Saturn Archives

October 5, 2010December 24, 2015 by Nancy Atkinson

Saturn’s Rings Formed from Large Moon’s Destruction

Raw image of Saturn's rings. Credit: NASA/JPL/Space Science Institute

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The formation of Saturn’s rings has been one of the classical if not eternal questions in astronomy. But one researcher has provided a provocative new theory to answer that question. Robin Canup from the Southwest Research Institute has uncovered evidence that the rings came from a large, Titan-sized moon that was destroyed as it spiraled into a young Saturn.

Over the years, different theories have evolved on how the rings formed around Saturn. The two leading theories involve a small moon that was shattered by meteor impacts, or the tidal disruption of a comet coming too close to Saturn.

But Saturn’s main rings are about 90% water ice by mass, and because bombardment of the rings by micrometeoroids increases their rock content over time, Canup said the rings’ current composition implies that they were essentially pure ice when they formed.

However, disruption of a small moon would generally lead to a mixed rock-ice ring, while tidal disruptions of comets would occur much more often at Jupiter, Uranus and Neptune than at Saturn.

Additionally, neither of these theories would explain Saturn’s inner moons, which have low enough densities that they too must be comprised of nearly pure ice.

Canup’s new alternative theory is that Titan-sized moon with a rocky core and an icy mantle spiraled into Saturn early in solar system history. Tidal forces ripped off part of the icy mantle, distributing it into what would become the rings. But the rocky core was made of more durable material that held together until it hit Saturn’s surface. “The end result is a pure ice ring,” Canup said in an article in Nature.

Over time the ring spreads out and its mass decreases, and icy moons are created. Due to changes in the evolving Saturn system, these “spawned” moons then spiraled outward rather than inward. In this way, ice rings and ice-enhanced inner moons originate as a primordial byproduct of the same process that produces Saturn’s regular satellite system, making the whole process simpler than if there were several events.

Canup studies formation events with detailed computer simulations, including studying how our own Moon formed.

She presented her findings at the American Astronomical Society’s Division for Planetary Science meeting this week, in Pasadena, California, and her presentation was detailed in an article in Nature.

Sources: Canup’s abstract, Nature

October 4, 2010December 24, 2015 by Nancy Atkinson

Titan-ic Tsunami Causing Crack in Saturn’s C Ring

This graphic shows an angled view of a newly discovered “crack” in one of Saturn’s rings, known as the C ring. This view shows the 3-D quality of the puzzling crack associated with a wave-like feature that was discovered earlier by NASA’s Voyager 1 spacecraft. Image credit: NASA/JPL/Cornell

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Saturn’s rings have several gaps, most of which are caused by small moons shepherding ring debris into breaks in the rocky rings. But one gap may be caused by gravitational perturbations from Saturn’s largest moon, Titan, sending tsunami-like waves up to 3 kilometers (2 miles) high in the C ring. This causes one region of the ring to spin like a warped, uneven vinyl record on a turntable. A new model of this action explains why the gap was narrower than expected and also why is seems to disappear from time to time. “What looked like a 15-kilometer-wide gap actually was this gap with a vertical displacement of about 3 kilometers projected and seen almost edge on,” said Phillip Nicholson from Cornell University, speaking at a press briefing at the American Astronomical Society’s Division for Planetary Sciences meeting in Pasadena, California. “It’s a little like a tsunami propagating away from an earthquake fault.”

The Cassini spacecraft looks close at Saturn to frame a view encompassing the entire C ring. Image credit: NASA/JPL/SSI

The gap in the middle of the C ring has been known since Voyager 1 flew by Saturn in the 1980, and it appeared there was a 15 km-wide gap. But when Cassini arrived in 2004 and began observations, the gap was only 2 km (1.5 miles) and sometimes it wasn’t there at all.

Nicholson said only when they began to think in three dimensions were they able to solve the mystery of this gap. While most of Saturn’s rings are flat, in 2009, the angle of sunlight during Saturn’s spring equinox revealed there were lumps and bumps in the rings are as high as the Rocky Mountains.

The model Nicholson and colleagues created suggests the actual gap in the ring is about a half a kilometer wide, but part of the ring rises 3 km (2 miles) ~~in the air~~ up. The different angles the two spacecraft observed from made the gap look wider to Voyager than to Cassini.

“The whole pattern rotates around at the same rate as the satellite Titan orbits Saturn, once every 16 days,” said Nicholson said. Sometimes, the tsunami-like wave couldn’t be seen by the spacecraft, which accounts for how the gap seems to appear and disappear.

Nicholson said this model explains the C ring gap, “better than you have any right to expect,” but there could be three or four dynamical processes going on that explains the other gaps.

Nicholson and Cassini Deputy Project Scientist Linda Spilker said the same types of processes seen in Saturn’s rings could also explain what is seen in disks of debris around other stars, with the theory that there are gaps forming in the disks associated with the formation of planets.

“Saturn provides a wonderful natural laboratory of how protoplanetary nebula may evolve,” said Spilker.

The Cassini scientists also noted how the Cassini mission has now moved past the “Equinox” mission and is now in another extension of the mission called the Solstice mission, which will keep the spacecraft going until 2017.

Spilker shared how as the end of the mission approaches, they might try some riskier moves, such as try flying between Saturn’s D ring or heading into Saturn’s into upper atmosphere to “study new things about planet itself, for the end of the mission.”

Source: DPS meeting webcast

October 1, 2010December 24, 2015 by Nancy Atkinson

Simply Astonishing: Enceladus, the Jet-Powered Moon

The plumes of Enceladus are highlighted in this Cassini image. Credit: NASA/JPL/Space Science Institute

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What an astonishing view of Saturn’s moon Enceladus, as seen by Cassini! At least four different plumes of water ice are spewing out from the south polar region, highlighted because of the black space behind the Moon. On Twitter, Carolyn Porco said that we see four jets because we’re looking down the four tiger stripe fractures crossing the south pole. “How lovely it is to know!” she added.

Cassini was about 617,000 kilometers (383,000 miles) away from Enceladus when it captured this image.

More info: Cassini website

September 24, 2010December 24, 2015 by Nancy Atkinson

Conjoined Moons

Saturn's moons Dione and Rhea appear conjoined in this optical illusion-like image taken by the Cassini spacecraft. Credit: NASA/JPL/Space Science Institute

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This latest image from the Cassini spacecraft will make you do a double-take! It is an optical illusion, but the two moons appear like conjoined, identical twins! The two moons are fairly close in size, but Dione, the smaller of the two at the top in the image, is actually closer to the spacecraft, making the two look almost identical. And because of the similar albedo, or reflectivity, of the two moons and because of the location of a particularly large crater near the south polar region of Dione, the moon appears blended seamlessly with Rhea. Double your pleasure!

Dione is 1123 kilometers (698 miles) across and Rhea is 1528 kilometers (949 miles) across.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 27, 2010.

See more about the image at the CICLOPS website.

September 24, 2010December 24, 2015 by Nancy Atkinson

Cassini Flies Through Saturn’s Aurora

Cassini crossed the radio aurora of Saturn on 17 October 2008, at a distance of 4 Saturn's radii above the atmosphere. These radio emissions, generated by fast electrons, are strongly beamed. They were characterised by simultaneous observations of three different experiments. Credit: NASA/JPL/University of Iowa/CNES/Observatoire de Paris

Saturn’s mysterious aurora has fascinated astronomers and space enthusiasts since it was first observed back in 1979. Now, the Cassini spacecraft has made the first observations from within the giant radio aurora of Saturn. The spacecraft flew through an active auroral region in 2008, and scientists say there are both similarities and contrasts between the radio auroral emissions generated at Saturn and those at Earth. Additionally, Cassini’s visual and infrared mapping spectrometer instrument (VIMS) took data to create a new movie (above) showing Saturn’s shimmering aurora over a two-day period. All this new data are helping scientists understand what drives some of the solar system’s most impressive light shows.

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“So far, this is a unique event,” said Dr. Laurent Lamy at the European Planetary Science Congress in Rome this week. “Whereas the source region of Earth’s radio aurora has been studied by many missions, this is our first opportunity to observe the equivalent region at Saturn from the inside. From this single encounter, we have been able to build up a detailed snapshot of auroral activity using three of Cassini’s instruments. This gives us a fascinating insight into the processes that are generating Saturn’s radio aurora.”

See an animation created from the radio instrument on Cassini at this link. On the left hand side are the radio sources as seen from Cassini. The right hand side shows the projection of the radio sources down onto the southern pole of the planet. Credit: NASA/JPL/University of Iowa/CNES/Observatoire de Paris

Separately, Tom Stallard, lead scientist on a joint VIMS and Cassini magnetometer collaboration, presented the VIMS movie at the conference.

Source: European Planetary Science Congress

In the movie, the aurora phenomenon clearly varies significantly over the course of a Saturnian day, which lasts around 10 hours 47 minutes. On the noon and midnight sides (left and right sides of the images, respectively), the aurora can be seen to brighten significantly for periods of several hours, suggesting the brightening is connected with the angle of the sun. Other features can be seen to rotate with the planet, reappearing at the same time and the same place on the second day, suggesting that these are directly controlled by the orientation of Saturn’s magnetic field.

Image of Saturn’s aurora seen at ultraviolet wavelengths. The spiral shape seen here is similar to the distorted radio aurora visualised by the team and also indicates enhanced auroral activity. Credit: ESA/NASA/Hubble

“Saturn’s auroras are very complex and we are only just beginning to understand all the factors involved,” Stallard said. “This study will provide a broader view of the wide variety of different auroral features that can be seen, and will allow us to better understand what controls these changes in appearance.”
Auroras on Saturn occur in a process similar to Earth’s northern and southern lights. Particles from the solar wind are channeled by Saturn’s magnetic field toward the planet’s poles, where they interact with electrically charged gas (plasma) in the upper atmosphere and emit light. At Saturn, however, auroral features can also be caused by electromagnetic waves generated when the planet’s moons move through the plasma that fills Saturn’s magnetosphere.

This false-color composite image shows Saturn’s rings and southern hemisphere. The composite image was made from 65 individual observations by Cassini’s visual and infrared mapping spectrometer in the near-infrared portion of the light spectrum on Nov. 1, 2008. Credit: NASA/JPL/University of Arizona

September 21, 2010December 24, 2015 by Nancy Atkinson

Titan Weather Report for Spring: Still Cold, but Clearing Skies

Left: T43 flyby of Titan - 12 May 2008 – VIMS images a large cloud that caps the north pole of Titan (yellowish tones). Right: T63 flyby of Titan - 12 December 2009 – VIMS still observes a huge cloud system at 40°S (yellowish tones) and the north pole of Titan free of clouds, a few months after the equinox. Credit: NASA/JPL/University of Arizona/University of Nantes/ University of Paris Diderot

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The beauty of an extended space mission is that scientists can make long term observations and find out things we’ve never known before. The Cassini spacecraft’s Visual and Infrared Mapping Spectrometer (VIMS) instrument has been monitoring clouds on Titan continuously since the spacecraft went into orbit around Saturn in 2004, and a team led by Sébastien Rodriguez (AIM laboratory – Université Paris Diderot) has used more than 2,000 VIMS images to create the first long-term study of Titan’s weather. Are they ready to make a weather forecast? They say Titan’s northern hemisphere is set for mainly fine spring weather, with polar skies clearing since the equinox in August last year.

Together with Saturn in its 30-years orbit around the Sun, Titan has seasons that last for 7 terrestrial years. The team has observed significant atmospheric changes between July 2004 (early summer in the southern hemisphere) and April 2010, the very start of northern spring. The images showed that cloud activity has recently decreased near both of Titan’s poles. These regions had been heavily overcast during the late southern summer until 2008, a few months before the equinox.

“Over the past six years, we’ve found that clouds appear clustered in three distinct latitude regions of Titan: large clouds at the north pole, patchy cloud at the south pole and a narrow belt around 40 degrees south. However, we are now seeing evidence of a seasonal circulation turnover on Titan – the clouds at the south pole completely disappeared just before the equinox and the clouds in the north are thinning out. This agrees with predictions from models and we are expecting to see cloud activity reverse from one hemisphere to another in the coming decade as southern winter approaches,” said Dr Rodriguez.

Fractional cloud coverage in Titan’s atmosphere integrated between July 2004 and April 2010. Black areas are cloud free and yellow are fully covered. Credit: NASA/JPL/University of Arizona/University of Nantes/ University of Paris Diderot

The team has used results from the Global Climate Models (GCMs) developed by Pascal Rannou (Institut Pierre Simon Laplace) to interpret the evolution of the observed cloud patterns over time. Northern polar clouds of ethane form in the Titan’s troposphere during the winter at altitudes of 30-50 km by a constant influx of ethane and aerosols from the stratosphere. In the other hemisphere, mid- and high-latitudes clouds are produced by the upwelling from the surface of air enriched in methane. Observations of the location and activity of Titan’s clouds over long periods are vital in developing a global understanding of Titan’s climate and meteorological cycle.

In Feburary 2010, the Cassini mission was extended to a few months past Saturn’s northern summer solstice in May 2017. This means that Rodriguez and his team will be able to observe the seasonal changes right the way through from mid-winter to mid-summer in the northern hemisphere.

“We have learned a lot about Titan’s climate since Cassini arrived in at Saturn but there is still a great deal to learn. With the new mission extension, we will have the opportunity to answer some of the key questions about the meteorology of this fascinating moon,” said Rodriguez.

Rodriguez presented the results at the European Planetary Science Congress 2010 in Rome.

Source: European Planetary Science Conference

August 30, 2010January 20, 2016 by Nancy Atkinson

Astronomy Cast Ep. 195: Planetary Rings

Saturn is best known for its rings. This huge and beautiful ring system is easy to spot in even the smallest backyard telescope, so you can imagine they were a surprise when Galileo first noticed them. But astronomers have gone on to find rings around the other gas giant worlds in the Solar System – the differences are surprising.

Click here to download the episode.

Or subscribe to: astronomycast.com/podcast.xml with your podcatching software.

Astronomy With the Unaided Eye shownotes and transcript.

August 20, 2010January 20, 2016 by Nancy Atkinson

Stunning Flyover Videos of Saturn’s Moons

Saturn’s moons as you’ve never seen them before! By day, Dr. Paul Schenk works at the Lunar and Planetary Institute mapping the topography and geology of the moons of Saturn and Jupiter, as well as the icy bodies of the outer solar system. But because “it’s just plain cool,” he has created some flyover videos of Saturn’s satellites, using data from the Cassini spacecraft. Very cool, indeed! Above is a close-up, 3-D look at the walnut-shaped moon Iapetus. Scientists don’t know why there is a ridge along the moon’s equator, but in 2007, Cassini acquired a strip of color and stereo images along the ridge, and Schenk has created a flyover which shows the contrast in color and topography. There are “sharp peaks 15 to 20 kilometers above the surrounding dark cratered plains,” Schenk writes. “These are among the highest peaks in the Solar System. Patches of bright pure water ice can be seen flanking these dark peaks, which have the brightness of soot.”

And there’s more! Below is one of my favorites from Schenk’s collection of flyover videos, 3-D views of Inktomi, a very young crater on the moon Rhea.

Continue reading “Stunning Flyover Videos of Saturn’s Moons”

August 15, 2010December 24, 2015 by Nancy Atkinson

Amazing New Close-up Images of Enceladus

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Oh, wow! This is one of the best images yet from the Cassini spacecraft of the “tiger stripes” in the south polar region of Saturn’s moon Enceladus. Over the weekend, Cassini flew by Enceladus, and has sent back some incredible new images, such as the one above. The tiger stripes are actually giant fissures that spew jets of water vapor and organic particles hundreds of kilometers, or miles, out into space, and here, Cassini is staring right down into one of the fissures. See more great images of Enceladus below, plus images of the moons Dione and Tethys.

Close-up of the cracked, crevassed surface of Enceladus. Credit: NASA/Space Science Institute.

While the winter is darkening the moon’s southern hemisphere, Cassini has its own version of “night vision goggles” — the composite infrared spectrometer instrument – to track heat even when visible light is low. It will take time for scientists to assemble the data into temperature maps of the fissures.

Enceladus against Saturn's limb. Credit: NASA/Space Science Institute.

More plumes on Enceladus. Credit: NASA/Space Science Institute.

Close-up of Tethys. Credit: NASA/Space Science Institute

Dione from 115,370 kilometers away. Credit: NASA/Space Science Institute. — Dione from 115,370 kilometers away. Credit: NASA/Space Science Institute

See more amazing images from Cassini’s latest at the CICLOPS website.

Emily Lakdawalla at the Planetary Blog also has created some very cool movies from the flyby images.

Hat tip to Stu Atkinson

July 29, 2010December 24, 2015 by Nancy Atkinson

Ring Around Rhea? Probably Not

Rhea, taken by the Cassini spacecraft in March, 2010. Credit: NASA/JPL/Space Science Institute

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Back in 2005, a suite of six instruments on the Cassini spacecraft detected what was thought to be an extensive debris disk around Saturn’s moon Rhea, and while there was no visible evidence, researchers thought that perhaps there was a diffuse ring around the moon. This would have been the first ring ever found around a moon. New observations, however, have nixed the idea of a ring, but there’s still something around Rhea that is causing a strange, symmetrical structure in the charged-particle environment around Saturn’s second-largest moon.

Researchers announced their findings in 2008 that there was a sharp, symmetrical drop in electrons detected around Rhea. This moon is about 1,500 kilometers (950 miles) in diameter, and scientists began searching for what could have caused the drop. If there were a debris disk around Rhea, it would have had to measure several thousand miles from end to end, and would probably be made of particles that would range from the size of small pebbles to boulders.

Testing the hypothesis, Cassini flew by the moon several times and took 65 images between 2008 and 2009, flying at what would be edge-on to the rings, where the greatest amount of material would be within its line of sight.

Using light angles to their advantage — and if the ring was there – the scientists should have been able to detect micron-sized particles up to boulder size objects.

But they saw nothing.

“There are very strong and interesting and unexplained electromagnetic effects going on around Rhea,” said Matthew Tiscareno from Cornell University, who led the imaging campaign. “But we’re making a pretty strong case that it’s not because of solid material orbiting the moon….For the amount of dust that you need to account for [the earlier] observations, if it were there, we would have seen it.”

While the ring hypothesis has been disproved, there’s still a mystery about the cause of the symmetrical structure in the charged-particles around the moon.

But the Cassini spacecraft and team are up for the challenge.

Source: Cornell University