One of the articles that I found most interesting in 2015 was published in the summer issue of Geography. It addressed how water and historical climate change have transformed the landscape not of Earth but of Mars. The landscape of Mars has not changed drastically in its recent past due to the absence of plate tectonics and water for billions of years. However, there is evidence of erosion by water and wind at some time, and the planet appears to have undergone many of the same geophysical transformations that can be seen on Earth.
Extraterrestrial physical geography is a fascinating field of study, but without being able to visit these sites our understanding is based on competing explanations and remote sensing of particular landforms. The article uses a collection of these observable landforms and geoprocesses to show how liquid water could have existed on Mars and to prove its role in shaping the landscape. Shortly after the publication of this research, NASA announced that they believe liquid water exists even now on Mars which takes some of the excitement out of this research. However, it looks deeper into how this has changed throughout time and what may occur in the future. It also operates on a much smaller budget than NASA, yet reaches some of the same conclusions by connecting Martian landforms to similar ones on Earth for which we know the geographical processes that created them.
Ice can be seen on Mars, and is believed to be quite common. Models show that ice cannot melt on Mars, but rather sublimates to vapor. However, the observation of gullies points toward the ancient presence of liquid water on Mars. The article gives the idea that extreme changes in the obliquity of the planet’s orbit create warmer periods. During these warmer times, polar ice is circulated toward the equator and potentially becomes liquid. Another idea is that perchlorate salts, which have been found in the soil by the Phoenix Lander mission and change the melting point of water, enabled the existence of water. If compared to similar features on Earth, the observation of certain scars and cracks on the surface of Mars, and elsewhere thermokarst features, suggests many cycles of the freezing and thawing of the top layer of permafrost. In high latitudes, stripes and lobes on hillsides are further evidence of thawing ice.
By dating impact craters and assigning the time of these events to markings on the land, the some surprising conclusions are drawn and some bold statements are made: “the freeze/thaw cycles occurred within the last few million years and perhaps as recently as a few hundred thousand years ago” and the relationship between the dates taken from this evidence “point[s] to switching between periglacial modification, fluvial processes, and thermal cracking without melt.” From this, another conclusion is drawn. We may now be observing a cold and dry stage in the climate cycle of Mars, but a warmer climate may return “in the relatively near future” with thawing ice and erosion processes.
You can read “New insights on the roles of ice, water and climate change in recent landscape development on Mars” by Colman Gallagher and Matthew R. Balme in the Summer 2015 issue of Geography (Vol. 100, Part 2).