Decoding the Chromium Clues: NASA’s MESSENGER Mission Unravels Mercury’s Metallic Mystery

by Manuel Costa
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chromium distribution

Caption: An artistic representation of NASA’s MESSENGER spacecraft orbiting Mercury. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Scientists Decode Chromium Distribution on Mercury Using NASA’s MESSENGER Mission Data

In a remarkable breakthrough, researchers have utilized data from NASA’s MESSENGER mission to map the distribution of chromium on Mercury, uncovering its substantial presence within the planet’s expansive metallic core. By combining observations with laboratory simulations that replicated Mercury’s unique formation conditions characterized by oxygen deficiency, this study offers unprecedented insights into the elemental composition and geological history of the planet.

Mercury, the closest planet to the Sun, has long remained enigmatic due to its distinctive characteristics. While possessing a metallic core akin to Earth, its core constitutes a significantly larger fraction of its overall volume—85% compared to Earth’s 15%.

The MESSENGER mission, the first spacecraft to orbit Mercury, classified under NASA’s Discovery program, has revolutionized our understanding of the planet’s chemical composition by capturing measurements that underscore its marked divergence from Earth. Notably, Mercury exhibits a relatively lower abundance of oxygen, signifying its formation from distinct building blocks in the early solar system. However, determining Mercury’s precise oxidation state based on available data has proven challenging.

Led by Arizona State University scientist Larry Nittler from the School of Earth and Space Exploration, a recent study employed data acquired during the MESSENGER mission to gauge and map the distribution of chromium, a minor element, across the surface of Mercury.

The resulting color-coded chromium abundance map, superimposed on an image captured by MESSENGER, revealed intriguing variations in chromium content across the planet. Chromium is renowned for its exceptional luster and resistance to corrosion in metallic objects, while also contributing to the vibrant hues of rubies and emeralds. However, it can manifest in various chemical states, making its abundance a valuable indicator of the chemical conditions during its incorporation into rocks.

Nittler and his collaborators observed a fourfold fluctuation in the amount of chromium across Mercury. By employing theoretical models to estimate the anticipated chromium concentration on Mercury’s surface during the planet’s separation into a crust, mantle, and core under different conditions, the researchers compared these models with the measured chromium abundance. Consequently, they deduced that Mercury’s extensive metallic core contains chromium and established new constraints on the planet’s overall oxidation state.

The study, featured in the July issue of the Journal of Geophysical Research Planets, marks the first direct detection and mapping of chromium across the surface of any celestial body. Nittler expressed, “Depending on the amount of available oxygen, [chromium] likes to be in oxide, sulfide, or metal minerals, and by combining the data with state-of-the-art modeling, we can glean unique insights into the origin and geological history of Mercury.”

Co-author Asmaa Boujibar from Western Washington University, responsible for the modeling described in the paper, added, “Our model, based on laboratory experiments, confirms that the majority of chromium in Mercury is concentrated within its core. Due to the unique composition and formation conditions of Mercury, we cannot directly compare its surface composition with data obtained from terrestrial rocks. Therefore, it is essential to conduct experiments that simulate the specific oxygen-deficient environment in which the planet was formed, distinct from Earth or Mars.”

The research team, comprising Nittler, Boujibar, and other co-authors, synthesized data from laboratory experiments and scrutinized the behavior of chromium under varying oxygen abundances in the system. They subsequently constructed a model to investigate the distribution of chromium among Mercury’s distinct layers.

The findings affirm that, akin to iron, a substantial portion of chromium is indeed sequestered within Mercury’s core. Furthermore, the researchers noted that as the planet becomes increasingly oxygen-deficient, a greater quantity of chromium remains concealed within its interior. This discovery significantly enhances our comprehension of the elemental composition and geological processes at work within Mercury.

Reference: “Chromium on Mercury: New Results From the MESSENGER X-Ray Spectrometer and Implications for the Innermost Planet’s Geochemical Evolution” by Larry R. Nittler, Asmaa Boujibar, Ellen Crapster-Pregont, Elizabeth A. Frank, Timothy J. McCoy, Francis M. McCubbin, Richard D. Starr, Audrey Vorburger, and Shoshana Z. Weider, 20 June 2023, Journal of Geophysical Research Planets.
DOI: 10.1029/2022JE007691

Frequently Asked Questions (FAQs) about chromium distribution

What mission data was used to map chromium abundance on Mercury?

The researchers utilized data from NASA’s MESSENGER (Mercury Surface, Space Environment, Geochemistry, and Ranging) mission to measure and map the abundance of chromium across Mercury’s surface.

How does Mercury’s chromium distribution differ across the planet?

The amount of chromium on Mercury varies by a factor of about four across the planet’s surface, as revealed by the research findings.

What insights does the study provide about Mercury’s composition?

By comparing theoretical models with measured chromium abundance, the researchers determined that Mercury’s large metallic core contains chromium. This finding sheds light on the planet’s overall elemental composition and provides insights into its geological history.

How does the presence of chromium on Mercury contribute to our understanding of its formation?

Chromium’s distribution and abundance on Mercury provide valuable information about the chemical conditions and processes involved in the planet’s formation. It offers insights into the unique environment in which Mercury was created, distinct from other terrestrial planets like Earth or Mars.

What significance does this study hold for planetary exploration?

This study marks the first direct detection and mapping of chromium across the surface of any celestial body. It showcases the power of combining observational data with laboratory simulations to unravel mysteries about a planet’s composition and evolution, furthering our knowledge of the solar system’s diversity.

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