Astronomers watch two planets slam into each other 3,000 light-years away
For the first time humanity has a ringside seat to a planetary demolition derby. A University of Washington team led by Anastasios Tzanidakis and James Davenport has caught the exact millisecond when two worlds the size of Neptune rammed together around the star Gaia20ehk, vaporizing rock at 627 °C and spraying a glowing shroud of debris across orbital space.
The flash arrived in 2021, the chase began in 2016
Back then the star was just another flickering entry in Gaia’s all-sky catalogue. Every 30 minutes the Washington robots recorded its brightness; every 30 minutes the curve wobbled. By 2021 the wobble had mutated into a wild strobe. Infrared data ballooned overnight. Something bright, hot and fast was blocking the starlight. The astronomers ran the numbers: only a head-on collision could spit out enough silicon vapor to form an opaque cloud three times wider than the Sun.
The geometry matched the ancient crash that forged our own Moon. Four and a half billion years ago proto-Earth kissed the Mars-sized body Theia; the splash condensed into the lunar companion that now steadies our axial tilt and stirs the tides. The new impact plays out at the same one-AU distance, but with molten rock instead of cooling magma.
Vera rubin will spot 100 more before 2036
Current telescopes catch these fireworks only by accident. The upcoming Vera C. Rubin Observatory will scan the entire southern sky every three nights, turning accidents into routine. Davenport crunched the statistics: if one collision pops every five years in a sample of 10,000 Sun-like stars, Rubin’s 20 million-star movie will deliver a hundred replays before the Paris Olympics of 2036.
Each replay is a fossil in reverse. Instead of digging into crust layers, astronomers watch fresh planets disassemble themselves, revealing the recipes that cook rocky atmospheres, magma oceans and maybe, somewhere in the spray, future moons. The Washington team has already booked Rubin time; they are not planning to blink.