Terrestrial Analogues

Dr. Jim Zimbelman

Since missions to Mars and the other planets in our solar system are expensive and require abundant manpower, scientists often turn to studying Earth as a simple alternative. Using terrestrial terrains, referred to as terrestrial analogs, amplifies our understanding of planetary ones and allows researchers to make inferences about past processes on other planets. The study of analogs for Mars is especially prevalent these days. Currently, many areas in the dry landscapes of the southern/westerns parts of the US1,2 represent potential analogs for aeolian and volcanic processes exhibited on Mars. Dr. Zimbelman and others have meticulously outlined specific examples of American landscapes and features that directly correlate to Martian ones for those two processes in chapter 4 and 9 of the textbook, "The Geology of Mars: Evidence from Earth-Based Analogs", edited by Mary Chapman.

Volcanism is a process seen on a variety of planets in our solar system. Earth has a long history of volcanism, especially in the recent past that conveniently lends itself to being ideal for planetary analogues. Chapter 4, titled "Volcanic features of New Mexico analogous to volcanic features on Mars," details comparisons made between various New Mexico volcanic features with related Martian examples. New Mexico represents an arid environment with an extensional rift setting, and a wide range of both type and age of volcanoes with a fabulous array of particularly young volcanic features1, all aspects characteristic of, or aiding in the understanding of the degradation of Martian volcanic features. Specifically ash flows, calderas, large radial dikes, large lava flows, flow fields, and hydromagmatic vents1 represent some of the volcanic features found in New Mexico that can be related to certain Martian rough equivalents.

The New Mexico Valles Caldera, for example, is almost circular with a 20 km diameter and strongly resembles smaller Martian calderas1. This analog is not only similar to Martian calderas with its diameter size1, but also for having resurgent ash-flow. Hadriaca Patera, Apollinaris Patera, and Ceraunius Tholus are all examples of possible ash-flow type morphologies of Martian volcanoes1.

Wind is the current dominant erosive and degrading process on Mars, consequently studying terrestrial wind environments is very important for expanding our understanding of this process on Mars, as well as how and why it differs from Earth. Chapter 9, titled, "Eolian dunes and deposits in the western United States as analogs to wind-related features on Mars," identifies a suite of wind-formed features, such as sand dunes, in the western US that can be compared to similar features on Mars.

Figure 1. Image of large barchans and barchanoid ridges on the floor of Nil Patera on Mars.

One of the twenty-two sites detailed in this chapter is the Salton Sea Barchan Dunes located in California. Barchans are crescent-shaped dunes whose tips, called horns, point away from the primary wind direction2. On Earth, scientists have discovered there is an inverse relationship between barchan slip face height and dune advance rate2. Though barchans are seen on Mars, scientists are still in the process of determining if this inverse relationship seen on Earth also translates to barchan formation and movement on Mars.

Studying terrestrial analogues is often the lesser known and under-appreciated side of planetary study. Instead one hears about how a feature on Mars may be a certain type of volcano or sand dune with an 'x' type of formation, and 'y' type of history. It is the crucial investigation of landscapes on Earth that help planetary geologists make these x and y statements, and who knows, maybe even your backyard has a particular characteristic that may better our understanding of landscapes on Mars.

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1. Crumpler et al. (2007), Volcanic features of New Mexico analogous to volcanic features on Mars.
2. Zimbelman and Williams (2007), Eolian dunes and deposits in the western United States as analogs to wind-related features on Mars.