As I discussed two weeks ago, Venus and Earth are remarkably similar in terms of their size and composition. Both probably started out with large oceans of water. While Earth continues to maintain a global temperature that supports a vital stable water cycle, the surface of Venus is bone dry with temperatures near 800oF.
Unlike on Venus, Earth’s plate tectonics still operate and therefore perform the important function of removing greenhouse gases from Earth’s atmosphere. Without plate tectonics, a dense life-suffocating carbon dioxide atmosphere would surround Earth.
Research presented at the 211th meeting of the American Astronomical Society (AAS) puts tight constraints on how large a planet must be to sustain long-standing plate tectonics. Essentially, all rocky planets larger than twice the size of Earth will experience plate tectonics. However, as a consequence of thinner tectonic plates and greater geological stresses these “super-Earths” would experience more vigorous plate tectonics.
Furthermore, the research illuminates two limits for habitable, tectonically active planets. First, any planet larger than ten times Earth’s mass will attract a dense hydrogen and helium atmosphere, like the gas giants in our solar system. Consequently these planets cannot be habitable. On the other end of the spectrum, Earth is barely large enough to sustain plate tectonics. Earth’s large, liquid water oceans and abundant interior water both lubricate tectonic movements and give Earth’s interior the necessary characteristics to support tectonic activity. Thus, for any planet closer to Earth’s mass, the planet must exhibit the facilitating properties of water.
This research implies that scientists will discover more potentially habitable planets. However, the tectonic activity on these super-Earths will be far more destructive than on Earth. Thus, RTB’s creation model predicts that planets much larger than Earth will prove uninhabitable—or at least incapable of supporting human life.