August 8 photometry from Bulgaria’s Rozhen Observatory showed Comet 220P/McNaught’s second 2026 outburst was dust-dominated, unlike the gas-richer May eruption, giving astronomers direct evidence that the two blasts tapped different parts of the nucleus.
The August 5 eruption brightened the comet about 650 times to magnitude 6–7, and Rozhen measured Afρ at 12,245–14,566 cm—far above the roughly 100–1,000 cm typical for Jupiter-family comets—signaling an expanding dust shell rather than steady activity.
Color indices close to solar values supported a dust-scattering coma in August, contrasting with June follow-up data that found May’s outburst enriched in C2 relative to CN, a molecular signature linked to freshly exposed volatile-rich material.
That chemical mismatch between two eruptions only months apart favors a nucleus with compositionally distinct pockets or layers, not a broadly uniform interior.
220P, a 5.5-year Jupiter-family comet now in Cetus, remains one of the brightest comets visible from Earth, though astronomers expect the current surge to fade over days to weeks while monitoring for any third outburst.