Evaluating External Sources of Metals for the Development of Planetary Civilizations on Ocean Worlds

Abstract

By looking at the metal content of our oceans here on Earth, we can get a better understanding of possible metal contents of other ocean-world exoplanets in the universe. There are four main ways that metals get into oceans here on Earth: (1) Rivers or wind erode metal from the land and bring it into the water; (2) Metal-heavy ice caps in the Arctic melt and bring Arctic runoff into the ocean; (3) Underwater volcanoes erupt, bringing metals and other elements up from the Earth’s crust into its oceans; and (4) Meteors and other debris from space fall into the ocean. The main ways metals get removed from Earth’s oceans is through oxidation and human removal. Focusing on the metal gain from meteors (because this source is the most applicable to other ocean worlds), we looked at meteoric influx rates and determined how many kilograms of metals like iron and nickel meteors bring into Earth each year. Using the total concentrations of different metals in our oceans along with meteoric influx rates, we determined how long it would take to reach our current oceanic metal levels if all the metal came from outside meteors. This mimics the expected conditions on most water worlds with no land or ice caps to erode, and volcanoes that are too deep to impact metal levels. We then looked at the gravitational focusing of different-sized planets and calculated the number of meteors they would draw in based on the speed of the meteors and the escape velocity of the planet. We find that even excluding metal sources (1), (2), and (3) in exoplanets that are characterized by deep global oceans (hundreds of km deep), source (4) still provides a large enough source of metals that a developing civilization could use for tool-making and other technical applications.