Category: Saturn

Plumes of icy material extend above the polar region of Enceladus. Image credit: NASA/JPL/SSI Click to enlarge
Scientists have discovered geysers of liquid water streaming off Enceladus, one of Saturn’s moons, like a colder version of Yellowstone Hot Springs. Enceladus is one of the few objects in the Solar System that has volcanoes, joining the Earth, Io and possibly Neptune’s moon Triton. This occurrence of liquid water, right near the surface, raises the hopes that there could be life, like the ecosystems on Earth which exist around deep sea vents, using geothermal heat for energy.

NASA’s Cassini spacecraft may have found evidence of liquid water reservoirs that erupt in Yellowstone-like geysers on Saturn’s moon Enceladus. The rare occurrence of liquid water so near the surface raises many new questions about the mysterious moon.

“We realize that this is a radical conclusion — that we may have evidence for liquid water within a body so small and so cold,” said Dr. Carolyn Porco, Cassini imaging team leader at Space Science Institute, Boulder, Colo. “However, if we are right, we have significantly broadened the diversity of solar system environments where we might possibly have conditions suitable for living organisms.”

High-resolution Cassini images show icy jets and towering plumes ejecting large quantities of particles at high speed. Scientists examined several models to explain the process. They ruled out the idea that the particles are produced by or blown off the moon’s surface by vapor created when warm water ice converts to a gas. Instead, scientists have found evidence for a much more exciting possibility — the jets might be erupting from near-surface pockets of liquid water above 0 degrees Celsius (32 degrees Fahrenheit), like cold versions of the Old Faithful geyser in Yellowstone.

Mission scientists report these and other Enceladus findings in this week’s issue of Science.

“We previously knew of at most three places where active volcanism exists: Jupiter’s moon Io, Earth, and possibly Neptune’s moon Triton. Cassini changed all that, making Enceladus the latest member of this very exclusive club, and one of the most exciting places in the solar system,” said Dr. John Spencer, Cassini scientist, Southwest Research Institute, Boulder, Colo.

“Other moons in the solar system have liquid-water oceans covered by kilometers of icy crust,” said Dr. Andrew Ingersoll, imaging team member and atmospheric scientist at the California Institute of Technology, Pasadena, Calif. “What’s different here is that pockets of liquid water may be no more than tens of meters below the surface.”

Other unexplained oddities now make sense. “As Cassini approached Saturn, we discovered that the Saturnian system is filled with oxygen atoms. At the time we had no idea where the oxygen was coming from,” said Dr. Candy Hansen, Cassini scientist at NASA’s Jet Propulsion Laboratory in Pasadena. “Now we know that Enceladus is spewing out water molecules, which break down into oxygen and hydrogen.”

Scientists are also seeing variability at Enceladus. “Even when Cassini is not flying close to Enceladus, we can detect that the plume’s activity has been changing through its varying effects on the soup of electrically-charged particles that flow past the moon,” said Dr. Geraint H. Jones, Cassini scientist, magnetospheric imaging instrument, Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany.

Scientists still have many questions. Why is Enceladus currently so active? Are other sites on Enceladus active? Might this activity have been continuous enough over the moon’s history for life to have had a chance to take hold in the moon’s interior?

“Our search for liquid water has taken a new turn. The type of evidence for liquid water on Enceladus is very different from what we’ve seen at Jupiter’s moon Europa. On Europa the evidence from surface geological features points to an internal ocean. On Enceladus the evidence is direct observation of water vapor venting from sources close to the surface,” said Dr. Peter Thomas, Cassini imaging scientist, Cornell University, Ithaca, N.Y.

In the spring of 2008, scientists will get another chance to look at Enceladus when Cassini flies within 350 kilometers (approximately 220 miles), but much work remains after Cassini’s four-year prime mission is over.

“There’s no question that, along with the moon Titan, Enceladus should be a very high priority for us. Saturn has given us two exciting worlds to explore,” said Dr. Jonathan Lunine, Cassini interdisciplinary scientist, University of Arizona, Tucson, Ariz.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the Caltech, manages the mission for NASA’s Science Mission Directorate. The Cassini orbiter was designed, developed and assembled at JPL.

For images and more information, visit: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov.

Original Source: NASA News Release

Enceladus hanging against Saturn’s rings. Image credit: NASA/JPL/SSI Click to enlarge
This beautiful natural colour image shows Enceladus hanging in front of Saturn and its rings. This view of Saturn shows the terminator; the line across the planet that separates day from night. Cassini took separate images with its red, green, and blue filters, and then controllers combined the images together on computer. Cassini took this photograph on January 17, 2006 when it was 200,000 kilometers (125,000 miles) from Enceladus.

Enceladus hangs like a single bright pearl against the golden-brown canvas of Saturn and its icy rings. Visible on Saturn is the region where daylight gives way to dusk. Above, the rings throw thin shadows onto the planet.

Icy Enceladus is 505 kilometers (314 miles) across.

Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were taken using the Cassini spacecraft wide-angle camera on Jan. 17, 2006 at a distance of approximately 200,000 kilometers (100,000 miles) from Enceladus. The image scale is 10 kilometers (6 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 moon Iaptus. Image credit: NASA/JPL/SSI Click to enlarge
This view of Iapetus, one of Saturn’s moons, shows its terminator running from pole to pole. This is the line that separates night from day on the moon, and right along this line, the shadows are very long. This allows planetary geologists to see a tremendous amount of detail and measure the height of mountains and the depths of craters. Cassini took this photograph on January 22, 2006, when it was 1.3 million kilometers (800,000 miles) from Iapetus.

Sunlight strikes the terminator (the boundary between day and night) region on Saturn’s moon Iapetus at nearly horizontal angles, making visible the vertical relief of many features.

This view is centered on terrain in the southern hemisphere of Iapetus (1,468 kilometers, or 912 miles across). Lit terrain visible here is on the moon’s leading hemisphere. In this image, a large, central-peaked crater is notable at the boundary between the dark material in Cassini Regio and the brighter material on the trailing hemisphere.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Jan. 22, 2006, at a distance of approximately 1.3 million kilometers (800,000 miles) from Iapetus and at a Sun-Iapetus-spacecraft, or phase, angle of 67 degrees. Resolution in the original image was 8 kilometers (5 miles) per pixel. The image has been magnified by a factor of two and contrast-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 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 G ring. Image credit: NASA/JPL/SSI Click to enlarge
This Cassini photograph shows Saturn’s faint G ring, with its sharp inner edge and more diffuse outer boundary. When Cassini arrived at Saturn nearly two years ago, it flew directly through this ring, using its main antenna as a shield; a wise move as it was struck several times by icy particles. This image was taken on January 19, 2006 when Cassini was 1.2 million km (700,000 miles) from Saturn.

This contrast-enhanced view of Saturn’s faint G ring shows its extremely sharp inner edge and more diffuse outer boundary. Using its large high-gain antenna as a shield, the Cassini spacecraft flew through the region interior to the G ring during insertion into Saturn orbit. The spacecraft was struck many times by the fine icy particles that populate the region between the F and G rings.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Jan. 19, 2006, at a distance of approximately 1.2 million kilometers (700,000 miles) from Saturn. The image scale is 7 kilometers (4 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

Electron particles are flying away from Saturn’s polar region. Image credit: University of Cologne. Click to enlarge
Auroras on Earth happen when the solar wind interacts with our planet’s magnetic field; electrons are accelerated downwards into the atmosphere, and we see the pretty lights in the sky. On Saturn; however, this process also goes in reverse. Most electrons are accelerated down, but others go in the opposite direction, away from the planet.

Polar lights are fascinating to look at on Earth. On other planets, they can also be spectacular. Scientists from the Max Planck Institute for Solar System Research in Katlenberg, Lindau, Germany, have now observed Saturn’s polar region using the particle spectrometer MIMI, on the Cassini Space Probe. They discovered electrons not only being accelerated toward the planet, but also away from it (Nature, February 9, 2006).

We can see polar lights on Earth when electrons above the atmosphere are accelerated downwards. They light up when they hit the upper atmosphere. Some years ago, researchers discovered that electrons inside the polar region can also be accelerated away from the Earth – that is, “backwards”. These anti-planetary electrons do not cause the sky to light up, and scientists have been puzzled about how they originate.

Until now it has also been unclear whether anti-planetary electrons only occur on Earth. An international team led by Joachim Saur at the University of Cologne have now found electrons on Saturn that are accelerated “backwards” – that is, in an anti-planetary direction. These particles were measured using “Magnetospheric Imaging Instruments” (MIMI) on NASA’s Cassini Space Probe. One of these instruments’ sensors, the “Low Energy Magnetospheric Measurement System” (LEMMS), was developed and built by scientists at the Max Planck Institute for Solar System Research.

The rotation of the space probe helped the researchers to determine the direction, number, and strength of the electron rays. They compared these results with recordings of the polar region and a global model of Saturn’s magnetic field. It turned out that the region of polar light matched up very well with the lowest point of the magnetic field lines in which electron rays were measured.

Because the electron ray is strongly focussed (with an angle of beam spread less than 10 degrees), the scientists were able to determine where its source lies: somewhere above the polar region, but inside a distance of maximum five radii of Saturn. Because the electron rays measured on the Earth, Jupiter, and Saturn are so similar, it appears that there must be some fundamental process underlying the creation of polar lights.

Doing these measurements, Norbert Krupp and his colleagues Andreas Lagg and Elias Roussos from the Max Planck Institute for Solar System Research worked closely with scientists from the Institute for Geophysics and Meteorology at the University of Cologne and the Applied Physics Laboratory of Johns Hopkins University in Baltimore. US scientists led by Tom Krimigis are responsible for service and coordination of the instrument on the Cassini Space Probe.

Original Source: Max Planck Society

Cassini view of Titan’s hazy atmosphere. Image credit: NASA/JPL. Click to enlarge.
Titan is unique in the Solar System with its methane rich atmosphere. But where does all this methane come from? Scientists analyzing data returned by ESA’s Huygens probe think it’s being replenished by a layer of methane ice underneath the surface. They believe this crust of methane is floating on top of an ocean of liquid water mixed with ammonia. This ongoing out gassing of methane probably peaked hundreds of millions of years ago, and now it’s on a slow, steady decline.

Data from ESA’s Huygens probe have been used to validate a new model of the evolution of Titan, Saturn’s largest moon, showing that its methane supply may be locked away in a kind of methane-rich ice.

The presence of methane in Titan’s atmosphere is one of the major enigmas that the NASA/ESA/ASI Cassini-Huygens mission is trying to solve.

Titan was revealed last year to have spectacular landscapes apparently carved by liquids. The Cassini-Huygens mission also showed that there is not after all a lot of liquid methane remaining on the moon’s surface, and so it is not clear where the atmospheric methane gas comes from.

Using the Cassini-Huygens findings, a model of Titan’s evolution, focusing on the source of Titan’s atmospheric methane, has been developed in a joint study by the University of Nantes, France, and the University of Arizona in Tucson, USA.

“This model is in agreement with the observations made so far by both the Huygens probe that landed on Titan on 14 January 2005 and the remote sensing instruments on board the Cassini spacecraft,” said Gabriel Tobie, of the Laboratoire de Planetologie et Geodynamique de Nantes, and lead author of an article in Nature.

There is a difference between volcanism on Earth and ‘cryovolcanism’ on Titan. Volcanoes on Titan would involve ice melting and ice degassing, which is analogous to silicate volcanism on Earth, but with different materials.

Methane, playing a role on Titan similar to water on Earth, would have been released during three episodes: a first one following the accretion and differentiation period, a second episode about 2000 million years ago when convection started in the silicate core and a geologically recent one (last 500 million years ago) due to enhanced cooling of the moon by solid-state convection in the outer crust.

This means that Titan’s methane supply may be stored in a kind of methane-rich ice. The scientists suggest that the ice, called a ‘clathrate hydrate’, forms a crust above an ocean of liquid water mixed with ammonia.

“As methane is broken down by light-induced chemical reactions over a timescale of tens of millions of years, it can’t just be a remnant of the atmosphere present when Titan itself was formed, and it must be replenished quite regularly,” said Tobie.

“According to our model, during the last outgassing episode, the dissociation of the methane clathrate and hence release of methane are induced by thermal anomalies within the icy crust, which are generated by crystallisation in the internal ocean,” said Tobie.

“As this crystallisation started only relatively recently (500 to 1000 million years ago), we expect that the ammonia-water ocean is still present few tens of kilometres below the surface and that methane outgassing is still operating. Even though the outgassing rate is expected to decline now (it peaked about 500 million years ago), release of methane through cryovolcanic eruptions should still occur on Titan,” explained Tobie.

“Parts of the clathrate crust might be warmed from time to time by ‘cryovolcanic’ activity on the moon, causing it to release its methane into the atmosphere. These outbursts could produce temporary flows of liquid methane on the surface, accounting for the river-like features seen on Titan’s surface.

“Cassini’s instruments, in particular its Visible and Infrared Mapping Spectrometer (VIMS), should detect an increasing number of cryovolcanic features and, if we are lucky, may eventually detect eruptions of methane,” added Tobie.

If they are right, say the researchers, then Cassini and future missions to Titan should also be able to detect the existence of their possible subsurface liquid water-ammonia ocean.

Later in the mission, Cassini itself will make measurements that will confirm (or not) the presence of the internal water ocean, and also the existence of a rocky core.

Original Source: ESA News Release

Mimas captured against its parent planet Saturn. Image credit: NASA/JPL/SSI Click to enlarge
A small and battered reminder of the solar system’s violent youth, the ice moon Mimas hurtles around its gas giant parent, Saturn. At 397 kilometers (247 miles) across, Mimas is simply dwarfed by the immensity of Saturn. The planet is more than 150 times as wide as the moon.

Mimas is seen here against the night side of Saturn. The planet is faintly lit by sunlight reflecting off its rings.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Jan. 20, 2006, at a distance of approximately 1.4 million kilometers (900,000 miles) from Mimas and at a Sun-Mimas-spacecraft, or phase, angle of 145 degrees. Image scale is 9 kilometers (5 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 moon Enceladus. Image credit: NASA/JPL/SSI Click to enlarge
A false color look reveals subtle details on Enceladus that are not visible in natural color views.

The now-familiar bluish appearance (in false color views) of the southern “tiger stripe” features and other relatively youthful fractures is almost certainly attributable to larger grain sizes of relatively pure ice, compared to most surface materials.

On the “tiger stripes,” this coarse-grained ice is seen in the colored deposits flanking the fractures as well as inside the fractures. On older fractures on other areas of Enceladus, the blue ice mostly occurs on the exposed wall scarps.

The color difference across the moon’s surface (a subtle gradation from upper left to lower right) could indicate broad-scale compositional differences across the moon’s surface. It is also possible that the gradation in color is due to differences in the way the brightness of Enceladus changes toward the limb, a characteristic which is highly dependent on wavelength and viewing geometry.

See PIA07709 for a monochrome version of this view.

Terrain on the trailing hemisphere of Enceladus (505 kilometers, or 314 miles across) is seen here. North is up.

The view was created by combining images taken using ultraviolet, green and infrared spectral filters, and then was processed to accentuate subtle color differences. The images were taken with the Cassini spacecraft narrow-angle camera on Jan. 17, 2006 at a distance of approximately 153,000 kilometers (95,000 miles) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 29 degrees. Image scale is 912 meters (2,994 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 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 northern hemisphere. Image credit: NASA/JPL/SSI Click to enlarge
After a year and a half in orbit, the Cassini spacecraft has begun to image Saturn’s northern hemisphere in detail. The northern latitudes currently are experiencing winter, and atmospheric scientists are interested in determining whether the winter hemisphere is systematically different in appearance than the sunnier southern hemisphere.

This scene contains a great deal of bright, whorl-shaped cloud activity.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Jan. 6, 2006, at a distance of approximately 2.9 million kilometers (1.8 million miles) from Saturn. The image scale is 17 kilometers (11 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

The two moons Titan and Tethys with its great crater Odysseus. Image credit: NASA/JPL/SSI Click to enlarge
Cassini looks toward Tethys and its great crater Odysseus, while at the same time capturing veiled Titan in the distance (at left).

Titan (5,150 kilometers, or 3,200 miles across) is shrouded in a thick, smog-like atmosphere in which many small, potential impactors burn up before hitting the moon’s surface. Crater-pocked Tethys (1,071 kilometers, or 665 miles across) has no such protective layer, although even a thick blanket of atmosphere would have done little good against the impactor that created Odysseus.

The eastern limb of Tethys is overexposed in this view.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Jan. 6, 2006, at a distance of approximately 4 million kilometers (2.5 million miles) from Titan and 2.7 million kilometers (1.7 million miles) from Tethys. The image scale is 25 kilometers (16 miles) per pixel on Titan and 16 kilometers (10 miles) per pixel on Tethys.

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