Titan, Saturn’s largest moon and one of the top candidates for extraterrestrial life in our solar system, may have been born from the collision of two smaller moons, astronomers say.
The research, led by SETI Institute scientist Matija Ćuk and recently published in The Planetary Science Journal, builds on previous work suggesting that moon collisions may also have generated Saturn’s famous rings.
NASA’s Cassini mission to study Saturn up close provided an essential starting point for the new research, questioning long-held assumptions about both Saturn and Titan.
Cassini Explore Saturn
Overturning decades of scientific assumptions about Saturn, including the unexpected discovery that the planet’s precession period does not match that of Neptune, NASA’s Cassini mission played a key role in the recent research.
Astronomers have long assumed that this suspected match allows for a gravitational interaction between the two planets, causing Saturn to tilt and present its rings to us. Instead, Saturn’s center of gravity is more centrally located than expected, opening the question of how Saturn acquired its spin-axis wobble.
Researchers at MIT and UC Berkeley first proposed that an extra moon in Saturn’s past could explain the discrepancy. Their hypothesis was that the moon came too close to Titan, ejecting it from its orbit and smashing it into dust to form Saturn’s rings.
Computer simulations used in the SETI-led research sought to determine whether an extra moon could have come close enough to Saturn to be behind formation of the ring. They established that a collision with Titan could have produced such a result, with the small moon Hyperion providing a few important clues related to this possibility.
Simulating Titan
“Hyperion, the smallest among Saturn’s major moons provided us the most important clue about the history of the system,” said Ćuk. “In simulations where the extra moon became unstable, Hyperion was often lost and survived only in rare cases.”
In simulations in which Hyperion was present during impact, it was usually destroyed. After noting this and comparing it to the age of the Saturn-Hyperion lock, the researchers suspected that instead of merely surviving the impact, Hyperion was seemingly born out of it. Notably, the theoretical impact models showed large fragments of the former moon landing in Hyperion’s present location, suggesting that it could have been essential to forming the small moon.
“We recognized that the Titan-Hyperion lock is relatively young, only a few hundred million years old. This dates to about the same period when the extra moon disappeared,” Ćuk continued. “Perhaps Hyperion did not survive this upheaval but resulted from it. If the extra moon merged with Titan, it would likely produce fragments near Titan’s orbit. That is exactly where Hyperion would have formed.”
What Came Before Titan
The researcher’s new model suggests that two earlier moons merged to form the current moons Titan and Hyperion, known as Proto-Titan and Proto-Hyperion. Notably, the impact would explain another of Titan’s puzzling features: its relatively smooth surface. The researchers say that this massive collision would likely have erased existing impact craters. Additionally, while Titan’s orbit is eccentric, it is continually growing more circular, suggesting that the disturbance would have to be relatively recent.
Intriguingly, the Proto-Titan may have been a cratered rock similar to Jupiter’s moon Callisto, lacking any atmosphere before the collision. In this regard, the concept of a proto-Hyperion solves yet another mystery, as it accounts for the strange tilted orbit of another of Saturn’s moons: Lapetus.
While this neatly ties up some lingering questions about the Saturnian moons, it still leaves a major question unanswered: how did Saturn’s rings form?
The resolution to this cosmic conundrum could involve additional collisions between moons. Instead of the Sun triggering the destruction, the researchers suggest that many smaller moons on tight orbits could have collided into one another as a result of Titan’s expanding orbit. Thus, when Titan’s orbit aligns in such a way with much smaller moons, it could cause their orbits to elongate, sending them careening into other moons.
In the next decade, researchers will get another close-up look at Titan. NASA’s Dragonfly mission is scheduled to arrive at the moon in 2034, unleashing a nuclear-powered octocopter to analyze the moon’s surface. Data from this mission may reveal whether Titan is indeed the result of a massive impact.
The paper, “Origin of Hyperion and Saturn’s Rings in A Two-Stage Saturnian System Instability,” is available now arXiv.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.