The Planet Saturn

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Podcast Transcript

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

The seventh and slowest movement of these 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 from all the other planets in the solar system in this episode of Everything Everywhere Daily.

The names of the planets that we use in English come from the Romans. There was a kind of logic in the way the names were given. The planet that moved the most is named after the winged messenger god, Mercury.

The planet that appeared 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 point of light was named after the Roman god of time: Saturn.

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

Saturn is about 1.4 billion kilometers from the Sun on average. To put that into perspective, that’s just under twice the distance between Jupiter and the sun and about 10 times the distance between Earth and the sun.

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

Yes, Saturn is quite large, but that’s not the planet’s defining feature. The thing about Saturn that is really different is its density.

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

This 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 can do it, Saturn might be floating on water.

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

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

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

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

Dutch astronomer Christiaan Huygens was the first to see the rings and to have a telescope large enough to discern them.

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

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

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

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

Starting 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 the sending of probes to the planet.

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

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

Fortunately, the following probes were not long in arriving. Just over a year later, Voyager 1 flew past the planet on November 12, 1980, then Voyager 2 passed by on August 26, 1981.

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

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

What was needed was a probe that could actually orbit Saturn for an extended period of time. That’s 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 obtain detailed images of the planet and its moons. The second part was the Huygens probe which was sent into Titian’s atmosphere and landed on the surface.

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

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

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

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

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

The liquid 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 evaporates into a gas and then precipitates out as liquid methane rain.

The mission launched on October 15, 1997 and spent seven years traveling to Saturn. It arrived there on June 30, 2004, and orbited Saturn by flying through a gap between two of the rings.

On Christmas Day 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 of them. It did not have a long operational life after landing. But it sent back some images, the first ever taken on the surface of another planet’s moon.

Other 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 much longer than originally planned. The initial mission was only supposed to last 3 years, but it ended up lasting more than 12 years.

The orbiter was ultimately destroyed by flying it into Saturn’s atmosphere on September 15, 2017.

In the 12 years he flew around Saturn, he collected an enormous amount of data.

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

Scientists don’t know exactly what causes the hexagonal pattern to appear in the clouds. The best guess right now is that it’s some sort of standing wave. The researchers were able to replicate a similar pattern by performing tests on rotating fluids.

The hexagon changed color during the Cassini mission, changing from blue to a golden color.

The hexagonal shape does not appear at the south pole. Instead, there appears to be a hurricane-like storm with its own eye.

It flew over the moon Enceladus which was 50 kilometers from the surface. He actually passed through a geyser plume where he detected water, CO2 and hydrocarbons.

In 2012 he witnessed an event known as the Great White Spot. It was a huge storm that appeared in the northern hemisphere. It seems to occur regularly about every 28.5 years. It’s similar to the Great Red Spot on Jupiter, but it’s temporary.

Another discovery was to learn more about the rings of Saturn.

For starters, the rings are 99.9% water ice with a small amount of rocky material. There is not much material in the rings. They are very thin, varying from only 10 meters to 1 kilometer.

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

The particles that make up the rings are also not very large, ranging from a few millimeters to perhaps a maximum of 10 meters.

One of the current theories is that Saturn’s rings are only temporary. We happen to live in a time when we can observe them.

It seems what is happening is that the ice particles are slowly being pulled towards Saturn due to its magnetic field. It is estimated that the amount of ice lost fills an Olympic-size swimming pool every half hour.

This means that the ring may only be 100 million years old and has less than 100 million years left. It may seem like a long time, but in the age of the solar system, it’s next to nothing.

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

The gaps in the rings arise primarily from gravitational resonance with Saturn’s various moons.

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

There aren’t as many future missions on offer as there are for planets like 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 could include a balloon that would float in Titan’s methane atmosphere as well as a ship that could navigate one of its methane lakes.

The mission has not yet been approved and no funding has been allocated. If and when that happens, the launch might not happen until 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 liquid surface provide the only opportunity to study such an environment.

On a personal level, if you ever get the chance, attend a star party in your area. This usually involves amateur astronomers pulling out their telescopes for the public to look through.

I remember going on a visit to the Mount Kilauea Visitor Center in Hawaii. If you happen to visit while Saturn is away, you will be able to clearly see Saturn’s rings with your own eyes, and possibly even Titan.

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

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