Erosion on Mars?

Image Credit:  NASA

Image Credit: NASA

Arabia Terra, with an area of approximately 10 million square kilometers centered at (25E, 5N), is an anomalous region along the Martian dichotomy boundary. Traditionally considered part of the ancient southern highlands, Arabia Terra provides a more gradual transition from the southern highlands to the northern lowlands in both topography and crustal thickness. While the geological processes leading to the formation of the region have not been clearly identified, Arabia Terra contains morphological evidence indicative of surface erosion including isolated mesas and partially degraded craters. Though surface modification has been suggested for the entirety of the highlands, the anomalous nature of Arabia Terra and its geomorphology may indicate preferential erosion of the region. The amount of erosion may have generated a significant volume of sediment, possibly contributing to the resurfacing of the northern lowlands.

Though previous workers have attempted to constrain the amount of erosion for Arabia Terra and the southern highlands in general, much of the analyses have been based on crater degradation with anywhere between 200 m to 2300 m of material being eroded, as put forth by other work. Recent analysis of data from the Mars Exploration Rover landing site at Meridiani Planum within Arabia Terra suggests smaller amounts of erosion have occurred since 3.0 Ga, though evidence for this erosion is found on sedimentary deposits that lie above the original surface and thus does not constitute net loss. It has generally been suggested that erosion during the Noachian and early-mid Hesperian may have been greater due to a warmer and wetter environment. Widespread layered deposits across the region suggest an early period of deposition as well.

Prior analyses of erosion in Arabia Terra relied on the geomorphology of the terrain and craters. We emplace constraints for the erosion of Arabia Terra based on geodynamical modeling coupled with limitations established from topography and gravity data returned by the Mars Orbiter Laser Altimeter (MOLA) on the Mars Global Surveyor (MGS) and the gravity field investigation on the Mars Reconnaissance Orbiter (MRO), respectively. By comparing the expected flexural response and gravitational signature of various erosional loads to the observational data, we establish an upper limit on the amount of material that could have been removed from within Arabia Terra. We employ a lithospheric flexure model to attain the flexural rebound and gravitational signature associated with a given erosional load. Exploiting recent advances in spherical harmonic localization techniques, we better constrain the elastic lithosphere thickness  — a crucial parameter in resolving the flexural response to erosion. Our flexure model, based upon the thin elastic shell method, estimates the membrane and bending stresses for a load supported by an elastic lithosphere underlain by a fluid-like medium. We test the viability of several erosional scenarios, including loads capable of reproducing the unique topography and crustal structure of Arabia Terra from an initial, highlands-like terrain.

Collaborators:  Jeffrey C. Andrews-HannaMaria T Zuber

Acknowledgements:  Thanks to B. Hager, P. James, E. Lev, J. T. Perron, S. Tikoo, and O. Westbrook for discussions reviews in addition to F. J. Simons for assistance with localization techniques. This work was supported as part of the Radio Science Gravity Investigation of NASA’s Mars Reconnaissance Orbiter mission.