March 30, 2016

Natural color image of Saturn and its rings taken by Cassini’s narrow angle camera on March 27, 2004. Credit: NASA/JPL/Space Science Institute

Imagine what Saturn would be like without its rings. Though large, it would be quite unremarkable as a planet compared to Jupiter, given that planet’s even greater size, colorful cloud bands, and swirling storms. Aside from its large moon Titan, there would be little about Saturn to excite astronomers and the general public. This ringless state may have been Saturn’s plight in the relatively recent past, according to a new report. Matija Cuk from the Search for Extra-terrestrial Intelligence (SETI) Institute and Luke Dones and David Nesvorny from the Southwest Research Institute of San Antonio, Texas, published findings in The Astrophysical Journal that Saturn’s rings and some of its moons are only about 100 million years old.

Saturn’s rings consist of ice particles that travel around the planet. It has seven main rings, which vary greatly in width. The outermost ring, called the E ring, may measure more than 180,000 miles (300,000 kilometers) across. All of the the rings also vary greatly in thickness. Most are probably under 100 feet (30 meters) thick. They are, however, all so thin that they cannot be seen with Earth-based telescopes when their edge is in direct line with Earth.

Like Saturn itself and the rest of the planets in the solar system, scientists had assumed that Saturn’s rings and satellites (moons) formed about 4.6 billion years ago and had been around ever since. In 2012, however, a team of French scientists suggested that tidal forces (forces created by the uneven pull of gravity on large objects) should have pushed Saturn’s rings and inner moons further from the planet. Thus, the researchers thought the rings might not be as old as the rest of the Saturn system.

Cuk, Dones, and Nesvorny helped support this idea. Occasionally, moons of large planets drift into orbital resonances, when the amount of time each one takes to orbit the planet forms a simple fraction. (For example, if one moon orbits a planet two times for every three orbits another moon makes, those moons are in orbital resonance.)  When this happens, the interaction of gravity between the moons—even if they are small—can fling them into longer, more eccentric, orbits. The three scientists found that the orbits of three satellites of Saturn—Dione, Rhea, and Tethys—had not been changed much due to the effects of orbital resonances. They suggested the moons were formed—along with Saturn’s rings—close to where they orbit today about 100 million years ago.

While 100 million years seems like quite a long time indeed, it is the blink of an eye in astronomical terms. Most of the solar system hasn’t changed much in 4 billion years. The scientists speculate that around 100 million years ago, changes in the orbits of two or more earlier moons caused them to collide. Dione, Rhea, and Tethys would have formed from portions of this debris. Some of the debris would have also rained down on the rest of the Saturn system, peppering older moons with fresh craters. The rest of the debris remained locked in orbit around Saturn as the gorgeous rings we see today. More research must be done to confirm the findings, but it appears that Saturn’s most distinctive feature may be its most recent one.

June 15, 2015

The ring system of Saturn was found to be even more spectacular last week. A team led by Douglas Hamilton of the University of Maryland observed the planet’s giant outer ring using the Spitzer Space Telescope and found it to be even larger than scientists previously thought. They reported their findings in the journal Nature.

This artist’s conception shows a nearly invisible ring around Saturn — the largest of the giant planet’s many rings. It was discovered by NASA’s Spitzer Space Telescope. The artist’s conception simulates an infrared view of the giant ring. Saturn appears as just a small dot from outside the band of ice and dust. The inset shows an enlarged image of Saturn, as seen in infrared light. The ring, stars and wispy clouds are an artist’s representation. (Credit: NASA/JPL-Caltech/Keck)

Saturn’s seven most recognizable rings surround the planet at its equator but do not touch it. They consist mainly of pieces of ice, ranging from dust-sized grains to chunks more than 10 feet (3 meters) in diameter. These rings are named after the letters of the alphabet. The largest and most distant of these rings, the E ring, extends from about 110,000 miles (180,000 kilometers) from the center of Saturn to 300,000 miles (480,000 kilometers) away from the planet.

In 2009, Hamilton and other scientists found a diffuse doughnut-shaped ring far beyond the orbit of the previously known rings using the Spitzer Space Telescope. This year, Hamilton and his colleagues reexamined the ring and were able to better estimate its size and makeup. They found it extended from about 3.7 million miles (6 million kilometers)  to about 10 million miles (16 million kilometers) from Saturn’s surface. They also discovered that the ring is mostly made up of small pieces less than 8 inches (20 centimeters) in diameter, as opposed to the chunkier main rings.

This giant ring may show a strange interaction between two of Saturn’s natural satellites (moons). The ring is centered around the orbit of the moon Phoebe. Scientists suspect that Phoebe released the dust that now forms the giant outer ring. Furthermore, some scientists think that this dust gave another moon its odd coloration. One side of Iapetus is made up of very bright material, while the other side is dark. Its orbit crosses through the Phoebe ring, so dust landing on one side of the satellite may have caused the color differentiation.

Other World Book articles:

• Space exploration
• Astronomy (2003-a Back in Time article)
• Close Encounters with Saturn (a Special Report)

July 23, 2013

The people waving at Saturn knew they would be too far away to be seen, but that didn’t stop tens of thousands of Earthlings from posing for a rare portrait of our home planet and Saturn taken by the Cassini space probe. In the photograph–a mosaic of images released yesterday–Earth appears as a pale blue dot hanging in the darkness of space between several of Saturn’s outer rings. NASA planned the “Wave at Saturn” event to coincide with a rare opportunity for Cassini to photograph Saturn and its entire ring system in the same frame as it was backlit by the sun on July 19. Scientists hope the new photographs will reveal additional details about Saturn’s thinner rings and allow them to study how the rings have changed since 2006, the last time Cassini was able to capture all of the Saturn system at once. The new images, taken 898 million miles (1.44 billion kilometers) from Earth, also show the moon as a bright white dot.

Earth appears as a pale blue dot in an image of Saturn and its glorious rings taken by the Cassini space probe. (NASA/JPL-Caltech/Space Science Institute)

The 2006 images and the new Cassini photos mark only the second and third times, respectively, that Earth has been photographed from the outer solar system. The first image was taken by the Voyager 1 spacecraft in 1990, from about 3.7 billion miles (6 billion kilometers) away. NASA engineers ordered the spacecraft to take the photograph at the request of American astronomer Carl Sagan.

Additional World Book articles:

• Close Encounters with Saturn (a special report)
• Exploring the Suburban Solar System (a special report)