Rings

I’ve talked before about our solar system as if it were a family, with the sun as the parent, and the planets as the children. The moons, asteroids and other bits would be the grandchildren, I suppose.

I am quite fascinated with our solar system. Until scientists find facts about other solar systems, this is the only one I’ve got to study; these are the only planets I can use as a springboard when my imagination wants to design one for a story. So I keep looking for new things about them that I didn’t know before. Luckily, NASA and scientists keep looking at them, too.

Today’s subject is Saturn and its rings.

You’d think the solar system was a big family, with 9 8 planets and several dwarf planets. But for Saturn, 8 or 9 was not enough. Saturn has 62 moons that have names, and another 9 that have not yet been named. Wow! Can you imagine 71 kids? I’d have lots of trouble remembering half their names, not just 9 of them. I had a couple batches of cousins who had 8 siblings in each family. Gram gave up trying to remember our names; all the girls became ‘Pigtails’ and the boys were ‘Junior’.

I didn’t realize just how many moons Saturn has. One day I will have to start looking more closely at them, but today, I’m looking at the rings.

There are 7 rings. They don’t exactly have names, but each is designated by a letter. I suspect the letters were assigned as the individual rings were discovered, because otherwise, there doesn’t appear to be any rhyme or reason for the assignments.

If you start at Saturn and move away from the planet, you arrive at Ring D, then Ring C, Ring B and Ring A. Continue outward, and you will find Ring F, Ring G and Ring E. Between each pair of rings is a gap, a space that is not absolutely empty, but is relatively empty compared to the rings. (I haven’t figured out if any of the gaps is home to a moon, but I do know that some of the moons are somewhere in the ‘rings’. Some day, I have to figure that out.) Each ring and gap is its own width, meaning the distance between the side closest to Saturn and the side furthest from Saturn.

But they are also thin, meaning the distance from the ‘top’ of the ring to the ‘bottom’. Thickness for all the rings is less than 1 km.

If there is one thing Saturn’s rings are, it’s not consistent. The various rings are made up of water ice particles (with a trace of rock for flavoring), but those particles range from the size of a grain of sugar to the size of a house.

The rings are a very busy place. With 71 moons of various sizes orbiting around this big ol’ gas giant, the gravity and magnetic fields are forever fluctuating. The latest probe documented ‘lines’ in some rings, which are called spokes. The spokes come and go, and they aren’t sure what causes them, but they suspect they are a temporary ‘pile-up’ (traffic jam) of particles caused by the gravity or magnetic fields. Or maybe by electricity leaking from storms in Saturn’s upper atmosphere.

And spokes are not the only oddity in the rings. Ring F seems to be ‘braided’. Who taught those particles how to do that?

But don’t worry about Saturn’s rings. Some of the moons (bigger siblings) act as shepherds for the rings, using their gravity/magnetic fields to keep the ring particles where they belong. More or less.

I’ve just barely touched on Saturn, but that’s all for today. After all, it is a gas giant, with a huge family; too big a subject for me to explore the entire thing in one sitting.

  

http://nineplanets.org/saturn.html

Dione

I thought we’d talk about Dione today. That was before I found out there were 4 ‘Dione’s’ in Greek mythology and one in the Phoenician mythology of Sanchuniathon. Rather than try to sort through all those, I changed my mind and decided to discuss Dione, a moon of Saturn. (What or who is Sanchuniathon? I may have to come back to that one sometime.)

This moon was discovered by Giovanni Domenico Cassini in 1684. It is also sometimes called Saturn IV.

Dione’s orbit around Saturn is an ellipse, and at its closest approach, it is slightly closer to Saturn’s center than our own moon is to the Earth’s center. Because Saturn is a lot bigger than Earth, Dione races around it, taking 2.74 days to complete an orbit, as well as a Dione ‘day’. It never turns its face away from Saturn. It’s interesting that every time Dione completes one orbit, Enceladus (another Saturn moon) completes two. Each time they pass each other, the gravimetric tugging generates internal heat in both moons.

Also interesting is that Dione is one of a set of triplets. Two other moons of Saturn, Helene and Polydeuces, share the same orbit as Dione. They run around Saturn in single file, one 60° ahead of Dione, and the other 60° behind.

Who knew this kind of stuff could actually happen ‘naturally’? May I should have stuck with mythology after all.

It is believed that Dione is about 2/3 water in various forms, and the remainder is a dense core of silicate rock. The top of the ‘water’ is an ice crust, probably as thick as 99 kilometers ( 62 miles). The temperature at Dione’s surface is about -121°F, which would make the ice so hard, it would act like rock. Between the rock core and the ice crust is about 65 km ( 41 miles) of liquid ocean. The crust does have various features, such as chasms, ridges, long narrow depressions, craters and crater chains.

Dione is pretty well covered in craters, as large as 100 km (62 miles) across. However, most of the craters are on the opposite side as scientists expect them to be. The theory is that on something the size and mass of Dione, anything big enough to make a 35 km (22 mile) crater would be able to spin the moon about. There are enough large craters to indicate Dione did a lot of spinning in the past. So maybe she keeps her back to Saturn, trying to see the next spin-inducing attacker before it hits?

Oh, and let’s not forget the ice cliffs (formerly known as ‘wispy terrain’ when it was discovered by the Voyager space probe). At the time, they were called ‘wispy’ because whatever they were, they didn’t hide the countryside in their vicinity. But more recent photos by Cassini show that these ‘wispy’ lines were, in fact, ice cliffs, fractures created by chasms. We now know that some of them are several hundreds of meters tall.

In 2010, the Cassini probe detected oxygen ions around Dione, but there were so few of them, scientists prefer to call it an exosphere rather than a tenuous atmosphere.

en.wikipedia.org/wiki/Dione_(moon)

https://solarsystem.nasa.gov/planets/dione