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Interpreting the Stellar Occultations of (15094) Polymele – a Lucy Target

Presentation #107.05 in the session Asteroids: Future Mission Targets (Oral Presentation)

Published onOct 23, 2023
Interpreting the Stellar Occultations of (15094) Polymele – a Lucy Target

NASA’s Lucy mission is the first reconnaissance of the Jovian Trojan asteroids. It will visit a total of eight of these mysterious objects between Aug. 2027 and Mar. 2033. In order to prepare for these encounters, the Lucy team is performing an extensive set of Earth-based observations intended to both determine the size and shape of its targets, and search for satellites. Here we report on a preliminary analysis of a series of six stellar occultations of (15094) Polymele. Understanding the shape of Polymele is particularly important because it is the smallest of the Lucy targets and thus is the most challenging for the spacecraft to observe. In addition to supplying limb profiles for Polymele at six different epochs, a satellite was serendipitously discovered during these observations. We have observed this satellite twice as of the writing of this abstract. We performed two separate Monte Carlo fits to the available data. The first uses the available limb profiles to determine the shape and rotational pole position of Polymele itself. The second uses the projected relative position of the satellite with respect to Polymele to determine the orbital radius and pole position of the satellite, under the reasonable assumption that it is on a circular orbit about the primary. By assuming that the satellite is sitting in Polymele’s equatorial plane due to tidal damping, we constrain the shape of Polymele and orbital radius of the satellite. We find that the pole is at λ = 231.8° ± 4.5°, β = -80.9° ± 2.1°. Assuming that Polymele’s shape is an ellipsoid, its semi-axes are 13.5 ± 1.0 km, 12.2 ± 0.8 km, and 5.2 ± 0.8 km. The satellite’s orbital radius is 204.4 ± 2.6 km. Assuming that the density of Polymele is between 0.7 and 1 g cm-3, the satellite’s orbital period is between 16.6 and 14.4 days.

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