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CAI's |
| Listing of Structures |
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| Meteorite - Axtel, CV3 |
| Figure 1. Scale bar 1.3 mm. |
| Meteorite - Axtel, CV3 |
| CAI's, (1), amoeboid olivine inclusion (2), chondrules, (3). |
| Calcium-aluminum-rich inclusions
(CAI's) represent some of the most ancient solid materials in our Solar System,
with origins tracing back over 4.567 billion years. These remarkable structures
emerged directly from the searing, turbulent environment of the protoplanetary
disk. Formed during the earliest chapter of Solar System history, CAIs
crystallized from hot, chemically primitive gases amidst intense radiation and
the dynamic processes accompanying the protosun's birth. They are a window into
the extreme conditions that prevailed before planets took shape. CAIs are distinguished by their abundance of refractory elements, notably calcium and aluminum, which are capable of withstanding extraordinarily high temperatures. This resilience allowed them to condense and solidify in the scorching environment near the protosun, making them key relics of the Solar System's infancy. Their mineral composition is equally remarkable, featuring a suite of "first-generation" minerals that reflect the primordial chemistry of this formative environment. Among these are melilite, a silicate mineral rich in calcium and aluminum; perovskite, a titanium-bearing oxide; spinel, a durable magnesium-aluminum oxide; anorthite, a calcium-rich feldspar; hibonite, an exceptionally refractory calcium-aluminum oxide; and pyroxene, a versatile group of silicates. Together, these minerals present a picture of a high-temperature, volatile setting where the building blocks of planets first began to coalesce. CAI inclusions are most commonly found embedded within carbonaceous chondrites, a class of primitive meteorites that have undergone minimal alteration since their formation. As primary structures in these meteorites, CAIs are largely unaltered by later processes like melting or metamorphism, preserving their original textures and compositions. Their isotopic signatures, particularly in elements like oxygen and magnesium, further reveal details about the timing and mechanisms of their formation, often pointing to rapid condensation events in a hot, gas-rich environment close to the protosun. The significance of CAIs extends beyond their age and composition. They serve as critical markers for understanding the physical and chemical conditions of the early protoplanetary disk. Their formation is believed to have occurred in a region where temperatures exceeded 1,500 Kelvin (approximately 1,227°C or 2,240°F), likely near the center of the disk, before they were transported outward by dynamic processes such as turbulent mixing or continuous stellar outflows. This migration helps explain their presence in meteorites that eventually accreted into larger bodies far from the Sun. |
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