THE THERMOCHEMISTRY OF THE EARLY SOLAR PROTOPLANETARY DISK AS REVEALED THROUGH ATOMIC-SCALE ANALYSIS OF THE FIRST SOLAR-SYSTEM SOLIDS

Here I report on atomic-scale investigation of calcium- and aluminum-rich inclusions (CAIs). So named because of the Ca- and Al-rich materials they contain, CAIs are composed of mineral phases formed at very high temperatures and which are predicted by thermodynamic models to be among the first solids to have condensed within a cooling gas of solar composition. Perovskite, nominally CaTiO₃, is the major Ti-bearing phase in type-A CAIs and is predicted to host rare-earth elements and (minor) lithophile elements. Using aberration-corrected scanning transmission electron microscopy (STEM), we find nano- to atomic-scale structure that is at odds with longstanding thermochemical models of solar-system formation. I will discuss the implications of such structure at the meeting.