Kepler-108: A Mutually Inclined Giant Planet System

Abstract

The vast majority of well studied giant-planet systems, including the solar system, are nearly coplanar, which implies dissipation within a primordial gas disk. However, intrinsic instability may lead to planet–planet scattering, which often produces non-coplanar, eccentric orbits. Planet scattering theories have been developed to explain observed high-eccentricity systems and also hot Jupiters; thus far their predictions for mutual inclination (I) have barely been tested. Here we characterize a highly mutually inclined ( °), moderately eccentric ( ) giant planet system: Kepler-108. This system consists of two approximately Saturn-mass planets with periods of approximately 49 and 190 days around a star with a wide (∼300 au) binary companion in an orbital configuration inconsistent with a purely disk migration origin.

Robustly Detecting Changes in Warm Jupiters’ Transit Impact Parameters

“…Our inferred parameters in Table 5 are consistent with those of Mills & Fabrycky (2017)'s mutually inclined fit. Mills & Fabrycky (2017) found an average impact parameter of b = 0.28 +0.18 −0.14 for Kepler-108b and b = 0.65 +0.06 −0.11 for Kepler-108c (Sean Mills, personal communication, March 10th 2017). Their average scaled planet-star separation corresponds to ρ circ = 0.30 +0.30 −0.07 ρ for Kepler-108b and ρ circ = 0.35 +0.14 −0.07 ρ (Sean Mills, personal communication, March 10th 2017).…”

“…Moreover, planet c exhibits clear TDVs, with the transit duration changing by almost an hour over the course of about three years. Mills & Fabrycky (2017) note that planet b may also have TDVs but the change in duration is smaller and less significant (their Fig. 1).…”

“…The Kepler-108 system contains two transiting warm Saturns on orbits mutually inclined by I( • ) = 24 +11 −8 (Mills & Fabrycky 2017). Both transiting planets exhibit TTVs.…”

Eccentric Companions to Kepler-448b and Kepler-693b: Clues to the Formation of Warm Jupiters

“…A striking difference is the clear trend in the duration that points to non-zero i 21 . The trend comes from the nodal precession of the inner orbit (Miralda-Escudé 2002) and has also been observed in the Kepler-108 system recently (Mills & Fabrycky 2017). While a similar duration drift can also be caused by the apsidal precession of the eccentric inner orbit, this is unlikely to be the case given the failure of the coplanar model.…”

“…Here I also fit the planet-to-star radius ratio, R p /R , so that the possible transit depth modulation due to the different crowding depending on observing seasons does not mimic duration variations (cf. Mills & Fabrycky 2017). As shown in Figure 1, I find significant TTVs consisting of a longterm modulation and a short-term, sharp feature (top panels).…”