The Planet Saturn

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Podcast Transcript

Ancient astronomers from almost every culture knew of seven things in the sky that moved.  the Sun, the Moon, Mercury, Venus, Mars, and Jupiter.

The seventh and slowest moving of those was the one named after the Roman god of time: Saturn. 

For centuries Saturn was a dot in the sky. Then when telescopes were invented, our perception of the planet changed dramatically. 

Learn more about Saturn and what makes it different than every other planet in the solar system on this episode of Everything Everywhere Daily.

The names of the planets that we use in English came from the Romans. There was a sort of logic to how the names were given out. The planet that moved the most was named after the winged messenger god, Mercury. 

The planet that showed up at dusk and dawn was named after the goddess of beauty: Venus. 

The reddish point of light was named after the god of war: Mars.

The slowest moving point of light was named after the Roman god of time: Saturn. 

The ancients couldn’t have known, but it turned out that the reason why Saturn moved so slowly was because it was the farthest away.

Saturn lies about 1.4 billion kilometers on average away from the Sun. To put that into perspective, it is a little under twice as far as Jupiter is from the sun and about 10x the distance the Earth is from the Sun. 

In terms of size, Saturn is the second largest planet in the solar system. Jupiter is around 143,000 kilometers in diameter, and Saturn is about 120,000 kilometers in diameter. 

Yes, Saturn is pretty big, but that isn’t the defining charistic of the planet. The thing about Saturn, which is really different, is its density. 

To put it in perspective, Saturn has 764x the volume of the Earth but only 95x the mass of the Earth. 

That means its density is only 12% that of Earth, or to put it in a way that might be a bit more visceral, assuming you could do it, Saturn could float on water. 

The reason why Saturn has such a low density is that most of its atmosphere consists of hydrogen and helium, the two lightest elements. It is believed to have a solid core which is quite dense, but overall, light elements in the atmosphere reduce its overall density.

It takes Saturn 29.5 years to travel around the Sun, but it only takes 10.5 hours for the planet to rotate around its axis. 

Our understanding of Saturn changed dramatically with the invention of the telescope. Galileo was the first person who looked at Saturn with a telescope, but his telescope wasn’t good enough to resolve its primary feature: its rings.

Galileo just saw two blobs on the side and figured they were moons, but they weren’t like the moons he saw around Jupiter. 

The first person to see the rings and who had a telescope big enough to discern them was the Dutch astronomer Christiaan Huygens.

He also made the discovery of Saturn’s largest moon, Titan. More on Titan in a bit.

As telescopes improved, other moons were discovered including Iapetus, Rhea, Tethys, Dione, Mimas, Enceladus, and finally Phoebe in 1899.  These are just the major moons that were discovered by astronomers on Earth. There are a total of 83 moons of Saturn which have been discovered in total.

The other major discovery before the 20th century was the fact that Saturn’s ring were, in fact, multiple rings with gaps between them. 

The various rings were named by letter, but they were named in the order that they were discovered by the gaps between them. As a result, the sequence makes little sense. 

Going outward from the innermost ring, the order is D, C, B, A, F, G, E, with minor rings and gaps getting unique names.

The big advance in our understanding of Saturn came with sending probes to the planet. 

The first probe sent to Saturn was Pioneer 11.  Launched in 1977, it passed within 21,000 kilometers from the top of the atmosphere on September 1, 1979.

The images it captured were the best ever taken, but they weren’t great.

Thankfully, it wasn’t long before the next probes arrived. A little more than a year later, Voyager 1 flew by the planet on November 12, 1980, and then Voyager 2 flew by on August 26, 1981. 

The images captured by these three probes dramatically increased our understanding of Saturn, its moons, and its rings.  In addition to the images sent back, they were also able to take measurements on the planet’s temperature and its magnetic field.

These three probes were limited in the amount of information they could gather because they were only fly-bys. There were only a few days when they could take images and collect data. 

What was needed was a probe that could actually orbit around Saturn for an extended period of time. That is exactly what NASA did with the Cassini–Huygens mission. 

The Cassini–Huygens mission had two parts. The first was the Cassini orbiter which was to orbit Saturn to get detailed images of the planet and its moons. The second part was the Huygens probe which was sent into the atmosphere of Titian and landed on the surface.

Here I probably need to talk about Titan, which, quite frankly, is one of the most interesting parts of Saturn and the entire solar system. 

Titan is the largest moon of Saturn and the second largest moon in the solar system after Jupiter’s moon of Ganymede.

Titan also happens to be the only other place in the solar system that has an atmospheric pressure comparable to Earth. In theory, if you were to walk on the surface of Titan, you would need a space suit, but you wouldn’t need the suit to be pressurized. 

Titan is also the only other place in the solar system which is known to have stable liquids on the surface. 

Now before you get excited and think that this is like Earth, it is not. For starters, the temperature on the surface averages ?179 °C or ?290 °F. 

The liquid that is on the surface is actually liquid methane. As far as we know, there is a methane cycle on Titan, which mirrors the water cycle on Earth. Liquid methane will evaporate into a gas and then precipitate down as liquid methane rain. 

The mission was launched on October 15, 1997, and spent seven years traveling to Saturn. It arrived there on June 30, 2004, and put itself into orbit around Saturn by actually flying in a gap between two of the rings. 

On Christmas Day of that year, Huygens and Cassini separated, and Huygens landed on January 15, 2005.

The images returned by the Huygens lander weren’t great, and there weren’t many. It didn’t have a long operational life after it landed. But it did return some images, the first ever taken on the surface of the moon of another planet.

Further radar observations of Titan by the Cassini orbiter found evidence of lakes near the north pole region.

While the Huygens part of the mission didn’t last very long, the Cassini part of the mission lasted far longer than originally intended. The original mission was only supposed to last 3 years, but it actually ended up going over 12 years.

The orbiter was finally destroyed by flying it into the atmosphere of Saturn on September 15, 2017. 

Over the 12 years it flew around Saturn, there was an enormous amount of data that it collected. 

One of the things we didn’t know much about before was the hexagon at north pole of Saturn. This was originally discovered on Voyager 1, but it was investigated further with Cassini. 

Scientists aren’t exactly sure what causes the hexagon pattern to appear in the clouds. The best guess currently is that it is some sort of standing wave. Researchers were able to replicate a similar pattern doing tests of rotating fluids. 

The hexagon did change color during the Cassini mission from bluish to a golden color. 

The hexagon shape doesn’t appear at the south pole. Instead, there appears to be a hurricane-like storm with its own eye. 

It did a flyby of the moon Enceladus which was 50 kilometers from the surface. It actually flew through a geyser plume where it detected water, CO2, and hydrocarbons. 

In 2012 it was witness to an event known as the Great White Spot. This was a huge storm that appeared in the Northern Hemisphere. It seems to occur on a regular basis about every 28.5 years. It is similar to Great Red Spot on Jupiter, but it is temporary. 

Another discovery was learning more about Saturn’s rings. 

For starters, the rings are 99.9% water ice and a small amount of rocky material. There isn’t a lot of material in the rings. They are very thin, varying, from only 10 meters to 1 kilometer. 

The entire mass of ice in the rings is only about half the mass of the ice found in Antarctica. 

The particles which make up the rings are also not very large ranging in size from a few millimeters to maybe a maximum of 10 meters. 

One of the current theories is that the rings of Saturn are only temporary. We just happen to be living at a time when we can observe them. 

It appears what is happening is that the ice particles are slowly being pulled into Saturn due to its magnetic field. The amount of ice being lost is estimated to fill an Olympic sized swimming pool every half hour. 

It means that the ring might only be 100 million years old and may have less than 100 million years left. That might sound like a long time, but in the age of the solar system, it’s almost nothing. 

The source of the ice making up the rings was probably a comet or moon, which disintegrated at some point.

The gaps in the rings primarily come from gravitation resonance with the various moons of Saturn. 

Because Saturn is so far away, it is a very difficult place to reach. Without the planets being in the correct alignment to get a gravitational slingshot, it can take many years.

There aren’t as many future proposed missions as there are for planets such as Mars, which are much easier to reach.

One of the only proposed future missions is NASA’s Titan Saturn System Mission. Some of the current ideas being floated for this mission might include a balloon that would float in Titan’s methane atmosphere as well as a boat that could sail in one of its methane lakes.

The mission hasn’t been approved yet, and no funding has been allocated. If and when that does happen, the launch might not occur until sometime around 2030.

Saturn is an interesting planet, but the really interesting things to explore will probably be its moons, especially Titan. 

There is nothing else in the solar system like Titan. Its relatively thick atmosphere and its liquid surface provide the only opportunity to study such an environment. 

On a personal level, if you ever get the chance, participate in a star party in your area. It will usually involve some amateur astronomers who bring out their telescopes so the public can look through them. 

I remember participating in one at the visitor center on Mount Kilauea in Hawaii. If you happen to visit while Saturn is out, you will clearly be able to see the rings of Saturn with your own eyes, and maybe even Titan. 

If you see Saturn and its rings with your own eyes, you will be able to see something that even Galileo couldn’t.