Predictions of the LSST Solar System Yield: Neptune Trojans

TL;DR

The paper predicts that LSST will discover approximately 130-300 Neptune Trojans, with a detection bias favoring the L5 cloud, and highlights the potential for detailed characterization of their properties.

Contribution

First predictions of LSST Neptune Trojan yield using survey simulations, revealing detection biases and potential for extensive population characterization.

Findings

Forecasts 130-300 Neptune Trojans detected by LSST.

Identifies a 2:1 detection bias favoring the L5 cloud.

Enables robust statistical analysis of Trojan color and size distributions.

Abstract

The NSF-DOE Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST), beginning full operations in late 2025, will dramatically transform solar system science by vastly expanding discoveries and providing detailed characterization opportunities across all small body populations. This includes the co-orbiting 1:1 resonant Neptune Trojans, which are thought to be dynamically hot captures from the protoplanetary disk. Using the survey simulator $\texttt{Sorcha}$, combined with the latest LSST cadence simulations, we present the very first predictions for the Neptune Trojan yield within the LSST. We forecast a model-dependent median number of $\sim130-300$ discovered Neptune Trojans, and infer a notable 2:1 detection bias toward the recently emerged L5 cloud near the galactic plane versus the L4 cloud, reflecting the lower-cadence coverage in the Northern Ecliptic Spur region that suppresses L4 detections. The additionally simulated Science Validation survey will offer the very first early insights into this understudied cloud. Around 60\% of detected main survey Neptune Trojans will meet stringent color light curve quality criteria, increasing the sample size more than fourfold compared to existing datasets. This enhanced sample will enable robust statistical analyses of Neptune Trojan color and size distributions, crucial for understanding their origins and relationship to the broader trans-Neptunian population. These comprehensive color measurements represent a major step forward in characterizing the Neptune Trojan population and will facilitate future targeted spectroscopic observations.