Explaining the Formation of the Galilean Moons and Titan in the Grand Tack Scenario

The formation of the Galilean moons and Titan in the Grand Tack scenario

Authors:

Heller et al

Abstract:

In the "Grand Tack" (GT) scenario for the young solar system, Jupiter formed beyond 3.5 AU from the Sun and migrated as close as 1.5 AU until it encountered an orbital resonance with Saturn. Both planets then supposedly migrated outward for several 105 yr, with Jupiter ending up at ~5 AU. The initial conditions of the GT and the timing between Jupiter's migration and the formation of the Galilean satellites remain unexplored. We study the formation of Ganymede and Callisto, both of which consist of ~50% water and rock, respectively, in the GT scenario. We examine why they lack dense atmospheres, while Titan is surrounded by a thick nitrogen envelope. We model an axially symmetric circumplanetary disk (CPD) in hydrostatic equilibrium around Jupiter. The CPD is warmed by viscous heating, Jupiter's luminosity, accretional heating, and the Sun. The position of the water ice line in the CPD, which is crucial for the formation of massive moons, is computed at various solar distances. We assess the loss of Galilean atmospheres due to high-energy radiation from the young Sun. Ganymede and Callisto cannot have accreted their water during Jupiter's supposed GT, because its CPD (if still active) was too warm to host ices and much smaller than Ganymede's contemporary orbit. From a thermal perspective, the Galilean moons might have had significant atmospheres, but these would probably have been eroded during the GT in < 105 yr by solar XUV radiation. Jupiter and the Galilean moons formed beyond 4.5 (+/-0.5) AU and prior to the proposed GT. Thereafter, Jupiter's CPD would have been dry, and delayed accretion of planetesimals should have created water-rich Io and Europa. While Galilean atmospheres would have been lost during the GT, Titan would have formed after Saturn's own tack, because Saturn still accreted substantially for ~106 yr after its closest solar approach, ending up at about 7 AU.

Jupiters Grand Attack and Shaping of our Solar System in Light of Exoplanetary Systems (a seti talk)

One of the problems with his model and its predictions (as he discusses at the end) is that he states close in, tightly packed systems like Gliese 667C or the like, are going to be mutually exclusive of having gas giants in orbits in the outer system.  Yet, we know of several where there are close-in, tightly packed systems with gas giants or giant planets in the outer system, for example, HD 10180, HD 187123 or HD 125612 or the list goes on.  These contradict the predictions  of the Grand Track model based as he lays them out.

Minimally, his model ought to be taking into account these systems.  And should be reworked with the currently known exoplanetary systems in mind.

Describing Jupiter's Role in Shaping the Solar System According to Batygin and Laughlin 2015.

Jupiter’s role in sculpting the early Solar System

Author:

Naoz

Abstract:

Recent observations made by the Kepler space mission, combined with statistical analysis of existing ground and space-based data, have shown that planets somewhat bigger than the Earth—but substantially smaller than Jupiter—are extremely common in our Galaxy (1–4). These systems are typically found to be tightly packed, nearly coplanar, and have nearly circular orbits. Furthermore, these planets tend to have very short-period orbits, ranging from days to months. In contrast, our innermost planet, Mercury, orbits the Sun once every 88 d. Thus, taken at face value, these observations imply that the architecture of our Solar System is unique compared with the galactic population. In other words, why are there no short-period planets in our Solar System? In PNAS, Batygin and Laughlin (5) demonstrate that Jupiter is to blame. In particular, Jupiter’s inward-followed-by-outward migration during the Solar System’s early evolution could have driven a collisional cascade that would grind planetesimals to smaller size. Gas drag, which dominates these small planetesimals, may then have driven preexisting short-period planets into the Sun. Thus, Batygin and Laughlin (5) suggest that the terrestrial planets in our Solar System are in fact “second-generation planets,” which formed after the first short-period planets were destroyed, in mass-dispersed, gas-depleted conditions (see Fig. 1 for the description of the scenario). The developed model suggests that systems with short-period Earth and super-Earth planets are anticorrelated with the existence of giant planets within the same system.

Did Wandering Jupiter (Grand Track Scenario) Explain our Solar System's Architecture, Terrestrial Planets' 'Dryness?'

Jupiter’s decisive role in the inner Solar System’s early evolution

Authors:

Batygin et al

Abstract:

The statistics of extrasolar planetary systems indicate that the default mode of planet formation generates planets with orbital periods shorter than 100 days and masses substantially exceeding that of the Earth. When viewed in this context, the Solar System is unusual. Here, we present simulations which show that a popular formation scenario for Jupiter and Saturn, in which Jupiter migrates inward from a greater than 5 astronomical units (AU) to a ≈ 1.5 AU before reversing direction, can explain the low overall mass of the Solar System’s terrestrial planets, as well as the absence of planets with a less than 0.4 AU. Jupiter’s inward migration entrained s ≳ 10−100 km planetesimals into low-order mean motion resonances, shepherding and exciting their orbits. The resulting collisional cascade generated a planetesimal disk that, evolving under gas drag, would have driven any preexisting short-period planets into the Sun. In this scenario, the Solar System’s terrestrial planets formed from gas-starved mass-depleted debris that remained after the primary period of dynamical evolution.