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Is there evidence for extraterrestrial plate tectonics?

Question:

Is there evidence for extraterrestrial plate tectonics?

Mechanics of Plate Tectonics

There are still many questions about the details of plate tectonics, however, a number of contributing factors are known. Convection currents in the Earth's mantle are one major force that can move plates, along with dragging, or pulling of plates at subduction zones, and spreading at midoceanic ridges. All three of these mechanisms rely on a liquid mantle.

Answer and Explanation:

The simple answer is yes, there is evidence for extra-terrestrial plate tectonics. We have a very limited scope in which to look (our solar system) and within that scope, we have some limited observational capabilities, but evidence has been found that tectonics happens on other worlds.

One necessary condition is agreed upon in order to have plate tectonics: there must be a hot liquid phase underneath a solid exterior crust, which limits us to terrestrial type planets and moons. One indication of hot, liquid subterranean activity is geothermal activity at the surface, i.e. volcanoes. Another is visible fault lines.

Interestingly, the terrestrial planets do not provide a lot of evidence for tectonics in the present, or past. Our understanding of both Mars and Mercury is that there has not been volcanic activity on either planet for a very long time and the general consensus is that in both cases, heat initially trapped inside has long since dissipated. Neither planet has fault lines visible at the surface. Both of those planets are considered to be solid to the core.

There is currently no known volcanic activity on Venus, but Venus is very obscure and mysterious. It is hot, but that is generally considered to be due to it's intense greenhouse effect, not geothermal energy. However because of it's harsh atmosphere, little is really known about the Venusian surface, so Venus might be a candidate for plate tectonics. Pluto is the only other terrestrial planet in our solar system and it is far too cold to have a molten interior.

Other than actual planets, some moons are considered candidates for tectonic activity. Jupiter's largest moon, Ganymede is currently the best example known of extraterrestrial "plate tectonics" probably happening now. It is bigger than Mercury and has been hypothesized to have a molten iron core and is assumed to have a liquid water mantle. Ganymede's surface is solid ice and satellites have seen large cracks that appear to be like faults. Another of Jupiter's moons, Io, is known to have volcanic activity, in fact so much that it has not yet formed permanent, or semi-permanent plates on a geologic time scale, so it does not yet have plate tectonics.Satellite images of Titan, a moon of Saturn, show mountain ranges and other features that are though to have been formed by tectonics in the distant past. Enceladus is another such candidate.

So, yes, there is evidence for "plate tectonics" on other worlds, in our solar system, primarily on moons of outer planets.


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Plate Tectonics: Theory & Definition

from General Studies Earth & Space Science: Help & Review

Chapter 7 / Lesson 5
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