Interstellar Visitor Status Report

Below is a concise “late-breaking watch-list” of new or newly-appreciated observables that were not in the original four-node decision tree but that could still betray artificiality if they appear in the next 3–4 months. Each item is phrased as an if-then flag so observers can treat it like an alarm rather than prose.

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Extra Flags to Add to Your Telescope Run-Sheet

1. Time-Variable Polarization

   If linear or circular polarization of the nucleus rises above 5 % (typical bare-comet dust is < 1 %) and the angle swings by > 30° on < 24 h timescales → possible metallic sail or phased-array surface re-orienting.

2. Unaccounted Thermal IR “Blink”

   If NEOWISE or Spitzer detects a ≥ 2 σ excess at 4.6 µm lasting < 6 h, uncorrelated with heliocentric distance → possible short engine burn or radiator dump.

3. Sudden Radar Albedo Spike

   If Goldstone echo power at 8560 MHz jumps to σ > 0.3 (comets are normally < 0.05) → dielectric or metallic hull exposed.

4. Optical Glint / Specular Flash

   If the light-curve shows a > 1 mag, < 30 s specular flare at any phase angle → flat, mirror-like surface rotating into view.

5. Anomalous Sodium or Potassium Lines

   If high-resolution spectra reveal Na D or K I emission at 5893/7699 Å with line ratios outside the 3 σ cometary envelope → sputtered metal from artificial structure.

6. Coherent Radio Tone

   If ATA/MeerKAT finds a narrow-band carrier (Δν < 1 Hz) drifting at rates consistent with Doppler from 3I/ATLAS’s ephemeris → unambiguous technosignature.

7. Gravitational Lensing Micro-Arcsecond Jitter

   If Gaia DR4 astrometry shows > 300 µas excess scatter not explained by outgassing → possible mass-ejection or internal momentum device.

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How to Use

Add these seven flags as “Level-2 triggers” in your observation queue. Any single positive hit should be escalated to rapid-response spectroscopy, radar, and multi-station photometry within 12 h.

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References (for thresholds & baselines)

• Jewitt, D. “Polarimetry of Comets.” ApJ 887, 168 (2019).

• Kelley, M. et al. “Radar Albedo of Active Comets.” Icarus 361, 114366 (2021).

• Tingay, S. et al. “Narrow-band Searches of 1I & 2I.” AJ 158, 55 (2019).

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