83-5 The Recipe for Stardust: Cooking Up Alumina 'Smokes' in the Lab

Session: Asteroid Observations, Return Missions, and Meteoritics: Interweaving Perspectives and Data

Presenting Author:

Cody Cly

Authors:

Cly, Cody P.¹, Speck, Angela², Whittington, Alan³, Ponce, Arturo⁴, Sargent, B.⁵, Nuth, Joseph⁶, Brancaleon, Elena⁷, Pacheco, Francisco⁸

(1) Department of Physics & Astronomy, University of Texas at San Antonio, San Antonio, Texas, USA, (2) Department of Physics & Astronomy, University of Texas at San Antonio, San Antonio, Texas, USA, (3) Department of Earth & Planetary Sciences, University of Texas at San Antonio, San Antonio, TX, USA, (4) Department of Physics & Astronomy, University of Texas at San Antonio, San Antonio, Texas, USA, (5) Space Telescop Science Institute, Baltimore, Maryland, USA; Department of Physics & Astronomy, Johns Hopkins University, Baltimore, Maryland, USA, (6) NASA Goddard Space Flight Center, Greenbelt, Maryland, USA, (7) Department of Earth & Planetary Sciences, University of Texas at San Antonio, San Antonio, Texas, USA, (8) Department of Mechanical Engineering, University of Puerto Rico-Mayaguez, Mayagüez, Puerto Rico, USA; Department of Physics & Astronomy, University of Texas at San Antonio, San Antonio, Texas, USA,

Abstract:

Aluminous minerals play a key role in understanding space mineralogy, with applications to protoplanetary disks, debris disks, and dust shells around asymptotic giant branch stars. Alumina is important because it is abundant and one of the first mineral species to condense at relatively high temperatures.

Astronomers classically consider alumina dust to be either amorphous or corundum (α-Al₂O₃), but alumina can react with other abundant metals in these systems to form different alumina-bearing minerals. In this work, we incorporated magnesium (Mg) and iron (Fe) to make samples of AlO, MgAlO, and AlFeO. This work aims to collect optical information from various transitional alumina to improve astronomical modeling of cosmic dust.

Our samples are "smokes," synthesized at NASA Goddard by quenching partly combusted material from the gas phase to produce highly disordered chaotic solid particles often far from internal chemical equilibrium. Samples were characterized initially by using X-ray diffraction (XRD) and differential scanning calorimetry (DSC) up to 1600°C. The samples were then annealed at different temperatures based on phase transitions detected from the DSC data.

Initial XRD results on the smoke samples indicate that AlO was observed to be amorphous and γ-alumina, AlFeO was observed to be amorphous, and MgAlO was observed to be periclase (MgO) with spinel (Al₂MgO₄). The DSC data allowed us to observe crystallization in our samples and demonstrated their uniqueness. AlFeO was the only sample to melt, at ~1250°C. Unfortunately, the samples could not be recovered after this annealing episode, so we do not know what it formed. Subsequently, the smoke samples were annealed at the temperatures where we observed crystallization events in the apparent heat capacity curves.

Future work includes annealing the smoke samples at higher temperatures to investigate their mineralogy using XRD and FTIR. Subsequent data such as optical constants will be passed on to astronomers to better help with radiative transfer modeling. These aluminous minerals will elucidate our understanding of cosmic dust evolution and highlight a critical aspect often overlooked in astronomical models: the physical state of dust particles—whether chaotic, glassy, or crystalline—can dramatically influence their optical properties and thermal behavior.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9045

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