In case you missed it, cryovolcanoes – or ice volcanoes – exist. Not on Earth, mind you, but on the dwarf planets Pluto and Ceres, and on Saturn’s moon Enceladus. Speaking of which, this icy satellite seems to only have eruptions coming out of its South Pole and nowhere else – something that strikes plenty of planetary scientists and volcanologists as being quite unusual.

There have been a few hypotheses banded about as to why the chilly geyser-like plumes are only seen emerging from the moon’s proverbial rear-end, but, as reported by New Scientist, a paper presented at the Lunar and Planetary Science Conference in Texas earlier this month brings up a previously unconsidered possibility.

The idea, touted by a team at Johns Hopkins University in Maryland, posits that a gigantic asteroid impact took place on Enceladus’ South Pole around 100 million years ago. This would coincide with a period of chaos and collisions in the region that led to the destruction of many younger moons and the formation of Saturn’s beautiful rings.

A large enough asteroid would have put some serious cracks in the icy crust, while also transferring plenty of thermal energy from the impactor to the moon’s underside.

Enceladus, despite having a subterranean liquid ocean, is extremely cold throughout – all, except, for its South Pole, which is unusually warm. An ancient collision, one that generated a weaker crust and a fresh heat source, would neatly explain the specificity of the moon’s cryovolcanism.

The impact may not have been at the South Pole originally, but as the planet’s mass would have been dramatically shifted by it, it’s likely the impact zone would have oriented at the South Pole regardless.

^{Explaining the enigmatic plumes of Enceladus. New Scientist via YouTube}

Although the definition is not set in stone, ice volcanoes essentially have a “magma” made of water and ammonia, and their “rock” is actually built of a mixture of ices.

Enceladus doesn’t yet have mountains or craters that resemble other types of cryovolcano edifices found elsewhere, but it does have supercool geysers much like frigid versions of Yellowstone’s Old Faithful or the fabulous fountains you’ll find in Iceland. The Earthbound versions are powered by subterranean volcanic systems, and an internal source of heat within Enceladus is certainly fueling its southern paroxysms.

Enceladus has long been thought to derive its internal heat source from either primordial heat (unlikely, as it’s too small to retain it), radioactive decay (as Pluto probably does), or tidal heating (as the Jovian moon of Io does).

However, all three require that it should have volcanoes or geysers more evenly distributed across its surface as the planet uniformly cools down. It does not, and this new study offers a rather elegant explanation as to why.

[H/T: New Scientist]