Nasa telescope catches two planets smashing into each other at 1,000 °c

Two alien worlds just crashed, vaporized and turned into a 900-degree rubble cloud 1,700 light-years away—and astronomers watched the whole thing live. The collision, caught in 2021 around the star Gaia20ehk, is the closest real-time replay we have of the ancient smash that forged our own Moon.

A flash that blocked the star

The first clue was a glitch in the light curve. Since 2016 University of Washington grad student Anastasios Tzanidakis and prof James Davenport have been scraping every public archive for weird stellar flickers. Gaia20ehk kept hiccupping, then in August 2020 it tripled in infrared brightness for six months while visible light dimmed—classic signature of fresh, incandescent debris spinning between us and the star. Back-of-the-envelope math: 900 K dust spread across an area the size of Earth's orbit. Translation: something Mars-sized hit something twice as big at 30 km/s, sprayed molten rock into space and temporarily built a Saturn-like ring of lava.

The team plugged the numbers into a radiation-transfer model and matched spectra from NASA's NEOWISE and the Zwicky Transient Facility. Fit is perfect; alternative explanations—giant star spots, a comet swarm—fail.