Diameter of Saturn

Saturn has an equatorial diameter of 120,536 km, 9.44 times that of Earth. That makes it the second largest planet in our Solar System, trailing only Jupiter. Saturn, like all of the other planets, is an oblate spheriod. This means that its equatorial diameter is larger than is diameter measured through the poles. In the case of Saturn this distance is quite a bit different due to the planet’s high rotational speed. The polar diameter of Saturn is 108,728 km, meaning that it is flattened by a factor of 9.796%.

Scientist know that Saturn rotates very quickly, but the exact speed of that rotation has been hard to determine because of the thick clouds in the atmosphere. With terrestrial planets, scientists are able to find surface features and basically time how long it takes for that feature to reappear in the same position. This is a simplified description of how they determine rotational speed. The problem with Saturn is that the surface can not be observed. To make things even more difficult, the visible features of the planet’s atmosphere rotate at different speeds depending on their latitude.

The atmosphere of Saturn is broken down into systems. System I is the equatorial zone has a rotational period of 10 hours and 14 minutes. System II encompasses all other areas of Saturn and has a rotational speed of 10 hours 38 minutes and 25.4 seconds. System III is based on radio emissions and has mostly replaced the use of the term System II. It has a rotational speed of 10 hours 39 minutes and 22.4 seconds. Despite these numbers, the rotational speed of the planet’s interior is currently impossible to measure precisely. The Cassini spacecraft found the radio rotational speed of Saturn to be 10 hours 45 minutes and 45 seconds. In 2007, it was determined that the varying radio emissions from the planet did not match Saturn’s rotation rate. Some scientists think that the variance is due to geyser activity on the Saturnian moon Enceladus. The water vapor from these geysers enter Saturn’s orbit become charged, thus creating a drag effect on Saturn’s magnetic field. This slows the magnetic field’s rotation slightly compared to the rotation of the planet. The current estimate of Saturn’s rotation is based on various measurements from the Cassini, Voyager and Pioneer probes. That estimated speed is 10 hours 32 minutes and 35 seconds as of September 2007.

Again, the equatorial diameter of Saturn is 120,536 km and its polar diameter is 108,728 km. It is very important to understand why the difference in these diameters is so large, that is why so much detail is given on the rotational speed of the planet. You can take many of the same factors into account when thinking about all of the gas giants.

Here’s an article about how long a day is on Saturn, and another article about how the storms never end on Saturn.

Here’s Hubblesite’s News Releases about Saturn, and more information from Solar Views.

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.

Source: NASA

What are Saturn’s Rings Made Of?

Saturn is sometimes called the ”Jewel of the Solar System” because its ring system looks like a crown. The rings are well known, but often the question ”what are Saturn’s rings made of” arises. Those rings are made up of dust, rock, and ice accumulated from passing comets, meteorite impacts on Saturn’s moons, and the planet’s gravity pulling material from the moons. Some of the material in the ring system are as small as grains of sand, others are larger than tall buildings, while a few are up to a kilometer across. Deepening the mystery about the moons is the fact that each ring orbits at a different speed around the planet.

Saturn is not the only planet with a ring system. All of the gas giants have rings, in fact. Saturn’s rings stand out because they are the largest and most vivid. The rings have a thickness of up to one kilometer and they span up to 482,000 km from the center of the planet.

The rings are named in alphabetical order according to when they were discovered. That makes it a little confusing when listing them in order from the planet. Below is a list of the main rings and gaps between them along with distances from the center of the planet and their widths.

  • The D ring is closest to the planet. It is at a distance of 66,970 – 74,490 km and has a width of 7,500 km.
  • C ring is at a distance of 74,490 – 91,980 km and has a width of 17,500 km.
  • Columbo Gap is at a distance of 77,800 km and has a width of 100 km.
  • Maxwell Gap is at a distance of 87,500 km and has a width of 270 km.
  • Bond Gap is at a distance of 88,690 – 88,720 km and has a width of 30 km.
  • Dawes Gap is at a distance of 90,200 – 90,220 km and has a width 20 km.
  • B ring is at a distance of 91,980 – 117,580 km with a width: 25,500 km.
  • The Cassini Division sits at a distance of 117,500 – 122,050 km and has a width of 4,700 km.
  • Huygens gap starts at 117,680 km and has a width of 285 km – 440 km.
  • The Herschel Gap is at a distance of 118,183 – 118,285 km with a width of 102 km.
  • Russell Gap is at a distance of 118,597 – 118,630 km and has a width of 33 km.
  • Jeffreys Gap sits at a distance of 118,931 – 118,969 km with a width of 38 km.
  • Kuiper Gap ranges from 119,403 -119,406 km giving it a width of 3 km.
  • Leplace Gap is at a distance of 119,848 – 120,086 km and a width of 238 km.
  • Bessel Gap is at 120,305 – 120,318 km with a width of 10 km.
  • Barnard Gap is at a distance of 120,305 – 120,318 km giving it a width of 3 km.
  • A ring is at a distance of 122,050 – 136,770 km with a width of 14,600 km.
  • Encke Gap sits between 133,570-133,895 km for a width of 325 km.
  • Keeler Gap is at a distance of 136,530-136,565 km with a width of 35 km.
  • The Roche Division is at 136,770 – 139,380 km for a width 2600 km.
  • F ring is begins at 140,224 km, but debate remains as to whether it is 30 or 500 km in width.
  • G ring is between 166,000 – 174,000 km and has a width of 8,000 km.
  • Finally, we get to the E ring. It is between 180,000 – 480,000 km giving it a width of 300,000 km.

As you can see, a great deal of observation has been dedicated to understanding and defining Saturn’s rings. Hopefully, having the answer to ”what are Saturn’s rings made of” will inspire you to look more deeply into the topic.

We have written many articles about Saturn for Universe Today. Here’s an article about the orbit of Saturn, and here’s an article about the temperature 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 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.

Source: NASA

Astrosphere for April 15, 2008

Don’t just look inward, look outward. There’s a whole astrosphere out there. Your picture for the day is Saturn (of course), captured by Stargazer 7000.

Astronomy Picture of the Day has a beautiful shot of the night sky over Sweden.

PZ Myers has spoken and I must obey. Here’s all you need to know about expelled.

And here’s a review for another movie, Dark Matter.

Speaking of dark matter, Ethan Siegel explains the practical uses for his research.

Astroprof recalls famed astronomer John Archibald Wheeler; the man who coined the term “black hole” passed away this week.

Bad Astronomer Phil Plait celebrated Yuri’s night, in style.

Cassini Finds Patterns and Rhythm in Saturn’s Rings

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Cassini has been orbiting around Saturn for almost four years, and amazingly, the spacecraft keeps discovering new and unexpected features about this world and its system of rings and moons. Recently, in two of Saturn’s rings, Cassini found orderly lines of densely grouped, boulder-size icy particles that extend outward across the rings like ripples from a rock dropped in a calm pond. Surprisingly, the distances between these ring particles stay relatively equal even though their velocities may change. This type of pattern is completely new, as normally, the distances between particles change with their velocity.


The pattern was detected when Cassini sent out three signals toward Earth. The signals crossed Saturn’s rings, and the frequencies were scattered from the passing ring particles. Once the signals were captured by Earth-based antennas of NASA’s Deep Space Network, Cassini scientists saw a regular pattern in the received signal frequencies.

“This particular feature is the smallest and most detailed of anything seen in Saturn’s rings so far,” said Cassini radio science team member Essam Marouf. “In the chaotic environment of the rings, to find such regularity in the most cramped areas is nothing short of amazing.” The regular structure can only be found in locations where particles are densely packed together, such as the B ring and the innermost part of the A ring. The signals were sent to capture a complete view of the rings.

The unexpected pattern within Saturn’s rings may give scientists some new ideas of what to expect from other similar planets and solar systems.

Scientists call this pattern of particles “enormously extended natural diffraction grating.” A diffraction grating has parallel lines like a picket fence; when light hits this fence, it separates according to wavelength, from ultraviolet to infrared light.

“The signals showed that the particle groups were arranged in an unexpectedly regular formation that had rhythm within the rings of Saturn,'” said Marouf. “Each particle is in its own orbit, and sometimes they collide and move apart as their velocities change. As a result, you have particles bunched together into dense groups that extend across the ring in harmony with each other.”

Original News Source: Cassini Press Release

Enceladus: Cold Moon With a Hot Spot

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Saturn’s tiny moon Enceladus is a cold and icy place. But somehow, there’s enough heat being generated on Enceladus’ south pole to eject plumes of ice and vapor high above the moon. These plumes are extremely intriguing to the Cassini mission scientists and they want to know more about this hot spot on a very cold moon. In fact, Enceladus has become a major priority for study by the Cassini team and they are anticipating learning more about the moon in an upcoming fly-by.

The temperature at Enceladus’ south pole is about -220 degrees Celsius, but the hot spot is at least 100 degrees warmer. The leading model for the cause of the plumes on Enceladus is that the moon’s tides cause its crust to ratchet, or rub back and forth, in a set of faults near the south pole. The forces between Enceladus, the big planet Saturn and another moon, Dione cause what’s called dynamical resonance, and Enceladus is continually squeezed under this gravity field. This process creates a small hot spot, in relative terms, for an icy satellite.

Cassini has actually flown through the plumes, giving scientists a glimpse of the plume’s make-up.

“The plume particles are like smoke, ice smoke,”said William B. McKinnon, professor of earth and planetary sciences at Washington University in St. Louis. “If you were standing on Enceladus’ surface you wouldn’t even be able to see the plumes. The particles are just larger than the wavelength of light, about one-thousandths of a millimeter. Most icy bodies of this size are geologically inert, but this is a clear indication of geological activity. Cassini has found active venting of water vapor. This leads to scientifically intriguing speculations and questions.”

The scientists are pondering if Enceladus has active ice volcanism, and if so, is it due to ice sublimating, like a comet, or due to a different mechanism, like boiling water as in Old Faithful at Yellowstone. Even though there may be water on the moon, McKinnon doesn’t believe there is the possibility of life on Enceladus. This is because measurements made from Earth don’t indicate there is enough sodium present in the plumes to warrant the “life” question.

“The emerging view is that there’s not obvious evidence for a subterranean ocean in contact with rock, no boiling or venting,” said McKinnon.

The Cassini science team has made Enceladus a major priority and there will be seven additional close fly-bys of the moon by the spacecraft through mid-2010 (provided the mission is extended to that period.) The next fly-by will be on March 8, 2008 and Cassini will approach Enceladus at an incredibly close 25 km in altitude at the low latitudes and fly over the south pole at 580 km altitude. The spacecraft will actually fly through the plumes and should be able to take high-phase images of the plumes, map the temperatures of that region, search for any activity at other latitudes as well as image other interesting features on Enceladus, such as “tiger-stripe”-like fissures found near the south pole.

“We still can’t say how truly ‘hot’ the hot spots are,” said McKinnon. “We’ll probably learn this in March.”

Original News Source: Washington University Press Release