Could Some Craters on Mars Have Acid Water Origins?

Introduction: Physical sedimentology experiments using a 39% concentration of sulfuric acid have produced three distinct features, which are similar to features seen on Mars. However, these sedimen-tary features could not be created using pure water in the laboratory. These three features include deeply-incised, narrow channels, cracks that run parallel to the flow direction, and circular depressions that are concentrated along the toes of alluvial fans. These circular depressions, which form syndepositionally, are likely produced by the release of trapped air or possibly by gases escaping to the surface. They closely resemble impact crater features, though they are on a significantly smaller scale [1]. Background: Clark (2-5) first proposed the possibility that sulfuric acid could exist on Mars. This theory was based on the elemental composition of Mars' surface fines with their unusual abundances of sulfur, the lack of carbonates, as well as the physical characteristics of a 39% sulfuric acid solution. A 39% sulfuric acid solution, based on its freezing point, would be stable on Mars' surface today. Burns (6,7) noted that some minerals and chemical compositions from the Martian surface indicate that Mars likely has experienced long-term oxida-tive weathering such as in Australia, perhaps due to acid saline meltwaters (6,7). Recently, a mineralogi-cal and chemical similarity has been demonstrated between data returned from Mars and shallow, acid saline lake systems in modern Western Australia and the Permian of the midcontinent of the U.S. (8). Our physical sedimentology experiments have shown that many of the surface features seen on Mars, which have historically been attributed to creation by water [9], could have been created by a 39% sulfuric acid solution [1]. Such features produced only during acid runs that resemble features on Mars include deeply incised, narrow channels and valleys, surface cracks that run parallel to the flow direction, and " crater " air bubbles, which are circular depressions that tend to form along the edges of alluvial fans or along the base of slopes [1]. Martian Analogs: The Martian surface is pockmarked with numerous impact craters. Many are large complex craters, but many more are smaller (<1km) in diameter. In some regions on the planet there are debris flows that contain concentrations of circular depressions along the toe of the flows (Fig. 1). These features have been interpreted to be impact cra