Doing Planetary Geology on Venus!! An in-class and at-home exercise!
Looking at surface pictures of Venus is a little different than looking at pictures of Mars or the Moon, because on Venus the dense, CO2-rich "ultra-greenhouse" atmosphere obscures the planet's surface. However, the Magellan orbiter, and the Mariner orbiters that preceded it, all were able to "map" the surface of this planet using Radar. Radar images are a bit different to look at than photographic images, because radar reflectance is largely a product of surface roughness: the rougher the land, the brighter its radar signal. Thus, on Venus, the smooth lowland plains come off looking very dark, while volcanoes, highlands and crater debris fields look bright. ("Relief" view of Venusian surface, from processed Magellan radar images. This and all other imagery are from the Jet Propulsion Laboratory web archives: http://www-pdsimage.jpl.nasa.gov/PDS/public/magellan/
Features you've seen on other planets look a bit different on Venus, both because of the mode of imaging, and because of the different, hotter conditions.
Craters on Venus are almost always dark in the center (due to impact-related melting in the hot Venusian environment), and are always surrounded by bright debris fields.
Volcanoes on Venus come in many sizes and shapes, and can generally be distinguished by the occurrence of sinuous lava flows emanating from them. (Clockwise from the left: "pancake" domes, a Venusian shield volcano, a "tick", and a series of coronas with intermingled lava flows.) Lots of volcanoes is a characteristic of a large planet that is still hot on the inside.
Tectonically altered terranes also occur on Venus, and typically look quite bright in the images because of their rough character. These terranes are usually on the Venusian highgrounds, and are thus called Montes ("mountains"). Extremely rough and rugged terranes are called Tesserae.
What we have for you to start on is a set of images, randomly chosen from the Magellan image archives housed at the Jet Propulsion Laboratory:
Working in groups, take a close look at these images in class, and take advantage of me and the TA's to ask questions about what you're seeing. Then, on your own, at home, thumb through the images more carefully, and catalog for each the following information:
1) The number of impact craters observed.
2) The dominant geological features (flat plains, volcanic features, tectonic features)
3) The different kinds of volcanic edifices you found (those named above, or other different ones you read about in the book (or see on the NOVA program) and find!)
4) Any evidence for successive events (i.e., craters folded in the tesserae, or overprinting them, or craters filled by lava flows from volcanoes - anything that might mean that one event had to have happened before another.)
In our next class meeting, using y'all's observations, we'll try and answer the following two questions:
1) How old is the surface of Venus, as compared to Mars or the Moon?
2) Is Venus geologically active today?
Venus Surface Images for Examination:
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