Examples for Integrating Venus Magellan Imagery into Geoscience Classes

Journal of Geoscience Education, Mar 2008 by Lang, Nicholas P

ABSTRACT

Spacecraft-collected remotely sensed datasets provide an excellent vehicle for illustrating and conveying geologic principles and scientific reasoning to students. A particularly useful dataset includes synthetic aperture radar (SAR) imagery from NASA's Magellan mission to Venus. To help illustrate this dataset's usefulness in amplifying geoscience lessons, this paper serves as a virtual field trip guide to three Venusian field areas; each region displays geologic relations that provide ideal settings to address fundamental geologic principles and practice scientific reasoning. The images are available online at no cost through the USGS webpage, map-a-planet. Specific class exercises are limitless and easily integrated into petrology/volcanology, geomorphology, structure, field methods, and introductory courses. Further, Venus' extreme surface conditions (~450° C, ~100 bars surface pressure) add a unique twist in geologic studies and emphasize the universality of fundamental geologic principles.

INTRODUCTION

Geology is a discipline fundamentally rooted in fieldwork. The field serves as the laboratory in which we learn, teach, and perform our trade. However, when teaching geology, it is not always practical or possible to take students into the field. School location, transportation, budgetary issues, or disabilities may make taking students into the field a difficult or impossible task. So, if the students cannot go into the field, how about bringing the field to the students? Remotely sensed data sets provide a means to do just that. Specifically, images beamed to Earth by space probes provide unprecedented views that show alien worlds as natural laboratories in which to study geologic processes and principles and practice scientific reasoning an ideal situation when teaching students. A particularly useful planetary dataset is Synthetic Aperture Radar (SAR) imagery of Venus collected by NASA's Magellan mission. The resolution of Magellan SAR imagery (~100 m/pixel) means that one can delineate the presence of fine-scale features such as faults, fractures, small shield edifices, and channels. Analyzing and interpreting images of Venus draws from several geologic disciplines including (but not limited to) geomorphology, volcanology, structural geology, and sedimentology illustrating the usefulness of interdisciplinary approaches to studying geologic problems. The data is obtainable online at no cost, which makes Magellan SAR imagery a unique means of teaching geology lessons. Here, the potential usefulness of Magellan imagery in geoscience instruction is highlighted through a virtual field trip to three field sites on Venus; although only three areas are highlighted, any region on Venus is useful.

BACKGROUND

Venus Background and Assumptions - Venus and Earth are often referred to as sister planets because of their similar size, mass, density, and relative positions in the solar system. However, the surface conditions and physiographic characteristics of the two planets vary significantly. Whereas Earth contains an atmosphere composed chiefly of nitrogen and oxygen, Venus hosts an atmosphere dominated by CO2. This CO2-rich atmosphere has resulted in harsh surface conditions on Venus (compared to Earth) where the surface temperature is ~450° C and the surface pressure is ~100 bars (Crisp and Titov, 1997). In addition, Venus lacks the global-scale curvilinear chains of troughs and ridges that mark plate tectonics on Earth. Instead, circular to quasi-circular features of various diameters characterize Venus. These circular features include: 1) hundreds of thousands of small (1-20 km in diameter) shield edifices (Guest et al., 1992; Grumpier et al., 1992)), 2) ~1000 impact craters (2-270 km in diameter) (McKinnon et al., 1997), 3) ~500 volcano-tectonic structures referred to as coronae (60->1000 km in diameter) (Stofan et al., 1992, 1997), 4) nine volcanic rises (1000-2500 km in diameter) (Smrekar et al., 1997), ana 5) five crustal plateaus (~1000-3000 km in diameter) (Ghent and Hansen, 1999). Coronae are generally interpreted as surface expressions of mantle diapirs (Squires et al., 1992; Stofan et al., 1992) whereas volcanic rises and crustal plateaus are generally interpreted as representing thermal plume signatures (Smrekar et al., 1997; Hansen, 2003).

Despite Venus' surface conditions and physiographic characteristics, workers assume that Venus could host only the three basic rock types observed on Earth: igneous, metamorphic, and sedimentary. The extremely dehydrated state of the lower atmosphere (Donahue et al., 1997) and lithosphere (Mackwell et al., 1998) as well as the high, current surface temperature preclude the current presence of surface water, dismissing the idea that many surface rocks are of sedimentary origin. In addition, the apparent absence of widespread erosion suggests that surface rocks are not likely exposed crustal metamorphic rocks or intrusive igneous rocks. Thus, surface rocks most likely originated as extrusive igneous (i.e. volcanic) rocks (Banerdt et al., 1997), an interpretation consistent with the abundance of volcanic-like features on Venus (Head et al., 1992), and Soviet geochemical measurements of a basaltic surface composition (Grimm and Hess, 1997). Exceptions to volcanic rocks on Venus include impact related materials (Schultz, 1992; Campbell et al., 1992), eolian deposits (Arvidson et al., 1992; Greeley et al, 1992), and atmospheric chemical precipitates (Fegley et al., 1997). Although these materials are present on Venus, their aerial extent appears limited. However, given the uncertainty of past Venus climatic conditions (e.g., Bullock and Grinspoon, 1996; Donahue et al., 1997; Phillips et al., 2001) and our nascent understanding of Venusian surface processes, it is best to keep an open mind when interpreting Venus' rock record. Venus could indeed have hosted vast oceans in the past (e.g., Donahue et al., 1982; Donahue and Russell, 1997; Donahue, 1999; Hunten, 2002; see also Jones and Pickering, 2003; Hamilton, 2005). These uncertainties of past Venusian conditions, together with Venus' current surface conditions, make for an exciting laboratory in which to work with students.