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Spectroscopy of Asteroid (93) Minerva: Insights into the Formation of the Early Solar System

Presentation #321.04 in the session Asteroids: Origins (Oral Presentation)

Published onOct 23, 2023
Spectroscopy of Asteroid (93) Minerva: Insights into the Formation of the Early Solar System

The primitive C-type asteroid (93) Minerva is known to bear widespread amorphous iron-bearing silicates on its surface; these materials are highly vulnerable to thermal metamorphism and aqueous alteration. For the presence of amorphous material to be possible, Minerva must have formed in one of two ways. Minerva could have formed after the peak heat flux of the short-lived radioactive materials (i.e., 26Al) responsible for thermal metamorphism in the early Solar System. Alternatively, if Minerva did form early enough for thermal metamorphism and aqueous alteration to affect its mineralogy, only the inside of the asteroid was affected, leaving an outer-surface shell untouched. Regardless of the formation scenario, Minerva’s surface could be affected by numerous impact craters, potentially exposing thermally-metamorphized sub-surface material. Minerva’s surface composition distribution may inform which formation scenario is plausible— a heterogeneous surface, consisting of both primitive surface material and thermally altered inner material exposed by impacts, would suggest the latter scenario. In contrast, a homogeneously primitive surface would suggest the former. As such, the surface distribution of Minerva is directly related to the formation of early Solar System bodies.

To help investigate these formation scenarios, the Infrared Telescope Facility (IRTF), located In Mauna Kea, Hawaii, was used to measure PRISM spectra (0.7-2.52 μm) and long-wavelength cross-dispersed (LXD) spectra (1.67-4.2 μm) of Minerva; the latter spectra have never been measured. Data were taken over multiple datasets to cover as much of Minerva’s surface (rotational period = 5.982hrs) as possible. The raw data of Minerva were reduced using Spextool, an IDL-based spectral reduction program provided by the IRTF.

A broad feature, approximately 1μm wide and centered at 1.4 μm, is likely attributed to amorphous silicates. The depth and shape of this feature were found to vary greatly over three consecutive sets of PRISM data, suggesting that Minerva’s surface is heterogeneous. Additionally, a broad feature centered at 3.1 μm is statistically present in all four observed LXD data sets, which could confirm the presence of hydrated minerals and is consistent with observations of other large Ceres-like asteroids.

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