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An overabundance of single-transiting Kepler planets suggests the existenceof a sub-population of intrinsically multi-planet systems possessing largemutual inclinations. However, the origin of these mutual inclinations remainsunknown. Recent work has demonstrated that mutual inclinations can be excitedsoon after protoplanetary disk-dispersal due to the oblateness of therapidly-rotating host star, provided the star is tilted. Alternatively, distantgiant planets, which are common in systems of close-in Kepler planets, coulddrive up mutual inclinations. The relative importance of each of thesemechanisms has not been investigated. Here, we show that the influence of thestellar oblateness typically exceeds that of an exterior giant soon afterplanet formation. However, the magnitude of the resulting mutual inclinationsdepends critically upon the timescale over which the natal disk disperses.Specifically, we find that if the disk vanishes over a timescale shorter than10^(3-4) years, comparable to the viscous timescale of the inner ~0.2AU, theinner planets impulsively acquire misalignments that scale with the stellarobliquity. In contrast, if the disk disperses slowly, the inner planets remaincoplanar. They first align with the stellar equator but subsequently realignwith the distant giant's plane as the star spins down. Our findings areconsistent with recent observations that giants tend to be aligned withclose-in multis but misaligned with singles. Stellar obliquity measurementsoffer a promising test of our proposed framework.

Stellar Oblateness versus Distant Giants in Exciting Kepler Planet Mutual Inclinations