Neptune is tilted at a weird angle because its moon Triton basically grabbed it like a handle and slowly tipped it over.
March 20, 2026
Original Paper
Neptune's obliquity was likely engendered by Triton's tidal evolution
arXiv · 2603.19035
The Takeaway
While most planetary tilts are blamed on violent prehistoric collisions, this research demonstrates that Neptune's captured moon, Triton, could have done the job alone. Over millions of years, the moon's changing orbit acted as a slow-motion gravity handle, dragging the entire planet's axis into its current slanted position.
From the abstract
Neptune's present axial tilt of approximately 28 deg. with respect to its orbital plane can be explained by collisions that its primordial core may have experienced with surrounding planetary embryos during the final stages of its formation. Alternatively, Neptune could have attained its present mass solely through pebble accretion, without the formation of nearby planetary embryos. The embryo-collision scenario has the advantage of naturally explaining the large axial tilts observed in the ice