1.5 Cryovolcanism on Enceladus

Volcanism does not just occur on rocky bodies like Io; it has also been seen occurring on Saturn’s small icy moon Enceladus. In March 2006, the Cassini probe captured images of large icy jets erupting from cracks near Enceladus’ south pole. House-sized boulders of ice litter the neighbourhood of the cracks, which turns out to be a volcanic ‘hot’ spot. The volcanoes responsible for the jets seen were, however, not erupting molten rock. Cassini has flown through the plume and measured its composition as mostly salty water-ice, tainted by traces of carbon dioxide, ammonia, methane and other hydrocarbons, and microscopic particles of silica that show that the water has reacted with warm rock inside Enceladus.

The contaminants lower the melting temperature of the ice on Enceladus’ crust and allow the generation of cryomagma. This can be erupted in plumes reaching hundreds of kilometres from the surface.

In this video David Rothery of The Open University and Michele Dougherty of Imperial College London describe the amazing world of Enceladus.

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DAVID ROTHERY

Well, Enceladus now - that’s a much smaller satellite than Jupiter’s active satellites. It’s only few hundred kilometres across, and nobody expected Enceladus to be an exciting place. Its surface is very intensely ridged and fractured. The crust has clearly been broken and shunted around a lot.

But the real surprise is, over the southern hemisphere, close to the south pole, you can see jets of crystallised water ice, with ammonia and various organic compounds being jetted into space. So clearly inside Enceladus, there’s either a layer that’s completely molten, or just, maybe, below the south pole, a pod of molten material, which is going to be salty water. And there’s something to pressurise it, to jet it out into space.

Stuff has been collected by the Cassini mission, there is a particle detector that was designed to detect particles captured in Saturn’s magnetic field, but having got to Saturn and found the active jets, or the geysers, on Enceladus, they flew through those plumes and sampled the material.

[MUSIC PLAYING]

MICHELE DOUGHERTY

This is the image that we took when we went really close to Enceladus, and you can clearly see this large plume of water vapour coming off from the south pole. It’s a gorgeous image.

NARRATOR

As Cassini has shown us that water definitely exists under Enceladus’s ice, that makes it a fantastic place to search for evidence of extraterrestrial life.

MICHELE DOUGHERTY

The reason that this discovery is so amazing is that it’s telling us that there’s water underneath the surface of Enceladus. And in the plume itself, there is water vapour, there are ice crystals, and there are organic compounds – nitrogen, carbon, hydrogen – all the things you would need for the basic building blocks of life.

NARRATOR

Michele and her colleagues are currently working on building much smaller probes that will be able to analyse the plumes jetting out from Enceladus. They look for more evidence of life. Ice in space may take us one step closer to finding out if other life forms have evolved in our Solar System.

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See also:

• The Plumes of Enceladus [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] . A three-minute TED talk by Carolyn Porco, leader of the Cassini imaging team, reporting the latest (as of 2009) findings.
• Learn more about Enceladus. This NASA page is a good place to begin if you want to study Enceladus in more detail.
• Molecular hydrogen from hydrothermal activity inside Enceladus? David Rothery’s October 2015 article discussing new experimental simulations relevant to Cassini’s closest fly-by through Enceladus’s plumes.
• David Rothery 2015 Enceladus radio interview. Interview about Cassini’s closest flyby of Enceladus broadcast 31 October.