Amateur telescopes discover a kilometre-sized Kuiper belt object from stellar occultation

TL;DR

This study reports the first observational detection of a kilometre-sized Kuiper belt object via stellar occultation using small telescopes, providing insights into early solar system planetesimal formation.

Contribution

It presents the first confirmed occultation event by a 1.3 km KBO detected with low-cost equipment, supporting models of planetesimal growth in the early solar system.

Findings

Detected a 1.3 km KBO occultation event.

Estimated a surface number density of ~6×10^5 deg^-2 for km-sized KBOs.

Supports a size distribution model with an excess at 1-2 km radius.

Abstract

Kuiper belt objects (KBOs) are thought to be the remnant of the early solar system, and their size distribution provides an opportunity to explore the formation and evolution of the outer solar system. In particular, the size distribution of kilometre-sized (radius = 1-10 km) KBO represents a signature of initial planetesimal sizes when planets form. These kilometre-sized KBOs are extremely faint, and it is impossible to detect them directly. Instead, monitoring of stellar occultation events is one possible way to discover these small KBOs. Hitherto, however, there has been no observational evidence for the occultation events by KBOs with radii of 1-10 km. Here we report the first detection of a single occultation event candidate by a KBO with a radius of $\sim$1.3 km, which is simultaneously provided by two low-cost small telescopes coupled with commercial CMOS cameras. From this detection, we conclude that a surface number density of KBOs with radii exceeding $\sim 1.2$ km is $\sim 6 \times 10^5 \ {\rm deg^{-2}}$. This surface number density favours a theoretical size distribution model with an excess signature at a radius of 1-2 km. If this is a true detection, this implies that planetesimals before their runaway growth phase grow into kilometre-sized objects in the primordial outer solar system and remain as a major population of the present-day Kuiper belt.