The Proceedings of the Eighth International Conference on Creationism (2018)

orbital distances from the Sun of Jupiter and Saturn at the start of the Nice scenario is quite important. Saturn begins the Nice model at approximately 8.5 A.U., which places it just inside the 1:2 Jupiter-Saturn resonance. Saturn migrates outward and passes through the 1:2 resonance. In most simulations of the Nice model, Neptune begins the Nice scenario nearer to the Sun than Uranus. Neptune and Uranus have strong interactions with Saturn via resonance as well. Neptune and Uranus begin the Nice model in the distance range of 11 to 17 A.U. from the Sun. Neptune and Uranus migrate outward due resonances with Saturn and due to the influence of a massive belt of rocky objects in the region from about 15 to 35 A.U. from the Sun. Neptune and Uranus undergo a period of rapid migration outward and are believed to have likely exchanged positions multiple times until they came to a more stable configuration as they are now. Migration in the Nice model involves a limited outward migration of Saturn and outward migration of Uranus and Neptune. The migration is associated with changes in the orbital eccentricities of Saturn, Neptune, and Uranus as well. Though today Saturn’s orbital eccentricity is 0.052, the Nice model suggests it reached a maximum of 0.12. Though Neptune today has an orbital eccentricity of 0.004, the Nice model suggests it reached 0.04. These changes in eccentricity may not seem very significant but they are enough to have significant effects due to orbit resonances between the four outer planets. The higher eccentricities are believed to have eventually been reduced to the present values due to dynamical friction, as planetesimals are scattered by the planets. Though the Grand Tack scenario encompasses a period of approximately 600,000 years, the Nice scenario covers a period of approximately 100 million to 700 million years. Before the application of planet migration models, the formation of the four outer planets tended to have difficulty with the protosolar disk dissipating before the planets could reach their full present size (Spencer 1994, p. 517). Taylor (1992) summarizes the state of the research in 1992 as follows. “Other estimates for the times taken to form a 10-Earth-mass core are 700,000 years for Jupiter, 3.8 m.y. for Saturn, 8.4 m.y. for Uranus, and 23 m.y. for Neptune” (p. 16-17). Note that this is not the time for the planet to reach its full size and mass, but the time for a 10-Earth-mass core to form. If gas dissipated in the outer region of the disk in less than 8 million years, then Uranus and Neptune would not be likely to reach their present size. The disk has always been modeled as thicker and denser near the Sun and thinning with increasing distance. Thus models prior to orbit migration had the most difficulty reproducing the present masses of Uranus and Neptune. A more recent study estimated Jupiter could reach its full mass in a time from 1 to 5 million years (Hubickyj, Bodenheimer, and Lissauer 2005). In the Nice model the protoplanetary disk, consisting of planetesimals, is assumed to be more dense and more massive than in older models. Also, the four outer planets start forming nearer to the Sun and nearer to each other, which puts them in regions more dense than in older solar system models. Note that the initial orbital positions of the four outer planets are usually free parameters chosen at the start of the simulations, and various orbital starting positions have been modelled. Another issue addressed by the Nice model is the origin of the Trojan asteroids of Jupiter. A large number of asteroids exist near the L4 and L5 Lagrange Points of the Jupiter orbit. The L4 position is a 60° angle ahead of Jupiter along Jupiter’s orbit. The L5 position lies at 60° behind Jupiter along the orbit. The Jupiter Trojans (also sometimes called coorbitals) orbit near these two positions, generally oscillating around them. Any planet can have small bodies in or near the L4 and L5 positions. In recent years Trojan asteroids have been found sharing the orbits of Venus (de la Fuente Marcos and de la Fuente Marcos 2014), Earth (Connors, et. al. 2011), Mars (Connors, et. al. 2005), Uranus (Alexandersen, et. al. 2013), and Neptune (Guan, Zhou, and Li 2012). The total number of Jupiter Trojans has been estimated as on the order of 600,000, however this is an estimate, not actual known objects. Jupiter Trojans that have actually been observed are listed on the IAU Minor Planet Center website, with 6,521 objects as of 9/24/2017. The other planets in our solar system only have small numbers of known Trojan companions to date. The Trojan asteroids of Jupiter (and of Uranus and Neptune) are taken to be evidence in support of the Nice model. The Nice model presumes that when Jupiter formed in the protosolar disc, many small bodies formed in its vicinity and some small percentage of these objects were captured into the L4 and L5 regions. Various studies considered the effect of orbit migration of the outer planets on Trojan asteroids. Simulations show that some Trojan asteroids can survive the migration of their planet. This is especially true for Jupiter and Neptune. However, simulations starting Saturn with Trojan asteroids almost always lead to the loss of the Saturn Trojans. After the outward migration of Jupiter and Saturn in the Grand Tack, a new population of Trojan asteroids would be captured by Jupiter (Morbidelli, et. al. 2005). In the Nice model, most of Jupiter’s early collection of Trojan asteroids would have been lost during Jupiter’s migration. But because Saturn, Uranus, and Neptune are being caused to migrate by a large population of planetesimals scattering off them, it would be expected that temporary Trojan asteroids could exist. The Nice model assumes that there was a very massive belt of large planetesimals in the outer solar system. This region, sometimes now referred to as the transneptunian region, today has objects totaling only approximately one tenth of an Earth mass (Gladman, et. al. 2001). But in the Nice model this region is assumed to include a large population of objects totaling approximately 35 Earth masses (Gomes, et. al. 2005). As Saturn migrates outward in the Nice model, it eventually reaches a more stable orbit as it gets farther from the 2:1 resonance with Jupiter. Uranus and Neptune also get farther apart and the planetesimals eventually become depleted in the transneptunian region. Thus, the Trojans of Jupiter would have represented a changing population of temporary Trojans, until outer planet migration stopped. Then the Trojans left at the end of the migrations of Saturn, Uranus, and Neptune are the objects observed today. The Nice model also argues that the Late Heavy Bombardment (LHB) of impacts in the inner solar system could have been caused by the instability among planetesimals that was due to outer planet migration. This aspect of the Nice model is still being debated today. To connect outer planet migration to the LHB, it is argued that the time of when Saturn crossed the 2:1 resonance could have Spencer ◀ Origin of our solar system with planet migration ▶ 2018 ICC 76