How Many Moons Does Saturn Have?

Saturn is well known for being a gas giant, and for its impressive ring system. But would it surprise you to know that this planet also has the second-most moons in the Solar System, second only to Jupiter? Yes, Saturn has at least 150 moons and moonlets in total, though only 62 have confirmed orbits and only 53 have been given official names.

Most of these moons are small, icy bodies that are little more than parts of its impressive ring system. In fact, 34 of the moons that have been named are less than 10 km in diameter while another 14 are 10 to 50 km in diameter. However, some of its inner and outer moons are among the largest and most dramatic in the Solar System, measuring between 250 and 5000 km in diameter and housing some of greatest mysteries in the Solar System.

Saturn’s moons have such a variety of environments between them that you’d be forgiven for wanting to spend an entire mission just looking at its satellites. From the orange and hazy Titan to the icy plumes emanating from Enceladus, studying Saturn’s system gives us plenty of things to think about. Not only that, the moon discoveries keep on coming. As of April 2014, there are 62 known satellites of Saturn (excluding its spectacular rings, of course). Fifty-three of those worlds are named.

The Cassini spacecraft observes three of Saturn's moons set against the darkened night side of the planet. Credit: NASA/JPL/Space Science Institute
The Cassini spacecraft observes three of Saturn’s moons set against the darkened night side of the planet. Credit: NASA/JPL/Space Science Institute

Discovery and Naming:

Prior to the invention of telescopic photography,  eight of Saturn’s moons were observed using simple telescopes. The first to be discovered was Titan, Saturn’s largest moon, which was observed by Christiaan Huygens in 1655 using a telescope of his own design. Between 1671 and 1684, Giovanni Domenico Cassini discovered the moons of Tethys, Dione, Rhea and Iapetus – which he collectively named the “Sider Lodoicea” (Latin for “Louisian Stars”, after King Louis XIV of France).

n 1789, William Herschel discovered Mimas and Enceladus, while father-and-son astronomers W.C Bond and G.P. Bond discovered Hyperion in 1848 – which was independently discovered by William Lassell that same year. By the end of the 19th century, the invention of long-exposure photographic plates allowed for the discovery of more moons – the first of which Phoebe, observed in 1899 by W.H. Pickering.

In 1966, the tenth satellite of Saturn was discovered by French astronomer Audouin Dollfus, which was later named Janus. A few years later, it was realized that his observations could only be explained if another satellite had been present with an orbit similar to that of Janus. This eleventh moon was later named Epimetheus, which shares the same orbit with Janus and is the only known co-orbital in the Solar System.

Saturn and its moons. Image credit: NASA/JPL/SSI
Collage of Saturn and its largest moons. Credit: NASA/JPL/SSI

By 1980, three additional moons were discovered and later confirmed by the Voyager probes. They were the trojan moons (see below) of Helene (which orbits Dione) as well as Telesto and Calypso (which orbit Tethys).

The study of the outer planets has since been revolutionized by the use of unmanned space probes. This began with the arrival of the Voyager spacecraft to the Cronian system in 1980-81, which resulted in the discovery of three additional moons – Atlas, Prometheus, and Pandora – bringing the total to 17. By 1990, archived images also revealed the existence of Pan.

This was followed by the Cassini-Huygens mission, which arrived at Saturn in the summer of 2004. Initially, Cassini discovered three small inner moons, including Methone and Pallene between Mimas and Enceladus, as well as the second Lagrangian moon of Dione – Polydeuces. In November of 2004, Cassini scientists announced that several more moons must be orbiting within Saturn’s rings. From this data, multiple moonlets and the moons of Daphnis and Anthe have been confirmed.

The study of Saturn’s moons has also been aided by the introduction of digital charge-coupled devices, which replaced photographic plates by the end of the 20th century. Because of this, ground-based telescopes have begun to discovered several new irregular moons around Saturn. In 2000, three medium-sized telescopes found thirteen new moons with eccentric orbits that were of considerable distance from the planet.

The moons of Saturn, from left to right: Mimas, Enceladus, Tethys, Dione, Rhea; Titan in the background; Iapetus (top) and irregularly shaped Hyperion (bottom). Some small moons are also shown. All to scale. Credit: NASA/JPL/Space Science Institute
The moons of Saturn, from left to right: Mimas, Enceladus, Tethys, Dione, Rhea; Titan in the background; Iapetus (top) and Hyperion (bottom). Credit: NASA/JPL/Space Science Institute

In 2005, astronomers using the Mauna Kea Observatory announced the discovery of twelve more small outer moons. In 2006, astronomers using Japan’s Subaru Telescope at Mauna Kea reported the discovery of nine more irregular moons. In April of 2007, Tarqeq (S/2007 S 1) was announced, and in May of that same year, S/2007 S 2 and S/2007 S 3 were reported.

The modern names of Saturn’s moons were suggested by John Herschel (William Herschel’s son) in 1847. In keeping with the nomenclature of the other planets, he proposed they be named after mythological figures associated with the Roman god of agriculture and harvest – Saturn, the equivalent of the Greek Cronus. In particular, the seven known satellites were named after Titans, Titanesses and Giants – the brothers and sisters of Cronus.

In 1848, Lassell proposed that the eighth satellite of Saturn be named Hyperion after another Titan. When in the 20th century, the names of Titans were exhausted, the moons were named after different characters of the Greco-Roman mythology, or giants from other mythologies. All the irregular moons (except Phoebe) are named after Inuit and Gallic gods and Norse ice giants.

Saturn’s Inner Large Moons:

Saturn’s moons are grouped based on their size, orbits, and proximity to Saturn. The innermost moons and regular moons all have small orbital inclinations and eccentricities and prograde orbits. Meanwhile, the irregular moons in the outermost regions have orbital radii of millions of kilometers, orbital periods lasting several years, and move in retrograde orbits.

Enceladus. Credit: NASA/JPL/Space Science Institute
Saturn’s moon of Enceladus. Credit: NASA/JPL/Space Science Institute

Saturn’s Inner Large Moons, which orbit within the E Ring (see below), include the larger satellites Mimas, Enceladus, Tethys, and Dione. These moons are all composed primarily of water ice, and are believed to be differentiated into a rocky core and an icy mantle and crust. With a diameter of 396 km and a mass of 0.4×1020 kg, Mimas is the smallest and least massive of these moons. It is ovoid in shape and orbits Saturn at a distance of 185,539 km with an orbital period of 0.9 days.

Some people jokingly call Mimas the “Death Star” moon because of the crater in its surface that resembles the machine from the Star Wars universe. The 140 km (88 mi) Herschel Crater is about a third the diameter of the moon itself, and could have created fractures (chasmata) on the moon’s opposing side. There are in fact craters throughout the moon’s small surface, making it among the most pockmarked in the Solar System.

Enceladus, meanwhile, has a diameter of 504 km, a mass of 1.1×1020 km and is spherical in shape. It orbits Saturn at a distance of 237,948 km and takes 1.4 days to complete a single orbit. Though it is one of the smaller spherical moons, it is the only Cronian moon that is endogenously active – and one of the smallest known bodies in the Solar System that is geologically active. This results in features like the famous “tiger stripes” – a series of continuous, ridged, slightly curved and roughly parallel faults within the moon’s southern polar latitudes.

Large geysers have also been observed in the southern polar region that periodically release plumes of water ice, gas and dust which replenish Saturn’s E ring. These jets are one of several indications that Enceladus has liquid water beneath it’s icy crust, where geothermal processes release enough heat to maintain a warm water ocean closer to its core.

Dione's trailing hemisphere, showing the patches of "whispy terrain". Credit: NASA/JPL
Dione’s trailing hemisphere, showing the patches of “whispy terrain”. Credit: NASA/JPL

The moon has at least five different kinds of terrain, a “young” geological surface of less than 100 million years. With a geometrical albedo of more than 140%, which is due to it being composed largely of water ice, Enceladus is one of the brightest known objects in the Solar System.

At 1066 km in diameter, Tethys is the second-largest of Saturn’s inner moons and the 16th-largest moon in the Solar System. The majority of its surface is made up of heavily cratered and hilly terrain and a smaller and smoother plains region. Its most prominent features are the large impact crater of Odysseus, which measures 400 km in diameter, and a vast canyon system named Ithaca Chasma – which is concentric with Odysseus and measures 100 km wide, 3 to 5 km deep and 2,000 km long.

With a diameter and mass of 1,123 km and 11×1020 kg, Dione is the largest inner moon of Saturn. The majority of Dione’s surface is heavily cratered old terrain, with craters that measure up to 250 km in diameter. However, the moon is also covered with an extensive network of troughs and lineaments which indicate that in the past it had global tectonic activity.

It’s covered in canyons, cracking and craters and is coated from dust in the E-ring that originally came from Enceladus. The location of this dust has led astronomers to theorize that the moon was spun about 180 degrees from its original disposition in the past, perhaps due to a large impact.

Saturn’s Large Outer Moons:

The Large Outer Moons, which orbit outside of the Saturn’s E Ring, are similar in composition to the Inner Moons – i.e. composed primarily of water ice and rock. Of these, Rhea is the second largest – measuring 1,527 km in diameter and 23×1020 kg in mass – and the ninth largest moon of the Solar System. With an orbital radius of 527,108 km, it is the fifth-most distant of the larger moons, and takes 4.5 days to complete an orbit.

Views of Saturn's moon Rhea. Credit: NASA/JPL/Space Science Institute
Views of Saturn’s moon Rhea. Credit: NASA/JPL/Space Science Institute

Like other Cronian satellites, Rhea has a rather heavily cratered surface, and a few large fractures on its trailing hemisphere. Rhea also has two very large impact basins on its anti-Saturnian hemisphere – the Tirawa crater (similar to Odysseus on Tethys) and an as-yet unnamed crater – that measure 400 and 500 km across, respectively.

Rhea has at least two major sections, the first being bright craters with craters larger than 40 km (25 miles), and a second section with smaller craters. The difference in these features are believed to be evidence of a major resurfacing event at some time in Rhea’s past.

At 5150 km in diameter, and 1,350×1020 kg in mass, Titan is Saturn’s largest moon and comprises more than 96% of the mass in orbit around the planet. Titan is also the only large moon to have its own atmosphere, which is cold, dense, and composed primarily of nitrogen with a small fraction of methane. Scientists have also noted the presence of polycyclic aromatic hydrocarbons in the upper atmosphere, as well as methane ice crystals.

The surface of Titan, which is difficult to observe due to persistent atmospheric haze, shows only a few impact craters, evidence of cryovolcanoes, and longitudinal dune fields that were apparently shaped by tidal winds. Titan is also the only body in the Solar System beside Earth with bodies of liquid on its surface, in the form of methane–ethane lakes in Titan’s north and south polar regions.

ASA's Cassini spacecraft looks toward the night side of Saturn's largest moon and sees sunlight scattering through the periphery of Titan's atmosphere and forming a ring of color. Credit: NASA/JPL-Caltech/Space Science Institute
Image of Titan’s taken by the Cassini spacecraft, showing light passing through the periphery of the moon’s atmosphere. Credit: NASA/JPL-Caltech/Space Science Institute

Titan is also distinguished for being the only Cronian moon that has ever had a probe land on it. This was the Huygens lander, which was carried to the hazy world by the Cassini spacecraft. Titan’s “Earth-like processes” and thick atmosphere are among the things that make this world stand out to scientists, which include its ethane and methane rains from the atmsophere and flows on the surface.

With an orbital distance of 1,221,870 km, it is the second-farthest large moon from Saturn, and completes a single orbit every 16 days. Like Europa and Ganymede, it is believed that Titan has a subsurface ocean made of water mixed with ammonia, which can erupt to the surface of the moon and lead to cryovolcanism.

Hyperion is Titan’s immediate neighbor. At an average diameter of about 270 km, it is smaller and lighter than Mimas. It is also irregularly shaped and quite odd in composition. Essentially, the moon is an ovoid, tan-colored body with an extremely porous surface (which resembles a sponge).  The surface of Hyperion is covered with numerous impact craters, most of which are 2 to 10 km in diameter. It also has a highly unpredictable rotation, with no well-defined poles or equator.

At 1,470 km in diameter and 18×1020 kg in mass, Iapetus is the third-largest of Saturn’s large moons. And at a distance of 3,560,820 km from Saturn, it is the most distant of the large moons, and takes 79 days to complete a single orbit. Due to its unusual color and composition – its leading hemisphere is dark and black whereas its trailing hemisphere is much brighter – it is often called the “yin and yang” of Saturn’s moons.

The two sides of Iapetus. Credit: NASA/JPL
The two sides of Iapetus, Saturn’s “yin-yang moon”. Credit: NASA/JPL

Saturn’s Irregular Moons:

Beyond these larger moons are Saturn’s Irregular Moons. These satellites are small, have large-radii, are inclined, have mostly retrograde orbits, and are believed to have been acquired by Saturn’s gravity. These moons are made up of three basic groups – the Inuit Group, the Gallic Group, and the Norse Group.

The Inuit Group consists of five irregular moons that are all named from Inuit mythology – Ijiraq, Kiviuq, Paaliaq, Siarnaq, and Tarqeq. All have prograde orbits that range from 11.1 to 17.9 million km, and from 7 to 40 km in diameter. They are all similar in appearance (reddish in hue) and have orbital inclinations of between 45 and 50°.

The Gallic group are a group of four prograde outer moons named for characters in Gallic mythology -Albiorix, Bebhionn, Erriapus, and Tarvos. Here too, the moons are similar in appearance and have orbits that range from 16 to 19 million km. Their inclinations are in the 35°-40° range, their eccentricities around 0.53, and they range in size from 6 to 32 km.

Last, there is the Norse group, which consists of 29 retrograde outer moons that take their names from Norse mythology. These satellites range in size from 6 to 18 km, their distances from 12 and 24 million km, their inclinations between 136° and 175°, and their eccentricities between 0.13 and 0.77. This group is also sometimes referred to as the Phoebe group, due to the presence of a single larger moon in the group – which measures 240 km in diameter. The second largest, Ymir, measures 18 km across.

Saturns rings and moons Credit: NASA
Saturn’s rings and moons Credit: NASA

Within the Inner and Outer Large Moons, there are also those belonging to Alkyonide group. These moons – Methone, Anthe, and Pallene – are named after the Alkyonides of Greek mythology, are located between the orbits of Mimas and Enceladus, and are among the smallest moons around Saturn.  Some of the larger moons even have moons of their own, which are known as Trojan moons. For instance, Tethys has two trojans – Telesto and Calypso, while Dione has Helene and Polydeuces.

Moon Formation:

It is thought that Saturn’s moon of Titan, its mid-sized moons and rings developed in a way that is closer to the Galilean moons of Jupiter. In short, this would mean that the regular moons formed from a circumplanetary disc, a ring of accreting gas and solid debris similar to a protoplanetary disc. Meanwhile, the outer, irregular moons are believed to have been objects that were captured by Saturn’s gravity and remained in distant orbits.

However, there are some variations on this theory. In one alternative scenario, two Titan-sized moons were formed from an accretion disc around Saturn; the second one eventually breaking up to produce the rings and inner mid-sized moons. In another, two large moons fused together to form Titan, and the collision scattered icy debris that formed to create the mid-sized moons.

However, the mechanics of how the moon’s formed remains a mystery for the time being. With additional missions mounted to study the atmospheres, compositions and surfaces of these moons, we may begin to understand where they truly came from.

Much like Jupiter, and all the other gas giants, Saturn’s system of satellites is extensive as it is impressive. In addition to the larger moons that are believed to have formed from a massive debris field that once orbited it, it also has countless smaller satellites that were captured by its gravitational field over the course of billions of years. One can only imagine how many more remain to be found orbiting the ringed giant.

We have many great articles on Saturn and its moon’s here at Universe Today. For example, here’s How Many Moons Does Saturn Have? and Is Saturn Making a New Moon?

Here’s an article about the discovery of Saturn’s 60th moon, and another article about how Saturn’s moons could be creating new rings.

Want more information about Saturn’s moons? Check out NASA’s Cassini information on the moons of Saturn, and more from NASA’s Solar System Exploration site.

We have recorded two episodes of Astronomy Cast just about Saturn. The first is Episode 59: Saturn, and the second is Episode 61: Saturn’s Moons.

Sources:

New Flyover Video Takes You on a Tour of Titan’s Lake Region

Saturn’s moon Titan has the only known liquid lakes beyond planet Earth, and new data from the Cassini spacecraft’s radar instrument provides an intriguing 3-D flyover of these hydrocarbon lakes and seas at the north pole region. Steve Wall, Cassini acting radar team lead, provided a guided tour as he presented the video at the American Geophysical Union conference in San Francisco, noting that the vertical heights are exaggerated tenfold and the data has been colorized, both for visual effect.

The video starts by zooming into the southern end of Kraken Mare, the largest of Titan’s seas, and as you fly a little farther, Wall said the things that look like little islands are just noise in the radar data. Next, comes Ligea Mare, with its rugged coastline, and you’ll see that the liquid flow into the surrounding terrain, which appear like river valleys.

The “smooth” area that stretches farther from Ligea Mare is actualy not so smooth, but is just an area when the science team doesn’t have topographical data yet.

The video then continues to other smaller lakes that are nestled into valleys and rugged terrain.

“Learning about surface features like lakes and seas helps us to understand how Titan’s liquids, solids and gases interact to make it so Earth-like,” said Wall. “While these two worlds aren’t exactly the same, it shows us more and more Earth-like processes as we get new views.”

The new data is not only visually stunning, but provides previously unknown details about these lakes and the region. For example, Kraken Mare is more extensive and complex than previously thought. They also show nearly all of the lakes on Titan fall into an area covering about 600 miles by 1,100 miles (900 kilometers by 1,800 kilometers). Only 3 percent of the liquid at Titan falls outside of this area.

“Scientists have been wondering why Titan’s lakes are where they are. These images show us that the bedrock and geology must be creating a particularly inviting environment for lakes in this box,” said Randolph Kirk, a Cassini radar team member at the U.S. Geological Survey in Flagstaff, Ariz. “We think it may be something like the formation of the prehistoric lake called Lake Lahontan near Lake Tahoe in Nevada and California, where deformation of the crust created fissures that could be filled up with liquid.”

Additionally, scientists now know that Ligeia Mare is about 560 feet (170 meters) deep. This is the first time scientists have been able to plumb the bottom of a lake or sea on Titan. This was possible partly because the liquid turned out to be very pure, allowing the radar signal to pass through it easily. The liquid surface may be as smooth as the paint on our cars, and it is very clear to radar eyes.

“Ligeia Mare turned out to be just the right depth for radar to detect a signal back from the sea floor, which is a signal we didn’t think we’d be able to get,” said Marco Mastrogiuseppe, a Cassini radar team associate at Sapienza University of Rome. “The measurement we made shows Ligeia to be deeper in at least one place than the average depth of Lake Michigan.”

The new results indicate the liquid is mostly methane, somewhat similar to a liquid form of natural gas on Earth.

Sources: AGU press conference, JPL press release

Earthlings Wave at Saturn as Cassini Images Us

Earth Waves at Saturn and Cassini on July 19, 2013
From more than 40 countries and 30 U.S. states, people around the world shared more than 1,400 images of themselves as part of the Wave at Saturn event organized by NASA’s Cassini mission on July 19, 2013. The Cassini team created this image collage as a tribute to the people of Earth
Credit: NASA/JPL-Caltech/People of Earth
See link below to the absolutely gigantic full resolution version [/caption]

On July 19, millions of Earthlings worldwide participated in NASA’s ‘Wave at Saturn’ campaign as the NASA Cassini Saturn orbiter turned about and imaged all of us.

Earthlings from 40 countries and 30 U.S. states heeded NASA’s call to photograph themselves while smiling and waving at Saturn and Cassini across 1 billion miles of interplanetary space and shared over 1400 images.

The results of all those images has now been assembled into a fabulous collage in the shape of our planet and released today (Aug. 21) by NASA and the Cassini team as a tribute to the People of Earth.

“Did you wave at Saturn and send us your photo? Then here’s looking at you!” NASA announced on the Cassini Facebook page.

This event was the first time that the citizens of Earth knew in advance that a distant interplanetary spacecraft was photographing portraits of our home planet and our Moon. NASA invited everyone to participate.

Photos flooded into NASA via Twitter, Facebook, Flickr, Instagram, Google+ and email.

Click here for the full resolution version. But be forewarned – it weighs in at over 26 MB and it’s far too big to post here.

The Day the Earth Smiled: Sneak Preview In this rare image taken on July 19, 2013, the wide-angle camera on NASA's Cassini spacecraft has captured Saturn's rings and our planet Earth and its moon in the same frame. Image Credit: NASA/JPL-Caltech/Space Science Institute
The Day the Earth Smiled: Sneak Preview
In this rare image taken on July 19, 2013, the wide-angle camera on NASA’s Cassini spacecraft has captured Saturn’s rings and our planet Earth and its moon in the same frame. Image Credit: NASA/JPL-Caltech/Space Science Institute

“Thanks to all of you, near and far, old and young, who joined the Cassini mission in marking the first time inhabitants of Earth had advance notice that our picture was being taken from interplanetary distances,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory, Pasadena, Calif, in a statement.

“While Earth is too small in the images Cassini obtained to distinguish any individual human beings, the mission has put together this collage so that we can celebrate all your waving hands, uplifted paws, smiling faces and artwork.”

The Cassini imaging science team is still assembling the hundreds of images of Saturn and Earth snapped by the spacecraft as we were waving, to create individual color composites and a panoramic view of the ‘pale blue dot’ and the entire Saturnian system.

To capture all of Saturn and its wide swath of rings, Cassini’s wide angle camera snapped a mosaic of 33 footprints on July 19, 2013.

“At each footprint, images were taken in different spectral filters for a total of 323 images,” says Carolyn Porco, Cassini Imaging Team leader, Space Science Institute in Boulder, Colo.

Cassini took the pictures of Earth from a distance of about 898 million miles (1.44 billion kilometers) away from the home to every human being that has ever lived.

Here is our partial version of Cassini’s mosaic.

Partial context mosaic of the Earth and Saturn taken by NASA’s Cassini orbiter on July 19, 2013.   This mosaic was assembled from five wide angle camera raw images.  Credit: NASA/JPL-Caltech/Ken Kremer/Marco Di Lorenzo
Partial context mosaic of the Earth and Saturn taken by NASA’s Cassini orbiter on July 19, 2013. This mosaic was assembled from five Cassini wide angle camera raw images and offers a sneak peek of the complete panorama. Earth at lower right. Credit: NASA/JPL-Caltech/Ken Kremer/Marco Di Lorenzo

Cassini was launched from Florida in 1997.

It achieved orbit at Saturn in 2004 and has transmitted breathtaking images and science that revolutionized our understanding of the Saturnian system.

The mission is scheduled to continue until 2017 when it will commit a suicide death dive into the humongous gas giant.

Coincidentally, the first humans (Neil Armstrong and Buzz Aldrin) set foot on the Moon 44 years ago nearly to the day of Cassini’s Earth-Moon portrait on July 20, 1969 aboard Apollo 11.

And likewise on July 19, 2013, billionaire space enthusiast Jeff Bezos announced that his dive teams had recovered components of an Apollo 11 first stage F-1 rocket engine from the Saturn V moon rocket that propelled the first humans to the Moon.

Ken Kremer

JPL Waves at Saturn As NASA's Cassini spacecraft turned its imaging cameras to Earth, scientists, engineers and visitors at NASA's Jet Propulsion Laboratory, Pasadena, Calif., gathered to wave at our robotic photographer in the Saturn system on July 19, 2013. Credit: NASA/JPL-Caltech
JPL Waves at Saturn As NASA’s Cassini spacecraft turned its imaging cameras to Earth, scientists, engineers and visitors at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., gathered to wave at our robotic photographer in the Saturn system on July 19, 2013. Credit: NASA/JPL-Caltech

Sneak Peeks of the Earth and Saturn Panorama from Cassini on July 19

The Day the Earth Smiled: Sneak Preview
In this rare image taken on July 19, 2013, the wide-angle camera on NASA’s Cassini spacecraft has captured Saturn’s rings and our planet Earth and its moon in the same frame. Image Credit: NASA/JPL-Caltech/Space Science Institute
See below our wider context mosaic of the Earth, Saturn and its majestic rings[/caption]

Breathtaking raw images of the Earth and Saturn system snapped by NASA’s Cassini spacecraft on July 19 during the worldwide ‘Wave at Saturn’ campaign are streaming back across 1 billion miles of interplanetary space.

Science team members are now busily processing the images to create individual color composites and a panoramic view of the ‘pale blue dot’ and the entire Saturnian system.

NASA just released the first individual color composite focusing on Earth – see above. And its spectacular!

See below our preliminary mosaic showing the Earth in context with nearly half of Saturn and floating in between its incomparably majestic rings.

Partial context mosaic of the Earth and Saturn taken by NASA’s Cassini orbiter on July 19, 2013.   This mosaic was assembled from five wide angle camera raw images.  Credit: NASA/JPL-Caltech/Ken Kremer/Marco Di Lorenzo
Partial context mosaic of the Earth and Saturn taken by NASA’s Cassini orbiter on July 19, 2013. This mosaic was assembled from five wide angle camera raw images and offers a sneak peek of the complete panorama. Credit: NASA/JPL-Caltech/Ken Kremer/Marco Di Lorenzo

To capture all of Saturn and its wide swath of rings, Cassini’s wide angle camera snapped a mosaic of 33 footprints.

“At each footprint, images were taken in different spectral filters for a total of 323 images,” says Carolyn Porco, Cassini Imaging Team leader of the Space Science Institute in Boulder, Colo.

Cassini took the pictures of Earth between 2:27 and 2:42 p.m. PDT on Friday, July 19 from a distance of about 898 million miles (1.44 billion kilometers) away from the home to every human being that has ever lived.

The images show the Earth and the Moon as dots barely about a pixel wide but do reveal the ‘pale blue dot’ that is home to all of humanity and our whitish colored neighbor.

Coincidentally, the first humans (Neil Armstrong and Buzz Aldrin) set foot on the Moon 44 years ago nearly to the day of Cassini’s new images on July 20, 1969.

Distant views of the Earth from our robotic explorers, especially from the outer reaches of our Solar System, are few and far between, and are therefore events for space and astronomy enthusiasts and everyone else to savor.

“One of the most exciting Cassini events in 2013 will be the unusual opportunity on July 19 to image the whole Saturn system as it is backlit by the sun,” explained Linda Spilker, Cassini project scientist of NASA’s Jet Propulsion Laboratory, Pasadena, Calif.

“With Saturn covering the harsh light of the sun, we will be gathering unique ring science and also catching a glimpse of our very own home planet.”

Cassini previously took an absolutely fabulous mosaic of Saturn and Earth back in 2006 that stands as one of the landmark images of the space age.

Besides being picturesque, such mosaics also serve science. For example, the 2006 image “revealed that the dusty E ring, which is fed by the water-ice plume of the moon Enceladus, had unexpectedly large variations in brightness and color around its orbit,” says Spilker.

“We’ll want to see how that looks seven Earth years and a Saturnian season later, giving us clues to the forces at work in the Saturn system. We’ll do this analysis by collecting data from our visual and infrared mapping spectrometer, composite infrared mapping spectrometer and ultraviolet imaging spectrograph in addition to the imaging cameras.”

This simulated view from NASA's Cassini spacecraft shows the expected positions of Saturn and Earth on July 19, 2013, around the time Cassini will take Earth's picture. Cassini will be about 898 million miles (1.44 billion kilometers) away from Earth at the time. That distance is nearly 10 times the distance from the sun to Earth. Image credit: NASA/JPL-Caltech
This simulated view from NASA’s Cassini spacecraft shows the expected positions of Saturn and Earth on July 19, 2013, around the time Cassini will take Earth’s picture. Cassini will be about 898 million miles (1.44 billion kilometers) away from Earth at the time. That distance is nearly 10 times the distance from the sun to Earth. Image credit: NASA/JPL-Caltech

“July 19 marked the first time people on Earth had advance notice their planet’s portrait was being taken from interplanetary distances,” says NASA.

I waved fondly at Saturn and hope you had the chance to wave at Saturn from all across the globe. NASA reports that nearly 20,000 participated in organized events. Countless others waved too.

Cassini was launched in 1997 and achieved orbit at Saturn in 2004. The mission is scheduled to continue until 2017 when it will commit a suicide death dive into the gas giant.

“We can’t see individual continents or people in this portrait of Earth, but this pale blue dot is a succinct summary of who we were on July 19,” said Spilker in a NASA statement.

“Cassini’s picture reminds us how tiny our home planet is in the vastness of space, and also testifies to the ingenuity of the citizens of this tiny planet to send a robotic spacecraft so far away from home to study Saturn and take a look-back photo of Earth.”

Ken Kremer

JPL Waves at Saturn As NASA's Cassini spacecraft turned its imaging cameras to Earth, scientists, engineers and visitors at NASA's Jet Propulsion Laboratory, Pasadena, Calif., gathered to wave at our robotic photographer in the Saturn system on July 19, 2013. Credit: NASA/JPL-Caltech
JPL Waves at Saturn
As NASA’s Cassini spacecraft turned its imaging cameras to Earth, scientists, engineers and visitors at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., gathered to wave at our robotic photographer in the Saturn system on July 19, 2013. Credit: NASA/JPL-Caltech

Cassini Watches as Meteors Hit Saturn’s Rings

From tell-tale evidence, we know that Earth, our Moon and other bodies in our Solar System are constantly barraged with both small meteoroids and larger asteroids or comets. And sometimes – like in the case of seeing meteors fling across our sky, or flashes on the Moon or Jupiter getting hit by Comet Shoemaker-Levy 9 — we even get to watch as it happens. Now, for the first time the Cassini spacecraft has provided direct evidence of small meteoroids crashing into Saturn’s rings.

Researchers say that studying the impact rate of meteoroids from outside the Saturnian system helps scientists understand how different planet systems in our solar system formed.

Saturn’s rings act as very effective detectors of many kinds of surrounding phenomena, including the interior structure of the planet and the orbits of its moons. For example, a subtle but extensive corrugation that ripples 12,000 miles (19,000 kilometers) across the innermost rings tells of a very large meteoroid impact in 1983.

“These new results imply the current-day impact rates for small particles at Saturn are about the same as those at Earth — two very different neighborhoods in our solar system — and this is exciting to see,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “It took Saturn’s rings acting like a giant meteoroid detector — 100 times the surface area of the Earth — and Cassini’s long-term tour of the Saturn system to address this question.”

The Saturnian equinox in summer 2009 was an especially good time to see the debris left by meteoroid impacts. The very shallow sun angle on the rings caused the clouds of debris to look bright against the darkened rings in pictures from Cassini’s imaging science subsystem.

This animation depicts the shearing of an initially circular cloud of debris as a result of the particles in the cloud having differing orbital speeds around Saturn. Image credit: NASA/Cornell

“We knew these little impacts were constantly occurring, but we didn’t know how big or how frequent they might be, and we didn’t necessarily expect them to take the form of spectacular shearing clouds,” said Matt Tiscareno, lead author of the paper and a Cassini participating scientist at Cornell University in Ithaca, N.Y. “The sunlight shining edge-on to the rings at the Saturnian equinox acted like an anti-cloaking device, so these usually invisible features became plain to see.”

Tiscareno and his colleagues now think meteoroids of this size probably break up on a first encounter with the rings, creating smaller, slower pieces that then enter into orbit around Saturn. The impact into the rings of these secondary meteoroid bits kicks up the clouds. The tiny particles forming these clouds have a range of orbital speeds around Saturn. The clouds they form soon are pulled into diagonal, extended bright streaks.

“Saturn’s rings are unusually bright and clean, leading some to suggest that the rings are actually much younger than Saturn,” said Jeff Cuzzi, a co-author of the paper and a Cassini interdisciplinary scientist specializing in planetary rings and dust at NASA’s Ames Research Center in Moffett Field, Calif. “To assess this dramatic claim, we must know more about the rate at which outside material is bombarding the rings. This latest analysis helps fill in that story with detection of impactors of a size that we weren’t previously able to detect directly.”

Source: JPL

Outer Space – Mind Blowing Video from Jupiter and Saturn

Video Caption: This mesmerizing video unveils incredibly amazing sequences around Jupiter and Saturn from NASA’s Cassini and Voyager missions set to stirring music by “The Cinematic Orchestra -That Home (Instrumental)”. Credit: Sander van den Berg

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