Can Kozai-Lidov cycles explain Kepler-78b?

Kepler-78b is one of a growing sample of planets similar, in compositionand size, to the Earth. It was first detected with NASA's Keplerspacecraft and then characterized in more detail using radial velocityfollow-up observations. Not only is its size very similar to that of theEarth (1.2 R⊕), it also has a very similar density (5.6g cm-2). What makes this planet particularly interesting isthat it orbits its host star every 8.5 h, giving it an orbital distanceof only 0.0089 au. What we investigate here is whether or not such aplanet could have been perturbed into this orbit by an outer companionon an inclined orbit. In this scenario, the outer perturber causes theinner orbit to undergo Kozai-Lidov cycles which, if the periapse comessufficiently close to the host star, can then lead to the planet beingtidally circularized into a close orbit. We find that this process canindeed produce such very-close-in planets within the age of the hoststar (˜600-900 Myr), but it is more likely to find suchultrashort-period planets around slightly older stars (>1 Gyr).However, given the size of the Kepler sample and the likely binarity,our results suggest that Kepler-78b may indeed have been perturbed intoits current orbit by an outer stellar companion The likelihood of thishappening, however, is low enough that other processes - such asplanet-planet scattering - could also be responsible.