Determinação da forma tridimensional de (50000) Quaoar por ocultações estelares utilizando algoritmo genético para minimização

Abstract

Trans-Neptunian Objects (TNOs) are primordial bodies that orbit the Sun beyond Neptune’s orbit. The analysis of their orbital dynamics, internal and surface composition, and size and mass distribution provides valuable data on the formation and evolution processes of the Solar System. Discovered in 2002 as one of the largest objects in its class, (50000) Quaoar was the first minor body found to have rings beyond the Roche limit, making the determination of its physical properties crucial for understanding the stability of ring systems. These detections were made using the technique of stellar occultations, which allows for the determination of the size and shape of Solar System objects when they cross the line of sight between an observer and a given star. To study Quaoar’s three-dimensional shape, a total of 62 sets of positive stellar occultation data observed during 20 different events between 2011 and 2024 were analyzed. Passing through observation, data analysis, and the development of computational tools, such as the application of the genetic algorithm. As a result, an ellipsoidal shape was obtained for Quaoar, verified using physical and observational properties published in the literature. Three possible configurations for the object’s dimensions were identified. The first, which best fits the occultation chords, suggests that Quaoar is a triaxial body with dimensions of 585.5 ± 2.6 km, 554.3 ± 1.0 km, and 509.5 ± 1.0 km for the equatorial and polar axes, respectively, and a density of 1.744±0.028 g cm−3. However, this configuration does not show a rotation light curve amplitude comparable to those published. By constraining the results só that the body’s dimensions are entirely responsible for the rotation curve amplitude, an ellipsoid with semi-axes of 605.8 ± 1.7 km, 540.6 ± 1.5 km, and 501.1 ± 1.9 km is obtained, resulting in a density of 1.758 ± 0.029 g cm−3. The possibility that Quaoar is in hydrostatic equilibrium as an oblate spheroid was also considered. In this case, the equatorial axes would be equal at 563.0 ± 1.1 km, and the polar axis would measure 511.8 ± 0.9 km (or a flattening of 𝜖 = 0.0905 ± 0.0035), which would result in a density of 1.779 ± 0.022 g cm−3, with the rotational light curve being entirely caused by albedo variations on its surface. This dissertation presents the results of 20 stellar occultations by Quaoar. To determine its three-dimensional shape, it demonstrates that this analysis is possible using occultation data. For this, computational methods developed throughout this work, based on machine learning, were employed to enhance the results.