We’ve mentioned before in the live chats, and Talk about how the science team would like to test whether the fan directions and the blotch measurements we ask you to make are indicators of the prevailing direction of surface winds on the South Polar regions. We think that the wind is the mostly likely culprit for the sculpting of the fans and that blotches occur when the wind was not strong enough to blow the material into the fans you see in other Planet Four images.

How will we check this? Unlike on Earth, there aren’t weather stations covering most of the globe of Mars taking pressure, temperature, and wind measurements. We’ll have to rely on computer simulations, on the output from a Global Circulation Model/Global Climate Model (GCM) of Mars. A GCM is a computer model of Mars’ atmosphere and climate that simulates all the conditions of the planet’s atmosphere and evolve it over time. PlanetWRF and Ames Mars General Circulation Model are two examples of Mars GCMs.

A GCM attempts to contain in it all the physics and chemistry that planetary scientists know and believe are acting in the planet’s atmosphere. This includes dealing with winds, pressure, atmospheric temperature, chemical reactions, impact of dust and particulate transport in the atmosphere on the whole planet and smaller scales. The simulations also have to take into account how solar insolation varies on the surface of the planet over time accounting for Mars’ orbital parameters changing as well. In addition the climate and weather impact the  surface conditions which evolve on the planet over time and feedback into the climate. If you’re interested in reading more about the processes that impact the Martian climate check out the NASA AMES Mars Climate Modeling Group Climate page

Martian GCMs are trying to represent and replicate complicated processes that are happening in the Martian atmosphere. Sometimes things are parametrized to make it possible to program into a computer and may not fully represent the reaction but it is the best scientists can do. The models are continuously improved by comparing to what limited weather and atmospheric  measurements we do have of Mars. Mars is the best studied and detailed climate besides Earth in the Solar System.  There have been weather stations on the Mars rovers (Curiosity, Spirit, and Opportunity) and landers (including Viking, Pathfinder, Phoenix etc) measuring the wind direction, temperature, pressure etc on the ground. Both Opportunity and Curiosity are continuing to measure the current conditions at their landing sites. Also the fleet of US and European spacecraft (and two new Mars orbiters – one from  India and one from the  US  are currently on their way to Mars) are monitoring the Martian atmosphere providing  rich data sets of the upper and middle atmosphere. For example  the vertical distribution of dust in the Martian atmosphere and how it changes over the Martian year is obtained from observations from the Mars Climate Sounder aboard the Mars Reconnaissance Orbiter (which also is the home for the HiRISE camera that takes the images you classify).

Once we have the fan pointings  and the locations of the blotches over several Martian seasons we’ll use GCMs to predict wind directions and speeds at different times and dates on the ground at the locations the images were taken and see how they compare.