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 The Surface of Venus:

Research by UMD's Vicki Hansen


Venus's surface may be much older than thought
Vicki Hansen, University of Minnesota

UMD's Vicki Hansen is doing research on the surface of the planet Venus and her work may have resulted in a startling dicovery. The surface of Venus may be older than scientists commonly speculate. Hansen, a McKnight Presidential Professor of Earth and Planetary Sciences is also director of Graduate Studies for the UMD Department of Geological Sciences.

Vicki Hansen is a structural geologist/tectonisist with interests in large scale tectonic processes of planetary bodies. Her regional field areas on Earth include: the western U.S., Yukon, Alaska, Arizona, and Antarctica. Over the last 10-15 years she and her students have concentrated on mapping large regions of Venus, commonly with emphasis on tectonic and magmatic processes. Their goal is to interpret geologic relations at all scales, and decipher local, regional, and global scale geological histories in order to understand Venus' evolution and dynamic processes through time. Specific topics on Venus include: crustal plateau formation and implications for Venus evolution, deformation belt formation, coronae evolution, circular low formation, Venus resurfacing (evidence does NOT support catastrophic resurfacing of Venus contrary to popular views), lowland processes, and tessera-terrain evolution. Hansen and her students have been involved in 1:5 million scale mapping of eight VMaps (30°x25°) for publication through the USGS, and they have just begun 1:10 million scale mapping of two quadrangles (each 120° x 57°).

Planetary Processes Lab
We study large scale magmatic and tectonic processes focusing on the terrestrial planets. Geologic mapping from remote sensing data sets and structural analysis help unravel the geologic history of planetary bodies and provides insight into their inner workings. Recent work has focused on Venus; you can view our publications and the status of our geologic mapping through the links to the left. If you are interested in working on a MS or PhD with our group please contact Dr. Vicki L. Hansen at
The colossal outpouring of lava thought to have almost totally resurfaced Venus 500 million years ago never happened, a new study says. If correct, it means that a much longer record of Venus's history is preserved on the planet's surface.
Planetary scientists estimated the age of Venus's surface after studying radar mapping data from NASA's Magellan spacecraft, which operated in the early 1990s.
Assuming Venus was exposed to the same rain of asteroids and comets that the other planets experienced, they expected Magellan would spot about 5000 craters on the planet's surface.
But they found only about 1000, suggesting that the planet's surface is actually very young – perhaps 500 million to 1 billion years old. And those craters appear remarkably well preserved, unaltered by erosion or other geological processes. That suggests that whatever erased the 4000 or so "missing" craters was an all-or-nothing process.
The most popular explanation is that a brief but enormous episode of volcanism blanketed most of the planet in a layer of lava 1 kilometre to 3 km deep – thick enough to bury all of the craters made before that time.

Now, a new analysis of Magellan data suggests that such a deep layer of solidified lava cannot be present on the surface, casting doubt on the "catastrophic resurfacing" hypothesis.
Valley floor

Study leader Vicki Hansen of the University of Minnesota in Duluth, US, and colleagues analysed areas where islands of terrain poke up through flat "plains".

They looked at the slopes that lead down from these islands and disappear below the plains. By studying neighbouring islands, they were able to extrapolate where the slopes would reach a common base – the floor of a valley between them.

They found that this base was buried less than 1 km below the surface of the plains. The researchers say this is at odds with the catastrophic volcanism idea, which calls for a global blanket of lava up to 3 km deep.

They believe the islands are ancient terrain and the plains were laid down more recently – evidence that bits and pieces of the planet have been resurfaced at different times, leaving much of the planet's older surface intact.

Gradual decline
That meshes well with a study presented at a conference in March by Timothy Bond and Michael Warner of Imperial College London, UK. They found a gradual decline in volcanic activity over a period as long as 2 billion years fit Venus's crater statistics better than a single violent episode.
Ellen Stofan of University College London in the UK agrees that the resurfacing process on Venus was probably more drawn out than in the catastrophic volcanism scenario.

And Fred Taylor, a member of the Venus Express mission at Oxford University in the UK, says Hansen's study adds to the evidence against a catastrophic resurfacing event, which now appears to be "too simplistic", he told New Scientist. "Personally, I have always thought so."

Rich history
Based on their study, Hansen's group argues that much of Venus's surface is more than 1 billion years old. If this is correct, sending new missions to the planet could probe much further into its past than previously realised, Hansen says.
"The implication is that Venus, on its surface, preserves an extremely long record of rich geological history," Hansen told New Scientist. "That's what so exiting about it. It says Venus actually has a lot of secrets to tell us."
If the planet once had water on its surface, for example, a robotic lander might be able to find evidence in the form of water-related minerals, she says.
The study by Hansen's group was presented on 24 October at a meeting of the Geological Society of America in Philadelphia, Pennsylvania, US.


Vicki Hansen, professor, and undergraduate student Taylor Nordberg, both of the Department of Geological Sciences, made two presentations “Venus was not catastrophically resurfaced” and “Clues from Ribbon Tessera Terrain” at the Geological Society of America National Meeting, Philadelphia, PA in October 2006. Ivan Lopez, was also a coauthor on the work. Hansen’s work was also mentioned in an article at be-much-older-than-thought.html

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