Rattle-and-break: The Impact of Planetesimal Scattering on Super-Earth Resonant Chains

Abstract The spacings of super-Earths in multitransiting systems exhibit a distribution that is broad and mostly featureless, with the exception of notable excesses of planet pairs situated a few percent wide of first-order mean-motion resonances (MMRs). In this work, we extend the so-called “breaking-the-chains” model to account for both of these characteristics. Assuming that super-Earths are settled into stable chains of resonances after disk-driven migration, we show that scattering a planetesimal population that contains only a few percent of a system’s mass can reorganize primordial chains in remarkable ways. The planetesimal scattering “rattles” the chains by repelling adjacent planet pairs wide of their initial MMRs. Some rattled chains remain stable afterward and make up the observed excesses wide of MMRs. In other systems, however, this initial rattling sows the seeds of later orbital instabilities that break the chains entirely. If the masses of individual planetesimals are sufficiently small, of the order of a Pluto mass for our example systems, the onset of these instabilities can occur tens to hundreds of Myr after birth, naturally explaining the apparent disappearance of near-resonant pairs on this timescale. The origin of such Pluto-mass debris is currently unknown.