Ringed versus Ringless Worlds: How Poynting-Robertson Drag Shapes Rings across the Solar System

TL;DR

This study models how Poynting-Robertson drag influences the presence of planetary rings, explaining why outer Solar System bodies retain rings while inner ones do not, and predicts more distant ringed objects will be discovered.

Contribution

It provides a numerical and analytical model showing PR drag as the key factor in the distribution of rings across the Solar System, explaining the ringed versus ringless dichotomy.

Findings

PR drag can explain the longevity of rings around outer Solar System bodies.

Rings around inner planets are short-lived due to faster PR drag effects.

Future surveys are likely to find more ringed objects in the distant Solar System.

Abstract

Planetary rings are not only ubiquitous around the giant planets in the outer Solar System, but have also been discovered around several small distant bodies. In contrast, no rings have been observed around any inner Solar System objects. To constrain the dynamical origin of this ringed-versus-ringless dichotomy, we employ a numerically cross-checked analytical model of gigayear-scale Poynting-Robertson (PR) drag due to the solar flux acting on an isolated particle, expressed as a function of the host body's heliocentric distance \(\,a_{\mathrm{pla}}\) and the particle radius \(\,r_{\mathrm{par}}\). Here we show that, in the absence of additional perturbations, PR drag alone can explain the observed ring architecture of the Solar System: outer planets and Centaurs/TNOs are able to retain rings for the age of the Solar System, whereas any rings around the inner planets are removed on much shorter timescales. Because the PR-drag lifetime scales steeply with heliocentric distance \(\bigl(\tau_{\mathrm{decay}}\propto a_{\mathrm{pla}}^{2} \,r_{\mathrm{par}}\bigr)\), we predict that forthcoming surveys will reveal an ever-growing population of ring-bearing bodies in the distant Solar System.