An artist's rendition of liquid water lakes and a deep, frozen ocean on Jupiter's moon, Europa. New research suggests these bodies of water give rise to 'chaotic terrain' on the surface.
Credit: Britney Schmidt/Dead Pixel VFX/University of Texas at Austin.
Enhanced-colour regional view of Conamara Chaos, showing its location south of the intersection of two large 'tripleband' lineae. White areas are ejecta rays from the large (26-km diameter) crater Pwyll 1000 km to the south.
Credit: Wikimedia
SHROPSHIRE: Astronomers have explained how chaotic regions of ice form above subsurface lakes on Jupiter's enigmatic moon, Europa.
Their discovery, reported today in Nature, was inspired by observing the Earth's icy regions, and provides further evidence for what could be a habitable waterworld beneath Europa's surface.
"We find evidence for large liquid lakes perched at shallow depths inside the ice shell of Europa," said Britney Schmidt, lead author of the study from the University of Texas at Austin in the U.S.. "This result is exciting because it implies that Europa is probably active today."
Chaotic ice terrains
Slightly smaller than our own Moon, Europa is the most petite of Jupiter's four 'Galileo satellites'. It's also one of the most intriguing bodies in the Solar System, as it hides a potentially habitable ocean of water under its barren, icy surface.
Although the majority of the moon's surface is remarkably smooth, regions of rough, jumbled ice known as 'chaos terrains' freckle Europa's skin. Until now, there had been no satisfactory explanation for how these features are created.
The two most popular theories - that the features are formed by deep upwellings of ice, or by the melt-through of water close to the surface - could not account for all of the observed terrains.
"Chaos features can initially appear so different that there are many models out there," said Schmidt. "However, each of these models has difficulties explaining some or many observations of chaos."
Earth's icy interactions
Using archived data from NASA's Galileo mission, Schmidt and colleagues studied two chaos terrains on Europa's surface: Conamara Chaos, which features ice domes as tall as 200 m, and Thera Macula, - sunken chaos terrain.
The astronomers developed a model to explain the formation of these terrains, based on geological processes that occur on our very own planet.
Firstly, in southeast Iceland there is a subglacial volcano with the exotic name of Grímsvötn. When Grímsvötn erupts, its ice cap melts, leading to the formation of a lens-shaped subglacial lake. Secondly, on the other side of the globe, Antarctic ice shelves frequently encounter seawater. Fractures in the ice allow this water to enter, which can weaken the ice shelves and ultimately lead to their collapse.
Four-phase model
Inspired by these processes, the researchers came up with a model for chaos terrain formation on Europa. First, a heated plume of subsurface ice rises towards Europa's surface. This causes melting, which produces a sealed, pressurised lens of water, similar to the subglacial lake in Iceland. Then, just as with the Antarctic ice shelves, the meltwater trickles into cracks in the overlying ice, helping to create floating icebergs, like ice cubes in a glass of water. The chaos terrains are formed when the lake and floating ice refreeze.
Schmidt and her colleagues propose that this 'lens-collapse' process can explain how the icy domes of Conamara Chaos were formed. Intriguingly, the sunken terrain of Thera Macula is likely to be a still-active region of chaos formation, situated above a melt lake containing enough water to fill all of America's Great Lakes.
A life-harbouring ocean?
"It's exciting that the model predicts huge lakes at shallow depths within the ice shell of Europa today," said Robert Pappalardo, a planetary scientist at the Jet Propulsion Laboratory in California. "This model also suggests a way by which surface ice charged in 'oxidants' can be swallowed into the icy interior of Europa to eventually end up in the ocean below, where it might be able to serve as a fuel for life."
So maybe, just maybe, there's life hidden beneath Europa's ice sculptures. "The oceans on Europa appear to be remarkably suitable for life - there's liquid water; there's oxygen; there's a heat source. It seems like a lot of the things that life would require are there," commented Richard Greenberg, a Europa expert from the University of Arizona.
