I study exoplanet theory using numerical and computational tools, with a current focus on sub-Neptune and super-Earth planets. Previously, I worked on planet formation and orbital dynamics through hydrodynamic and N-body simulations.
Photoevaporation vs. core-powered mass loss vs. boil-off
Over the past decade, the question of which mass-loss mechanism shapes the sub-Neptune population has been actively debated. Three mechanisms have been proposed and studied largely independently. SEAMIST unifies all three into a single self-consistent framework.
Using this model, we revisited the physical foundations of core-powered mass loss by refining several key modeling assumptions. We find that rock/iron core luminosity plays only a limited role in driving mass loss. Instead, planets undergo a rapid early stage of hydrodynamic escape, boil-off, that operates on ~1 Myr timescales and is followed by a negligible, long-lived bolometric-driven outflow, previously known as core-powered mass loss. Photoevaporation takes over immediately after boil-off ends.
Our results show that boil-off accounts for 80–90% of the total envelope mass lost, while photoevaporation removes only 10-20%. However, this final few weight percent of the envelope, removed by photoevaporation, is crucial in determining the planet’s long-term radius and whether it ends up as a sub-Neptune or a super-Earth. Tang et al. 2024 (ApJ)
Refined structure and evolution modeling
To match an observed planetary radius, our model predicts an envelope masse that is, on average, a factor of two lower than previously inferred. This implies that sub-Neptunes are more resilient to mass loss than earlier models suggested. This insight comes from our revised understanding that the apparent radii of low-mass sub-Neptunes are dominated by their radiative atmospheres rather than by their deep interiors. We also find that the solidification timescales of sub-Neptune rock/iron cores are significantly longer than those of super-Earths. Larger core masses, more massive envelopes, and stronger stellar irradiation all act to prolong solidification, typically pushing it beyond gigayear timescales. Tang et al. 2025a (ApJ)
A new photoevaporation regime explains super-puff exoplanets
Super-puffs are a class of low-mass, large-radius planets whose unusually low densities have been challenging to explain with previous sub-Neptune evolution models. By self-consistently incorporating hydrodynamic modeling of photoevaporation into our evolution framework, we identify a thermal-energy-mediated photoevaporation (TEMP) regime. This regime commonly occurs in super-puffs at present and in all other sub-Neptunes at young ages that have undergone significant boil-off mass loss. This regime revises previous theoretical understanding, which considered photoevaporation to be energy-limited by the gravitational energy required to lift the gas. Our results highlight the crucial role of energy conversion in accelerating the outflow and maintaining the wind temperature. Our model successfully reproduces the observed super-puffs and provides testable predictions for future observations. Tang et al. 2025b (ApJ)
H/He dissolution and its impact on planetary radius
. We have self-consistently incorporated H/He into SEAMIST and coupled it with thermal evolution, atmospheric escape, solidification, and compositional evolution. Using this framework, we explored the role of H/He dissolution on sub-Neptune radii in high-dimensional parameter space and its potential impact on planetary populations. Our study reveals new physical processes and feedback mechanisms linking H/He dissolution to radius evolution. Manuscript under review.
