by Kristian Marinez (a 2016 Adler Astro-Journalist)
The goal of the project, Planet Four: Terrains, is to have citizen scientists (average people who probably don’t work in the field of science) review the terrain of the South Pole of the 4th planet in the Solar System, Mars. The terrain is usually formed by the melting of CO2 and ice in the polar ice caps during summer and spring. The images reviewed by the citizen scientists come from Context Camera aboard the Mars Reconnaissance Orbiter. In other words , the images come from a camera that takes pictures of Mars’ terrain from orbit. With the feedback citizen scientists give back, the team will send out the HiRISE (the highest resolution camera ever sent out into space) to new interesting areas of Mars to analyze and see how the terrain changes over time. But features of the terrain are being studied? In the Martian terrain, we can find “Spiders”/“Baby Spiders” and the “Swiss Cheese Terrain”.
Examples of Spiders and Baby Spiders – Image Credit:NASA/JPL-Caltech/Malin Space Science System , taken from the Planet Four Terrains Research Page
Example diagram of how spiders are formed, original figure from Piqueux et al., 2003, taken from the Planet Four Terrains Research Page
Spiders (not real arachnids, just terrain that has an image like spiders) is just a name for shallow, patternized channels (passages) on the surface of Mars. These channels are several meters deep and vary in size concerning width. Spiders form when dry ice (carbon dioxide ice) forms in the South Pole. When the Spring season come around, sunlight penetrates the ground, causing the ice to turn into gas from the bottom up. The gas then gets trapped in a layer of ice. When a crack forms in the terrain, the gas erupts out of the opening and also carries loose materials out. Finally, when Summer comes around, the CO2 evaporates and the material on the ground is no longer visible. This happens again in the Autumn and slowly erodes channels in the ground, which are the spiders. The actual term for Spiders is araneiform. Baby Spiders are just the beginning features of the spiders.
The Swiss Cheese Terrain are curvy pits in the surface of thin layers of CO2 ice. Basically, Swiss Cheese Terrain pops up because of repeated cycles of condensation (gas to liquid) and sublimation (solid to gas without going through the liquid stage) of CO2. Thin layers of CO2 ice deposit in excess amounts on some areas. The ice sublimes (solid changed to vapor when heated) and a new layer appears. Areas with no sunlight accumulate CO2 while areas with sunlight lose CO2. This causes irregularities in the terrain. Eventually, pits appear in the CO2 layer. The pits absorb a large quantity of CO2 and they grow.
After a lot of scientific explanations and what not, the goal of Planet Four: Terrain is pretty simple: it’s to give back feedback on the images of the terrain of the South Pole in Mars to analyze and notice how the terrain changes over time.
To learn more, check out the Planet Four: Terrain Blog :).