Where did the ice for Saturn's inner moons come from?

Origins of an Ice Moon

Part 1

Tethys: Ice Moon among Saturn's Rings
Credit: NASA/JPL-Caltech/SSI, via Wikimedia Commons

Saturn has a lot going on.  The breath-taking rings steal most of the attention.  Every kid at some point has a T-shirt, a sticker, or a coloring book with Saturn's Rings proudly displayed. For most, this is enough: Saturn is the planet with the rings.  Others may wonder about the size of Saturn. They may sort out if it is closer or further off than Jupiter.  They may ponder what exists beneath the impenetrable atmosphere of Saturn. Fewer still might hang around long enough to notice the enormous moon, fittingly named Titan. 

The lucky ones hang around even longer. The Bright Red Spot on Jupiter may beckon, but they hang on. Is there something more for Saturn aficionados to savor, they ask? The Ice Moons are their reward. Ice Moons like Enceladus, Tethys, Mimas, and Dione are bit players in the grand drama of the Saturnian System. Yet their roles may be ultimately the most amazing. Emerging evidence suggest some, like Enceladus, might support life. So how did they come into being? To understand that, let us go back to the famous rings.

The rings of Saturn: how did they happen?

Saturn seen by the Cassini Orbiter in 2004
Credit: By NASA/JPL/SSI, via Wikimedia Commons

Saturn's rings, though easily one of the most recognized features in the Solar System, in many ways remain a great mystery. It has been over 400 years since their discovery, yet it seems that the question of how they formed is still out there.

Let's start with the discovery of the rings. Early humans looked up in antiquity to witness the wandering planets. In time, humans developed technology capable of probing deeper into the nature of these mysterious bodies. With the invention of the telescope, finer details emerged.

Galileo Galilei sighted the giant planet Saturn with his telescope in 1610. At the time, his telescope was the cutting edge: a pinnacle of human achievement. Even so, initially Galileo could not make out the presence of the rings. What he saw was certainly not the perfect orb he expected. Uncertain what to make of the images, he considered that there were three separate planets: the largest in the middle, Saturn.

"Has Saturn swallowed his children?"

Early drawing of Saturn, summer 1666

Credit: Robert Hooke, via Wikimedia Commons

Two years later, the orientation of Saturn's rings shifted, angled such that they were no longer visible from Earth. Galileo, and the world astronomy community were at a loss.

In mythology, prophecy held that Saturn would be overthrown by his own children. To prevent this from playing out, he devoured them. When Galileo looked up to see that the planet Saturn now stood alone, he perhaps jokingly wondered if this had played out in the sky above. Galileo pondered, "has Saturn swallowed his children?" When the rings returned to view some time later, Galileo still had no answer.

After another generation of technological advances, astronomers were finally able to clearly see the rings. In the late 1600s, a new group of astronomers came along, better equipped. Christiaan Huygens described the rings in finer detail. Robert Hooke resolved the shadow of the planet upon the rings. Giovanni Domenico Cassini discovered a wide gap, since known as the Cassini Division.

 These were the first of many discoveries to bring us closer to an understanding of the rings of Saturn. We were learning more about what they are, yet it remained a mystery as to how they formed. 

Ice Moon Station will publish more Origins of an Ice Moon in future posts.
Subscribe by Email, or follow us on Facebook and Twitter for updates.