Astronomers have reported evidence of two planets colliding around a distant Sun-like star, Gaia20ehk, located about 11,000 light-years away. The star’s light output remained steady until 2016, when it exhibited three minor dimming events; by 2021, the light curve reportedly “went completely bonkers.” Follow-up infrared observations revealed a burst of heat coinciding with the fading of visible light, a hallmark of a hot debris cloud resulting from a massive impact. This debris likely originated from a cataclysmic planet-on-planet smash-up.
Signs of a Planetary Smash-up
According to the research, the star’s light curve showed long, irregular dips in visible light accompanied by bright infrared emission. “As the visible light began to flicker and dim, the infrared light spiked,” explained Anastasios Tzanidakis, indicating the blocking material is extremely hot.
This process is similar to what happened in the case of two planets that first grazed each other and then catastrophically collided, resulting in the heating of a superheated cloud of debris. Other theories, such as cometary debris, cannot account for such high infrared heating.
Implications for Planet Formation
Planetary smash-ups were common in early star systems, but witnessing one happening is extremely rare. Here, the cloud of debris will be orbiting just one astronomical unit (the Earth-Sun distance). Eventually, over millions of years, it might coalesce into a moon-like body as it cools. So far, only a handful of such events are known, and none resemble our Moon-forming event.
Researchers expect that surveys like the Vera Rubin Observatory’s Legacy Survey of Space and Time will likely find many more such collisions. Co-author James Davenport notes that our own Moon may be a “magical ingredient” for life, so understanding these violent events helps reveal how common Earth-like worlds might be.
