Subsurface ice bursts rip apart comet 220P, boosting its brightness thousands of times

A faint comet dramatically brightened by thousands of times this summer after solar heat triggered sudden eruptions beneath its crust. Comet 220P/McNaught, originally discovered in 2004, follows a five-and-a-half-year orbit around the sun. It is typically too dim to spot without large telescopes, but escaping gas broke through its surface and blasted huge amounts of debris into space.

Trapped gas creates massive dust clouds

Comets contain water, carbon dioxide, and nitrogen ice beneath a dusty layer. As comet 220P approached perihelionPerihelionThe point in an object's orbit where it is nearest to the sun. Open in glossary—its closest orbital point to the sun—solar warmth penetrated the surface. This heat caused the trapped ice to rapidly turn straight into gas. The resulting pressure ruptured sections of the outer crust.

Models show the eruptions spewed between tens of billions and hundreds of billions of pounds of dust into the comaComaThe glowing, nebulous envelope of gas and dust surrounding a comet's core. Open in glossary, the cloud surrounding the comet nucleus. The tiny dust grains shot outward at roughly 1,280 feet per second. This expanding cloud reflected extra sunlight, triggering sharp spikes in brightness.

Two separate explosions

The first outburst began on May 31, lifting the comet from magnitude +17.39 to +11.05 in less than 14 hours. It soon reached magnitude +8.23, making it visible through basic binoculars. The comet later faded to magnitude +12 before a second explosion hit in late July. By August 6, it peaked at magnitude 6.1.

Astronomers value these events because 220P is a Jupiter-family comet that likely migrated inward from regions beyond Neptune. Studying the structural failures of such comets helps researchers measure their physical strength. If a similar comet ever heads toward Earth, knowing how fragile its crust is could help scientists design disruptive deflection missions that differ from plans meant for solid asteroids.

The comet made its closest flyby of Earth on October 12 at 97 million miles away. It is now growing dimmer as it travels back toward Jupiter’s orbit. Researchers expect it to return to the inner solar system in late 2031.