Saturn Archives

February 11, 2010December 24, 2015 by Nancy Atkinson

Hubble Captures Double Aurorae Light Show on Saturn

Hubble's view of Saturn with a double view of its fluttering aurorae. Credit: NASA, ESA and Jonathan Nichols (University of Leicester)

In January and March 2009, researchers using Hubble took advantage of a rare opportunity to record Saturn when its rings are edge-on, resulting in a unique look featuring both of the giant planet’s poles. And Saturn cooperated by providing an incredible double light show with Saturn’s own northern and southern lights. Since Saturn is only in this position every 15 years or so, this favorable orientation has allowed a sustained study of the two beautiful and dynamic aurorae.

Since it takes Saturn almost thirty years to orbit the Sun, the opportunity to image both of its poles occurs only twice in that period. Hubble has been snapping pictures of the planet at different angles since the beginning of the mission in 1990, but 2009 brought a unique chance for Hubble to image Saturn with the rings edge-on and both poles in view. At the same time Saturn was approaching its equinox so both poles were equally illuminated by the Sun’s rays.

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These recent observations go well beyond just a still image and have allowed researchers to monitor the behavior of both Saturn’s poles in the same shot over a sustained period of time. The movie they created from the data, collected over several days during January and March 2009, has aided astronomers studying both Saturn’s northern and southern aurorae. Given the rarity of such an event, this new footage will likely be the last and best equinox movie that Hubble captures of our planetary neighbor.

Despite its remoteness, the Sun’s influence is still felt by Saturn. The Sun constantly emits particles that reach all the planets of the Solar System as the solar wind. When this electrically charged stream gets close to a planet with a magnetic field, like Saturn or the Earth, the field traps the particles, bouncing them back and forth between its two poles. A natural consequence of the shape of the planet’s magnetic field, a series of invisible “traffic lanes” exist between the two poles along which the electrically charged particles are confined as they oscillate between the poles. The magnetic field is stronger at the poles and the particles tend to concentrate there, where they interact with atoms in the upper layers of the atmosphere, creating aurorae, the familiar glow that the inhabitants of the Earth’s polar regions know as the northern and southern lights.

At first glance the light show of Saturn’s aurorae appears symmetric at the two poles. However, analysing the new data in greater detail, astronomers have discovered some subtle differences between the northern and southern aurorae, which reveal important information about Saturn’s magnetic field. The northern auroral oval is slightly smaller and more intense than the southern one, implying that Saturn’s magnetic field is not equally distributed across the planet; it is slightly uneven and stronger in the north than the south. As a result, the electrically charged particles in the north are accelerated to higher energies as they are fired toward the atmosphere than those in the south. This confirms a previous result obtained by the space probe Cassini, in orbit around the ringed planet since 2004.

Source: ESA

February 3, 2010December 24, 2015 by Nancy Atkinson

More Stunning Images and Discoveries Ahead: Cassini Mission Extended to 2017

Saturn from Cassini. Image credit: NASA/JPL/SSI

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With the new 2011 NASA budget allowing for more space science activities, the space agency has extended the Cassini mission to explore Saturn and its moons to 2017. “This is a mission that never stops providing us surprising scientific results and showing us eye popping new vistas,” said Jim Green, director of NASA’s planetary science division. “The historic traveler’s stunning discoveries and images have revolutionized our knowledge of Saturn and its moons.” This is the second mission extension for Cassini, and the new “Solstice Mission” will allow scientists to study seasonal and other long-term weather changes on the planet and its moons.

The Cassini mission will get $60 million per year to continue its study of the Saturn system.

“The extension presents a unique opportunity to follow seasonal changes of an outer planet system all the way from its winter to its summer,” said Bob Pappalardo, Cassini project scientist. “Some of Cassini’s most exciting discoveries still lie ahead.”

Cassini arrived just after Saturn’s northern winter solstice, and this extension continues until a few months past northern summer solstice in May 2017. The northern summer solstice marks the beginning of summer in the northern hemisphere and winter in the southern hemisphere.

The plumes of Enceladus as imaged by the most recent Cassini flyby. Image Credit: NASA/JPL/Space Science Institute

A complete seasonal period on Saturn has never been studied at this level of detail. The Solstice mission schedule calls for an additional 155 orbits around the planet, 54 flybys of Titan and 11 flybys of the icy moon Enceladus.

The mission extension also will allow scientists to continue observations of Saturn’s rings and the magnetic bubble around the planet known as the magnetosphere. The spacecraft will make repeated dives between Saturn and its rings to obtain in depth knowledge of the gas giant. During these dives, the spacecraft will study the internal structure of Saturn, its magnetic fluctuations and ring mass.

Cassini launched in October 1997 with the European Space Agency’s Huygens probe. The spacecraft arrived at Saturn in 2004. The probe was equipped with six instruments to study Titan, Saturn’s largest moon. Cassini’s 12 instruments have returned a daily stream of data from Saturn’s system for nearly six years.

“The spacecraft is doing remarkably well, even as we endure the expected effects of age after logging 2.6 billion miles on its odometer,” said Bob Mitchell, Cassini program manager at JPL. “This extension is important because there is so much still to be learned at Saturn. The planet is full of secrets, and it doesn’t give them up easily.”

Cassini’s travel scrapbook includes more than 210,000 images; information gathered during more than 125 revolutions around Saturn; 67 flybys of Titan and eight close flybys of Enceladus. Cassini has revealed unexpected details in the planet’s signature rings, and observations of Titan have given scientists a glimpse of what Earth might have been like before life evolved.

For more info on the mission, check out the Cassini website.

February 2, 2010December 24, 2015 by Fraser Cain

Cassini Images

Launch of Cassini Orbiter and Huygens Probe on Titan IV

Here are some amazing Cassini images. There are some pictures of the spacecraft, and some pictures taken by the spacecraft.

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Here’s a picture of the launch of Cassini and Huygens atop a Titan IV rocket. This was the beginning of a 7-year journey to travel from Earth all the way to Saturn, with a few detours along the way.

Cassini Begins Transmitting Data From Enceladus Flyby

This is an artist’s impression of Cassini flying past Saturn’s moon Enceladus. Cassini discovered strange geysers on Enceladus, blasting water ice into space. These geysers are coming from cracks at Saturn’s south pole, and scientists think it could mean there’s an ocean of liquid water underneath the ice.

This is an artist’s impression of Cassini approaching Saturn. It arrived at Saturn in 2004, beginning many years of incredible research about the ringed planets and its intriguing moons.

Here’s another view of Saturn’s moon Enceladus, with Saturn itself as a backdrop. You can see Saturn’s rings at the bottom of the image, cutting a line across the photo.

You’re looking at a photo of Saturn’s moon Rhea passing in front of Saturn. Both Rhea and Saturn are cloaked in shadow.

We’ve written many articles about Cassini for Universe Today. Here’s an article about the sunlight glinting off a lake on Titan, and here are some amazing pictures of Saturn during its equinox.

If you’d like more Cassini images, check out Hubblesite’s News Releases about Saturn. And here’s a link to the homepage of NASA’s Cassini spacecraft, which is orbiting Saturn.

We’ve also recorded an episode of Astronomy Cast all about Saturn. Listen here, Episode 59: Saturn.

January 29, 2010December 24, 2015 by Nancy Atkinson

Scientists Find Water Ice Creates the Spokes in Saturn’s B Ring

Spokes visible in Saturn's B ring. Credit: NASA/JPL/Space Science Institute

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The mysterious spokes that sometimes appear in Saturn’s largest ring, the B ring, have been unexplained. But new measurements from Cassini’s Visual Infrared Mapping spectrometer (VIMS) suggests the radial spokes that sometimes form across the ring are entirely composed of water ice. The existence of the spokes were unexpected and were first observed when the Voyager spacecraft flew by Saturn in 1980. When Cassini arrived at Saturn in 2004, the spokes were not visible, but later appeared in 2005; the VIMS instrument was not able to observe the spokes until 2008. Even with this new information, the spokes are still mysterious, as they appear to be a seasonal phenomenon and can become visible and then fade within a few hours. The process that creates and dissipates the spokes is unknown.

Another view from Cassini of spokes. Credit: Credit: NASA/JPL/Space Science Institute

Early hypotheses on the spokes speculated that gravitational forces and/or electrostatic repulsion between ring particles played a role in creating the spokes. One clue was that the spokes are more commonly observed when Saturn’s rings are more nearly edge on to the Sun. Other scientists had suggested ice, but believed the spokes were composed mainly of smaller ice grains. However, the new data show a large portion of the grains are larger than expected; a micrometer or more in radius.

E. D’Aversa and his team from the Institute for Interplanetary Space Physics in Rome, Italy used the VIMS instrument on Cassini to observe the infrared spectrum emitted by these spokes on July 9, 2008. These were the first measurements of the complete reflectance spectrum of the spokes in a wide spectral range (0.35–0.51 ?m). The team said that radiative transfer modeling supports a pure water ice composition for the spoke’s grains, but their size distribution is found to be wider than previously thought.

The preliminary results showed a modal value of about 1.90 ?m (reff = 3.5 ?m, veff = 0.3) and a number density of about 0.01–0.1 grains/cm3. The researchers say the unexpected abundance of micron-sized grains in the spokes may have implications for the formation models since the energy requirement increases by at least one order of magnitude. Future observations could help constrain the size as well as shed more light on the how the spokes form, evolve and change.

Paper: The spectrum of a Saturn ring spoke from Cassini/VIMS

December 28, 2009December 24, 2015 by Fraser Cain

Largest Moon of Saturn

The largest moon of Saturn is Titan, measuring 5,150 km across. In fact, Titan is the second largest moon in the Solar System, after Jupiter’s Ganymede. Titan is so big that it’s even larger than planet Mercury, which is only 4,879 km across. And it’s much bigger than the Earth’s moon at 3,474 km.

Astronomers used to think that Titan was actually the largest moon in the Solar System, but when NASA’s Voyager spacecraft first arrived at the moon in the 1980s, they were able to make detailed observations of the moon at its atmosphere. They proved that Titan’s atmosphere extended out for dozens of kilometers, and so the physical moon itself was actually smaller than previously thought, making it smaller than Ganymede.

Titan orbits Saturn at an average distance of 1,221,870 km, completing an orbit every 15.945 days. It’s tidally locked to Saturn, so it always presents the same face to Saturn. So a day on Saturn is also the same amount of time it takes to orbit Saturn.

Titan is the only moon in the Solar System known to have a thick atmosphere. In fact, the pressure of the atmosphere on the surface of Saturn is 1.5 times greater than the atmospheric pressure here on Earth. Of course, the atmosphere of Titan is almost entirely nitrogen, and the temperature is -179° C. So it wouldn’t be a comfortable place to visit without a spacesuit.

We’ve written many articles about Titan for Universe Today. Here’s an article about seasonal changes on Titan, and here’s an article about how Titan’s haze acts like an ozone layer.

If you’d like more info on Titan, check out Hubblesite’s News Releases about Saturn. And here’s a link to the homepage of NASA’s Cassini spacecraft, which is orbiting Saturn.

We’ve also recorded an episode of Astronomy Cast just about Saturn’s moons. Listen here, Episode 61: Saturn’s Moons.

December 23, 2009December 24, 2015 by Nancy Atkinson

May Visions of Saturn’s Moons Dance in Your Head

Moons dancing around Saturn. Credit: NASA/JPL/Space Science Institute

The Cassini CICLOPS imaging team has released some new movies of several moons orbiting Saturn as if in a cosmic ballet around the ringed planet. In one scene that blends 12 images taken over the span of 19 minutes, Rhea skates in front of Janus, as Mimas and Pandora slide across the screen in the opposite direction.

“As yet another year in Saturn orbit draws to a close, these wondrous movies of an alien place clear across the solar system remind us how fortunate we are to be engaged in this magnificent exploratory expedition,” said Carolyn Porco, Cassini imaging team leader.

Click here to see the movies.

While the dance appears leisurely on screen, Rhea actually orbits Saturn at a speed of about 8 kilometers per second (18,000 mph). The other moons are hurtling around the planet even faster. Mimas averages about 14 kilometers per second (31,000 mph), and Janus and Pandora travel at about 16 kilometers per second (36,000 mph).

Sources: JPL, CICLOPS

December 20, 2009December 24, 2015 by Fraser Cain

Saturn Fact Sheet

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The following Saturn fact sheet is based on NASA’s excellent planetary fact sheets. Saturn is the 6th planet from the Sun, and the second largest planet in the Solar System.

Mass: 568.46 x 10²⁴ kg
Volume: 82,713 x 10¹⁰ km³
Average radius: 58,232 km
Average diameter: 116,464 km
Mean density: 0.687 g/cm³
Escape velocity: 35.5 km/s
Surface gravity: 10.44 m/s²
Natural satellites: 60
Rings? – Yes
Semimajor axis: 1,433,530,000 km
Orbit period: 10,759.22 days
Perihelion: 1,352,550,000 km
Aphelion: 1,514,500,000 km
Mean orbital velocity: 9.69 km/s
Orbit inclination: 2.485°
Orbit eccentricity: 0.0565
Sidereal rotation period: 10.656 hours
Length of day: 10.656 hours
Axial tilt: 26.73°
Discovery: Known since prehistoric times
Minimum distance from Earth: 1,195,500,000 km
Maximum distance from Earth: 1,658,500,000 km
Maximum apparent diameter from Earth: 20.1 arc seconds
Minimum apparent diameter from Earth: 14.5 arc seconds
Maximum visual magnitude: 0.43

We’ve written many articles about Saturn for Universe Today. Here’s an article about the rotation of Saturn, and here’s an article about the atmosphere of Saturn.

If you’d like more info on Saturn, check out Hubblesite’s News Releases about Saturn. And here’s a link to the homepage of NASA’s Cassini spacecraft, which is orbiting Saturn.

We’ve also recorded an entire episode of Astronomy Cast just about Saturn. Listen here, Episode 59: Saturn.

December 9, 2009December 24, 2015 by Nancy Atkinson

Saturn’s Hexagon Endures!

This movie from Cassini, made possible only as Saturn’s north pole emerged from winter darkness, shows new details of a jet stream that follows a hexagon-shaped path and has long puzzled scientists.

You can also check out these cool telescopes that will help you see the beauty of planet Saturn.

The Cassini spacecraft was able to take another look at one of Saturn’s strangest features – a bizarre six-sided cloud structure circling the entire north pole. This structure was hinted at when the Voyager spacecraft first visited the planet nearly 30 years ago, and Cassini was able to take a brief look a few years ago with Cassini’s infrared camera. But these latest images provide evidence the hexagon-shaped jet stream is still there, (the north pole has been shrouded in darkness but has now recently emerged into sunlight) and gives scientists the most detail yet to study the intriguing hexagon shape crowning the planet.

The hexagon shape is the path of a jet stream flowing around the north pole, and new images reveal concentric circles, curlicues, walls and streamers not seen in previous images. Much to the delight and bafflement of Cassini scientists, the location and shape of the hexagon in the latest images match up with what they saw in the Voyager pictures.

“The longevity of the hexagon makes this something special, given that weather on Earth lasts on the order of weeks,” said Kunio Sayanagi, from the Cassini imaging team. “It’s a mystery on par with the strange weather conditions that give rise to the long-lived Great Red Spot of Jupiter.”

The hexagon was originally discovered in images taken by the Voyager spacecraft in the early 1980s. It encircles Saturn at about 77 degrees north latitude and has been estimated to have a diameter wider than two Earths. The jet stream is believed to whip along the hexagon at around 100 meters per second (220 miles per hour).

But what causes the hexagon? Scientists aren’t quite sure. Particularly intriguing is where it gets and expels its energy and how it has stayed so organized for so long. The Cassini team plans to search the new images for clues, taking an especially close look at the newly identified waves that radiate from the corners of the hexagon — where the jet takes its hardest turns — and the multi-walled structure that extends to the top of Saturn’s cloud layer in each of the hexagon’s six sides. There’s also the a large dark spot that appeared in a different position in a previous infrared image from Cassini. In the latest images, the spot appears in the 2 o’clock position.

Early hexagon images from Voyager and ground-based telescopes suffered from poor viewing perspectives. Cassini, which has been orbiting Saturn since 2004, has a better angle for viewing the north pole. But the long darkness of Saturnian winter hid the hexagon from Cassini’s visible-light cameras for years. Infrared instruments, however, were able to obtain images by using heat patterns. Those images showed the hexagon is nearly stationary and extends deep into the atmosphere. They also discovered a hotspot and cyclone in the same region.

The visible-light cameras of Cassini’s imaging science subsystem, which have higher resolution than the infrared instruments and the Voyager cameras, got their long-awaited glimpse of the hexagon in January, as the planet approached equinox. Imaging team scientists calibrated and stitched together 55 images to create a mosaic and three-frame movie. The mosaics do not show the region directly around the north pole because it had not yet fully emerged from winter night at that time.

Because Saturn does not have land masses or oceans on its surface to complicate weather the way Earth does, its conditions should give scientists a more elementary model to study the physics of circulation patterns and atmosphere, said Kevin Baines, an atmospheric scientist at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., who has studied the hexagon with Cassini’s visual and infrared mapping spectrometer.

“Now that we can see undulations and circular features instead of blobs in the hexagon, we can start trying to solve some of the unanswered questions about one of the most bizarre things we’ve ever seen in the solar system,” Baines said. “Solving these unanswered questions about the hexagon will help us answer basic questions about weather that we’re still asking about our own planet.”

Source: JPL

November 27, 2009May 4, 2017 by Fraser Cain

Who Discovered Saturn?

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Were you wondering who discovered Saturn? Well, nobody knows. Here’s the problem. Saturn is one of the 5 planets that you can see with the unaided eye. In fact, if you’re seeing a bright star in the sky, there’s a good chance it’s Saturn. It takes a telescope to see the rings, but anybody can find Saturn, even in a bright city.

So perhaps a better question might be to ask, when did astronomers realize that Saturn was a planet? The ancient astronomers believed in the geocentric model of the Universe. The Earth was at the center of the Universe, and everything else orbited around it in crystal shells: the Sun, the Moon, the planets and the stars. One problem with this model was the strange movements of the planets. They would sometimes slow down, stop and even travel backwards in the sky. And to explain this, astronomers had to create elaborate models for the planets where the orbited inside spheres within spheres.

Anyway, this model was turned on its ear by Nicolaus Copernicus in the 1500s. He placed the Sun at the center of the Solar System, and had all the planets orbiting around it. This nicely explained the strange movements of the planets. They weren’t going backwards, it was just a change in perspective, since the Earth is also going around the Sun.

The first person to actually look at Saturn in a telescope was Galileo. He saw a strange oval-shaped planet. He thought the planet might have ears, or two small balls on either side. Later observations showed that these were actually Saturn’s grand ring system. Galileo also discovered Saturn’s moon Titan.

Better observations of Saturn by Giovanni Cassini turned up 4 additional moons of Saturn, as well a division in the rings that would later be named after him: the Cassini division.

But it wouldn’t be until 1979 that the first spacecraft flew past Saturn. NASA’s Pioneer 11 spacecraft made the journey, getting within 20,000 km of the planet’s cloud tops. This was followed by the Voyager spacecraft, and eventually NASA’s Cassini spacecraft that’s orbiting the planet today. All of our best images of Saturn were sent back by orbiting spacecraft.

We have written many articles about the discovery of planets for Universe Today. Here’s an article about the discovery of Uranus, and here’s an article about the discovery of Neptune.

If you’d like more info on Saturn, start with the NASA Cassini mission homepage. That’s where you’ll see all the latest news and photos sent back from Saturn. Then check out Hubblesite’s News Releases about Saturn.

We’ve also recorded an entire episode of Astronomy Cast just about Saturn. Check it out here, Episode 59: Saturn.

Reference:
NASA

November 21, 2009December 24, 2015 by Nancy Atkinson

De Plume! De Plume! Enceladus Raw Flyby Images

Raw images are already being returned from Cassini’s Nov. 21 “E-8” or eighth flyby of the tiger-striped moon Enceladus. Visible in this raw image are several plumes from fissures in the south polar region of the moon. These fissures spew jets of water vapor and other particles hundreds of kilometers from the surface. This flyby included a very different geometry to the flyby trajectory – and a different look at the plumes — approaching within 1,606 kilometers (997.9 miles) of the surface, buzzing over 82 degrees south latitude. This is the last look we’ll have for several years at this intriguing area of Enceladus before winter darkness blankets the area. See below for looks at Baghdad Sulcus, the “tiger stripe” that scientists were focusing on.

While Cassini was taking these high-resolution images of the southern part of the Saturn-facing hemisphere, the Composite Infrared Spectrograph (CIRS) instrument was collecting data to create a contiguous thermal map of Baghdad Sulcus. This image was taken approximately 1,858 kilometers away.

Here’s a look at Baghdad Sulcus from 3,556 kilometers away. And below is a 3-D version, created by Stu Atkinson. Stay tuned for more details on the data gathered from the flyby!

Enceladus canyon 3-D. Credit: NASA/JPL, 3-D by Stu Atkinson

Source: Cassini raw images

Thanks to Stu for alerting us the images were here!

* The title is in reference to the “Fantasy Island” television show.