Even though the landscape on the surface is completely white, there are some variations. Plains (planitia, plural form planitiae) alternate with ridges 500 to 2,000 meters high (dorsum, plural dorsa), and both can contain trenches (sulcus, plural sulci), depressions (fossa, plural fossae) and cliffs (rupe, plural rupes), or be covered to some extent with craters.
If you try to find your way around Enceladus with a map, you might get the impression you are in the Arabian Nights. This is because the International Astronomical Union (IAU) decided to use geographical names from this famous work of world literature for this moon—except for the craters, which are named after protagonists from these stories.
Geologically speaking, the plains on Enceladus are very young. You can see that they—for example, the Sarandib Plain—contain far fewer craters than one would expect on a moon. It is estimated that many of its plains are less than a couple of hundred million years old. The impact craters, as the photos taken by the Cassini probe show, are in various stages of aging. While the climate on Earth makes craters wear away, and on Earth’s moon they are destroyed by new impacts, on Enceladus shifting of the ice erodes the craters.
The trenches and canyons are witnesses to this activity, and they can be up to 200 kilometers long, 5 to 10 kilometers wide, and up to 1,000 meters deep. They often cut through other geological features, so one must assume that they are relatively new phenomena. On Earth, rocky continental plates collide, but on Enceladus it seems to be ice plates. This sometimes creates cliffs up to 1,000 meters high.
Chaos in the South
The area around the South Pole of Enceladus plays a special role. Even in the pictures taken by Voyager 2, scientists discovered a chaotic terrain, a mixture of very different terrains. Since the Cassini probe sent its spectacular images, we know a lot more. The area reaching up to 60 degrees southern latitude (about the position of Tierra del Fuego on Earth) is characterized by fractures and cliffs, but it contains even fewer craters than the rest of the moon. The surface must therefore be far younger. Scientists estimate it to be an average of 500,000 years old. Geologically speaking, that is very young.
From above, the center of this region looks particularly chaotic. Besides the fractures and plates, there are also giant ice boulders measuring 10 to 100 meters. The area is dominated by four fractures with a depth of up to 300 meters, the so-called Tiger Stripes, each of which is several hundred kilometers long. Pictures show that the ice at their edges has a considerably different composition from the ice on the regular plains. Organic compounds have been found here.
The Tiger Stripes, which are up to 25 degrees Celsius warmer than their surroundings, form the source of the famous Enceladus Geysers. The entire world saw the photos of them taken by Cassini. Across almost the entire length of the stripes, large amounts of crystallizing water vapor are shot into space at high speeds, between 400 and 1250 meters per second (m/s). Part of it falls back on the moon as snow, part of it replenishes the material of the E Ring. As the escape velocity on Enceladus is below 240 m/s (860 km/h), an outgassing into space is perfectly possible.
The activity of the geysers changes periodically. It is suspected the Tiger Stripes are squeezed by the gravity of Saturn when the moon approaches the planet, which increases the pressure at which the material is ejected, and reduces its quantity.
The Cassini probe even managed to fly directly through a geyser plume. Therefore we know these consist primarily of rapidly freezing water vapor, but also include percentages of methane and carbon dioxide, as well as simple-to-more-complex organic molecules. The composition resembles that of a comet. How these compounds could have been created will be explained next.
With/Without an Atmosphere
Due to its low gravity, Enceladus does not possess a true atmosphere. The disadvantage of this fact is that a spaceship could not use the braking effect of the atmosphere during landing.
However, near the South Pole, enough of the geyser eruptions remain so that traces of an atmosphere have been detected, comprised of 91 percent water vapor, 4 percent nitrogen, 3.2 percent carbon dioxide, and 1.7 percent methane.
A Great View
An astronaut who has just landed on Enceladus’ surface might look up to the sky first. It would be completely black, as the moon has no atmosphere to speak of. No clouds could obscure this sun, which appears at 3.5 minutes of arc, just one ninth of the size we are used to on Earth.
Saturn can only be seen from the side of the moon that faces the planet. Here it appears in the sky at a height dependent on the geographical latitude of the observer’s current position. Therefore, at the equator, Saturn shines vertically above you, but the closer you get to the poles, the lower the planet sits above the horizon. It is always impressive, though, as its disc with a diameter of 60 degrees is about 120 times the size of Earth’s moon in our night sky.
Unfortunately, a space tourist would not get a good view of the rings of Saturn. After all, these surround Saturn in the same plane as the moon. Therefore, you are looking directly at their (very narrow) edge and will only see them as a line. Depending on the position of the sun, though, the shadows of the rings may be seen upon the planet.
If during your visit to Enceladus you experience a moonrise, don’t worry. You are not confused—you just saw the inner moon Minas, which moves past Saturn every 72 hours and has an apparent size in the sky like that of the Earth’s moon. Tethys, on the other hand, appears to be twice as big, though you could only observe this outer moon from the side of Enceladus facing away from Saturn.
Other of Saturn’s moons appear in the sky as star-like objects, or cannot even be detected with the naked eye.
Hiking on Enceladus
Let’s say you are not satisfied with just looking at the moonscape facing Saturn, but want to also explore the other side of the moon. No problem. The low gravity lets you almost float. If you weigh 86 kilograms, you would weigh only 1 kilogram on Enceladus using a spring scale—a beam balance would indicate 86 kilograms, as it compares weights. Even with a heavy spacesuit, this would not add up to more than 2 kilograms.
That does not mean you can jump 40 times higher than on your home planet. For one thing, the space suit is cumbersome. On Earth, no one can jump in a spacesuit. On our moon, you could jump to a height of about two meters in a spacesuit, though no human astronaut has attempted so high a jump yet. On Enceladus you could perform a 20-meter jump (even 40 meters without a spacesuit)—though that is not recommended. The issue is one of safety. After all, you return to the ground with the speed you jumped up with. A spacesuit ought to withstand that, but the risk is simply too great.
A hike on Enceladus is rather like a spacewalk. Outside there is a vacuum—almost. Therefore, the preparations should resemble those of an EVA in space. The fact that there is no atmosphere is actually rather fortunate. At minus 200 degrees Celsius your suit will cool off much faster in an environment filled with some kind of air than by just giving off heat as radiation.