by Kari Hetcher and Scott Hughes

Reading:

Chapter 8, "Venus" by R. Stephen Saunders

Chapter 12, "Surfaces of the Terrestrial Planets", by James W. Head, III

Chapter 13, Atmospheres of the Terrestrial Planets, by Bruce M. Jakosky.

NOTE: Imagery and other information concerning the geology of Venus is available on various websites, thanks to NASA and affiliate institutions (LPI, JPL, LANL, Hawaiian Astronomical Society, and others). You could spend weeks surfing around for materials in order to learn everything there is to know about Venus. We suggest that you visit all sites shown in this module to know what is available, but spend more time on those areas directly related to learning new concepts and answering module questions.

Introduction to Venus

Venus is often considered to be Earth’s sister planet because of their similarities in size and density, and their neighborly positions in the Solar System. Assuming two planets so close to each other would have condensed in a similar fashion during the birth and growth of the Solar System, many scientists believed that the two would have similar histories and features. Up until the 1970’s and 1980’s, however, we humble earthlings were unable to see the surface of Venus due to the thick carbon dioxide clouds that shroud the entire planet. Radar and photographic information obtained during the Venera, Pioneer Venus, Vega, and Magellan missions provide new insights into the surface features and forces acting on our close planetary neighbor.

Visit the Magellan homepage produced by NASA and the Jet Propulsion Laboratory. Study the major geologic provinces, tectonics and atmosphere.   http://www.jpl.nasa.gov/magellan/mgn.html

Once radar imaging and the Soviet landers had pierced the intimidating cloud cover, we were able to find out much about this fascinating planet. The surface appears relatively young, possibly due to a dramatic resurfacing of the entire planet between 300 and 500 million years ago. No liquid water exists on the planet because of extremely high temperatures and atmospheric pressures, caused by a runaway greenhouse effect that occurred early in Venus’ development.

Three major geologic provinces exist on Venus. They are the smooth lowland plains which comprise about 20 percent of the total surface area, the rolling volcanic uplands, ~70 percent, and the mountainous highlands, ~10 percent. This module will show features from each of these provinces, and outline the geologic forces acting on each in order to help you better understand their formation.

VenusGlobe-Thmb.gif (15772 bytes)

 

Image of Venus and explanation, generated from radar digital topography obtained during the Magellan Mission, provided by NASA, Jet Propulsion Laboratory.

 

 

venusvis-Thmb.gif (10212 bytes)NASA Galileo spacecraft image of Venus illustrating thick cloud cover. Image produced by Calvin J. Hamilton, provided by Los Alamos National Laboratory.

 

More Information on Venus is available on the following websites:

http://windows.ivv.nasa.gov/ NASA's Windows to the Universe page, find and click on "Venus" or any thing else that looks interesting.

http://seds.lpl.arizona.edu/nineplanets/nineplanets/venus.html Students for the Exploration and Development of Space page about Venus.

1. Venus Topography
venustop-Thmb.gif (13897 bytes)

Topographic color images generated from digital radar elevation data, provided by NASA in conjunction with the Jet Propulsion Laboratory (#1) and Los Alamos National Laboratory (#2, can take a while to load).

http://www.jpl.nasa.gov/magellan/image2.html

2. Labeled Topography of Venus

Ven-topo1-Thmb.gif (26838 bytes)

Most of Venus’ surface lies within 500 m of the mean planetary radius (which is the equivalent of sea level). A relatively small area (less than 5 percent) is more than 2 km above this level.

Visit UCLA's Venus Hypermap for access to a huge database of information gathered by Magellan.

 

Lowlands:

These large plains consist of extensive, probably basaltic, lava flows and could be compared to the Earth’s ocean basins in respect to extent and composition. Features seen within the lowlands include broad bowl-like depressions, flood lavas (similar to the Columbia River Basalts on Earth), lava channels that can extend for hundreds of kilometers, and compressional ridges. The largest lowland feature is Atalanta Planitia, which is located east of Ishtar Terra (~165° E Long., 65° N Lat.) and is about the size of the Gulf of Mexico.

Venus-LongCh-Thmb.gif (48250 bytes)

Image and explanation of lava channel provided by NASA and the Jet Propulsion Laboratory.   http://www.jpl.nasa.gov/magellan/image19.html.

 

Important geologic concepts related to formation of the lowland plains include:

-Lowlands are typically manifested as circular depressions.

-Hotspot volcanism that would produce large shield volcanoes is not observed.

-Extensional rifts like those on hot spot swells have not been identified.

-Lowland plains are dominated by compressional features.

The lowland plains also contain ridges and valleys that comprise sinuous ridge belts braided together for thousands of kilometers around topographic basins such as Atalanta Planitia and Lavinia Planitia. A general lack of many large volcanic and impact related features in the lowlands indicates that this area may have been formed by strong compressional tectonic forces as the venusian mantle was convecting and thus wrinkling the surface.

How can these be used to interpret tectonics on Venus? (See Christiansen and Hamblin, 1995, for detailed discussion.)

 

Uplands:

Uplands represent a transition of terrain from the lowland plains to the highlands. Doming of the lithosphere implies large upwelling thermal plumes from the mantle that are possibly responsible for creating these uplands. Doming resulted in extension of the crust above, and led to predominantly extensional tectonic features, such as fracture belts, troughs, grabens, and rifts. The best example of an upland dome is Beta Regio, (Figure 12 in Chapter 7 of the text) located around 280° E. long. and 30° N. lat. This region is 2500 kilometers across and contains a huge shield volcano, numerous crisscrossing faults, and several circular coronae.

 

Aine Corona (with pancake domes)Corona-Thmb.gif (17889 bytes)

Coronae, features unique to Venus, are systems of ridges and fractures surrounding central plains. The largest of these structures is about 600 kilometers across. Coronae are believed to be volcano-tectonic features because they may have formed by the upwelling of mantle material and the subsequent subsidence of the crust above once the hot material cools and solidifies. The subsidence leads to depression of the central portion of the corona and extensional rifting around the edges. Arachnoids are similar to coronae in form but generally smaller.

 

Arachnoids

arach-Thmb.gif (27784 bytes) Image and explanation of arachnoids provided by NASA and the Jet Propulsion Laboratory.  http://pds.jpl.nasa.gov/planets/choices/venus1.htm

 

Study the following Volcanic Upland features:

Doming of the lithosphere above the hot, mantle plume under Beta Regio led to parallel linear scarps that form the rift valley, Devana Chasma, which is similar in appearance to the East African Rift on the Earth. A large shield volcano, Theia Mons lies in the southern part of the rift valley, which illustrates the similarities of Beta Regio to the volcanic features of the Tharsis and Elysium domes found on Mars.

SifMons-Thmb.gif (37414 bytes)Sif Mons Volcano

Three-dimensional perspective image and explanation provided by NASA and the Jet Propulsion Laboratory.  http://www.jpl.nasa.gov/magellan/image16.html

Sapas Mons Volcano

Image and explanation of Sapas Mons provided by NASA and the Jet Propulsion Laboratory.  See their image at http://www.jpl.nasa.gov/magellan/image28.html SapasMons-Thmb.gif (22652 bytes)

 

Pancake Domes in Eistla Regio

Because there is no evidence for plate tectonic movement on Venus, scientists speculate that the lithospheric doming, rifting, and volcanism associated with mantle plumes are the primary way heat is released from within the Venusian interior. 

Eistla-Thmb.gif (18090 bytes)

 

Highlands:

The highlands of Venus have been compared to the continents on the Earth. They are the highest elevations on Venus, with mountain peaks up to 11 kilometers above the mean, large wrinkled mountain chains, and relatively flat, plateau-like expanses. The highest area on Venus is located in Ishtar Terra which lies in the Northern Hemisphere and is about the size of Australia. The largest highland region on Venus is Aphrodite Terra which is located near the equator and is more than half the size of Africa. Like the lowlands, the features in the highlands seem to be primarily compressional in origin, suggesting that the area was formed by crustal thickening over a downwelling mantle. Compressional folds, ridges, and troughs within Maxwell Montes, the highest point on Venus and one of the large mountain belts within Ishtar Terra, indicate lateral crustal movement. Lakshmi-Thmb.gif (10994 bytes)

 

Lakshmi Planum in Ishtar Terra

Image provided by SEDS site at ftp://ftp.seds.org/pub/images/planets/venus/ and more images can be found at their public ftp site at ftp://ftp.seds.org/pub/images/

venpole-Thmb.gif (12933 bytes)

 

North Pole of Venus Ishtar Terra

mage and explanation of the polar region provided by NASA and the Jet Propulsion Laboratory.  http://www.jpl.nasa.gov/magellan/image3.html

 

Fig14p87Thmb.GIF (10741 bytes)

A terrain map of Venus' north pole

Compare to this map , a terrain map of the north pole generated from Venera digital radar topography data.

 

Alpha Regio Ridges and Troughs

alpha-Thmb.gif (20074 bytes) Image provided by the Planetary Display System of NASA and the Jet Propulsion Laboratory.

Complexly textured and dissected by tectonic forces, tesserae are strongly deformed terrain within the highlands that comprise densely packed systems of ridges and grooves. These areas are probably tectonic in origin, with complex graben superimposed upon folds. There are two theories about the development of the tesserae: (1) Tesserae are simply very old areas that have recorded all of the deformation that has occurred over a long period of time. Since they are elevated terranes, they were less likely to be covered up by basaltic flows. (2) Downwelling of the mantle "cold spot" led to crustal thickening and compression above the area.

 

Module Tasks: Answer Each of the Following Questions:

Review geologic features and processes by visiting the PDS Venus page and the NSSDC Planetary Images files if you have not already done so.
Answers to most of the following questions can be found from these sources. Some will require revisiting sites listed above and still others might require extended search of other resources.

Use this index of images when necessary: http://www.jpl.nasa.gov/magellan/images.html

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1. The topography of Venus is intriguing and provides much information for interpreting structures and planetary processes. What can be inferred initially from casual inspection of Venus’ topography? Refer to Figure 9, page 103 in the text.

2. Be able to briefly define the following terms and concepts:

3. No magnetic field has been detected on Venus, so what evidence is there that suggests Venus is an internally differentiated planet? List at least three reasons.

4. The primordial Venusian atmosphere would have been very similar to that on Earth because of their close proximity in the primordial solar nebula. Why is there such a dramatic difference between the two atmospheres now?

5. How would the presence of liquid water on Venus affect tectonic movements?

6. Describe three of the eolian features present on Venus. How does the atmospheric temperature, pressure and composition affect the weathering on the surface of Venus?

7. Why are so few small craters seen on Venus’surface?

8. What and where are the highest and lowest surface temperatures on Venus?

9. What and where are the highest an lowest elevations on Venus? With what terranes are they related?

10. What is the geologic significance of each of the following geologic features on Venus?

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Send in your answers by email to the instructor.

Extra web sites and URLs for imagery, plus general information and geology of Venus.

Spacelink - Venus Discoveries

http://seds.lpl.arizona.edu/nineplanets/nineplanets/venus.html

http://pds.jpl.nasa.gov/planets/welcome/venus.htm

Spacelink - Venus  Images, text, and more from NASA's Spacelink

Index of images

http://www.jpl.nasa.gov/magellan/images.html

Check out this jpg of all nine planets lined up! Note the similarities in size of Venus and Earth.

NinePlanets.jpg at ftp.seds.org

Glossary

Did you email your assignment???

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