Moonday: Volcanoes of Ice

Enceladus, an icy moon of Saturn. 99% of the light falling on Enceladus is reflected back into space, making it possibly the most reflective object in the Solar System. This and other photos of Enceladus in this post were taken by the Cassini probe currently in orbit around Saturn:

We Earthlings think of our Moon as being bright, but that’s only because it’s close to us: the Moon reflects only about 12% of the light that falls on it during its full phase, with some areas being slightly more reflective than others. The Moon, to put it succinctly, is as reflective as a chalkboard. Now imagine a moon with a surface of nearly pure, smooth ice, a landscape of such frozen austere beauty that reflects 99% of the light it receives. Even a tiny moon like that would be visible a long way away.

That moon is Enceladus, Saturn’s sixth-largest satellite. It’s large enough to be (mostly) spherical, but still quite tiny: about 500 kilometers (311 miles) in diameter, or roughly the distance between Richmond, Virginia (where I live) and New York City. William Herschel reported the first observation of Enceladus in 1789, which again reflects how bright it appears: most things only 500 kilometers across as far away as Saturn are very difficult to spot, even by a careful astronomer like Herschel.

Enceladus is tiny compared to Earth and its Moon.

However, small means neither uninteresting nor unimportant: Enceladus is considered by many scientists to be the most likely candidate for harboring life in the Solar System (other than Earth, of course). As with Europa, another potentially habitable world, Enceladus lacks a substantial atmosphere, but has a global shell of ice that protects liquid water beneath. The moon’s proximity to Saturn helps keep the interior warm through tidal forces, which also keep one face of Enceladus pointing toward its host planet (as with our Moon and indeed many other satellites in the Solar System). There is probably internal heating as well from radioactive decay of materials in the core, similar to the internal heat source on Earth.

"Tiger stripes": volcanic fissures on Enceladus.

How do we know about this water and warm interior? As with Earth and Io, the effect of the hidden turmoil beneath the surface is volcanism, though the volcanoes themselves are very different. Plumes of water and ice jet up from fissures in the surface of Enceladus known as tiger stripes: you can see these formations as bluish lines on the image to the left. Since the volcanoes are ice- rather than magma-based, they are called cryovolcanoes (where the prefix cryo– refers to cold, as in “cryogenic”; extra credit will be given to someone who can pun on  the word “cryovolcano”).

Jets of water and ice shooting up from a tiger stripe on Enceladus. These volcanoes are known as cryovolcanoes, meaning "volcanoes of ice".

The Cassini probe (my favorite robotic explorer) has flown through the plumes from the cryovolcanoes and analyzed the chemical composition. Though the jets are mostly water, they also contain ammonia, methane, carbon dioxide, nitrogen, and trace amounts of hydrocarbons—molecules containing hydrogen and carbon. While hydrocarbons are pollutants on Earth (which create that lovely yellow smog over our cities), they also are naturally-occurring compounds that may have played a role in the early biochemistry of life on Earth. To scientists, the word organic refers to the presence of carbon: all life as we know it is organic—carbon-based—in character. The jets of water are also the likely source of Saturn’s E ring, a tenuous watery ring encompassing the orbit of Enceladus and several other moons.

Though Enceladus be but little, it is fierce important. The combination of liquid water and organic compounds make it highly interesting to those studying the possibility of life beyond our planet. This distant icy moon has taught us much already; might there also be some form of alien life beneath the ice?


15 responses to “Moonday: Volcanoes of Ice”

  1. Richard Francis Avatar
    Richard Francis

    My favorite moon!

  2. […] RSS News Feed « Moonday: Volcanoes of Ice […]

  3. […] zone and hence freezes over. After all, a lot of water freezes on Earth, and if Europa and Enceladus are habitable, that stretches our range of possible conditions anyway. A planet with high […]

  4. […] like the previous three moons I’ve written about (Io, Europa, and Enceladus), our Moon is tidally-locked to Earth: it presents the same face to us all the time. Many people […]

  5. […] of liquid water. Its composition is mostly ice, which is fairly typical for Saturnian moons (like Enceladus), but the density is too low even for that. After all, most solids are more dense than water (ice […]

  6. […] big is Saturn? Sooooooo big! Phil Plait shows us why the Jovian planets are known as giants. (The moon featured is Enceladus, which is a nice connection to my earlier […]

  7. […] Several different models proposed by astronomers argue that Titan has a liquid interior, much like Enceladus or Europa. Methane lakes on Titan, as imaged by Cassini using infrared light. Kraken Mare is the […]

  8. […] a barren icy surface like its neighbor Europa, which may hide an ocean of saltwater, similar to Enceladus. Witness a moon that orbits the largest planet in the Solar System, and is the only moon known to […]

  9. […] and chaotic rotation), as well as Titan (with its thick atmosphere and methane seas) and of course Enceladus. Today’s moon is also weird and marvelous, with a number of mysterious aspects: Iapetus, […]

  10. […] All fantasy and much of science fiction depart from the physics of the real world, so my analysis isn’t criticism. The environment we live in on our Earth is a property of many things—a combination of mass, size, composition, location in the Solar System, and the like. Though the story of gravity is only part of the tale, it’s something interesting to look at as we explore asteroids and other objects, looking for the environment of life. There may not be a Little Prince with his flower living on an asteroid, but understanding why not is a part of science just as much as observing Enceladus. […]

  11. […] the passage. (Of course, several moons within our own Solar System are potentially habitable: Enceladus and Europa both have liquid oceans underneath the ice. However, they’re much smaller than the […]

  12. […] another interesting characteristic: it’s a lot denser than the regular satellites like Titan, Enceladus, and so forth. That indicates it has a lot more rock mixed into its composition, to the extent that […]

  13. […] significant mountains or valleys. In this way, it resembles Jupiter’s Europa, Saturn’s Enceladus, and other ice moons. Another way it resembles Enceladus is in its activity: Triton sends out […]

  14. […] for evolution to produce unique forms. That in turn could tell us about life on icy worlds like Enceladus or Europa. In other words, there could be real aliens out there, though odds are they’re […]

  15. […] as any planet, with its thick atmosphere, weird weather, methane lakes, and even rivers. Enceladus, while much tinier, ranks with Jupiter’s moon Europa as one of the best candidates for life […]

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