assuming 5 g/yr (0.005 kg/yr) loss over 4.5 billion years: total mass lost ≈ 2.25 × 10^7 kg (22,500 tons). for a 3 km diam nucleus (density 600 kg/m³, mass ~8.5 × 10^12 kg), that's a tiny 0.0003% erosion—negligible. even for the smallest 0.32 km est (mass ~1 × 10^9 kg), it's just 2% lost; larger 10 km ones barely notice, suggesting 3i/atlas was formed near this size.
nasa comet facts
https://solarsystem.nasa.gov/asteroids-comets-and-meteors/comets/comet-3i-atlas/in-depth/
avi loeb size
https://avi-loeb.medium.com/the-size-of-interstellar-comet-3i-atlas-8b3c4a2f4e0e
