In a potentially catastrophic occurrence revealing the ruthless nature of the universe, two colossal planets situated beyond our solar system have collided. This collision resulted in the expulsion of the outer layers of both planets, leaving behind a luminous, heated cloud of dust and gas that astronomers have recently observed. Nature reports that this discovery marks the initial evidence of a substantial collision between ice-giant exoplanets located outside our solar system.
The researchers spotted the aftermath of the cosmic collision using archived data from NASA’s now-retired WISE mission — which continues to operate under NEOWISE — on a star called BD +20 307. This star is about 300 light years away and has an orbit similar to our Sun. The team was examining the data when they noticed a sudden spike in infrared radiation around 900 days ago. The spike was accompanied by a cloud of dust that eclipsed the star, creating an unusual phenomenon known as a transit.
This skewed the star’s light, making it appear dim and redder than usual. The team realized that these changes were a result of the planetary collision. The scientists then compared the transit and infrared data to computer simulations of two giant exoplanets from several to tens of Earth masses crashing into one another. Their models confirmed that the crash liquified both worlds and created a hot, rocky, doughnut-shaped object called a synestia.
These types of planetary impacts aren’t uncommon. Scientists believe that a Mars-sized planet crashed into an early version of Earth about 4.5 billion years ago and spewed debris into space, which ultimately coalesced into our moon. Collisions between rocky exoplanets are so common that scientists expect them to be responsible for forming many of the worlds discovered using the Kepler Space Telescope and its successor, TESS.
While the collision of these two ice giants was relatively quick but highly violent, their fusion created tremendous energy, making the two celestial bodies glow and eclipse their parent star. The post-impact body, now a single molten core with a surrounding cloud of gas and dust, should still be visible to telescopes like the James Webb Space Telescope.
