Cryovolcanic flows on Ceres

Post contributed by Dr. Katrin Krohn, German Aerospace Center, Institute of Planetary Research

The dwarf planet Ceres is a weakly differentiated body with a shell dominated by an ice-rock mixture and ammoniated phyllosilicates, which has a variety of flow features visible on its surface. Flow features are common features on planetary surfaces and they indicate the emplacement of viscous material. Many of the observed flows on Ceres originate from distinct sources within crater interiors and on crater flanks.

Haulani_IAG

Image 1: LAMO FC mosaic of Haulani crater. A: Well-defined smooth lobes (LAMO FC21A0049392_16002071420F1F.IMG). B: Multiple flow stages on western crater flank (FC21A0046469_15350155540F1C.IMG).

Generally, flow-like morphologies in crater ejecta are thought to be a result of either an involvement of volatiles or gases, deceleration when the ejecta motion interacts with the local topography, or a post emplacement ground-hugging flow. Liquid cryolava features can be produced by heating or by a release of material from a liquid subsurface layer. Ascent and emplacement of a cryolava could be due to compositional buoyancy. A liquid ammonia-water mixture has a similar density to water ice and could be erupted by large-scale tectonic stress patterns like subsurface pressure gradients associated with topography. Moreover, cryolava could also be due to an overpressurization of liquid cryomagma chambers (fluid reservoirs of water ice) in an ice lithosphere.

A possible emplacement scenario for the flows on Ceres is the formation of subsurface reservoirs enriched in salt-bearing components driven upwards by density/temperature inhomogeneity. The observed craters may have tapped into salt-rich crustal reservoirs, triggering the mobility of material and formed the cryovolcanic features.

Image 1 shows the 34-diameter Haulani crater. Haulani exhibits interior smooth plains with flow features originating from a hummocky elongated mountainous ridge in the center, ponding toward mass-wasting deposits of the rim. Haulani shows several flow features running from the crater rim outward to the surrounding area, covering the preexisting surface. We can distinguish different types of flows: smooth narrow lobes with well-defined margins and a very smooth featureless surface; viscous flows with a relatively smooth surface, showing multiple flow stages on top of each other on the western crater flank; and flows through small narrow channels.

Occator_IAG

Image 2: Occator crater. The left LAMO FC image (FC21A0074996_16191121617F1B.IMG) shows that flows spread out from central white spot, and superimposed individual flows indicate multiple flow events. The right image (LAMO FC mosaic) shows a digital terrain model of Occator showing the the flows tend to be directed uphill.

Image 2 shows the center of Occator crater (92-km diameter). The interior of Occator has extended plains of ponded material. The center of Occator is dominated by a depression with a small bright dome in its center. Toward the northeast, flows spread out from the bright dome, which are affected by radial cracks, and appear to have moved uphill. These flows show at least three individual lobate flow surfaces superposed on each other, indicating multiple flow events. The uphill-sense of these flows in Occator indicates a feeding zone that pushes the flows forward by supplying low-viscosity material and a post-flow-collapse of the dome in the central region, possibly due to a discharge of a subsurface reservoir.

The bright spots within Occator predominantly consist of carbonates, which differs from the adjacent material predominantly consisting of phyllosilicates. Such carbonates have also been detected in the plumes of Enceladus, suggesting an endogenic origin.

Further Reading:

Boyce, J. M. et al. (2010), Rampart craters on Ganymede: Their implications for fluidized ejecta emplacement,  Meteoritics and Planetary Science, 45, 638-661.

Cassen, P. et al. (1979), Is there liquid water on Europa, Geophysical Research Letters, 6, 731-734.

Croft, S. K. et al. (1988), Equation of state of ammonia-water liquid – Derivation and planetological applications, Icarus, 73, 279-293.

De Sanctis, M. C., et al. (2015), Ammoniated phyllosilicates with a likely outer Solar System origin on (1) Ceres, Nature, 528, 241-244.

Fagents, S.A. (2003), Considerations for effusive cryovolcanism on Europa: The post-Galileo perspective, Journal of Geophysical Research (Planets), 108, 13-1.

Krohn, K. et al. (2016), Cryogenic flow features on Ceres: Implications for crater-related cryovolcanism, Geophysical Research Letters, 43, 1-10.

Mitri, G. et al. (2008), Resurfacing of Titan by ammonia-water cryomagma, Icarus, 196, 216-224.

Postberg, F. et al. (2011), A salt-water reservoir as the source of a compositionally stratified plume on Enceladus, Nature, 474, 620-622.

Tobie, G., et al. (2010), Surface, subsurface and atmosphere exchanges on the satellites of the outer Solar System, Space Science Reviews, 153, 375-410.

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