The Loeb Scale: Astronomical Classification of Interstellar Objects

Abstract

The Vera C. Rubin Observatory is expected to increase interstellar object (ISO) detections from a few over the past decade to potentially one per few months, demanding a systematic classification scheme. We present the Loeb Scale, formally the Interstellar Object Significance Scale (IOSS), a 0-10 classification system extending the proven Torino Scale framework, to address ISOs' unique anomalies, including potential technosignatures. The scale provides quantitative thresholds for natural phenomena (Levels 0-3) and graduated protocols for increasingly anomalous characteristics (Levels 4-7), with Levels 8-10 reserved for confirmed artificial origin. Each level specifies observable criteria and response protocols. We demonstrate the scale's application using 1I/'Oumuamua (Level 4), 2I/Borisov (Level 0), and 3I/ATLAS (Level 4) as test cases. The Loeb Scale provides the astronomical community with a standardized framework for consistent, evidence-based and dynamic evaluation while maintaining scientific rigor across the full spectrum of possibilities as we enter an era of routine ISO encounters.