2011 Annual Science Report
VPL at University of Washington Reporting | SEP 2010 – AUG 2011
Understanding the Early Mars Environment
By analyzing data from rovers and orbiters, we construct theoretical models to constrain the habitability of current and past Martian environments. VPL has re-analyzed data and called into question the existence of methane and ancient oceans on Mars. In additional, we have contributed to past and future NASA missions such as Phoenix lander and the Curiosity rover,
VPL team members have contributed to a number of projects that seek to constrain the environment and habitability of both present and ancient Mars. We have critically investigated putative evidence for methane plumes on modern Mars as well as claims of an ancient ocean. Following up on the surprising results from NASA’s Phoenix Lander, we continued to investigate the formation of perchlorate in the Martian atmosphere (and in Earth analog environments). Additional highlights include ongoing progress in climate modeling of the early Martian atmosphere, which included enhanced concentrations of CO2.
A major driver of current and future Mars missions (e.g. Curiosity, 2016 Trace Gas Orbiter) has been the putative detection of methane in the Martian atmosphere. While intriguing, the detection is puzzling from the standpoint of known atmospheric chemistry. The reported quantities of methane and its time-dependent disappearance in subsequent observations require two extraordinary factors: a) a large unknown source of methane and b) a large unknown chemical sink of methane. The first issue (methane production) could be feasibly explained by underground geochemistry (or biology). However, the second point (methane sink) is more troublesome given that the chemistry of methane oxidation has been very well studied in Earth’s atmosphere. In a critical re-examination of the primary data, Zahnle et al. (2011) postulate a blue-shifted isotopic line of methane in Earth’s atmosphere may have been confused for primary methane in the Martian atmosphere. Given the possibility for contamination in the original data, along with the two extraordinary environmental circumstances that would be required to support the methane detection, the new analysis may point to the lack of methane in the current Martian atmosphere, with important implications for NASA’s mission planning.
A longer-held hypothesis regarding Mars involves the presence of an ancient circumpolar ocean in the northern plains. A topographic low is suggestive of Earth’s continental/ocean floor dichotomy, and evidence for ancient shorelines has been presented. A contrasting hypothesis is that the northern plains may have been formed by a catastrophic impact event, and never hosted a global ocean. Catling et al. (2011) reasoned that a global ocean would have led to formation of sedimentary rocks and searched for evidence within smaller impact craters in the northern plains. Rather than impact physics suggestive of sedimentary rocks, the data pointed to basaltic lava as the underlying substrate. This evidence – supportive of the giant impact (and the lack of a global ocean) – was presented to the LPSC during the period of performance and has been submitted for publication.
Another challenge for the oceanic hypothesis is that climate modelers have severe difficulties in determining geochemically self-consistent scenarios resulting in clement conditions on early Mars. In an attempt to provide additional warming for early Mars, we are updating prior VPL climate calculations for early Mars (Tian et al 2010) to incorporate updated CO2 collision-induced parameterization (Ramirez, 2011), which should enhance the early Martian greenhouse effect.
The detection of perchlorate on Mars by the Phoenix lander continues to intrigue VPL, as it may provide clues to ancient atmospheric chemistry on Mars. Building upon the study of perchlorate in unique regions of Earth, Smith et al. (2011) have begun an exploration of perchlorate formation on Mars. The chemistry of perchlorate formation is affected by concentrations of nitrogen, total pressure, and volcanic chlorine and bromine emissions. How the detection of perchlorate coupled with the absence of nitrate constrains the past atmospheric chemistry remains under active investigation.
PROJECT INVESTIGATORS:Mark Claire
PROJECT MEMBERS:David Catling
David Des Marais
RELATED OBJECTIVES:Objective 1.1
Formation and evolution of habitable planets.