major gas in Titan’s atmosphere.

Lunine and five other Cassini scientists reported on the latest results from the Cassini-Huygens mission at the American Association for the Advancement of Science meeting in Washington, D.C. today (Feb. 19).

Cassini radar imaged a feature that resembles a basaltic flow on Earth when it made its first close pass by Titan in October 2004. Scientists believe that Titan has a rock core, surrounded by an overlying layer of rock-hard water ice. Ammonia in Titan’s volcanic fluid would lower the freezing point of water, lower the fluid’s density so it would be about as buoyant as water ice, and increase viscosity to about that of basalt, Lunine said. “The feature seen in the radar data suggests ammonia is at work on Titan in cryovolcanism.”

Both Cassini’s Ion Neutral Mass Spectrometer and Huygen’s Gas Chromatograph Mass Spectrometer (GCMS) sampled Titan’s atmosphere, covering the uppermost atmosphere down to the surface.

But neither detected the non-radiogenic form of argon, said Tobias Owen of the University of Hawaii, a Cassini interdisciplinary scientist and member of the GCMS science team. That suggests that the building blocks, or “planetesimals,” that formed Titan contained nitrogen mostly in the form of ammonia.

Titan’s eccentric, rather than circular, orbit can be explained by the moon’s subsurface liquid layer, Lunine said. Gabriel Tobie of the University of Nantes (France), Lunine and others will publish an article about it in a forthcoming issue of Icarus.

“One thing that Titan could not have done during its history is to have a liquid layer that then froze over, because during the freezing process, Titan’s rotation rate would have gone way, way up,” Lunine said. “So either Titan has never had a liquid layer in its interior — which is very hard to countenance, even for a pure water-ice object, because the energy of accretion would have melted water — or that liquid layer has been maintained up until today. And the only way you maintain that liquid layer to the present is have ammonia in the mixture.”

Cassini radar spotted a crater the size of Iowa when it flew within 1,577 kilometers (980 miles) of Titan on Tuesday, Feb. 15. “It’s exciting to see a remnant of an impact basin,” said Lunine, who discussed more new radar results that NASA released at an AAAS news briefing today. “Big impact craters on Earth are nice places for getting hydrothermal systems. Maybe Titan has a kind of analogous ‘methanothermal’ system,” he said.

Radar results that show few impact craters is consistent with very young surfaces. “That means Titan’s craters are either being obliterated by resurfacing, or they are being buried by organics,” Lunine said. “We don’t know which case it is.” Researchers believe that hydrocarbon particles that fill Titan’s hazy atmosphere fall from the sky and blanket the ground below. If this has occurred throughout Titan’s history, Titan would have “the biggest hydrocarbon reservoir of any of the solid bodies in the solar system,” Lunine noted.

In addition to the question about why Titan has an atmosphere, there are two other great questions about Saturn’s giant moon, Lunine added.

A second question is how much methane has been destroyed throughout Titan’s history, and where all that methane comes from. Earth-based and space-based observers have long known that Titan’s atmosphere contains methane, ethane, acetylene and many other hydrocarbon compounds. Sunlight irreversibly destroys methane in Titan’s upper atmosphere because the released hydrogen escapes Titan’s weak gravity, leaving ethane and other hydrocarbons behind.

When the Huygens probe warmed Titan’s damp surface where it landed, its instruments inhaled whiffs of methane. That is solid evidence that methane rain forms the complex network of narrow drainage channels running from brighter highlands to lower, flatter dark areas. Pictures from the UA-led Descent Imager-Spectral Radiometer experiment document Titan’s fluvial features.

The third question — one that Cassini was not really instrumented to answer — Lunine calls the “astrobiological” question. It is, given that liquid methane and its organic products rain down from Titan’s stratosphere, how far has organic chemistry progressed on Titan’s surface? The question is, Lunine said, “To what extent is any possible advanced chemistry at Titan’s surface at all relevant to prebiotic chemistry that presumably occurred on Earth prior to the time life began?”

The Cassini-Huygens mission is a collaboration between NASA, ESA and ASI, the Italian Space Agency. The Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology in Pasadena, is managing the mission for NASA’s Science Mission Directorate, Washington, D.C. JPL designed, developed and assembled the Cassini oribter while ESA operated the Huygens probe.

Original Source: University of Arizona News Release

This image was taken during Cassini’s first close approach to Enceladus.

The image was taken on February 17, 2005 in visible light with the narrow angle camera from a distance of approximately 10,750 kilometers (6,680 miles). Resolution in the image is 60 meters (197 feet) 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 Science Mission Directorate, 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: NASA/JPL/SSI Release

Scientists studying data from NASA’s Cassini spacecraft and Hubble Space Telescope have found that Saturn’s auroras behave differently than scientists have believed for the last 25 years.

The researchers, led by John Clarke of Boston University, found the planet’s auroras, long thought of as a cross between those of Earth and Jupiter, are fundamentally unlike those observed on either of the other two planets. The team analyzing Cassini data includes Dr. Frank Crary, a research scientist at Southwest Research Institute in San Antonio, Texas, and Dr. William Kurth, a research scientist at the University of Iowa, Iowa City.

Hubble snapped ultraviolet pictures of Saturn’s auroras over several weeks, while Cassini’s radio and plasma wave science instrument recorded the boost in radio emissions from the same regions, and the Cassini plasma spectrometer and magnetometer instruments measured the intensity of the aurora with the pressure of the solar wind. These sets of measurements were combined to yield the most accurate glimpse yet of Saturn’s auroras and the role of the solar wind in generating them. The results will be published in the February 17 issue of the journal Nature.

The findings show that Saturn’s auroras vary from day to day, as they do on Earth, moving around on some days and remaining stationary on others. But compared to Earth, where dramatic brightening of the auroras lasts only about 10 minutes, Saturn’s can last for days.

The observations also show that the Sun’s magnetic field and solar wind may play a much larger role in Saturn’s auroras than previously suspected. Hubble images show that auroras sometimes stay still as the planet rotates beneath, like on Earth, but also show that the auroras sometimes move along with Saturn as it spins on its axis, like on Jupiter. This difference suggests that Saturn’s auroras are driven in an unexpected manner by the Sun’s magnetic field and the solar wind, not by the direction of the solar wind’s magnetic field.

“Both Earth’s and Saturn’s auroras are driven by shock waves in the solar wind and induced electric fields,” said Crary. “One big surprise was that the magnetic field imbedded in the solar wind plays a smaller role at Saturn.”

At Earth, when the solar wind’s magnetic field points southward (opposite to the direction of the Earth’s magnetic field), the magnetic fields partially cancel out, and the magnetosphere is “open”. This lets the solar wind pressure and electric fields in, and allows them to have a strong effect on the aurora. If the solar wind’s magnetic field isn’t southward, the magnetosphere is “closed” and solar wind pressure and electric fields can’t get in. “Near Saturn, we saw a solar wind magnetic field that was never strongly north or south. The direction of the solar wind magnetic field didn’t have much effect on the aurora. Despite this, the solar wind pressure and electric field were still strongly affecting auroral activity,” added Crary. Seen from space, an aurora appears as a ring of energy circling a planet’s polar region. Auroral displays are spurred when charged particles in space interact with a planet’s magnetosphere and stream into the upper atmosphere. Collisions with atoms and molecules produce flashes of radiant energy in the form of light. Radio waves are generated by electrons as they fall toward the planet.

The team observed that even though Saturn’s auroras do share characteristics with the other planets, they are fundamentally unlike those on either Earth or Jupiter. When Saturn’s auroras become brighter and thus more powerful, the ring of energy encircling the pole shrinks in diameter. At Saturn, unlike either of the other two planets, auroras become brighter on the day-night boundary of the planet which is also where magnetic storms increase in intensity. At certain times, Saturn’s auroral ring is more like a spiral, its ends not connected as the magnetic storm circles the pole.

The new results do show some similarities between Saturn’s and Earth’s auroras: Radio waves appear to be tied to the brightest auroral spots. “We know that at Earth, similar radio waves come from bright auroral arcs, and the same appears to be true at Saturn,” said Kurth. “This similarity tells us that, on the smallest scales, the physics that generate these radio waves are just like what goes on at Earth, in spite of the differences in the location and behavior of the aurora.”

Now with Cassini in orbit around Saturn, the team will be able to take a more direct look at the how the planet’s auroras are generated. They will next probe how the Sun’s magnetic field may fuel Saturn’s auroras and learn more details about what role the solar wind may play. Understanding Saturn’s magnetosphere is one of the major science goals of the Cassini mission.

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

The Cassini-Huygens mission is a cooperative mission 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 Office of Space Science, Washington, D.C.

Original Source: NASA/JPL News Release

A giant impact crater the size of Iowa was spotted on Saturn’s moon Titan by NASA’s Cassini radar instrument during Tuesday’s Titan flyby.

Cassini flew within 1,577 kilometers (980 miles) of Titan’s surface and its radar instrument took detailed images of the surface. This is the third close Titan flyby of the mission, which began in July 2004, and only the second time the radar instrument has examined Titan. Scientists see some things that look familiar, along with scenes that are completely new.

The new radar images are available at: http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini.

“It’s reassuring to look at two parts of Titan and see similar things,” said Dr. Jonathan Lunine, Cassini interdisciplinary scientist from the University of Arizona, Tucson. “At the same time, there are new and strange things.”

This flyby is the first time that Cassini’s radar and the imaging camera overlapped. This overlap in coverage should be able to provide more information about the surface features than either technique alone. The 440-kilometer-wide (273-mile) crater identified by the radar instrument was seen before with Cassini’s imaging cameras, but not in this detail.

A second radar image released today shows features nicknamed “cat scratches”. These parallel linear features are intriguing, and may be formed by winds, like sand dunes, or by other geological processes.

On Thursday, Cassini will conduct its first close flyby of Saturn’s icy moon Enceladus (en-SELL-uh-duss) at a distance of approximately 1,180 kilometers (730 miles). Enceladus is one of the most reflective objects in the solar system, so bright that its surface resembles freshly fallen snow. 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 mission for NASA’s Science Mission Directorate, Washington, D.C. JPL designed, developed and assembled the Cassini orbiter.

Original Source: NASA/JPL News Release