Close views of the southern polar region, where jets of water vapor and icy particles spew from vents within the moon’s distinctive “tiger stripe” fractures, provide surprising evidence of earthlike tectonics. They yield insight into what may be happening within the fractures. The latest data on the plume — the huge cloud of vapor and particles fed by the jets that extend into space — show it varies over time and has a far-reaching effect on Saturn’s magnetosphere.

“Of all the geologic provinces in the Saturn system that Cassini has explored, none has been more thrilling or carries greater implications than the region at the southernmost portion of Enceladus,” said Carolyn Porco, Cassini imaging team leader at the Space Science Institute in Boulder, Colorado.

A panel of Cassini scientists presented these new findings Monday in a news briefing at the American Geophysical Union’s Fall Meeting in San Francisco.

“Enceladus has earthlike spreading of the icy crust, but with an exotic difference — the spreading is almost all in one direction, like a conveyor belt,” said Paul Helfenstein, Cassini imaging associate at Cornell University in Ithaca, New York.

“Enceladus has asymmetric spreading on steroids,” Helfenstein said. “We are not certain about the geological mechanisms that control the spreading, but we see patterns of divergence and mountain-building similar to what we see on Earth, which suggests that subsurface heat and convection are involved.”

The tiger stripes are analogous to the mid-ocean ridges on Earth’s seafloor where volcanic material wells up and creates new crust. Using Cassini-based digital maps of the moon’s south polar region, Helfenstein reconstructed a possible history of the tiger stripes by working backward in time and progressively snipping away older and older sections of the map, each time finding that the remaining sections fit together like puzzle pieces.

Images from recent close flybys also have bolstered a theory that condensation from the jets erupting from the surface may create ice plugs that close off old vents and force new vents to open. The opening and clogging of vents also corresponds with measurements indicating the plume varies from month to month and year to year.

“We see no obvious distinguishing markings on the surface in the immediate vicinity of each jet source, which suggests that the vents may open and close and thus migrate up and down the fractures over time,” Porco said. “Over time, the particles that rain down onto the surface from the jets may form a continuous blanket of snow along a fracture.”

Enceladus’ output of ice and vapor dramatically impacts the entire Saturnian system by supplying the ring system with fresh material and loading ionized gas from water vapor into Saturn’s magnetosphere.

“The ions added to the magnetosphere are spun up from Enceladus’ orbital speed to the rotational speed of Saturn,” said Cassini magnetometer science team member Christopher Russell of the University of California, Los Angeles. “The more material is added by the plume, the harder this is for Saturn to do, and the longer it takes to accelerate the new material.”

With water vapor, organic compounds and excess heat emerging from Enceladus’ south polar terrain, scientists are intrigued by the possibility of a liquid-water-rich habitable zone beneath the moon’s south pole.

“Cryovolcanoes are some of the most intriguing features in the solar system,” said Rosaly Lopes, a Cassini radar team investigation scientist from NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California.

Rather than erupting molten rock, it is theorized that the cryovolcanoes of Titan would erupt volatiles such as water, ammonia, and methane. Scientists have suspected cryovolcanoes might inhabit Titan, and the Cassini mission has collected data on several previous passes of the moon that suggest their existence. Imagery of the moon includes a suspect haze hovering over flow-like surface formations. Scientists point to these as signs of cryovolcanism.

“Cassini data have raised the possibility that Titan’s surface is active,” said Jonathan Lunine, a Cassini interdisciplinary scientist from the Lunar and Planetary Laboratory, University of Arizona, Tucson. “This is based on evidence that changes have occurred on the surface of Titan, between flybys of Cassini, in regions where radar images suggest a kind of volcanism has taken place.”

What led some Cassini scientists to believe that things are happening now were changes in brightness and reflectance detected at two distinct regions of Titan. Reflectance is the ratio of light that radiates onto a surface to the amount reflected back. These changes were documented by Visible and Infrared Mapping Spectrometer data collected on Titan flybys from July 2004 to March 2006. In one of the two regions, the reflectance of the surface surged upward and remained higher than expected. In the other region, the reflectance shot up but then trended downward. There is also evidence that ammonia frost is present at one of the two changing sites. The ammonia was evident only at times when the region was inferred to be active.

“Ammonia is widely believed to be present only beneath the surface of Titan,” said Robert M. Nelson of JPL, a scientist for Cassini’s Visual and Infrared Mapping Spectrometer team. “The fact that we found it appearing at times when the surface brightened strongly suggests that material was being transported from Titan’s interior to its surface.”

Some Cassini scientists indicate that such volcanism could release methane from Titan’s interior, which explains Titan’s seemingly continuous supply of fresh methane. Without replenishment, scientists say, Titan’s original atmospheric methane should have been exhausted long ago.

But other scientists familiar with the spectrometer data argue that the ammonia identification is not certain, and that the purported brightness changes might not be associated with changes on Titan’s surface. Instead they might result from the transient appearances of ground “fogs” of ethane droplets very near Titan’s surface, driven by atmospheric rather than geophysical processes. Nelson has considered the ground fog option, stating, “There remains the possibility that the effect is caused by a local fog, but, if so, we would expect it to change in size over time due to wind activity, which is not what we see.”

An alternative hypothesis to an active Titan suggests the saturnian moon could be taking its landform evolution cues from a moon of Jupiter.

“Like Callisto, Titan may have formed as a relatively cold body, and may have never undergone enough tidal heating for volcanism to occur,” said Jeffrey Moore, a planetary geologist at the NASA Ames Research Center, Moffett Field, California. “The flow-like features we see on the surface may just be icy debris that has been lubricated by methane rain and transported down slope into sinuous piles like mudflows.”

A team of scientists headed by Charles “Rick” Chappell, research professor of physics and director of the Dyer Observatory at Vanderbilt University, conducted the study. The team based its conclusion on measurements from five satellites.

The northern and southern polar lights — aurora borealis and aurora australis — are the only parts of the magnetosphere that are visible, but it is a critical part of Earth’s space environment.

“Although it is invisible, the magnetosphere has an impact on our everyday life,” Chappell said. “For example, solar storms agitate the magnetosphere in ways that can induce power surges in the electrical grid that trigger black outs, interfere with radio transmissions, and mess up GPS signals. Charged particles in the magnetosphere can also damage the electronics in satellites and affect the temperature and motion of the upper atmosphere.”

The other regions of the magnetosphere have been known for some time. Chappell and his colleagues pieced together a “natural cycle of energization” that accelerates the low-energy ions that originate from Earth’s atmosphere up to the higher energy levels characteristic of the different regions in the magnetosphere. This brought the existence of the new region into focus.

The warm plasma cloak is a tenuous region that starts on the night side of the planet, wraps around the dayside, and then gradually fades away on the afternoon side. As a result, it only reaches about three-quarters of the way around the planet. It is fed by low-energy charged particles that are lifted into space over Earth’s poles, carried behind Earth in its magnetic tail, and then turned around 180° by a kink in the magnetic fields that boosts the particles back toward Earth in a region called the plasma sheet.

Chappell and his colleagues — Mathew M. Huddleston from Trevecca University, Tom Moore and Barbara Giles from NASA, and Dominique Delcourt from the Centre d’etude des Environments Terrestre et Planetaires, Observatoire de Saint-Maur in France — used satellite observations to measure the properties of the ions in different locations in the magnetosphere.

An important part of their analysis was a computer program developed by Delcourt that can predict how ions move in Earth’s magnetic field. “These motions are very complicated. Ions spiral around in the magnetic field. They bounce and drift. A lot of things can happen,” said Chappell.

When the researchers applied this computer code to the satellite observations, some patterns became clear for the first time. One was the prediction of how ions could move upward from the ionosphere to form the warm plasma cloak.

“We have recognized all the other regions for a long time, but the plasma cloak was a fuzzy thing in the background which we didn’t have enough information about to make it stand out. When we got enough pieces, there it was!” said Chappell.

LTDs — martian sediments that most closely resemble sediments on Earth — are some of the most mysterious sediments on Mars. Causes for their origin remain unknown. Until now, different mechanisms, including volcanic processes, have been proposed for their formation.

LTDs were first discovered by the Viking spacecraft in the late 1970s and since have been at the center of scientific debate. These deposits occur on a large scale in Arabia Terra, Chaotic Terrain, and Valles Marineris, close to the Tharsis volcanic bulge. Now, based on Mars Express data, scientists propose that these sediments are actually younger than originally believed. Angelo P. Rossi and colleagues (ESA) report their findings in a paper published in September 2008. They propose that several LTDs may have been deposited by large-scale springs of groundwater that burst onto the surface, possibly at different times.

Analysis indicates that groundwater had a more wide-ranging and important role in martian history than previously believed. Hydrated minerals, relatively young in age, have been found in the region. Given that the deposits are relatively young in age, and associated with water, they may also have sheltered microbial life from the drier and harsher climate in more recent times on Mars, possibly eliminating the need for a stable atmosphere or a permanent water body.