Common Questions

Here is a list of the most frequently asked questions about the planet Saturn, its rings, its moons and the Cassini spacecraft.

Questions About The Planet Saturn

How far is Saturn from the sun? How far is Saturn from Earth?

Saturn travels in a slightly elliptical orbit, so its distance from the sun varies. At periapse, or the point in Saturn's orbit where it is closest to the sun, Saturn is roughly 1.4 billion kilometers (870 million miles) from the sun. When it is farthest from the sun, called apoapse, it's about 1.5 billion kilometers (932 million miles) from the sun. It is therefore about 10 times farther from the Sun than is the Earth. The distance between Saturn and Earth changes constantly because they are always moving in their orbits. When Saturn appears overhead at midnight in our night sky, it is typically about 1.3 billion kilometers (808 million miles) away.

How long does it take the signals from Cassini at Saturn to reach Earth?

The telemetry signals from Cassini consist of electromagnetic radiation. This is the same kind of radiation that forms the visible light that our eyes can see, only Cassini's signals are much longer in wavelength. All electromagnetic radiation travels at the speed of light: 300,000 kilometers per second (186,000 miles per second). Consequently, it takes between 70 to 90 minutes, depending on the relative positions of Saturn and the Earth, for light of any kind -- Cassini's telemetry signals or sunlight -- to travel from Saturn to Earth.

How big is Saturn?

Saturn is the second largest planet in the solar system. With an equatorial diameter of 120,660 kilometers (74,975 miles), it's almost 10 times wider than the Earth.

What is Saturn made of?

Saturn is one of our solar system's gaseous giants. It has a solid core of rock about the size of Earth, surrounded by a large envelope of lighter substances, dominated by hydrogen (96%) and helium (2%). Traces of other elements form methane, ammonia and other compounds in the Saturn atmosphere.

What is the surface of Saturn like? What's hidden underneath all that gas?

As a gas giant, Saturn does not have a terrestrial surface like the Earth. Moving from outside towards the interior, one first encounters the outer gaseous atmosphere which gives way to liquid, which eventually, under increasing pressure, gives way to metallic hydrogen surrounding a small, solid core of rock. The diameter of the core is about 12,000 kilometers (7, 500 miles) -- only a fraction of Saturn's overall diameter and about the size of Earth. Saturn's inner structure hasn't been measured directly but can be inferred from the detailed motions its inner moons and rings and orbiting spacecraft like Cassini, together with theoretical information about the behavior under extreme pressure and heat of its main constituent components, hydrogen and helium.

Are there storms in Saturn's atmosphere?

Yes, Saturn's atmosphere has lots of storms which take the form of large vortices. In the southern hemisphere, there seems to be a preferred latitude band, dubbed 'Storm Alley' by the Cassini imaging team, for storms to roil through the atmosphere. Some storms in this band are the sources of intense lightning bursts accompanied by huge electromagnetic bursts or static that can be picked up by Cassini. One of the planet's lightning-producing storms was monitored for months (see PIA 08411).

Why is Saturn colored as it is?

Scientists are investigating the reasons why the colors in the atmosphere of Saturn are what they are and why they change over time. When Cassini arrived in 2004, the northern hemisphere looked different than it did when the two Voyager spacecraft flew by Saturn in 1980 and 1981. In 1980, Saturn's northern hemisphere had just passed its vernal equinox and the northern hemisphere looked golden. In 2004, Cassini found a blue northern hemisphere draped in the shadows of the planet's rings. Scientists think, but have yet to verify, that these shadows probably cooled the atmosphere, causing the clouds seen in the Voyager images to sink to depths where they were no longer visible, and the deep clear atmosphere above the clouds became blue for the same reason the Earth's atmosphere is blue, a phenomenon called Rayleigh scattering. In August 2009, northern vernal equinox will return to Saturn, and as this special time approaches scientists have watched as the northern hemisphere has changed from an azure blue to the colors more reminiscent of the early 1980s (see PIA 10578).

How long is a day on Saturn?

Saturn spins quickly on its axis. Its rotation period -- one day and night on the planet -- is about 10 hours and 40 minutes. This rotation is faster than any other planet except Jupiter, and it makes Saturn bulge around the equator while flattening the planet at the poles.

How long is a year on Saturn?

One Saturn year, or revolution around the sun, takes 29.5 Earth years. In August 2009, Saturn will arrive at a special place, one of two, in its orbit called equinox. At that time, the plane of the rings will be aligned with the rays of the sun and the rings will darken. Only sunlight on the rings' edge and the dim light reflected off the planet onto the rings will illuminate them. Equinox won't happen again for almost 15 years.

What else will happen during Saturn's August 2009 equinox?

Surrounding the time of equinox, shadows from Saturn's moons are cast not onto the planet but onto the rings, creating exciting scenes of moving shadows and informing scientists about possible vertical warps in the rings. Moon shadows have already started to appear, and Cassini has captured some spectacular images as a result (see PIA 11651 and PIA 11652).

Questions about Saturn's rings

What are Saturn's rings made of?

The rings consist of countless, independently orbiting bodies, ranging in size from boulders as large as small apartment buildings to fine, dust-sized specks, and composed mostly of water ice contaminated with only trace amounts of rocky material.

How big are Saturn's rings?

Saturn's main rings -- from the inner D ring to the outer A ring -- are horizontally wide but vertically very thin. The main rings extend about 280,000 kilometers (174,000 miles) across the Saturn system, but they are only about 10 meters (about 30 feet) thick.

How many rings are there?

Saturn's rings appear to consist of thousands of narrow individual ringlets. However, in reality, the main rings are a broad continuous sheet of debris, with only a dozen or so genuine gaps, that is scored by many abrupt changes in transparency that give the appearance of separate ringlets. Nonetheless, different regions of the rings differ from each other in character so much that they have been given different names. There are 7 officially named rings in all, varying greatly in breadth, density and other characteristics. Four of the seven comprise the main rings. Working outward from the planet, the main rings are D, C, B, and A; beyond that lie the F, G and E rings. The C ring to the F ring can be clearly seen in PIA 11142. Cassini also has found several other very diffuse rings and ring arcs associated with small satellites, such as the coorbitals Janus and Epimetheus, Pallene, Methone, and Anthe (see PIA 11102).

Why are the rings' alphabet names out of order?

The rings were named in the order in which they were discovered. Galileo first looked at Saturn using a telescope in 1610, and noted the planet as having appendages of some kind, but he did not understand what they were. In 1676, Giovanni Cassini discovered the biggest gap in the ring system, now called the Cassini Division, between the A and B rings. Other ground-based astronomers over the years discovered the C, D and E rings. Coming last alphabetically, the narrow F ring and the faint G ring weren't added to the list until they were imaged by Voyager 1 in 1980.

Why are there gaps or divisions in the rings?

The separations in the rings -- called divisions when between two rings and called gaps when within one ring -- are usually created by one of two means: by moons that clear a path for themselves through the rings or by gravitational influences, called orbital resonances, from other moons that tug or kick the particles of the rings. Scientists are studying how some narrow gaps are created.

What are spokes?

Spokes are short-lived, radially-extended markings that stretch as far as 10,000 kilometers (6,000 miles) or more across Saturn's B ring (see PIA 11144). A typical spoke is 5,000 kilometers across. Scientists know, due to the way spokes scatter light, that they are composed of extremely small particles less than one micron (one millionth of a meter) across.

Questions about Saturn's moons

How many moons does Saturn have?

As of April 2009, after a tiny moon embedded in the G ring was found by the Cassini imaging team, Saturn has 61 moons officially recognized by the International Astronomical Union (IAU). Not all of these have yet been named. Jupiter, with 62 moons, has the most known moons in the solar system.

Which is Saturn's biggest moon?

Titan, at 5,150 kilometers (3,200 miles) across, is Saturn's biggest moon. Titan is the second largest moon in the solar system, after Jupiter's Ganymede, and the only one that has a significant atmosphere. Titan is bigger than the planet Mercury.

Which is Saturn's smallest moon?

A tiny moonlet, found in 2008 by the Cassini Imaging Team and temporarily designated S/2008 S1, may be Saturn's smallest moon with an estimated diameter of half a kilometer (a third of a mile). Many small objects orbit Saturn, and there may be many moonlets like this one yet to be discovered. Scientists think this moonlet may be a major contributor of the material of the G ring in which it orbits (see PIA 11148).

Are any of Saturn's moons like Earth?

In some limited respects, some of Saturn's moons are like Earth. Titan has a thick, hazy atmosphere made largely of molecular nitrogen, like the Earth's, and exhibits a thermal structure and slight greenhouse effect, just like the Earth's. Also, its surface is sculpted into geological forms reminiscent of the Earth's, with mountains, river channels, dunes, and even lakes. However, the atmosphere and the lakes contain not liquid water but hydrocarbons such as methane (see PIA 11147).

Do any of Saturn's moons offer the possibility life?

Cassini has found a young, geologically active and anomalously warm region capping the south pole of the small, perfectly white and bright Saturnian moon, Enceladus. Spectacular towering jets of vapor and fine icy particles are erupting from long, deep gashes -- the warmest of all places -- crossing the moon's south polar terrain. The vapor consists of water, nitrogen, carbon dioxide, and organic compounds (like methane, benzene, propane, hydrogen cyanide, etc.), and some of the icy particles are believed to be frozen salt water droplets. Moreover, the heat emerging from Enceladus can best be explained by tidal flexure enhanced by the presence of extensive liquid water, perhaps a subterranean sea, within the moon. Also, scientists have seen evidence of past geologic activity on the surface of Enceladus that resembles sea-floor spreading seen on Earth (see PIA 11138). All these findings point to the very exciting possibility that an organics-laden liquid water environment exists beneath the south pole of Enceladus that may be home to sustained pre-biotic chemistry, and perhaps life itself.

Do any of Saturn's moons have volcanic activity?

Saturn's moons have not shown unequivocal evidence of the kind of cryovolcanism that extrudes slushy ice onto the surface. Almost all the geologic features we see on the Saturnian moons, such as Dione and Tethys, can be explained by tectonics. However, on the moon Enceladus, scientists have found evidence of past geologic activity in the moon's south polar region and of course geysering activity in the form of jets of vapor and fine icy particles spewing out from the moon to form the E ring.

Questions about the Cassini spacecraft

When was the Cassini spacecraft launched?

Cassini was launched Oct. 15, 1997 from Cape Canaveral, Fla.

How long did it take Cassini to cross the solar system?

Cassini's took almost seven years to complete its circuitous journey to Saturn over a distance of 3.5 billion kilometers (2.2 billion miles).

What was the flight path the spacecraft followed to get to Saturn?

After the spacecraft's launch from Earth, its trajectory took it close to Venus twice, the Earth once, and then by massive Jupiter, all for the purpose of stealing a bit of each planet's angular momentum and energy in what is called a "gravity assist" maneuver. Each maneuver is like a slingshot that flings Cassini onward with increasing speed to shorten the time it takes to get into the outer solar system.

When did the spacecraft arrive at Saturn?

Cassini entered orbit around the planet July 1, 2004.

How big is the spacecraft?

Cassini is about half as long as a common 35- to 72-passenger school bus, but it is wider. It is 6.7 meters (22 feet) high and 4 meters (13 feet) wide. A boom extends 11 meters (36 feet) for the sensitive magnetometer instrument. Its mass at launch was 5,574 kilograms, or 12,288 pounds.

How fast does the Cassini spacecraft fly?

During Cassini's tour of Saturn in the extended Cassini Equinox Mission, the spacecraft's speed varies from 1 to 21 kilometers per second, or 2,200 to 47,000 miles per hour. During its journey to Saturn, Cassini flew even faster. After its second flyby of the planet Venus, Cassini was traveling at 42.3 kilometers per second, or 95,000 miles per hour!

Has the Cassini spacecraft flown through the rings?

No, the spacecraft has certainly not flown through the main rings, which would be certain death. During orbit insertion, it flew through the broad expanse separating the narrow F ring from the very diffuse and tenuous G ring, but was in no real danger during that passage. However, Cassini has flown through the icy plumes blasting out of the south polar region of Saturn's moon Enceladus (see PIA 10356). When the spacecraft nears the end of its life in 2017, assuming it receives a second extended mission, scientists plan to fly Cassini between planet and the D ring and then into the planet.

What is the magnification for Cassini images and does the magnification change?

A better term than magnification would be resolution, and the resolution of images taken by Cassini's Imaging Science Subsystem changes depending on several variables.

First, the spacecraft's distance to the target will affect the resolution. The resolution improves the closer Cassini is to the target, such as when the spacecraft flies by a moon.

Second, the camera used to take the picture will affect the resolution. Cassini's Imaging Science Subsystem (ISS) has two cameras. The narrow-angle camera (NAC) is a reflecting telescope with a focal length of 2,000 millimeters and a field of view of 0.35 degrees. The wide-angle camera (WAC) is a refractor with a focal length of 200 millimeters and a field of view of 3.5 degrees. Images taken with the NAC will appear 10 times closer than those taken with the WAC from the same distance. For example, an image of the moon Rhea captured with the NAC at a distance of 42,000 kilometers would have a resolution of about 250 meters per pixel. A WAC taken at that same distance would have a resolution of about 2,500 meters, or 2.5 kilometers, per pixel.

Third, data collection methods will also affect the resolution of the resulting image. For example, an image taken at the ISS's full 1024 pixels by 1024 pixels would have a higher resolution than one taken as a "summed" image of 512 by 512 pixels. See the ISS page to learn more .