Environmental Effects of Large Impacts on Mars

Abstract

The martian valley networks formed near the end of the period of heavy bombardment of the inner solar system, about 3.5 billion years ago. The largest impacts produced global blankets of very hot ejecta, ranging in thickness from meters to hundreds of meters. Our simulations indicated that the ejecta warmed the surface, keeping it above the freezing point of water for periods ranging from decades to millennia, depending on impactor size, and caused shallow subsurface or polar ice to evaporate or melt. Large impacts also injected steam into the atmosphere from the craters or from water innate to the impactors. From all sources, a typical 100-, 200-, or 250-kilometers asteroid injected about 2, 9, or 16 meters, respectively, of precipitable water into the atmosphere, which eventually rained out at a rate of about 2 meters per year. The rains from a large impact formed rivers and contributed to recharging aquifers.

New evidence for a magmatic influence on the origin of Valles Marineris, Mars

“…Mars has had a dynamic geologic history, influenced by both exogenic (including impact events; Segura et al, 2002) and endogenic processes such as illustrated by the evolution of the Tharsis magmatic complex/superplume Dohm et al, 2007). Tharsis is composed of giant shield volcanoes, igneous plateaus, magmaticdriven centers of tectonic activity, fault and rift systems, vast canyon system, and lava flow fields.…”

Paleohydrology of Eberswalde crater, Mars

“…Local, geologically brief effects of impacts have been implicated for groundwater release, meltwater production, or lake-effect precipitation, which could incise valleys into the crater rim or ejecta (e.g., Newsom et al, 1996;Abramov and Kring, 2005;Morgan and Head, 2009;Barnhart et al, 2010;Harrison et al, 2010;Newsom, 2010;Kite et al, 2011;Mangold et al, 2012a). Global environmental effects have been attributed to larger craters (Segura et al, 2002(Segura et al, , 2008Toon et al, 2010;Segura et al, 2012). Testing the hypothesis that impacts caused significant late fluvial erosion on a local to regional scale, where stratigraphic relationships are best constrained, could have broader implications for impact cratering as an environmental factor on early Mars as well.…”

“…Moore et al (2003) preferred a timescale of 2000 to 1,000,000 years under Earthlike intermittent flow conditions, but they did not rule out a short timescale resulting from a hypothetical large impact that generated short-term, nearly continuous runoff on a global scale (Segura et al, 2002). Bhattacharya et al (2005) estimated 150,000 years, based on timescales for meander development and avulsion on Earth.…”

“…This discrepancy between empirical and theoretical results has motivated investigations of higher-thanexpected solar luminosity, obliquity variations, more effective greenhouse gases, carbon dioxide clouds, albedo differences, and release of volatiles by impacts or volcanism as possible ways of warming the planet (e.g., Baker et al, 1991;Whitmire et al, 1995;Sagan and Chyba, 1997;Segura et al, 2002;Colaprete and Toon, 2003;Segura et al, 2008Segura et al, , 2012Mischna et al, 2013;Ramirez et al, 2014). Other investigators have examined ways to erode valleys under cold conditions, including ice flow, stream flow under an ice cover, or generation of meltwater by surface (impact ejecta) or subsurface (geothermal) heat sources (e.g., Wallace and Sagan, 1979;Carr, 1983;Brakenridge et al, 1985;Wilhelms and Baldwin, 1989;Brakenridge, 1990;Gulick and Baker, 1990;Carr, 1995;Goldspiel and Squyres, 2000;Harrison and Grimm, 2002;Carr and Head, 2003;Mangold et al, 2012a).…”

Episodic flood inundations of the northern plains of Mars

“…Another point of view to the concept of episodic oceans and lakes put forth in this work has recently been purported by Segura et al (2002), who estimate that the heat generated by impacts could provide a sufficient amount of water vapor to incorporate into the atmosphere, from the conversion of shallow subsurface or polar ice and water locallyderived from the impactors themselves. As the peak in highland valley network formation is roughly coincident with the period of heavy bombardment, Segura et al (2002) conclude that rains excavating the valley networks were triggered almost exclusively by large body impacts, a process which frequency made the persistence of temperate and wet conditions impossible.…”