Enabling discoveries of Solar System objects in large alert data streams

Abstract

Context. With the advent of large-scale astronomical surveys, such as the Zwicky Transient Facility (ZTF) and the forthcoming Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST), the number of alerts generated by transient, variable, and moving astronomical objects is growing rapidly, reaching millions of alerts per night. Concerning the minor planets of the Solar System, their identification requires linking the alerts for many observations over a potentially lengthy period of time, leading to a very large combinatorial number. Aims. The goal is to demonstrate how a third-party module dedicated to the identification of new minor planets of the Solar System can be integrated with the Fink alert broker real-time operations, which deals with massive alert data streams produced by large-scale surveys. Methods. Our analysis takes advantage of the scientific surplus brought on by the Fink alert broker classification capabilities to first reduce the 111 275 131 processed alerts from ZTF between November 2019 and December 2022 (755 observation nights) to only 389 530 new Solar System alert candidates over the same period. We implemented a simple, yet pedagogical linking algorithm called Fink-FAT to create trajectory candidates in real time from alert data and extract orbital parameters. The analysis was validated on ZTF alert packets linked to confirmed Solar System objects from the Minor Planet Center (MPC) database. Finally, the candidates were confronted with follow-up observations. Results. Between November 2019 and December 2022, Fink-FAT extracted 327 new orbits from candidate Solar System objects at the time of the observations, of which 65 had still remained unreported in the MPC database as of March 2023. After two late follow-up observation campaigns of six orbit candidates, four were associated with known minor planets of the Solar System, and two still remain unknown. In terms of performance, Fink-FAT took under 3 h to link alerts into trajectory candidates and to extract the orbital elements over the three years of Fink data, using a modest hardware configuration. Conclusions. Despite a much lower efficiency than present linking algorithms, Fink-FAT reaches a high level of purity in reconstructing orbits and it runs fast, making it suitable for the real-time discovery of new minor planets. Fink-FAT is deployed in the Fink broker and analyzes, in real time, the alert data from the ZTF survey by regularly extracting new candidates for Solar System objects. Tests of scalability also show that Fink-FAT is capable of handling the even larger volume of alert data that will be sent by the Rubin Observatory’s real-time difference image analysis processing.