Astronomy Question: Venus and Plate Tectonics?

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Judith asks:

Does Venus now, or ever, have plate tectonics? If so, when?
If an asteroid the size of Ceres, ever hit Venus, would it destroy its atmosphere and the terribly high pressure at its surface?

Nice question Judith!

Plate tectonics on Venus is a hot topic of debate (get it? hot?) for some planetary scientists, and while Geology isn’t my specialty, I know enough of the basics to help you out with this question.

Many theories on Plate Tectonics require water to be present, and scientists speculate that whatever provided Earth with its water, also provided water to Venus and Mars. We have evidence Mars was much warmer and wetter in it’s past, so it’s a logical assumption that Venus had water at some point in its past.

Currently Venus is really dry, as over time, Venus lost its water. One theory is that as Venus lost its water, the mechanisms that cause plate tectonics slowed down and eventually stopped, further exacerbating the runaway greenhouse effect. It’s difficult to test these theories, as landing a probe on Venus is a very difficult challenge, due to the intense heat and atmospheric pressure at the Venusian surface.

That being said, there are some theories that Venus has granite on its surface, which requires water and plate tectonics to form, so it is entirely possible that at some time in Venusian history, Venus did have plate tectonics and was relatively wet.

Recent (relatively speaking) geologic activity on Venus is speculated to be “flood events” where heat and pressure build up over time, and then is released by massive “flood” volcanoes. These “floods” of lava are believed to cover up to 80% of the Venusian surface. Currently there’s no known activity on Venus, so it’s unknown if the flood events are periodic, or a “last gasp” of some form of plate tectonics.

Ceres, being about 1/3 of the total mass of the Asteroid belt is pretty hefty, and if it were to collide with Venus, the results would be pretty devastating, depending of course on the angle of impact. (Side note: It’s widely theorized the impact that created our Moon was a “glancing” blow from a Mars-sized object) There is wide speculation that Venus has already been hit by a large object, explaining it’s odd rotation, and quite possibly the lack of water on the surface, and planet-wide lava flows.

So, could an impact with Ceres strip the Venusian atmosphere? It’s possible, but in doing so, would cause massive volcanic activity that would release hot gases and heat the surface to incredibly high temperatures.

You can read more on plate tectonics at this USGS page.

Ray Sanders is a Sci-Fi geek, astronomer and blogger. Currently researching variable stars at Arizona State University, he writes for Universe Today, The Planetary Society blog, and his own blog, Dear Astronomer

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