Mechanism driving 3I/ATLAS’s steep pre-perihelion brightening

Establish the physical mechanism responsible for the unusually steep pre-perihelion optical brightening (approximately scaling as r^{-7.5} at r ≲ 2 au) of interstellar comet 3I/ATLAS relative to typical Oort cloud comets at similar heliocentric distances.

Background

The authors measure a brightness scaling of n≈7.5±1.0 for 3I/ATLAS at r≲2 au, much steeper than earlier measurements and typical Oort cloud comet behavior.

They propose possibilities such as early suppression of H2O sublimation by CO2 cooling, nucleus property differences, and effects of rapid inbound speed, but they conclude the underlying cause is not established.