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

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 • with respect to the Sun's equator.

An exoplanet's response to anisotropic stellar mass loss during birth and death

“…The observed differences in velocities between both jet components vary but may be approximated by a factor of about two. This factor agrees with the estimate of Namouni (2013) and his references. The asymmetry in the mass-loss rate may similarly be approximated by a factor of a few.…”

“…The disc itself provides another perturbation on the planet (and vice versa). Namouni (2005) and Namouni (2013), who also consider the effect on planets of bipolar jets, neglect the disc mass. We similarly neglect the disc, but first provide some more detailed justification for doing so.…”

“…These studies include those by Boué et al (2012) and Iorio (2012), both of whom consider anisotropic evaporation from planetary atmospheres as the driver for orbital evolution. Investigators who instead consider asymmetric mass loss from the central star include Parriott & Alcock (1998), who quantify the escape of comets in different directions during post-MS evolution, and Namouni (2005), Namouni & Zhou (2006), Namouni & Guzzo (2007), and Namouni (2013), who instead look at the effects of bipolar jets on planetary orbits during the early stages of the life of a planetary system.…”

The Stark problem in the Weierstrassian formalism

“…In astrophysics and dynamical astronomy, the Stark problem is sometimes known as the accelerated Kepler problem, and it is studied in several contexts. Models based on the accelerated Kepler problem have been used to study the excitation of planetary orbits by stellar jets in protoplanetary disks and to explain the origin of the eccentricities of extrasolar planets (Namouni 2005;Namouni & Guzzo 2007;Namouni 2013). The Stark problem has also been used in the study of the dynamics of dust grains in the Solar System (Belyaev & Rafikov 2010;Pástor 2012).…”