The origin of Mercury, the closest planet to the Sun, is largely mysterious. It has a metallic core like Earth, but its core makes up a much larger portion of its volume – 85% compared to Earth’s 15%. NASA’s MESSENGER-class Reconnaissance mission (Mercury Surface, Space Environment, Geochemistry, and Range) and the first spacecraft to orbit Mercury recorded measurements that showed the planet was also very different from Earth, chemically. Mercury is relatively low in oxygen, indicating that it was composed of different building blocks in the early Solar System. However, it turned out to be difficult to accurately determine Mercury’s degree of oxidation from the available data.

A new study led by scientist Larry Nittler of the Arizona State University School of Earth and Space Studies used data obtained during the MESSENGER mission to measure and map the minor element chromium content on Mercury’s surface.

Chromium is known for being extremely shiny and corrosion resistant on metalwork, giving color to rubies and emeralds. But it can also exist in a wide variety of chemical states, so its excess can provide information about the chemical conditions in which it is incorporated into rocks.

Nittler and colleagues found that the amount of chromium on Mercury varied by about fourfold. They calculated theoretical models of the amount of chromium expected on Mercury’s surface when the planet splits into a crust, mantle, and core under different conditions. Comparing these models to the measured chromium content, the researchers found that Mercury must have chromium in its large metallic core and were able to place new constraints on the planet’s overall oxidation state.

The study was published in the July issue. Journal of Geophysical Research: Planets .

“This is the first time that chromium has been directly detected and mapped on any surface of the planet,” Nittler said. Said. “Depending on the amount of oxygen present, it likes to be in oxides, sulphides or metallic minerals, and by combining the data with cutting-edge modeling, we can gain unique insights into its origin and geological history.”

Co-author Asma Boujibar, from Western Washington University, who performed the simulations described in the paper, added: “Our model, based on laboratory experiments, confirms that most of the chromium in Mercury is concentrated in its core. Due to Mercury’s unique composition and formation conditions, we cannot directly compare the composition of its surface with data from terrestrial rocks. Therefore, it is important to conduct experiments that simulate the specific oxygen-deficient environment in which a planet other than Earth or Mars occurs.”

In the study, Nittler, Bujibar and their co-authors collected data from laboratory experiments and analyzed the behavior of chromium with varying oxygen content in the system. They then developed a model to study the distribution of chromium between different layers of Mercury.

The results show that, similar to iron, a significant amount of chromium is indeed absorbed by the core. The researchers also noticed that as the planet became increasingly deficient in oxygen, more chromium was lurking in its interior. This knowledge greatly improves our understanding of the basic composition and geological processes occurring on Mercury. Source