“Venus Unveiled” The movie you are about to watch today is a little long for most of my students, but the material you will see here is some incredible stuff. Here is a little background for the movie:

“Venus Unveiled” From Earth-based telescopes, Venus is completely covered with clouds, making it impossible to know what is underneath unless we somehow go there and drop below those clouds.

“Venus Unveiled” Therefore, the USSR sent a series of spacecraft called the Venera missions. Those that successfully landed on the surface took pictures like this.

“Venus Unveiled” The US sent a satellite called Magellan. I bounced radar signals off the surface and read the echoes. The result was a map like you see to the right … as if the entire planet was unveiled.

“Venus Unveiled” One thing that was an odd discovery was the apparently random distribution of volcanoes, and yet all of the volcanoes are of the same variety.

“Venus Unveiled” Earth’s uppermost layer (called the Crust) is cracked into huge plates that are in constant motion. This motion is called Plate Tectonics. When one plate dives underneath another, the friction of the sliding rock melts, forms magma, and erupts as a volcano. Where plates are colliding and sinking, volcanoes form, and the Ring of Fire is a huge circle of volcanoes … but they are a special kind.

“Venus Unveiled” Volcanoes that form from one plate diving under another are called “pyroclastic” volcanoes because the explode violently … like Mt. St Helens did. Rainier and the Alaska volcano shown above center and right will also explode. All of the volcanoes at plate boundaries are of this kind.

“Venus Unveiled” So, the Aleutian Islands, Japan, Phillipines, Andes, and Cascades in Washington are explosive pyroclastic volcanoes.

“Venus Unveiled” But a close look at Hawaii shows red circles. If there are no plate boundaries, then how can a volcano form there?

“Venus Unveiled” It turns out that the Hawaiian Islands are a special class of volcanoes called “shield volcanoes” because their shape is circular at the base, and the tops are not pointy … making them look like giant shields. The photograph is Mauna Loa, a huge volcano that makes up ½ of the Big Island of Hawaii. Notice how it is shaped.

“Venus Unveiled” Shield volcanoes erupt gently, as seen in the images above. The lava fountain in the center is not a spectacular explosion, but a giant “geyser” of gas and liquid rock. These volcanoes form from huge magma chambers deep in the Earth that vent their lava upward, regardless of plate movements. These volcanoes are found on Earth only where magma flows move upward.

“Venus Unveiled” The volcanoes on Venus (pictured above) are all like the Hawaiian volcanoes. In fact, the volcanoes EVERYWHERE else in the Solar System, planet or moon, are like the Hawaiian volcanoes … shield volcanoes. Pyroclastic volcanoes are ONLY found on Earth because only Earth has actively moving giant plates of crust.

“Venus Unveiled” So, even though Earth (above left) and Venus (above right) have identical topography of the crust, there are no movements of plates on Venus anywhere, so therefore no pyroclastic volcanoes.

“Venus Unveiled” Question? If there are no active plates on Venus, why are there so many volcanic mountains across the surface? By the way, it appears that all of them are dormant. Why are none of them active? When did they stop? And, why are they all appearing to be the same age?

“Venus Unveiled” Another even more odd feature of Venus is the completely random distribution of craters, and the apparent similarity in age of them. The possible cause of this random distribution of craters is the focus of the movie you are about to watch.

“Venus Unveiled” The craters of Venus all look similar … nice round impact basins with bright ejecta blankets around the rims. And they all appear to be “fresh,” meaning relatively young.

“Venus Unveiled” Why do ALL of the craters of Venus appear to be “fresh,” as if they were relatively recent events and of the same age? This is the great question the movie hopes to answer.

“Venus Unveiled” When this movie is completed, I hope that you will know more about Magellan, the history of thought regarding what is under the clouds of Venus, and the two leading theories that attempt to explain the random distribution of a bunch of similarly aged craters across the surface of the planet. If time permits, perhaps you can have a little class discussion about the findings shown in the movie.

“Venus Unveiled” PS … I know that I have just rushed through some of the Earth processes involved in Plate Tectonics, but believe me, there is so much more to understand about volcanoes. I just had to give you a little introduction to help you better understand the terms used in the movie and why the mystery of crater distribution leads scientists like Turkot to think that some major repeating catastrophe happens on Venus, and perhaps nowhere else in the Solar System. I can teach more on this when I get home on Friday.