Detecting minimoons with LSST -- building a dedicated approach

Background:  Earth’s temporary satellites, or minimoons, is a steady-state sub-population of near-Earth asteroids captured on a temporary orbit around the Earth (Granvik et al. 2012). It has been estimated that at any given time, the largest object on a temporary geocentric orbit is about 80 cm in diameter, and an object with a 3 m diameter appears every 10 years (Fedorets et al. 2017). Theoretical predictions indicate that temporary moons spend on average around nine months in the Earth’s vicinity, making three orbits. Their population is largely uncharted physically, as only two objects have been discovered so far. Moreover, recent results indicate that minimoons are also originating from Lunar impacts in addition to the main belt (Jedicke et al. 2025). Studying minimoons on a population level opens the path to bridge the gap in the size-frequency distribution studies of near-Earth asteroids between decametre-scale asteroids and small grains. 

Where does LSST stand? LSST is predicted to be the most prominent discovery machine for LSST (Fedorets et al. 2020). It is predicted that 1-5 minimoons can be discovered with LSST every year, effectively enabling their  population-level studies for the first time. However, in the course of the work it has been identified that the exceptional nature of minimoon orbits poses challenges when attempting to use the baseline small Solar System tools  tools. 

Synthetic population: For the study, we utilise the synthetic population of minimoons (Fedorets et al. 2017) and forward-model itto simulate LSST detections  using the state-of-the-art LSST survey simulator Sorcha (Merritt et al., 2025), assigning synthetic object typical small NEO colours.

Alert stream interfacing: We are building a lightweight  listening tool based on the broker architecture to enable the dedicated treatment of only the long streaks that indicate close passages to the Earth. Due to very rapid movement over the sky, we also include singleton observations.

Linking: the main linking algoritm in use for LSST uses a heliocentric linking paradigm. Although suitable for a general small Solar System case, it is not optimal for minimoons . We will discuss the selection of the suitable linking algorithms to enable the most efficient identification of minimoons from the LSST alert stream.

References: Granvik et al. (2012) ), Icarus 218, 262 – 277, Fedorets et al. (2017) Icarus 285, 83 – 94, Fedorets et al. (2020) Icarus 338 113517, Merritt et al. (2025) Accepted to AJ, Jedicke et al. (2025) Accepted to Icarus.