New studies uncover how hematite deposits were formed. This ubiquitous iron oxide, more formally known as hematite but more informally as rust, has an interesting connection to the lunar surface. This odd phenomenon is humorously named “Earth Wind.” It is created when Earth’s atmosphere combines with the moon — only in a specific combination, appropriate to specific phases of the lunar cycle. The discovery, published in the journal Geophysical Research Letters, offers new insights into the complex processes that shape the moon’s geology.
Earth Wind is experienced when Earth is positioned between the sun and moon for a period of five days each month. Earth atmosphere oxygen ions bombarding the surface of the Moon. There, they can react with various iron-bearing minerals in the lunar regolith like metallic iron, iron sulfide, and ilmenite.
The Role of Earth Wind in Hematite Formation
It is an important discovery that the oxygen ions of Earth Wind can oxidize some minerals. This process results in the production of hematite. This process is most pronounced in the moon’s higher latitudes, especially on its nearside. In 2020, those researchers found an unusual distribution of hematite across these varied regions.
To understand the importance of iron-bearing minerals on the moon, the study’s authors performed experiments to investigate them. They then irradiated these minerals with oxygen and hydrogen, the energies being similar to those expected from Earth Wind particles. Their results provide powerful support for the theory. They conclude that Earth wind-driven reactions are behind the hematite we see on the lunar surface.
“Although these iron‐bearing minerals may occur as micro‐particles or small crystals in lunar regolith, they can undergo direct oxidation upon exposure to Earth wind. The resulting hematite on the outer surface of regolith particles is readily detectable via optical spectrometry.” – Xiandi Zeng et al.
In essence, the presence of hematite on the moon’s surface hints at a dynamic interplay between Earth and its natural satellite. Numerous studies have found that solar wind protons repeatedly irradiate the lunar surface with far greater fluxes than Earth wind. Their effectiveness in oxidized material reduction is limited by the fact that they don’t penetrate very deep.
Implications for Future Lunar Missions
The findings from this study suggest that future lunar missions should focus on understanding how Earth Wind interacts with the moon’s geological features. By simulating these interactions, scientists hope to gain deeper insights into lunar processes and potentially uncover additional secrets about the origin of lunar materials.
In the current study, researchers traveling back to the moon highlight the importance of energy on hematite retention on the lunar surface. In addition, they emphasize the critical importance of the relative flux ratio of oxygen and hydrogen ions carried by Earth Wind. This complexity highlights the need for more exploration and experimentation in lunar research.
“The retention and preferential distribution of [hematite] in high‐latitude regions require careful consideration. Although the lunar surface outside Earth’s magnetosphere is continuously bombarded by solar wind protons at fluxes approximately 100 times higher than those in Earth wind, our low‐energy hydrogen implantation experiments demonstrate limited reduction efficiency due to the shallower penetration depth, which does not fully encompass the oxidized region. In contrast, higher‐energy protons achieve complete penetration, enabling more thorough reduction.” – Xiandi Zeng et al.
Understanding Lunar Oxygen Sources
The new study points out several theories about where the oxygen present in lunar rust might have originated. Two competing theories propose that lunar magma either sputtered volatiles or released them through degassing. Furthermore, asteroids, comets, and large impact events could have delivered oxygen-rich materials to the moon.
Earth Wind offers a great order of hematite formation. Researchers have been diving down this path. In doing so, they hope to improve their understanding of how geologic and atmospheric processes on Earth influence the state of its celestial neighbor.
