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# Program information file
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PROGRAM_ID           2024B035
PROGRAM_TITLE        Characterizing the compositional heterogeneity of [15] Eunomia over its full rotation
PROGRAM_INV1         Yu Yu Phua
PROGRAM_INV2         Katherine de Kleer
PROGRAM_INV3          
PROGRAM_INV4          
PROGRAM_INV5          
PROGRAM_SCICAT       main-belt / Trojan asteroids
PROGRAM_ABSTRACT_BEG
The process of differentiation in planetesimals is central to understanding their thermal and geochemical evolution following their accretion. Asteroid [15] Eunomia, the largest S-type asteroid in the main belt [mean diameter: 270 km; semimajor axis of 2.644 AU], has been suggested to be at least partially differentiated. Rotationally resolved visible photometry and near-infrared [NIR] spectroscopy showed that on one hemisphere Eunomia's surface is made up of Fe-rich olivine, similar to stony-iron meteorites, while the other hemisphere is more basaltic and dominated by pyroxene. Recent modeling of the 1.3 mm thermal emission data acquired with the Atacama Large Millimeter/submillimeter Array [ALMA] at ~30 km resolution suggests variable thermal inertia and dielectric constant on the surface of Eunomia at more localized spatial scales than the hemispherical-scale compositional variations suggested by the NIR spectra. As currently available NIR spectra do not provide sufficient information about how the surface composition of Eunomia changes as a function of rotation, we propose to obtain spectra of Eunomia at 0.7-2.5 um with the SpeX instrument using the SXD mode over its full rotation [6 hours] to make a compositional map of its surface. In 10 minutes of clock time, we can obtain a sufficiently high quality spectrum [S/N~100] to enable characterization of the shapes of the 1 and 2 um bands, providing rotational compositional variability at 10 degrees resolution. This map will be interpreted with the resolved ALMA data of the same viewing geometry, as well as spectra of the Eunomia family members available in the literature, to shed light on the degree of differentiation of Eunomia and understand the process of planetesimal differentiation.
PROGRAM_ABSTRACT_END