Ferrovolcanism: When Metal Worlds Erupt

Credit: Maxar/ASU/P. Rubin/NASA/JPL-Caltech.

Volcanic eruptions can reshape and chemically alter planetary surfaces, as well as provide important clues to the compositions of planetary interiors. The most common type of volcanic eruptions on Earth and other rocky planets are made of molten silicate rock. Another type of volcanism is the cryovolcanism observed on Saturn’s icy moon, Enceladus, where eruptions of liquid water and vapors occur. Arianna Soldati of North Carolina State University and colleagues from the Syracuse University Lava Project are studying a more exotic variety of volcanism by asking what volcanism on metal worlds looks like. NASA’s upcoming eponymous Psyche mission to main-belt asteroid 16 Psyche, a body suggested to have significant metal content, may hold the answer to that question.

Many scientists believe that Psyche is either the remnant metallic core of an early differentiated body or a differentiated body with a metallic core and a thin silicate mantle. To study possible ferrovolcanism on Psyche, Soldati and colleagues conducted large-scale experiments that melted nearly 1,000 pounds of terrestrial basalt rich in iron, the dominant element in metallic materials in our solar system. Within the highly chemically reducing furnace, the denser iron formed a metallic melt that segregated from the less-dense silicate melt and sank to the bottom of the furnace’s crucible, akin to the industrial process of smelting. Due to the segregation of silicate melt on top of metallic melt, the researchers were able to first pour out a silicate-dominated flow, followed by a silicate-metallic mixture, and finally a flow dominated by metallic melt as the crucible was fully emptied. The different varieties and forms of the pāhoehoe-sized flow lobes (1-2 meters) were then compared and contrasted.

One of the main findings of this work was that metallic lava flows are quite turbulent, which makes their behavior during a flow difficult to predict using current silicate flow models. The high turbulence of the metallic melts is due to their extremely low viscosity (a measure of how resistant a fluid is to flow; e.g., vegetable oil is less viscous than honey at room temperature), which means that ferrovolcanic landforms are expected to have low-topographic relief. These results provide the first-ever framework within which to study the potential surface morphology created by ferrovolcanism on metal-rich bodies. These results will help scientists to quickly assess the surface of Psyche once high-resolution imagery is returned and determine the nature of its geologic features. READ MORE