Stability Constrained Characterization of the 23 Myr-old V1298 Tau System: Do Young Planets Form in Mean Motion Resonance Chains?

TL;DR

This study uses dynamical stability analysis of the V1298 Tau system to assess whether young planets form in mean motion resonance chains, finding strong evidence against such configurations at its current age.

Contribution

It provides the first stability-based constraints on the orbital architecture of the young V1298 Tau system, ruling out resonant chain formation at 99% confidence.

Findings

V1298 Tau's planet b is near the instability limit.

Resonant chain configuration is highly unlikely for V1298 Tau.

Stability constraints can inform models of young planet formation.

Abstract

A leading theoretical expectation for the final stages of planet formation is that disk migration should naturally drive orbits into chains of mean motion resonances (MMRs). In order to explain the dearth of MMR chains observed at Gyr ages ($<1\%$), this picture requires such configurations to destabilize and scramble period ratios following disk dispersal. Strikingly, the only two known stars with three or more planets younger than $\lesssim 100$ Myrs, HR 8799 and V1298 Tau, have been suggested to be in such MMR chains, given the orbits' near-integer period ratios. We incorporate recent transit and radial velocity observations of the V1298 Tau system, and investigate constraints on the system's orbital architecture imposed by requiring dynamical stability on timescales much shorter than the system's age. We show that the recent radial-velocity mass measurement of V1298 Tau $b$ places it within a factor of two of the instability limit, and that this allows us to set significantly lower limits on the eccentricity ($e_b \leq 0.17$ at $99.7\%$ confidence). Additionally, we rule out a resonant chain configuration for V1298 Tau at $\gtrsim 99\%$ confidence. Thus, if the $\sim 23$ Myr-old V1298 Tau system did form as a resonant chain, it must have undergone instability and rearrangement shortly after disk dispersal. We expect that similar stability constrained characterization of future young multi-planet systems will be valuable in informing planet formation models.