The excitation of planetary orbits by stellar jet variability and polarity reversal

TL;DR

This paper models how stellar jet variability and polarity reversals can excite planetary orbits, revealing a resonance mechanism that influences orbital eccentricity and inclination, with implications for planetary system evolution.

Contribution

It introduces a stochastic model of stellar jet momentum loss, identifying a novel resonance between planetary orbital periods and jet variability timescales, including effects of polarity reversal types.

Findings

Resonance occurs when orbital period equals twice the jet variability timescale.

Periodic polarity reversals produce stronger orbital excitation than random reversals.

Resonance crossing can lead to outward planetary migration and explains Jupiter's orbital inclination.

Abstract

Planets form in active protoplanetary disks that sustain stellar jets. Momentum loss from the jet system may excite the planets' orbital eccentricity and inclination (Namouni 2005, AJ 130, 280). Evaluating quantitatively the effects of such excitation requires a realistic modeling of the momentum loss profiles associated with stellar jets. In this work, we model linear momentum loss as a time-variable stochastic process that results in a zero mean stellar acceleration. Momentum loss may involve periodic or random polarity reversals. We characterize orbital excitation as a function of the variability timescale and identify a novel excitation resonance between a planet's orbital period and the jet's variability timescale where the former equals twice the latter. For constant variability timescales, resonance is efficient for both periodic and random polarity reversals, the latter being stronger than the former. For a time variable variability timescale, resonance crossing is a more efficient excitation mechanism when polarity reversals are periodic. Each polarity reversal type has distinct features that may help constrain the magnetic history of the star through the observation of its planetary companions. For instance, outward planet migration to large distances from parent stars is one of the natural outcomes of periodic polarity reversal excitation if resonance crossing is sufficiently slow. Applying the excitation mechanism to the solar system, we find that the planet-jet variability resonance with periodic polarity reversal momentum loss is a possible origin for the hitherto unexplained inclination of Jupiter's orbit by 6 deg. with respect to the Sun's equator.