Aeolian activity in the last 400 ka driven by insolation changes: Can global and mesoscale atmospheric modeling explain when and how Meridiani Planum ripples last migrated?

Grant #: NNX12AH85G
Senior Scientist: Lori Fenton

The climatic system of Mars, composed chiefly of the atmosphere and the uppermost meters of the planet's crust, is primarily driven by the absorption of shortwave solar radiation (and modulated by the emission of longwave radiation to space). The chief parameters which control the insolation over seasonal and longer intervals are the axial obliquity, the orbital eccentricity, and the season (Ls) of perihelion. Large variations in insolation can result from relatively modest changes in the values of one or more insolation parameter(s). Such significant insolation changes may translate into potentially large changes in atmospheric density and winds, two of the most important parameters for aeolian surface processes. 

Over the course of Mars' history, the wind has played a major role in both sculpting the landscape and recording the planet's climate variations. In the last few years, evidence for active bedform migration on Mars has emerged, but it is equally clear that in other regions on Mars many bedforms are inactive. Although it is agreed that the stabilized aeolian features were once active under different climatic conditions, it is not known how old most aeolian bedforms are or what conditions are required to remobilize them. The only well-constrained ancient period of bedform migration has been identified for coarse-grained ripples in Meridiani Planum. By using observations of fresh craters with a combination of in situ data from the Mars Exploration Rover (MER) Opportunity and orbital imagery from the High Resolution Imaging Science Experiment (HiRISE), Golombek et al. [2010] carefully dated this active period to ~50,000 - ~200,000 years ago. They proposed that known variability in Mars' orbit was in some way responsible for influencing wind patterns enough to have mobilized these now-inactive coarse-grained ripples; the proposed work will directly test this hypothesis.

The OBJECTIVE of the proposed work is to use global and mesoscale atmospheric models to determine if recent (<400 ka) changes to Mars' orbital (i.e., insolation) state can create substantial changes in local wind patterns at Meridiani Planum, defining possible episodes during which 1) wind directions correspond to observed ripple morphology and 2) wind strengths are substantially stronger than those surmised today. 

Our METHODOLOGY involves running the NASA Ames Research Center Mars Global Climate Model (GCM, version 2.1), spanning the insolation parameter space (including orbital eccentricity, axial obliquity, and Ls of perihelion) from the previous 400 ka, to determine what conditions most greatly influence wind patterns in Meridiani Planum (with respect to their potential to drive sediment transport). Cases with the most potential aeolian transport will then be thoroughly examined using the Mars Regional Atmospheric Modeling System (MRAMS), using GCM output as the initial state and time-dependent boundary conditions for much more detailed study of local air flows at Meridiani Planum. This represents the first application of a mesoscale model to examine Mars' past, an innovative avenue of research that will certainly become more common in the future. Relative changes in the potential sediment flux and transport directions caused by changes in Mars' insolation will be estimated, from which we will produce a timeline of potential ripple migration. 

The SIGNIFICANCE of such work would include 1) a determination of how insolation parameters have influenced wind regimes in Mars' recent past as constrained by the "ground truth" provided by the MER Opportunity at two different periods (the present and ~50 ka - ~200 ka), and 2) production of the first specific timeline of aeolian activity on Mars, further constraining the dates of Golombek et al. [2010]. This will provide an understanding of the air flows that once mobilized the now-stabilized bedforms in Meridiani Planum and insight into past aeolian erosion elsewhere on Mars.