Transit Timing Observations from Kepler: IV. Confirmation of 4 Multiple Planet Systems by Simple Physical Models (1201.5415v2)

Abstract: Eighty planetary systems of two or more planets are known to orbit stars other than the Sun. For most, the data can be sufficiently explained by non-interacting Keplerian orbits, so the dynamical interactions of these systems have not been observed. Here we present 4 sets of lightcurves from the Kepler spacecraft, which each show multiple planets transiting the same star. Departure of the timing of these transits from strict periodicity indicates the planets are perturbing each other: the observed timing variations match the forcing frequency of the other planet. This confirms that these objects are in the same system. Next we limit their masses to the planetary regime by requiring the system remain stable for astronomical timescales. Finally, we report dynamical fits to the transit times, yielding possible values for the planets' masses and eccentricities. As the timespan of timing data increases, dynamical fits may allow detailed constraints on the systems' architectures, even in cases for which high-precision Doppler follow-up is impractical.

Overview of Confirming Multiple Planet Systems by Transit Timing Variations

The paper authored by Fabrycky et al. presents a sophisticated analysis leveraging Transit Timing Variations (TTVs) to confirm the presence of planets in four distinct multi-planet systems, namely Kepler-29, Kepler-30, Kepler-31, and Kepler-32. This paper notably contributes to the understanding of exoplanetary systems orbiting stars other than the Sun through detailed examination of light curves obtained from NASA's Kepler spacecraft.

Key Findings

1. Detection and Confirmation of Planetary Systems: The researchers confirmed the existence of nine planets across four systems by analyzing the deviations in transit timing from strict periodicity. The observed TTVs are consistent with gravitational perturbations expected from planets in the same orbital system, thereby confirming their co-existence.
2. Resonances and Orbital Dynamics: Notable in the findings is the proximity of the planets to low-order resonances, such as the 9:7 resonance observed in the Kepler-29 system, suggesting resonant interactions. The Kepler-30 system stands out with significant TTV amplitudes due to a near-2:1 resonance arrangement involving massive Jupiter-sized planets.
3. Dynamical Stability and Mass Constraints: The researchers applied dynamical stability analyses to constrain the planetary masses within these systems. Numerical simulations were used to set conservative mass upper limits based on necessary conditions for long-term stability. These limits validate the planets are firmly in the planetary mass regime rather than being stellar objects.
4. Host Star Characterization: Detailed follow-up observations, including spectra from various observatories, facilitated the determination of host star properties and reduced the potential for false positives due to stellar blends. The authors accounted for contamination and performed Bayesian analyses to characterize stellar mass and radii effectively.

Implications for Exoplanet Research

This paper harnesses transit timing data from Kepler, setting a precedent for verification methodologies that do not solely rely on radial velocity measurements or other traditional methods constrained by stellar brightness. The demonstrated ability to confirm planetary systems around relatively faint stars showcases the broad applicability of TTV analysis and hints at the potential for discovering and characterizing planets in challenging observational scenarios.

The detection of systems with resonant configurations contributes to ongoing discussions about planetary formation and migration theories. Observations suggest potential capture into resonance during planetary migration, aligning with theoretical models suggesting similar orbital architectures for forming compact systems of super-Earths and mini-Neptunes.

Theoretical and Practical Developments

The findings here invite theoretical advancements in understanding higher-order resonant interactions and the role eccentricities play within compact multi-planet systems. Practically, extensions of missions like Kepler may further improve detection capabilities and confirm additional systems based on longer observational baselines necessary for capturing extensive TTV cycles.

Furthermore, systems like Kepler-30, which displayed starspot transits allowing for spin-orbit alignment studies, indicate the kind of in-depth star-planet interaction analysis possible in such densely packed systems. The ability to use spot-crossing data offers a novel pathway for probing orbital dynamics relative to stellar rotational axes.

Conclusion

This paper marks a significant stride in exoplanet research, providing a robust approach to confirming planetary systems using transit timing variations. The work underlines the importance of comprehensive observational strategies and theoretical insights in unearthing the intricate dynamical architectures evident beyond our solar system. As the methodologies and datasets continue to evolve, they hold promise for advancing both the breadth and depth of planetary discovery and characterization.