Scientists studying data from NASA’s Galileo probe, which ended its mission to Jupiter in 2003, have discovered what appears to be a body of liquid water the volume of the North American Great Lakes underneath the surface of Jupiter’s moon Europa. Europa has a young, icy surface and sustains a liquid water ocean below an ice shell of highly debated thickness.
Galileo spacecraft images of two roughly circular, bumpy features on Europa’s surface called chaos terrains were examined. One of them, Thera Macula is a region of likely active chaos terrain production above a large liquid water lake.
Thera Macula (false color) is a region of likely active chaos production above a large liquid water lake in the icy shell of Europa. Color indicates topographic heights relative to background terrain. Purples and reds indicate the highest terrain. Credit: Paul Schenk/NASA
Based on similar processes seen here on Earth — on ice shelves and under glaciers overlaying volcanoes — the researchers developed a four-step model to explain how the features form on Europa. The four steps are: (1) Ascending thermal plumes of relatively pure ice produce surface deflection in response to volume change associated with melting of the ice (2) Resulting hydraulic gradients and driving forces produce a sealed, pressurized melt ‘lens’ (see figure) (3) Extension of the sinking brittle ice ‘lid’ over the lens ultimately generates deep fractures, allowing brine to percolate through overlying ice, forming a fluidized granular ice matrix and calving ice blocks. (4) Refreezing of the melt lens and now brine-rich matrix results in topographic heterogeneity. i.e. “chaos terrains”.
Four step process for building “chaos terrains” on Europa
This “lens-collapse” model makes testable predictions: liquid water may be found where the surface subsides and blocks ‘float’ above the surrounds. At Thera Macula, we are probably witnessing active chaos formation. The large concentric fracture system encircling Thera Macula resembles those of collapsing ice cauldrons. The inferred lakes are several km below the surface, hence, the only confirmation of their existence would come from a future spacecraft missions that could designed to land on and perhaps drill into the ice shell.
The data suggest that chaos terrains form above liquid water lenses perched within the ice shell as shallow as 3 km. The results suggest that ice–water interactions and freeze-out give rise to the diverse morphologies and topography of chaos terrains. For more details, see
- Active formation of ‘chaos terrain’ over shallow subsurface water on Europa, Schmidt et al. (2011), Nature, 479, pxx [Swinburne login]
- Planetary science: Europa awakening, Keszthelyi (2011), Nature News & Views, 479, 302 [Swinburne login]
- Scientists Find Evidence for “Great Lake” on Europa and Potential New
Habitat for Life (University of Texas at Austin website] (has video links) - New Evidence for Liquid Water on Europa
(NASA Science News website)
[Posting by Glen Mackie]
