The moon that made Saturn a pushover

Titan, Saturn’s biggest moon, probably helped to cause the ringed planet to start tipping off-kilter long ago.

Saturn is tilted with respect to its orbit around the Sun, by a little bit more than Earth is. Planetary scientists had thought that Saturn acquired its tilt more than 4 billion years ago, thanks to the gravitational influence of Neptune.

But recent measurements made with NASA’s Cassini spacecraft show that Titan is moving relatively rapidly away from Saturn. Melaine Saillenfest at the Paris Observatory and his colleagues capitalized on that finding to suggest that Titan is to blame for Saturn’s tilt.

Their calculations suggest that, around one billion years ago, Titan was migrating away from Saturn and led the planet into a gravitational interaction with Neptune — which steadily tilted Saturn over.

Big migrating moons could similarly cause giant planets in other solar systems to keel over.

Correction 27 January 2021: An earlier version of this article incorrectly used the gender pronoun ‘her’ for Melaine Saillenfest. It also misstated the journal that published the paper.

Correction 28 January 2021: This article has been changed to correctly describe how Titan influenced Saturn and how Saturn’s motion responded to that influence.