- Education and Science»
- Astronomy & Space Exploration
Saturns Moons: a Visual Guide
The Moons of Saturn
Saturn is the favourite planet of many people. With the most extensive, complicated and elegant ring system in the Solar System, many people get caught up talking about the Rings of Saturn without even considering its moons. This is a shame, hopefully rectified here, as the moons of Saturn are wonderful worlds in their own right. Indeed, in our search for life, it may be a moon orbiting Saturn that harbours extraterrestrial life.
Saturn may have the highest number of moons in the solar system; to date, 62 moons have been confirmed.The Saturnian system has been visited by several probes including Pioneer, Voyager and Cassini. These probes have given us a glimpse of these weird and wonderful worlds - far from passive observers of their parent planet, the moons of Saturn actively create, shape and maintain its ring system.
Images of IapetusClick thumbnail to view full-size
Discovered in 1671, Iapetus is the third largest moon of Saturn. It is also one of the most mysterious.
Just like the force, Iapetus has a light side and a dark side - a characteristic that baffled scientists for years. When Cassini (the astronomer, not the space probe) first discovered the moon, he couldn't understand why he could only observe it when on one side of Saturn. When the moon should have been on the east of Saturn, it simply disappeared from view.
After a closer look by Cassini (the space probe, not the astronomer) in the early 21st Century, it is now believe that half of the surface is covered in a layer of carbon. This carbon is thought to have initially come from a meteorite impact, but following that an intriguing aspect of physics has accentuated the difference in colour.
Dark surfaces absorb heat and tend to be hotter than lighter, more reflective surfaces. This means that the dark side of Iapetus gets hotter than the light side. When combined with the very long rotation (more than 79 days) of the moon, the dark side spends so long in the sun that any ice on the surface evaporates. This leaves behind a carbon residue that makes the dark side darker. At the same time, the ice that evaporates from the dark side, falls as snow on the light side, making it even lighter and more reflective. The darker the dark side gets, the more heat it absorbs, and so makes itself darker: this creates a runaway effect that has divided the surface in two over millions of years.
Images of TitanClick thumbnail to view full-size
Titan was discovered in 1655 and is the largest moon in the Saturnian system (the second largest in the solar system.) Titan is larger than Mercury and nearly the same size as Mars with an equatorial diameter of 5,150km (3,200 miles). Titan has an atmosphere four times more dense than our own on Earth that is around 600km (370miles) deep. Titan lies in a part of the Solar System that is so cold, methane condenses from a gas to a liquid; there is evidence of lakes of liquid methane on the surface of Titan
Images of Hyperion
Going on looks alone, this has to be my favourite moon out of all 170 in the Solar System. Discovered in 1848, Hyperion is not round (it was the first non round moon to be discovered) and has a battered surface analogous to the texture of a sponge. With its odd shape and chaotic, tumbling rotation, it is likely that Hyperion was a comet captured by Saturn's gravity.
Images of Dione
Dione is the Saturnian moon most like our own Moon. It was discovered by Cassini (the astronomer, not the space probe) in 1684 and, while it looks like our own Moon, it is very different in composition.
A true ice-moon, Dione is two-thirds water, but at -190°C the frozen surface behaves like rock. The surface of the moon is covered in craters and ice-cliffs, but lacks the deep fissures of Europa meaning there is unlikely to be a liquid ocean underneath the surface. Just like our moon, Dione is tidally locked to Saturn; if you stood on the surface of Saturn (not possible but still) you would always see the same face of Dione.
Interestingly, among all the craters, there is evidence of tectonic activity since the formation of Dione: long scars adorn her surface similar to those at the boundaries of our own tectonic plates.
Images of EnceladusClick thumbnail to view full-size
Enceladus is a tiny moon (smaller in diameter than the length of the United Kingdom). It is the most reflective moon in the Solar System, reflecting almost all light that hits it. When first photographed by Voyager, scientists were in for a shock: vast areas of the surface had no craters. This could mean only one thing - the surface of the moon was new. But how could this be? Such a tiny moon could not possibly hold onto any meaningful internal heat to power geologic activity.
The smoothest regions of the moon were centered around four huge parallel trenches in the southern hemisphere: the Tiger Stripes. These stripes have an average temperature of -143°C, compared to an average surface temperature of -200°C. There ismore heat coming out of the south pole of the moon than the equator! And it is here that we find the answer to the smooth surface and high reflectivity (albedo) of Enceladus: ice volcanoes.
Not only do these icy geysers resurface the ground near the Tiger Stripes, but the material is blasted so high that it escapes the moon's gravity and is instead captured by Saturn's gravity. Enceladus not merely nestled in the E-ring...it is creating it.
The heat powering these eruptions is thought to be caused by friction. As the moon orbits Saturn in a huge oval, it gets stretched and flexed. Just like stretching and twisting a metal coat hanger, this causes quite a bit of heat. In the case of Enceladus, enough to melt ice and power ice geysers that fire at 800mph! There may even be an ocean under the Tiger Stripes that may harbour life...