Comparison of “warm and wet” and “cold and icy” scenarios for early Mars in a 3‐D climate model

Abstract

We use a 3-D general circulation model to compare the primitive Martian hydrological cycle in "warm and wet" and "cold and icy" scenarios. In the warm and wet scenario, an anomalously high solar flux or intense greenhouse warming artificially added to the climate model are required to maintain warm conditions and an ice-free northern ocean. Precipitation shows strong surface variations, with high rates around Hellas basin and west of Tharsis but low rates around Margaritifer Sinus (where the observed valley network drainage density is nonetheless high). In the cold and icy scenario, snow migration is a function of both obliquity and surface pressure, and limited episodic melting is possible through combinations of seasonal, volcanic, and impact forcing. At surface pressures above those required to avoid atmospheric collapse (∼0.5 bar) and moderate to high obliquity, snow is transported to the equatorial highland regions where the concentration of valley networks is highest. Snow accumulation in the Aeolis quadrangle is high, indicating an ice-free northern ocean is not required to supply water to Gale crater. At lower surface pressures and obliquities, both H 2 O and CO 2 are trapped as ice at the poles and the equatorial regions become extremely dry. The valley network distribution is positively correlated with snow accumulation produced by the cold and icy simulation at 41.8 ∘ obliquity but uncorrelated with precipitation produced by the warm and wet simulation. Because our simulations make specific predictions for precipitation patterns under different climate scenarios, they motivate future targeted geological studies. BackgroundDespite decades of research, deciphering the nature of Mars' early climate remains a huge challenge. Although Mars receives only 43% of the solar flux incident on Earth, and the Sun's luminosity was likely 20-30% lower 3-4 Ga, there is extensive evidence for aqueous alteration on Mars' late Noachian and early Hesperian terrain. This evidence includes dendritic valley networks (VNs) that are distributed widely across low to middle latitudes [Carr, 1996;Mangold et al., 2004;Hynek et al., 2010], open-basin lakes [Fassett and Head, 2008b], in situ observations of conglomerates [Williams et al., 2013], and spectroscopic observations of phyllosilicate and sulfate minerals [Bibring et al., 2006;Mustard et al., 2008;Ehlmann et al., 2011].All these features indicate a pervasive influence of liquid water on the early Martian surface. Nonetheless, key uncertainties in the nature of the early Martian surface environment remain. These include the intensity and duration of warming episodes and the extent to which the total surface H 2 O and CO 2 inventories were greater than today. Broadly speaking, proposed solutions to the problem can be divided into those that invoke long-term warm, wet conditions [e.g., Pollack et al., 1987;Craddock and Howard, 2002] and those that assume the planet was mainly frozen, with aquifer discharge or episodic / seasonal melting of snow and ice deposits provid...

A map of D/H on Mars in the thermal infrared using EXES aboard SOFIA

“…Another open question is related to the very large amount of liquid water apparently required to account for the erosional features observed on Article published by EDP Sciences A62, page 1 of 12 the surface of Mars. These results have been discussed by several authors (Carr 1986(Carr , 1990(Carr , 1996Jakosky 1990;Krasnopolsky et al 1997;Lasue et al 2013;Wordsworth et al 2015).…”

The habitability of Proxima Centauri b

“…Low irradiated planets as Early Mars Wordsworth et al , 2015Turbet et al 2016b), Archean Earth (Charnay et al 2013), Snowball Earth-like planets (Turbet et al 2016a) or exoplanets like Gliese 581d ); 2. Planets receiving stellar flux similar to the Earth (Bolmont et al 2016a, this paper); 3.…”

Survivability of Soil and Permafrost Microbial Communities after Irradiation with Accelerated Electrons under Simulated Martian and Open Space Conditions

“…The modern concept of the Mars evolution assumes a scenario of the planet's development according to the terrestrial type with the possible emergence of the biosphere [24][25][26][27][28]. The impact of radiation could contribute to the origin of life, being, possibly, a key factor [108].…”

“…Laboratory experiments do not allow for studying the long accumulation of doses of relatively low intensity in the microbial biomass of natural soil. The main question of the present study is how long the biosphere of Mars could be maintained after the supposed catastrophic change in planetary conditions [24][25][26][27][28][29], the gradual loss of the atmosphere [30], and the formation of a modern climate.…”