Hydrological and glaciological activities on early Mars for the formation of valley networks simulated in a global climate model
Abstract
The environment of early Mars is thought to have been quite different from that on the current Mars. Many observations have shown geological evidences for the past Martian environment, which should have been moderate enough to allow both the large-scale surface runoff and ice-sheet activities. These well-known geological evidences are called as "valley networks (VNs)", which are widely distributed within a domain of latitudes ranging from 60$^\circ$S to 30$^\circ$N. The orientation of VNs in the boundary between the Late Noachian and Early Hesperian (3.85-3.6 Ga) should have been influenced by the Tharsis bulge, which is the largest volcanic plateau centered near the equator in the western hemisphere of Mars, but the formation epoch of the Tharsis bulge is still under debate. We have developed a paleo-Mars global climate model (PMGCM) assuming a CO$ _{2}$/H$ _{2}$O/H$ _{2}$ atmosphere under the "Faint Young Sun" condition (with a solar luminosity of $\sim$75% of the current value) for surface pressures between 0.5 and 2 bar. The PMGCM has a hydrologic cycle module, which includes ocean thermodynamics and water vapor advection, convection, condensation and precipitation processes, as well as calculations of surface fluvial activities assuming the rainfall infiltration, base runoff or direct runoff, and surface erosion and transportation associated with river channel activities. The simulated fluvial activities under the conditions of a mean surface pressure of 1.5 bar and an H$ _{2}$ composition of 3% were partly consistent with the observed distributions of VNs, but not consistent around the Tharsis bulge [Kamada et al., 2020, Icarus]. Thus, we also started on the simulation of global water cycle of early Mars before late Tharsis formation, implementing the pre-True Polar Wander topography [Bouley et al., 2016, Nature]. In addition, we newly developed a surface glaciological scheme and implemented into the PMGCM, which estimates the surface erosion and transportation associated with glacier activities from the accumulation, ablation, spatial velocity and temperature fields of the surface ice. Our results showed that large obliquity ($\sim$60 degrees) and moderate value of geothermal heat flux could help snow accumulation and basal sliding, which could create VNs in southern highlands within a million years, in early Mars.
- Publication:
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43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E.380K