Exoplanet demographics
1. Stellar kinematic correlations with planet properties
If planet properties and current stellar dynamics are correlated with the environment a star-planet system was born into, we would expect to be find evidence of differences in planet populations depending on the current kinematics of the host star.
In this paper, we show that exoplanet properties are indeed correlated with the local density of stars in position-velocity space. We did this through developing a distance-independent criterion to distinguish stars in co-moving groups. Hot Jupiters, massive planets with orbital periods shorter than 10 days, are more frequent compared to longer period planets for stars moving in co-moving groups. This might be linked to gravitational perturbations high density environments - see here for more!
2. Kepler multiples
Kepler multiple planets are interesting because they must have low mutual inclinations in order to be detected via transit. When we consider these multiples and account for Kepler detection biases, we find that the multiple systems are consistent with the 'isolation mass limit'. This limit (green line in plot below) is what we expect if massive planets do not migrate inwards rapidly via planet-disc interaction, and formed close to their current location. Click here for more details.
3. Putting it all together...
When comparing the non-hot Jupiter massive planet population divided by local kinematic density (1) to the Kepler multiples (2), a surprising pattern emerges! The massive planets hosted by stars in co-moving groups are the only ones that have masses greater than the Kepler multiples limit (2). It is possible that gravitational perturbation results in inwards 'scattering' of the planets indicated by red points in the plot below. Click here for more details.
