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Yu-Cian Hong

Astronomy & Space Sciences


I’m a PhD candidate in Cornell Astronomy.  My research focuses on the numerical simulations and orbital dynamics of extra-solar moons and extra-solar giant planets.  I work with my advisor Prof. Jonathan Lunine.  Over the course of my research projects, I have also worked with Prof. Phil Nicholson, Prof. Dong Lai, Dr. Matt Tiscareno, and Dr. Sean Raymond.

I have developed an N-body integrator that is capable of handling moon problems in close planet-planet interactions, based on Mercury (Chambers 1999).  The modified code treats planets realistically as oblate, and evolves planet spin with a non-secular equation of motion.

My most recent research project studies how planet-planet scattering affect the orbital stability of moons of extra-solar giant planets, using N-body numerical simulations.  Planet-planet scattering is the current best model that explains the eccentricities of extra-solar planets.  In the early stages of the evolution of planetary systems, after the planets form, they are closely packed, so their mutual perturbation helps develop orbit crossing and mutual close encounters.  Moons in this scenario receives strong perturbations from various sources, most dominantly during planetary close encounters.  The rapidly evolving orbits of planets, and the high inclination and obliquity planets developed through the instability phase, etc., could all provide strong perturbations that destabilize the moons.  Therefore, the orbital parameter space that allows for stable moons is small, mostly within 0.1 Hill radii from the moon hosting planet.  Moons exhibit rich dynamical behaviors and the dynamical outcomes are diverse.  Besides stable moons, there’re small populations of moons captured away by the perturbing planet, moons orbiting ejected free-floating planets, and moons that turned to orbit the star.  The majority of moons are removed after colliding with planets and the star (~ 40%) and being flung out of the system as free-floating moons (~ 40%).  The high fraction of moon ejection estimates a galactic population of order 0.01 - 1 free-floating exomoons per star.

AAS nova provides an interesting summary on this work:

I also experimented with placing moons around spherical planets, against a commonsensical notion that the orbital dynamics of close-in moons is dominated by the oblateness of their host planet.  Around spherical planets, close-in moons going unstable or acquiring high eccentricities and inclinations in a stable two-planet system mutually inclined by only 10 degrees.  The cause for such instability is the slowed precession of the moons' orbital plane in the absence of planet oblateness, which gives it a chance to enter the 3:2 and 1:1 resonance overlap zone or the chaotic zone around 1:1 resonance with the precession of the star's orbits (in the reference plane centered by the moon-hosting planet).

Outside of school, I enjoy doing winter sports, especially skiing.  I also like bonding with nature, sometimes through photography.



  • Astronomy

Graduate Fields

  • Astronomy and Space Sciences


Advisor: Professor Jonathan Lunine