The theory of plate tectonics is seminal in the geosciences, providing a testable framework to understand the existence and distribution of mountain belts, rifts, and basins on Earth. However, no other terrestrial planet has shown unambiguous evidence of plate tectonics, suggesting that it may be unique to Earth. This uniqueness leads to fundamental assumptions regarding the conditions necessary for plate tectonics. For example, Mars is typically assumed to be too small to allow for plate tectonics, fueling a debate as to whether extrasolar terrestrial planets larger than Earth are more or less likely to exhibit plate tectonics. While a plate-tectonic Earth may be unique in the inner solar system, Jupiter’s moon Europa may show a plate-tectonic corollary within its floating ice shell. 

Work led by Geoffrey Collins from Wheaton College tests the idea that the surface of Europa is composed of rigid plates, a fundamental requirement of plate tectonics. Here, plates are defined by the existence of continuous features (e.g., ridges), surrounded and contained by areas of discontinuities or offsets, which delineate plate boundaries. Crosscutting and offset relationships of features within, across, and bounding the plate are used to reconstruct the relative timing of activity and motion across distinct plates. While previous studies suggested that evidence for plates on the surface of Europa was ambiguous or contradictory, this study found that geologic evidence supported the existence of small plates with numerous but often difficult-to-discern boundaries. While the small plates identified in this study are widespread across the surface of Europa, they are not globally connected, which is a requirement of plate tectonics. Europa’s tectonics are very different from Earth’s, but what that means is not yet clear. High-resolution image mosaics of Europa’s surface from the upcoming Europa Clipper mission will help to clarify what Europa can teach us about plate tectonics. READ MORE