Searching For Tectonic Plates

Tectonic plates — which divide Earth’s crust and reshape our planet in an ongoing, dynamic process — may be the key to supporting life. In fact, because Earth is the only planet known to be home to both life and plate tectonics, researchers are now wondering if there is a relationship between the two. Some researchers believe that life is made possible only through the temperature regulation that is imparted to a planet through shifting plates.

If tectonic plates are essential to life, finding life elsewhere — or worlds that can support it — may depend on finding planets with tectonic activity. Cayman Unterborn, an Arizona State University astronomer, has published research that indicates few exoplanets could sustain plate tectonics for long periods of time.

The results that Unterborn and his team compiled suggest that not only are plate tectonics rare, but they may also be difficult to sustain even when they do occur. Still, if astronomers are correct that up to 40 billion potentially habitable planets exist in our galaxy, even if the study's findings are correct, about 13 billion planets may yet be habitable worlds.

The Field Of Exogeology

How critical to life are plate tectonics? They seem to have been vital here on Earth, keeping the planet from freezing. And while there is evidence of geological activity on planets without plate tectonics such as Mars, it is past activity. This suggests that such activity can't be sustained without plate tectonics. In other words, plate tectonics may not be the key to all geological activity — but could the key to sustaining geological activity and stabilizing temperature.

This latest research contradicts earlier work which theorized that plate tectonics would be almost inevitable on larger rocky planets. Unterborn's work takes into account not only a planet's size, but also its composition. Obviously there was no way to peer inside the core of other planets (at least not yet), so Unterborn and his team used computer models to predict what the mantle and crust of planets studied would look like based on the composition of their host stars.

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The results highlight that the habitability of a planet cannot be determined by the “Goldilocks zone,” or its orbital distance from its star, alone. Density alone is also insufficient to determine potential habitability. Unterborn sees his work as the next step in a new field: exogeology — the marriage of geology and astronomy.

Unterborn and his colleagues have proposed studying how different materials react under high temperatures and pressures to the NASA Astrobiology Institute. The goal would be to explore how plate tectonics begin on a planet, as changing materials crack the lithosphere. “I think it’s definitely the future,” Unterborn said to Scientific American. “I'm glad to be at the forefront of it.”

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