Outer-planet scattering can gently tilt an inner planetary system

Abstract

Chaotic dynamics are expected during and after planet formation, and a leading mechanism to explain large eccentricities of gas giant exoplanets is planet-planet gravitational scattering. The same scattering has been invoked to explain misalignments of planetary orbital planes with respect to their host star's spin. However, an observational puzzle is presented by Kepler-56, which has two inner planets (b and c) that are nearly coplanar with each other, yet are more than 45 degrees inclined to their star's equator. Thus the spin-orbit misalignment might be primordial. Instead, we further develop the hypothesis in the discovery paper, that planets on wider orbits generated misalignment through scattering, and as a result gently torqued the inner planets away from the equator plane of the star. We integrated the equations of motion for Kepler-56 b and c along with an unstable outer system initialized with either two or three Jupiter-mass planets. We address here whether the violent scattering that generates large mutual inclinations can leave the inner system intact, tilting it gently. In almost all of the cases initially with two outer planets, either the inner planets remain nearly coplanar with each other in the star's equator plane, or they are scattered violently to high mutual inclination and high spin-orbit misalignment. On the contrary, of the systems with three unstable outer planets, a spin-orbit misalignment large enough to explain the observations is generated 28% of the time for coplanar inner planets, which is consistent with the observed frequency of this phenomenon reported so far. We conclude that multiple-planet scattering in the outer parts of the system may account for this new population of coplanar planets hosted by oblique stars.

10 pages, 16 figures, 3 tables. Revised according to a positive referee report. Comments welcome

References in corpus (28)

• Dynamical Outcomes of Planet-Planet Scattering
• The Theory of Brown Dwarfs and Extrasolar Giant Planets
• Architecture of Kepler's Multi-transiting Systems: II. New investigations with twice as many candidates
• Obliquities of Hot Jupiter host stars: Evidence for tidal interactions and primordial misalignments
• Spin-orbit angle measurements for six southern transiting planets; New insights into the dynamical origins of hot Jupiters
• Chaotic star formation and the alignment of stellar rotation with disc and planetary orbital axes
• Stellar Spin-Orbit Misalignment in a Multiplanet System
• Orbital perturbations on transiting planets: A possible method to measure stellar quadrupoles and to detect Earth-mass planets
• Exoplanetary Spin-Orbit Alignment: Results from the Ensemble of Rossiter-McLaughlin Observations
• Internal Gravity Waves in Massive Stars: Angular Momentum Transport
• Misaligned spin-orbit in the XO-3 planetary system?
• Dynamical Instabilities in Extrasolar Planetary Systems Containing Two Giant Planets
• Evolution of Spin Direction of Accreting Magnetic Protostars and Spin-Orbit Misalignment in Exoplanetary Systems
• Low stellar obliquities in compact multiplanet systems
• Photometric Amplitude Distribution of Stellar Rotation of Kepler KOIs-Indication for Spin-Orbit Alignment of Cool Stars and High Obliquity for Hot Stars
• Constructing the secular architecture of the solar system II: The terrestrial planets
• WASP-52b, WASP-58b, WASP-59b, and WASP-60b: four new transiting close-in giant planets
• The destruction of inner planetary systems during high-eccentricity migration of gas giants
• The Turbulent Origin of Spin-Orbit Misalignment in Planetary Systems
• On the Migration of Jupiter and Saturn: Constraints from Linear Models of Secular Resonant Coupling with the Terrestrial Planets
• Discerning Exoplanet Migration Models Using Spin-Orbit Measurements
• The determination of planetary structure in tidally relaxed inclined systems
• The Fragility of the Terrestrial Planets During a Giant Planet Instability
• Spin-orbit inclinations of the exoplanetary systems HAT-P-8, HAT-P-9, HAT-P-16 and HAT-P-23
• Compact planetary systems perturbed by an inclined companion: II. Stellar spin-orbit evolution
• Generation of highly inclined protoplanetary discs through single stellar flybys
• The Dynamics of the Multi-planet System Orbiting Kepler-56
• 55 Cancri: A Coplanar Planetary System that is Likely Misaligned with its Star

Cited by in corpus (32)

• Stellar obliquities in exoplanetary systems
• The effects of external planets on inner systems: multiplicities, inclinations, and pathways to eccentric warm Jupiters
• DREAM I. Orbital architecture orrery
• A backward-spinning star with two coplanar planets
• The Rossiter-McLaughlin effect Revolutions: An ultra-short period planet and a warm mini-Neptune on perpendicular orbits
• Effects of Unseen Additional Planetary Perturbers on Compact Extrasolar Planetary Systems
• Eccentricities and Inclinations of Multi-Planet Systems with External Perturbers
• Dynamically hot Super-Earths from outer giant planet scattering
• Stellar ages, masses and radii from asteroseismic modeling are robust to systematic errors in spectroscopy
• Mutual Orbital Inclinations Between Cold Jupiters and Inner Super-Earths
• The Aligned Orbit of WASP-148b, the Only Known Hot Jupiter with a Nearby Warm Jupiter Companion, from NEID and HIRES
• Obliquities of Exoplanet Host Stars: 19 New and Updated Measurements, and Trends in the Sample of 205 Measurements
• K2-146: Discovery of Planet c, Precise Masses from Transit Timing, and Observed Precession
• Fly-by encounters between two planetary systems II: Exploring the interactions of diverse planetary system architectures
• Strong Scatterings of Cold Jupiters and their Influence on Inner Low-mass Planet Systems: Theory and Simulations
• The Origin of Systems of Tightly Packed Inner Planets with Misaligned, Ultra-Short-Period Companions
• Stellar Oblateness versus Distant Giants in Exciting Kepler Planet Mutual Inclinations
• Preliminary constraints on the location of the recently hypothesized new planet of the Solar System from planetary orbital dynamics
• The chaotic history of the retrograde multi-planet system in K2-290A driven by distant stars
• The Discovery of the Long-Period, Eccentric Planet Kepler-88 d and System Characterization with Radial Velocities and Photodynamical Analysis
• Prospects from TESS and Gaia to constrain the flatness of planetary systems
• Measuring the Obliquities of the TRAPPIST-1 Planets with MAROON-X
• Synergies between Asteroseismology and Exoplanetary Science
• ATREIDES I. Embarking on a trek across the exo-Neptunian landscape with the TOI-421 system
• Inclination Dynamics of Resonant Planets under the Influence of an Inclined External Companion
• Revisiting the Architecture of the KOI-89 System
• NIRPS and TESS reveal a peculiar system around the M dwarf TOI-756: A transiting sub-Neptune and a cold eccentric giant
• Asteroseismic determination of the stellar rotation period of the Kepler transiting planetary systems and its implications for the spin-orbit architecture
• A Trio of Giant Planets Orbiting Evolved Star HD 184010
• Evidence for a Non-Dichotomous Solution to the Kepler Dichotomy: Mutual Inclinations of Kepler Planetary Systems from Transit Duration Variations
• Constraints on the Obliquities of Kepler Planet-Hosting Stars
• Orbital alignment of HD 332231 b