It's a bit mind-boggling to imagine something as big as the planet Neptune crashing into a similar-sized planet, but astronomers caught this exact scenario, as described in a recent study in the journal Nature. A pair of ice giants — or massive planets the size of Uranus and Neptune, but composed of elements that are heavier than hydrogen and helium — collided into each other as they passed in front of the star they orbit, ASASSN-21qj. (If you say the name of the star ASASSN-21qj aloud, it sounds a bit like "assassin.")
ASASSN-21qj is described as an "otherwise unexceptional" star, but thanks to a tip from an amateur astronomer, it was observed being obscured by two of its own planets as they demolished one another. As they did so, they released a giant cloud of debris that ultimately managed to dim astronomers' ability to view the distant star, which is 1,800 light-years away from Earth.
