How wide is Comet Swift–Tuttle’s nucleus, the source of the 2026 Perseids?

Comet Swift–Tuttle’s nucleus is about 26 kilometers wide, making it the large parent body of the 2026 Perseids.

A comet's nucleus is its solid central body, made mainly of icy material mixed with dust and rock. When Swift–Tuttle travels closer to the Sun, heating causes some of its volatile material to escape. This activity releases dust particles into the comet's orbit, creating the debris stream that Earth encounters each year as the Perseid meteor shower.

The 26-kilometer figure refers to the nucleus itself, not the comet's coma or tail. Those surrounding features can expand dramatically near the Sun and are not solid parts of the comet. The nucleus is also much larger than most individual meteoroids that produce visible Perseid streaks.

Swift–Tuttle is unusually important because its orbit repeatedly brings its debris across Earth's path. Despite the comet's large size, the Perseids are caused by dispersed particles, not by the comet passing close to Earth during the annual shower.