New research indicates that Saturn's largest moon, Titan, may have originated from the collision of two earlier moons hundreds of millions of years ago. This event could have reshaped the planet's moon system and contributed to the formation of its rings. Clues include Titan's orbit, surface features, and the behavior of the moon Hyperion.
A study led by SETI Institute scientist Matija Ćuk suggests that Titan formed through the merger of two proto-moons, an event that occurred hundreds of millions of years ago. This colossal collision not only created Titan but also disrupted Saturn's satellite system, potentially leading to the planet's prominent rings.
NASA's Cassini spacecraft, during its 13-year mission, revealed inconsistencies in Saturn's internal mass distribution. Measurements showed the planet's mass is more concentrated toward its center than previously thought, altering its precession rate and decoupling it from Neptune's influence. Earlier proposals from researchers at MIT and UC Berkeley posited an additional moon that was ejected after interacting with Titan, with its debris forming the rings.
However, simulations by Ćuk's team indicate that this extra moon more likely collided with Titan. A key insight comes from Hyperion, Saturn's small, chaotically tumbling moon, whose orbit is locked with Titan's. "Hyperion, the smallest among Saturn's major moons provided us the most important clue about the history of the system," Ćuk stated. The team notes that this orbital lock is relatively young, dating to a few hundred million years ago, aligning with the disappearance of the extra moon.
In the model, Titan resulted from the fusion of a large body called Proto-Titan, nearly as massive as the current moon, and a smaller Proto-Hyperion. This impact would have resurfaced Titan, explaining its scarcity of craters and its slightly elongated orbit, which is gradually circularizing. Prior to the merger, Proto-Titan may have resembled Jupiter's cratered moon Callisto.
The merger's gravitational effects could have destabilized inner moons through orbital resonances, causing collisions whose debris formed the rings, estimated to be about 100 million years old. Additionally, the event might explain the tilted orbit of Saturn's distant moon Iapetus.
NASA's Dragonfly mission, set to reach Titan in 2034, may test these ideas by examining surface geology for signs of ancient resurfacing from a major collision roughly half a billion years ago. The research is accepted for publication in the Planetary Science Journal, with a preprint on arXiv.