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 Interstellar Object Significance Scale (IOSS), also known in the literature as the Loeb Scale, 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 IOSS 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.
