A Dedicated Lunar Trojan Asteroid Survey with Small Ground-Based Telescopes

TL;DR

This study conducted a modern survey using small ground-based telescopes to search for lunar Trojan asteroids near Earth, finding none but setting an upper limit on their population.

Contribution

First dedicated lunar Trojan asteroid survey in nearly 40 years using modern telescopes and techniques.

Findings

No lunar Trojans detected in the surveyed area.

Estimated upper limit of approximately 5 lunar Trojans with H<26.

Detected one fast-moving near-Earth object.

Abstract

A co-orbital asteroid shares the orbit of a secondary body about its primary. Though more commonly encountered as an asteroid that shares a planet's orbit around the Sun, a co-orbital asteroid could similarly share the orbit of the Moon around the Earth. Though such asteroids would be close to Earth and so relatively bright, their rapid on-sky motion is such that they might escape detection by near-Earth asteroid surveys. The discovery of such lunar co-orbital asteroids (which we will refer to generically here as Lunar Trojans or LTs) would advance our understanding of inner Solar System orbital dynamics and would provide research opportunities for the growing number of missions slated for cislunar space. No LT asteroids are currently known and the last published survey dedicated to these asteroids was conducted nearly 40 years ago. It has been theoretically determined that orbits near the Earth-Moon L4 and L5 points could survive for several million years. Although this timescale is shorter than the lifetime of the Solar System, it introduces the possibility of the temporary capture of asteroids into the LT state. This project aims to observationally evaluate the population of LTs with modern techniques. Using four small ground-based telescopes from the iTelescope network, $8340\;deg^2$ on the sky were surveyed down to $15^{th}$ magnitude. Though one fast-moving near-Earth object was detected, no LTs were observed. We deduce an upper limit of $\lesssim 5$ LTs with $H<26$.