Mass Wasting and Ground Collapse in Terrains of Volatile-Rich Deposits as a Solar System-Wide Geological Process: The Pre-Galileo View

✍ Scribed by Jeffrey M. Moore; Michael T. Mellon; Aaron P. Zent

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 633 KB
• Volume: 122
• Category: Article
• ISSN: 0019-1035
• DOI: 10.1006/icar.1996.0109

✦ Synopsis

volving moving gas or fluids, often in combination with internal disaggregation of the relief-forming material

The polar terrains of Mars are covered in many places with irregular pits and retreating scarps, as are some of the surfaces through the loss (or deteriorating alteration) of its cohesive of the outer-planet satellites. These features are interpreted by matrix. Exogenic degradation is often limited to slumping us as diagnostic of exogenic degradation due to the loss of a and mass wasting where there is no surface fluid or effective volatile rock-forming matrix or cement. In this study we proatmosphere. The polar terrains of Mars are covered in pose that sublimation degradation is a plausible Solar Systemmany places with irregular pits and retreating scarps (e.g., wide geological process. Candidate examples have been identi-Sharp 1973). These features are very probably manifestafied on Mars, Io, and Triton, and possibly Europa and Gations of exogenic degradation due to the loss of a volatile nymede. We envision this process as having two end-member rock-forming matrix or cement. It has gone generally unexpressions (pits and scarps), for which we hypothesize two recognized that the same (or very similar) geologic process end-member mechanisms (massive localized lenses and areally responsible for the martian polar terrains also operates on extensive basal layers). In this study we focus on the role this the surface at some localities on some of the outer-planet process may play on the surfaces of the galilean satellites. Our principle modeling results are that for these satellites, H 2 S, CO 2 , satellites, including the Galileans. We examine this process and NH 3 are the only viable candidate volatiles for sublimation and how it may act throughout the Solar System, with a degradation of landforms, in light of galilean satellite cosmoparticular emphasis on the role it may play on the surfaces chemistry. For Io's polar regions only H 2 S, and then only from of the galilean satellites.

slopes that face the Sun and have thin lags, is volatile enough Theoretical investigations of particulate mantles covto cause the observed sublimation-induced erosion at those ering and/or intimately mixed with sublimating ice rely latitudes. SO 2 is not a viable candidate as an agent of erosion, on simplified, idealized models amenable to mathematical especially for these polar landforms. In the case of Europa, analysis. Terrestrial examples where ice sublimation occurs only CO 2 and H 2 S are viable candidates (given surface age as a singular geologic process are rare and of limited extent constraints). Both species could be efficient eroders in nonpolar due to the pervasiveness of liquid water (Mercer 1971), regions. H 2 S could generate erosion within the polar regions if the deposition and erosion conditions were essentially identical rendering field studies poorly suited as a means to learn as those we invoked for Io's polar regions. For Ganymede (and more of this topic. The nearest terrestrial analogs may be Callisto) NH 3 might be an agent of erosion in equatorial terrains thermokarsts, but the shaping of these features is domiof great age. The sublimation of CO 2 and H 2 S is much more nated by melt water, not sublimation (see recent review robust than NH 3 . The much slower rate of sublimation degradaas applied to Mars in Costard and Kargel , 1995). Though tion from NH 3 might be detectable by Galileo and used as a some laboratory studies have been undertaken to study compositional indicator.