Category: Saturn

Cassini scientists know for sure their spacecraft isn’t in Kansas anymore. Cassini’s been keeping an eye on a powerful electrical storm that’s been raging on Saturn for five months now, with lightning bolts 10,000 times more powerful than those found on Earth. But Cassini has also been busy flying by moons like Enceladus and Titan during this time, and therefore can’t constantly watch the storm. So amateur astronomers have been assisting the Cassini science team by monitoring this tempest in the “Storm Alley” region of Saturn. It’s no Great Red Spot, but it’s the longest lasting electrical storm ever detected in our solar system.

This prolonged storm is located in Saturn’s southern hemisphere–in a region nicknamed “Storm Alley” by mission scientists–where previous, but much shorter-lived lightning storms (if month-long storms can be called short!) were observed by Cassini. Saturn’s electrical storms are similar to thunderstorms on Earth, but they’re much bigger and longer lasting. Storms on Saturn have diameters of several thousand kilometers (thousands of miles), and radio signals produced by their lightning are thousands of times more powerful than those produced by terrestrial thunderstorms.

The storm was first detected on Saturn on Nov. 27, 2007. The electrostatic discharges were picked up by Cassini’s radio and plasma wave science instrument.

“The electrostatic radio outbursts have waxed and waned in intensity for five months now,” said Georg Fischer, an associate with the radio and plasma wave science team at the University of Iowa, Iowa City. “We saw similar storms in 2004 and 2006 that each lasted for nearly a month, but this storm is longer-lived by far. And it appeared after nearly two years during which we did not detect any electrical storm activity from Saturn.”

Amateur astronomers have kept track of the storm over its five-month lifetime. “Since Cassini’s camera cannot track the storm every day, the amateur data are invaluable,” said Fischer. “I am in continuous contact with astronomers from around the world.”

The long-lived storm will help provide information on the processes powering Saturn’s intense lightning activity. Cassini scientists will continue to monitor Storm Alley as the seasons change, bringing the onset of autumn to the planet’s southern hemisphere.

Original News Source: Cassini Press Release

During a flyby of the small moon on March 12th, the Cassini probe detected significant amounts of organic chemicals as it flew through powerful geyser-like jets of ice blasting into space. This active moon appears to be generating organic chemicals much like the substances found in comets. As Cassini bravely travelled through the plume at a speed of 32,000 mph, it was able to take some indirect measurements of the density of the gas from the surprising amount of torque applied to spacecraft. Fortunately the craft was undamaged as the particles bounced off its bodywork…

Cassini took the daring journey through the plumes of ice crystals and gas at 200 km above the moon’s surface. It came within 50 km of the surface at closest approach, giving mission scientists an unprecedented view of the mysterious satellites northern hemisphere. Images acquired by Cassini showed a vast, ancient region of pits and craters mixed with cracks, with geysers fizzing chemicals into space. Enceladus is located in the densest region of Saturn’s E-ring, possibly indicating there is some relationship between the geyser emissions and ring density.

To discover significant quantities of organic compounds being emitted from the Saturn system is of particular interest to scientists trying to understand how Saturn evolved as the solar system formed.

“A completely unexpected surprise is that the chemistry of Enceladus, what’s coming out from inside, resembles that of a comet, to have primordial material coming out from inside a Saturn moon raises many questions on the formation of the Saturn system.” – Hunter Waite, principal investigator for the Cassini Ion and Neutral Mass Spectrometer, Southwest Research Institute, San Antonio

From measurements by the Ion and Neutral Mass Spectrometer on Cassini, scientists are able to deduce that the moon is highly active, driven by an internal energy source. There is also evidence for tectonic activity on the 500 km diameter body. The gases detected can be likened to the fizz of gas released from carbonated water, with a twist of organic chemicals mixed in. The spectrometer effectively “tasted and sniffed” the gas and was able to get a good idea about what the energetic geysers are spewing into space.

The gases detected, over 20 times more dense than estimated, contained water vapour, carbon dioxide, carbon monoxide, organic compounds and volatile molecules. Quite an explosive mix. The clouds of gas were so dense that the spacecraft felt the force of the emission, creating a torque. From this, some measurements on gas density were possible.

It is thought Cassini was unharmed during the flyby and it will return in August for an even more daring, lower flyby of this strange, gassy moon.

Source: NASA

The Cassini spacecraft’s audacious flyby of Saturn’s moon Enceladus on March 12 has provided scientists more information about the geyser-like jets of ice shooting from the moon’s southern hemisphere. It also highlighted the drastic geologic differences between the moon’s north and south pole. While the data collected from the geysers is still being analyzed, images from the flyby showed a north polar region that is older and pitted with fractured craters, compared to the relatively newer cracks in south pole area from which water jets are emanating. The spacecraft came within 50 kilometers (30 miles) of the surface at closest approach and 200 kilometers (120 miles) while flying through the plume.

“These new images are showing us in great detail how the moon’s north pole differs from the south, an important comparison for working out the moon’s obviously complex geological history,” said Carolyn Porco, Cassini imaging team leader. “And the success of yesterday’s daring and very low-altitude flyby means this coming summer’s very close encounter, when we get exquisitely detailed images of the surface sources of Enceladus’ south polar jets, should be an exciting ‘next big step’ in understanding just how the jets are powered.”

Cassini was traveling about 15 kilometers per second (32,000 mph) through plumes from the geysers. The flyby was designed so that Cassini’s particle analyzers could dissect the “body” of the plume for information on the density, size, composition and speed of the particles.

Cassini scientists are pouring over the data being returned, which will give them a better understanding of the unique plume environment of Enceladus and possibly how the geysers are being formed.

The images show the north polar region is much older and pitted with craters of various sizes. These craters are captured at different stages of disruption and alteration by tectonic activity, and probably from past heating from below. Many of the craters seem sliced by small parallel cracks that appear to be ubiquitous throughout the old cratered terrains on Enceladus.

Future close flybys may bring Cassini even closer to the surface of Enceladus. The spacecraft will come close to Enceladus again in August, and skim even closer to the moon’s surface in October.

Original News Source: JPL Press Release

Mark your calendars, this is going to be an amazing ride. NASA’s Cassini spacecraft is going to make a flyby of Saturn’s moon Enceladus on Wednesday, March 12, 2008. And this time, the spacecraft is going to fly right through the mysterious geysers of water ice blasting out of the moon’s Southern pole. At its closest approach, Cassini is going to get within 50 km (30 miles) of the surface. Now that’s close!

It was on a previous flyby that Cassini turned up evidence for the ice geysers in the first place. Images of the moon showed that huge plumes of water ice are pouring out of deep cracks around the moon’s southern pole. It’s believed that tidal interactions between Enceladus and Saturn are heating the moon’s interior. That heat has to escape, and this is how.

The particles really blast out of Enceladus, traveling at 1,285 km/h (800 miles per hour). The plumes expand out to distance three times as large as the moon itself. And this material even seems to be contributing to one of Saturn’s rings.

So on Wednesday, scientists will have an opportunity to get some of their questions answered. Cassini will fly on a trajectory that takes it through the edge of the plumes. At this point, it will be about 195 km (120 miles) above the surface. It will get even closer, skimming the moon at just 50 km (30 miles).

Although there will be pretty pictures, the main instruments used will be Cassini’s particle analyzers. These will study the composition of the plumes themselves – “sniffing and tasting” them.

“There are two types of particles coming from Enceladus, one pure water-ice, the other water-ice mixed with other stuff,” said Sascha Kempf, deputy principal investigator for Cassini’s Cosmic Dust Analyzer at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. “We think the clean water-ice particles are being bounced off the surface and the dirty water-ice particles are coming from inside the moon. This flyby will show us whether this concept is right or wrong.”

This will actually be the first of four Cassini/Enceladus flybys this year, and so if scientists don’t see what they’re looking for, there will be other chances.

Original Source: NASA/JPL Flyby Page

Saturn is known for the spectacular rings that circle the planet, and the Cassini spacecraft has been exploring Saturn’s rings, as well as its moons since 2004. And now Cassini has found evidence that there may be rings around one of Saturn’s moons, too: Rhea, the second largest moon in Saturn’s system. This is the first time rings may have been found around a moon. While no images yet have been taken of the rings (the picture here is an artist’s rendering) an extensive debris disk and at least one ring appear to have been detected by a suite of six instruments on Cassini specifically designed to study the atmospheres and particles around Saturn and its moons.

“Until now, only planets were known to have rings, but now Rhea seems to have some family ties to its ringed parent Saturn,” said Geraint Jones, a Cassini scientist and lead author on a paper that appears in the March 7 issue of the journal Science.

Rhea is about 1,500 kilometers (950 miles) in diameter. The apparent debris disk measures several thousand miles from end to end. The particles that make up the disk and any embedded rings probably range from the size of small pebbles to boulders. An additional dust cloud may extend up to 5,900 kilometers (3,000 miles) from the moon’s center, almost eight times the radius of Rhea.

Since the discovery, Cassini scientists have done simulations to determine if Rhea can maintain rings. The models show that Rhea’s gravity field, in combination with its orbit around Saturn, could allow rings that form to remain in place for a very long time. The discovery was a result of a Cassini close flyby of Rhea in November 2005.

One possible explanation for these rings is that they are remnants from an asteroid or comet collision in Rhea’s distant past. Such a collision may have pitched large quantities of gas and solid particles around Rhea. Once the gas dissipated, all that remained were the ring particles. Other moons of Saturn, such as Mimas, show evidence of a catastrophic collision that almost tore the moon apart.

“The diversity in our solar system never fails to amaze us,” said Candy Hansen, Cassini scientist and co-author on the paper. “Many years ago we thought Saturn was the only planet with rings. Now we may have a moon of Saturn that is a miniature version of its even more elaborately decorated parent.”

Original News Source: JPL/Cassini Press Release

Even in the smallest telescopes, Saturn’s bright rings pop into view. But those might be just the tip of the iceberg. During a recent flyby of the planet, NASA’s Cassini spacecraft noticed empty patches where the constant rain of high-energy electrons slowed down. Perhaps there are partial rings there, invisible to the spacecraft’s cameras. And where are these rings coming from?

When NASA’s Cassini spacecraft nears Saturn, its bombarded by a flurry of high energy electrons. But researchers from the Max Planck Institute for Solar System Research noticed that during the spacecraft’s journey, there were two times when it wasn’t being hit with so many particles. In their research article, published in the latest issue of the journal Icarus, they propose that there are invisible rings, generated by two of Saturn’s smallest moons: Methone and Anthe.

The gap in the rain of electrons occurred just as Cassini was passing through the orbits of Methone and Anthe. The drop in intensity lasted while the spacecraft covered a swath as wide as 1,000 to 3,000 km (600 to 1,900 miles) across. This is too wide for the tiny moons themselves, but arcs of ejected material could explain it.

“These observations tell us that even Saturn’s smallest moons could be a source of dust in the Saturnian system,” said Elias Roussos, the paper’s lead author from the Max Planck Institute for Solar System Research in Katlenburg-Lindau, Germany.

So, even the smallest moons around Saturn are feeding dust into the ring system. This released material may develop into partial ring arcs because of the gravitational “tug of war” between the planet’s larger moons, like Mimas. A situation like this has been found with Saturn’s G-ring.

Where’s all this material coming from? The researchers think that the constant rain of micrometeoroids on the surface of the tiny moons dislodges the icy material. Since they’re so small and have very little gravity, it doesn’t take much for the material to escape into space.

Strangely, these theorized rings are invisible. Meteoroids are thought to be generating the faint rings at Janus, Epimetheus and Pallene; but they’re visible to Cassini. The spacecraft can’t see these newly discovered rings with its cameras. Perhaps the two different classes of moons are releasing differently-sized grains of dust.

Original Source: NASA/JPL/SSI News Release

Yesterday I blogged about how particles jetting from Enceladus find their way to Saturn’s A-Ring. Now there’s a new report that models how ice and vapour come pouring out of cracks on Enceladus’ surface in the first place.

Since Cassini first discovered jets of water ice blasting out of Saturn’s moon Enceladus, scientists have been trying to explain the process that could make this happen. The moon is very very cold; too far away to be warmed by the Sun.

Scientists now know that the jets are emanating from a series of cracks near Enceladus’ southern pole; these cracks have been dubbed “tiger stripes”. A team of German researchers, led by Juergen Schmidt of the University of Potsdam, have developed a computer model that describes what the bottom of those tiger stripes might look like.

According to Schmidt, they have to be at a temperature of 0 degrees Celsius. This is the triple point of water, where vapour, ice and liquid can all exist at the same time.

Water vapour and ice grains are blasted through funnels in the tiger stripes. The heavier grains rub against the sides of the holes and slow down.

This helps explain why ice particles coming out of Enceladus move at a slower velocity than the water vapour.

The process of tidal heating is probably keeping the interior of Enceladus warm. As it orbits around Saturn, the powerful gravitational force causes the tiny moon to flex back and forth. This creates heat within it. A more dramatic version of this process can be seen with Jupiter’s moon Io, which is heated to the point that volcanoes erupt across its surface.

The surface of Enceladus is -193 degrees Celsius, while the tiger stripes are -133 C. This means that the interior of the moon must be even warmer.

The researchers have published their work in this week’s issue of the journal Nature.

Original Source: Nature

One of the biggest discoveries made by Cassini is at Saturn’s moon Enceladus, where great plumes of icy material were seen spewing from its southern pole. Now scientists think that this material is traveling all the way inward to get trapped into Saturn’s A-ring.

Scientists had already linked together Saturn’s E-ring with the material spewed out by Enceladus. And researchers had worked out that the whole magnetic environment around Saturn is weighed down by the Enceladus material, which becomes plasma.

But now this.

“Saturn’s A-ring and Enceladus are separated by 100,000 kilometers (62,000 miles), yet there’s a physical connection between the two,” says Dr. William Farrell of NASA’s Goddard Space Flight Center in Greenbelt, Md. “Prior to Cassini, it was believed that the two bodies were separate and distinct entities, but Cassini’s unique observations indicate that Enceladus is actually delivering a portion of its mass directly to the outer edge of the A-ring.” Farrell is lead author of a paper on this Saturn discovery that appeared in Geophysical Research Letters January 23.

The gas particles are ejected from Enceladus and then become electrically charged by sunlight and through interactions with other particles. Once they’re charged, the particles can come under the sway of Saturn’s magnetic field, which traps and directs them around. The particles can move around from pole to pole, but once they enter Saturn’s A-ring, they’re stuck there for good.

Scientists had actually predicted this in the early 1990s. Using the Hubble Space Telescope, they saw a large presence of water-related molecules in orbit around Saturn. The researchers modeled the motions of this icy material, and calculated that it could migrate all the way in to the A-ring. But the source of this water cloud was unknown.

This discovery backs up the prediction, and provides a source for the cloud of water-related molecules feeding into the A-ring.

They’re coming from Enceladus.

Original Source: NASA News Release