Mapping Giant Planet Birth: HR Diagram Tracks Could Rewrite Exoplanet Population Models and Solar System Origins
Preprint couples Bern model to hydro simulations to plot giant planet formation on HR diagram, revealing three branches that clarify accretion physics and link to exoplanet observations.
This 2026 arXiv preprint (not yet peer-reviewed) from Benedikt Gottstein and collaborators introduces planetary evolutionary tracks on the Hertzsprung-Russell diagram by extending the Bern planet formation model with time-dependent radiation-hydrodynamical accretion shock efficiencies. The methodology relies on coupled interior structure calculations and hydro simulations rather than direct observations, yielding theoretical tracks for varying solid accretion rates, migration, and hot versus cold accretion modes without a statistical sample size. Three distinct branches emerge: an ascending solid-dominated phase where luminosity scales as L ∝ T^8 for in-situ planetesimal accretion, a near-horizontal post-detachment gas accretion phase influenced by electron degeneracy, and a final descending cooling track with L ~ T^4. This visual framework goes beyond prior synthetic population studies by explicitly resolving the cold-hot start ambiguity and highlighting how pebble accretion or high-mass regimes bend tracks upward, an aspect underemphasized in earlier core-accretion papers such as Mordasini et al. (2012) on the Bern model itself. Original coverage overlooks connections to JWST direct-imaging results of young super-Jupiters, where luminosity excesses may trace the short-lived ascending branch rather than solely disk interactions. Limitations include idealized assumptions about circumplanetary disk reprocessing and migration timescales that could shift branch durations substantially. Synthesizing with Marley et al. (2007) on hot-start cooling and recent population synthesis from Emsenhuber et al. (2021), the work suggests solar-system giants like Jupiter likely followed a hybrid track, offering a predictive lens for interpreting upcoming Roman Space Telescope microlensing yields of forming planets.
HELIX: This HR mapping will let astronomers read formation history directly from a planet's position, explaining luminosity outliers in young systems that standard cooling models cannot.
Sources (3)
- [1]Primary Source(https://arxiv.org/abs/2605.18950)
- [2]Related Source(https://ui.adsabs.harvard.edu/abs/2012A%26A...541A..97M)
- [3]Related Source(https://arxiv.org/abs/0706.0483)