# Discovery and Characterization of Kepler-36b

## TL;DR

This paper reports the discovery and detailed characterization of the Kepler-36 planetary system, highlighting its unique properties, innovative detection methods, and implications for understanding planetary composition and system evolution.

## Contribution

It introduces a novel photometric-dynamical modeling approach using MCMC techniques for multi-planet system analysis and provides the first 3D orientation constraints from transit data.

## Key findings

- The system's planets have contrasting densities despite close proximity.
- The dense planet has an Earth-like composition with high measurement precision.
- Insights into planetary formation and evolution processes were gained.

## Abstract

We describe the circumstances that led to the discovery of Kepler-36b, and the subsequent characterization of its host planetary system. The Kepler-36 system is remarkable for its physical properties: the close separation of the planets, the contrasting densities of the planets despite their proximity, and the short chaotic timescale. Its discovery and characterization was also remarkable for the novelty of the detection technique and for the precise characterization due to the large transit-timing variations caused by the close proximity of the planets, as well as the precise stellar parameters due to asteroseismology. This was the first multi-planet system whose transit data was processed using a fully consistent photometric-dynamical model, using population Markov Chain Monte Carlo techniques to precisely constrain system parameters. Amongst those parameters, the stellar density was found to be consistent with a complementary, concurrent asteroseismic analysis. In a first, the 3D orientation of the planets was constrained from the lack of transit-duration variations. The system yielded insights into the composition and evolution of short-period planet systems. The denser planet appears to have an Earth-like composition, with uncertainties comparable to the highest precision rocky exoplanet measurements, and the planet densities foreshadowed the rocky/gaseous boundary. The formation of this system remains a mystery, but should yield insights into the migration and evolution of compact exoplanet systems.