Smooth Plains on Europa

Post contributed by Dr. Elodie Lesage, Laboratory of Geosciences Paris-Saclay, University of Paris-Saclay.

The young (60-100 Myrs) and active surface of the Jupiter’s icy moon Europa includes various geological features. In some locations, smooth plains have been observed on Europa, defined as features with no visible texture and an albedo lower than the surrounding terrains. The smooth plains overprint the preexisting terrains, and are confined within basins bounded by topographically high features.

Image 1: Four smooth plains on Europa. The arrows show the sunlight direction. Galileo images: (a) Image 5452r, resolution: 27 m/px; (b) Image 0713r, resolution: 57 m/px; (c) Image 0739r, resolution: 57 m/px; (d) Image 9352r, resolution: 60 m/px.

The best-resolved images of Europa’s surface were acquired by the Galileo spacecraft between 1996 and 2001. Image 1 shows four smooth plains visible in Galileo images, which share the following common characteristics: i) thin features occupying topographic lows, ii) a smooth appearance with little or no visible texture, and iii) kilometer-scale width with a quasi-circular, lobate shape. The morphology of these features suggests that they result from the flow of low-viscosity fluid, such as liquid cryomagma (i.e., briny water coming from Europa’s interior).

Image 2: (a) Digital Elevation Model of a smooth plain. (b) Schematic view of the AB cross-section and the subsidence mechanism that could possibly explain the morphology of the ridges.

The Digital Elevation Models (DEMs, i.e., 3D maps), of these four smooth plains can be obtained using the Shape from Shading technique, which is used to deduce the terrain relief from the shadows within an image. Image 2a shows the DEM obtained from Image 1a. One can notice that surprisingly, the ridges crossing the smooth plain seem to deepen towards the smooth plain center. This particular morphology can be explained by terrain subsidence before/during the smooth plain emplacement, as shown by Image 2b. Subsidence under a cryovolcanic feature could be caused by the presence of sub-surface reservoirs.

Further Reading

Fagents, S. A. (2003), Considerations for effusive cryovolcanism on Europa: The post-Galileo perspective, J. Geophys. Res., 108, 5139, doi: 10.1029/2003JE002128.

Greeley, R., et al. (2000), Geologic mapping of Europa, J. Geophys. Res., 105 (E9), 22559–22578, doi: 10.1029/1999JE001173.

Lesage, E., et al. (2021), Constraints on effusive cryovolcanic eruptions on Europa using topography obtained from Galileo images, Icarus, 361, 114373, doi: 10.1016/j.icarus.2021.114373.

Michaut, C., and Manga, M. (2014), Domes, pits, and small chaos on Europa produced by water sills, J. Geophys. Res. Planets, 119,  550– 573, doi: 10.1002/2013JE004558.

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