Tracing the Origin of Water in Terrestrial Planets: Insights from the Ribbeck Aubrite

The origin of water on terrestrial planets remains one of the unresolved questions in planetary science. Meteorites have been proposed as a potential source of water to terrestrial planets. Aubrites, one of the differentiated achondrites with their mineralogical similarity to enstatite chondrites, provide crucial constraints on the early stages of planetary accretion and differentiation, particularly concerning the evolution of water. In early 2024, asteroid 2024 BX₁ was recovered shortly after its fall near Ribbeck, Germany, and was subsequently classified as an aubrite based on initial mineralogical and isotopic analyses.

We conducted a detailed investigation of the Ribbeck aubrite through a comparative analysis with other aubrite, focusing on the distribution and characterization of water. We employed infrared spectroscopy to investigate the vibrational properties, bonding environments, and distribution heterogeneities of hydrogen in specimens, complemented by chemical analyses using electron probe microanalysis. The results will show that infrared imaging reveals a heterogeneous distribution of OH vibrations, and broad absorption feature between 3200 and 3800 cm^-1 indicates that water is not structurally incorporated into the primary silicate phases. Instead, hydrogen appears to be hosted predominantly within hydrous phases associated with melt inclusions.

Through this investigation, we deciphered the vibrational mechanisms and origins of hydrous phases in aubrites. Our findings will enhance the understanding of water evolution during the early accretion and differentiation processes of terrestrial planets and provide new insights into the origin of water on Earth.