Some of the most important information gathered by Voyager 1 on the Saturn system is presented pictorially in this publication and is supplemented here with brief summaries of the major discoveries, observations, and theories.

SATURN

Saturn’s atmosphere appears similar to Jupiter’s, with alternating dark belts and bright zones, circulating storm regions, and other dark and light cloud markings. Saturn’s belt and zone system extends to higher latitudes than those on Jupiter, and all of the features are muted by a thick atmospheric haze, perhaps 70 kilometers (40 miles) deep.

Wind speeds up to 1500 kilometers per hour (900 miles per hour) occur at the equator—four to five times faster than any Jovian winds. Temperatures near the cloudtops range from 86 to 92 kelvins (-305° to -294° Fahrenheit)—nearly 60 degrees colder than at Jupiter. Saturn still radiates about 2.8 times as much heat as it receives from the Sun. The coolest temperatures are found at the center of the equatorial zone.

Auroral emissions have been seen near Saturn’s poles, and auroral-type emissions have been seen in ultraviolet light near the illuminated limb of the planet.

Lightning bolts have not been seen on Saturn, but radio emissions typical of lightning discharges have been recorded. The source of these discharges is believed to be the rings rather than Saturn’s atmosphere.

RINGS

Hundreds of tiny ringlets—a few of them elliptical rather than circular—comprise the classic A-, B-, and C-Rings, once thought to be uniform disks of material. The F-Ring, which was first sighted by Pioneer 11 in 1979, was observed to be three separate, intertwined ringlets.

The existence of a D-Ring between the C-Ring and the planet has been confirmed by observations during Voyager 1’s passage through Saturn’s shadow. The tenuous E-Ring, previously observed from Earth only when Saturn’s rings could be viewed edge-on (every 15 years), has also been observed during shadow passage. At least one other ring has been found between the E- and F-Rings in Voyager images.

Long, radial, spoke-like features in the B-Ring were dark when viewed upon approach and bright when observed after encounter when the spacecraft looked back toward the planet and the Sun.

NEW SATELLITES

Voyager 1 photographed six tiny moons, some that had never been seen before. Satellites 10 and 11, dubbed the “co-orbitals,” share an orbit 91,000 kilometers (57,000 miles) above Saturn’s cloudtops. The leading satellite has a diameter of about 160 kilometers (100 miles), while the trailing satellite has an irregular shape, approximately 105 by 65 kilometers (65 by 40 miles).

Little is known about satellites 12, 13, 14, and 15 aside from their orbits and periods. Satellite 12 orbits at the same distance from Saturn as Dione, at a point about 60 degrees ahead of Dione. Satellites 13 and 14, outside and inside the F-Ring (respectively), appear to “herd” this thin ring between them. Satellite 15 appears to limit the outer edge of the A-Ring in a similar manner.

INNER SATELLITES

Mimas, Enceladus, Tethys, Dione, and Rhea represent a body size not previously explored by spacecraft. They are larger than Jupiter’s Amalthea and Mars’ Phobos and Deimos, yet smaller than Mercury, our Moon, or Jupiter’s large satellites. Their diameters range from 390 kilometers (240 miles) for Mimas to 1530 kilometers (950 miles) for Rhea, and they are probably composed primarily of water ice.

With the exception of Enceladus, all of these moons have heavily cratered surfaces, looking much like the Moon and Mercury. Mimas displays an impact crater whose diameter is one-fourth that of the satellite—such an impact must have nearly shattered the icy satellite. Tethys has a valley 70 kilometers (40 miles) wide that stretches 800 kilometers (500 miles) across the satellite, an apparent crustal fracture resulting from seismic activity. Several sinuous valleys, some of which appear to branch, are visible on Dione’s surface. Both Dione and Rhea have bright, wispy streaks on their already highly reflective surfaces, perhaps caused by ice thrown out of craters by meteorite impacts.

Of the five inner moons, Enceladus appears the smoothest, but we will have to wait for Voyager 2 to photograph the satellite at greater resolution in 1981. Since the maximum intensity of the E-Ring occurs near Enceladus’ orbit, Enceladus may be a source of E-Ring particles.

TITAN

Titan is now known to be smaller than Jupiter’s Ganymede. Its diameter is less than 5120 kilometers (3180 miles), which implies a density twice that of water ice. A dense, hazy atmosphere at least 400 kilometers (250 miles) thick obscures the surface. Voyager 1 determined that Titan has a nitrogen-rich atmosphere (as does Earth), but with concentrations of hydrocarbons such as methane (natural gas), ethane, acetylene, ethylene, and deadly hydrogen cyanide. The haze layers merge into a darkened hood over the north pole. At the poles, liquid nitrogen lakes may form. The surface temperature is probably near 100 kelvins (-280° Fahrenheit), only slightly warmer than the boiling point of liquid nitrogen.

Titan has no appreciable magnetic field and therefore possesses no large liquid conducting core. It does, however, supply a small amount of charged particles to Saturn’s magnetosphere.

The southern hemisphere is somewhat brighter than the northern, perhaps as a result of seasonal effects.

OUTER SATELLITES

Of the three known outer satellites, Voyager 1 studied from a distance only Hyperion and Iapetus. Tiny Phoebe, in its retrograde (clockwise) orbit, will be studied by Voyager 2 in the summer of 1981. Hyperion and Iapetus are most likely composed of water ice, although their masses and densities are uncertain. Iapetus has one bright and one dark hemisphere. The dark side, which faces forward as Iapetus circles Saturn, reflects about one-fifth as much light as the trailing, bright side.

MAGNETOSPHERE

Although it is only about one-third the size of Jupiter’s magnetosphere, Saturn’s magnetosphere is still an enormous structure, extending nearly two million kilometers from the planet toward the Sun. The size of the magnetosphere fluctuates rhythmically as the flow of charged particles in the solar wind increases or decreases in intensity. The magnetosphere can be pushed inside Titan’s orbit, so that at times the satellite finds itself outside of the magnetosphere altogether.

Charged particles in the planet’s magnetosphere are dragged along by the magnetic field, circling the planet at Saturn’s rotation rate of 10 hours, 39 minutes. These charged particles whiz by Titan at a dizzying rate of more than 200 kilometers (120 miles) per second. Titan leaves a motorboat-like wake in its orbital path.

Extending from the orbit of Titan inward to the orbit of Rhea, an enormous cloud of uncharged hydrogen atoms forms a doughnut-shaped torus of ultraviolet-emitting particles. Because of their neutrality, these atoms are not towed around by Saturn’s magnetic field.

Close to the planet, Saturn’s rings act as an effective shield or absorber of charged particles. The rings themselves are apparently substantially affected in this process, however, as evidenced by their “spokes” of fine particles and the lightning-like electrical discharges attributed to the rings.