Neptune is the farthest planet in the Solar System, a cold, blue, icy giant located nearly 30 times farther from the Sun than Earth. At such a great distance, the temperature drops to nearly minus 200 degrees Celsius, and one year there lasts 165 Earth years. However, despite its isolation, Neptune is a world where the fastest winds in the Solar System rage, and it is also home to one of the strangest moons.
Mystery of Neptune’s axial tilt
Every planet in our Solar System has an axial tilt. Earth’s 23-degree tilt causes the changing of the seasons, while Uranus is tilted so much that it practically orbits the Sun while lying on its side. But Neptune’s 28-degree axial tilt has quietly puzzled planetary scientists for decades. How did the farthest ice giant end up at such a peculiar angle? A new study by Rodney Gomes of the University of São Paulo suggests that the answer lies in one of the most remarkable moons in the Solar System.
Triton is a strange phenomenon. It is the only large moon in the Solar System that orbits its planet in the opposite direction, moving backward against Neptune’s rotation along a so-called retrograde orbit. It is believed that Triton was once a dwarf planet from the Kuiper Belt that was captured by Neptune’s gravitational field at some point early in its history. This event triggered a chain of consequences that, according to Gomez, may still be altering Neptune’s system.
Triton’s orbit explains the planet’s tilt
A new study suggests that Neptune’s current axial tilt is the result of an interaction between Triton’s orbit—which is altered by tidal forces—and Neptune’s axis of rotation, leading to a resonance with a specific frequency in the Solar System known as s8. In other words, as Triton slowly spiraled into its current orbit over millions of years, the gravitational tug-of-war between the moon and the planet effectively tilted Neptune away from its original axis, much like a spinning top pushed by a passing hand.
In simulations, Triton initially follows an inclined and highly eccentric orbit, gradually evolving under the influence of tidal interactions into its current path around Neptune. The results show that, in some cases, orbital inclinations exceeding 50 degrees are possible; in fact, in nearly one out of every four simulations, the inclination exceeds 20 degrees, which is sufficient to explain Neptune’s observed inclination.
Future of Triton
Triton’s orbit is already closer to Neptune than the Moon is to Earth, and tidal forces are causing it to move even closer to the planet; therefore, predictions indicate that in about 3.6 billion years, Triton will cross Neptune’s Roche limit. At that point, it will either collide with the planet or break apart, forming a stunning new ring system.
However, Triton continues to follow its slow spiral orbit, leaving its mark on the planet it now calls home. If Gomez is right, then Triton didn’t just arrive in Neptune’s vicinity—it completely replaced it.
According to phys.org
