Hot-Jupiter core mass from Roche lobe overflow

• Published in: Monthly notices of the Royal Astronomical Society Vol. 469; no. 1; pp. 278 - 285
• Main Authors: Ginzburg, Sivan, Sari, Re'em
• Format: Journal Article
• Language: English
• Published: Oxford University Press 01.07.2017
• Subjects: planets and satellites: gaseous planets; planets and satellites: composition; planet–star interactions
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stx832

Abstract The orbits of many observed hot Jupiters are decaying rapidly due to tidal interaction, eventually reaching the Roche limit. We analytically study the ensuing coupled mass-loss and orbital evolution during the Roche lobe overflow and find two possible scenarios. Planets with light cores Mc ≲ 6 M⊕ (assuming a nominal tidal dissipation factor Q ∼ 106 for the host star) are transformed into Neptune-mass gas planets, orbiting at a separation (relative to the stellar radius) a/R⋆ ≈ 3.5. Planets with heavier cores Mc ≳ 6 M⊕ plunge rapidly until they are destroyed at the stellar surface. Remnant gas Neptunes, which are stable to photoevaporation, are absent from the observations despite their unique transit radius (5–10 R⊕). This result suggests that Mc ≳ 6 M⊕, providing a useful constraint on the poorly known core mass that may distinguish between different formation theories of gas giants. Alternatively, if one assumes a prior of Mc ≈ 6 M⊕ from the core-accretion theory, our results suggest that Q does not lie in the range 106 ≲ Q ≲ 107.