Formation of exoplanetary satellites by pull-down capture

Area of Science:

• Exoplanetary science
• Planetary formation and evolution
• Astrophysics

Background:

• The exomoon candidate Kepler-1625b-i presents a formation challenge due to its large size and wide orbit.
• Traditional satellite formation theories struggle to account for these observed properties.

Purpose of the Study:

• To propose and validate a novel formation mechanism for the exomoon Kepler-1625b-i.
• To explain the unusual characteristics of Kepler-1625b-i within a new theoretical framework.

Main Methods:

• Numerical integrations were performed to simulate the proposed formation scenario.
• The stability of the initial co-orbital configuration and the subsequent capture process were analyzed.

Main Results:

• The study demonstrates that Kepler-1625b-i could have formed as a co-orbital body with the giant planet Kepler-1625b.
• A process termed "pull-down capture" during giant planet gas envelope accretion successfully reproduces the exomoon's observed properties.
• The exomoon is modeled as the protocore of a gas giant that failed to accrete a substantial envelope.

Conclusions:

• The "pull-down capture" model provides a viable explanation for the formation of large exomoons like Kepler-1625b-i.
• The findings suggest that giant planets might harbor Trojan-like companions, warranting further observational searches.