Terrestrial planet formation in low eccentricity warm-Jupiter systems

📝 Abstract

We examine the effect of giant planet migration on the formation of inner terrestrial planet systems. We consider situations in which the giant planet halts migration at semi-major axes in the range 0.13 - 1.7 AU due to gas disk dispersal. An N-body code is employed that is linked to a viscous gas disk algorithm capable of simulating: gas loss via accretion onto the central star and photoevaporation; gap formation by the giant planet; type II migration of the giant; optional type I migration of protoplanets; gas drag on planetesimals. We find that most of the inner system planetary building blocks survive the passage of the giant planet, either by being shepherded inward or scattered into exterior orbits. Systems of one or more hot-Earths are predicted to form and remain interior to the giant planet, especially if type II migration has been limited, or where type I migration has affected protoplanetary dynamics. Habitable planets in low eccentricity warm-Jupiter systems appear possible if the giant planet makes a limited incursion into the outer regions of the habitable zone (HZ), or traverses its entire width and ceases migrating at a radial distance of less than half that of the HZ’s inner edge. We conclude that Type II migration does not prevent terrestrial planet formation.

💡 Analysis

We examine the effect of giant planet migration on the formation of inner terrestrial planet systems. We consider situations in which the giant planet halts migration at semi-major axes in the range 0.13 - 1.7 AU due to gas disk dispersal. An N-body code is employed that is linked to a viscous gas disk algorithm capable of simulating: gas loss via accretion onto the central star and photoevaporation; gap formation by the giant planet; type II migration of the giant; optional type I migration of protoplanets; gas drag on planetesimals. We find that most of the inner system planetary building blocks survive the passage of the giant planet, either by being shepherded inward or scattered into exterior orbits. Systems of one or more hot-Earths are predicted to form and remain interior to the giant planet, especially if type II migration has been limited, or where type I migration has affected protoplanetary dynamics. Habitable planets in low eccentricity warm-Jupiter systems appear possible if the giant planet makes a limited incursion into the outer regions of the habitable zone (HZ), or traverses its entire width and ceases migrating at a radial distance of less than half that of the HZ’s inner edge. We conclude that Type II migration does not prevent terrestrial planet formation.

📄 Content

arXiv:0902.0052v1 [astro-ph.EP] 31 Jan 2009 Astronomy & Astrophysics manuscript no. fogg11305aph c⃝ESO 2018 October 24, 2018 Terrestrial planet formation in low eccentricity warm–Jupiter systems. Martyn J. Fogg & Richard P. Nelson. Astronomy Unit, Queen Mary, University of London, Mile End Road, London E1 4NS. e-mail: M.J.Fogg@qmul.ac.uk, R.P.Nelson@qmul.ac.uk Received/Accepted ABSTRACT Context. Extrasolar giant planets are found to orbit their host stars with a broad range of semi-major axes 0.02 ≤a ≤6 AU. Current theories suggest that giant planets orbiting at distances between ≃0.02 – 2 AU probably formed at larger distances and migrated to their current locations via type II migration, disturbing any inner system of forming terrestrial planets along the way. Migration probably halts because of fortuitously-timed gas disk dispersal. Aims. The aim of this paper is to examine the effect of giant planet migration on the formation of inner terrestrial planet systems. We consider situations in which the giant planet halts migration at semi-major axes in the range 0.13 – 1.7 AU due to gas disk dispersal, and examine the effect of including or neglecting type I migration forces on the forming terrestrial system. Methods. We employ an N-body code that is linked to a viscous gas disk algorithm capable of simulating: gas loss via accretion onto the central star and photoevaporation; gap formation by the giant planet; type II migration of the giant; optional type I migration of protoplanets; gas drag on planetesimals. Results. Most of the inner system planetary building blocks survive the passage of the giant planet, either by being shepherded inward or scattered into exterior orbits. Systems of one or more hot-Earths are predicted to form and remain interior to the giant planet, especially if type II migration has been limited, or where type I migration has affected protoplanetary dynamics. Habitable planets in low eccentricity warm- Jupiter systems appear possible if the giant planet makes a limited incursion into the outer regions of the habitable zone (HZ), or traverses its entire width and ceases migrating at a radial distance of less than half that of the HZ’s inner edge. Conclusions. Type II migration does not prevent terrestrial planet formation. There exists a wide variety of planetary system architectures that can potentially host habitable planets. Key words. planets and satellites: formation – methods: N-body simulations – astrobiology

1. Introduction. Giant planets are thought to form in the cool, outer, regions of a protoplanetary disk (e.g. Pollack et al. 1996; Papaloizou & Nelson 2005; Boss 2000), in roughly the region where Jupiter and Saturn are found in our solar system. However, numerous giant exoplanets have been found orbiting solar-type stars well inside the approximate position of their nebular snowline with semi-major axes from ∼3 AU down to just a few stellar radii (Butler et al. 2006). The most extreme examples of these are the so-called ’hot-Jupiters’, orbiting within 0.1 AU and account- ing for about a quarter of the known giant exoplanet inventory. Planetary migration may provide the best explanation for the presence of the hot-Jupiter population, in particular type II mi- gration, where the giant planet has grown massive enough to open a gap in its protoplanetary disk and migrates inward in step with the disk’s viscous evolution (e.g. Lin & Papaloizou 1986; Lin et al. 1996; Ward 1997; Nelson et al. 2000). Giant ex- oplanets at intermediate distances, where eccentricities can be high, might be explained by mutual scattering of giant planets (e.g. Lin & Ida 1997; Ford et al. 2001; Papaloizou & Terquem 2001; Marzari & Weidenschilling 2002), a combination of mi- gration and scattering (Adams & Laughlin 2003; Moorhead & Adams 2005), or migration along with eccentricity excitation from the disk (Papaloizou et al. 2001; Goldreich & Sari 2003; Ogilvie & Lubow 2003; Moorhead & Adams 2008). In the case of migrating planets, the mechanism that ter- minates the migration and strands exoplanets at their present orbital radii is unknown. Migration-halting mechanisms that might work when the planet ventures close to the central star include tidally-induced recession caused by the star’s rotation or Roche lobe overflow and mass loss to the star (Trilling et al. 1998), or intrusion by the planet into a central cavity or surface density transition in the disk, decoupling it from the evolution of the gas (Lin et al. 1996; Kuchner & Lecar 2002; Masset et al. 2006; Papaloizou 2007). Halting migration further out, beyond the ≲0.1 AU hot-Jupiter region, may require that gi- ant planets form late in the lifetime of the gas disk and hence only have time for a partial inward migration before stranding 2 M.J. Fogg & R.P. Nelson: Terrestrial planet formation in warm–Jupiter systems at an intermediate distance when the gas is lost (Trilling et al. 1998). Disks around T Tauri stars are observed to last for ∼1 – 10 M

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