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

terrestrial planets. By the time Jupiter migrates in to approximately 1.5 A.U., Saturn has migrated to a position near Jupiter and the two planets enter a 2:3 orbit resonance. In simulations entering this resonance changes the torques on Jupiter and causes Jupiter and Saturn to begin migrating outward. This reversing of the migration depends mainly on two conditions, a) the mass ratio of Jupiter to Saturn must be in the range of from 2 to 4 and b) the two gaps in the annular disk opened up by Jupiter and Saturn must overlap (Raymond and Morbidelli, 2014). The mass of Saturn determines much about how the inward migration occurs. If Saturn’s mass is too large, it will migrate inward too rapidly and then it will not have an adequate braking action on Jupiter. If Saturn’s mass is too small, it will migrate slower but it may not catch up with Jupiter and it may not be massive enough to stop Jupiter’s inward migration. Thus, if Saturn’s mass is either too large or too small, both Jupiter and Saturn would be likely to spiral into the Sun. After Jupiter and Saturn enter the 2:3 resonance they migrate outward essentially until the gas is largely dissipated from the disk. At the end of the Grand Tack Jupiter is slightly outside its current orbital position and Saturn, Uranus, and Neptune are well inside their current actual orbits (see Table 1). This configuration at the end is an intended result of the model in order to make it consistent with the Nice model scenario. Table 1. The approximate orbital positions of the four outer planets at the end of the Grand Tack and Nice scenarios, compared to the current semi-major axis positions of the same planets. The Grand Tack ends after 600,000 years has elapsed in the simulations. Positions at the end of the Nice model migration are after up to 700 million years has elapsed. Variations on these numbers are possible from the simulations of various researchers. PLANET CURRENT POSITION (A.U.) END OF GRAND TACK (A.U.) END OF NICE (A.U.) Earth 1.00 1.00 1.00 Mars 1.52 1.52 1.52 Jupiter 5.20 5.4 5.2 Saturn 9.58 7.1 8.8 Uranus 19.3 9.8 19.0 Neptune 30.2 12.8 26.0 In the Grand Tack, the region near the Sun is a densely packed zone where the terrestrial planets form over a period of up to 150 million years. In this near-Sun zone some planet embryos which may have formed early before Jupiter’s inward migration could be destroyed. Thus, the terrestrial rocky planets do not really have opportunity to form until Jupiter begins its outward migration phase. The terrestrial planets grow by oligarchic growth. This is where the planet embryos are of much larger mass than the surrounding planetesimals. The planetesimals are drawn to the embryos by gravity and are also swept up by the embryos in their orbits. Embryos also undergo collisions with each other. Simulations typically assume that every collision with a planet embryo results in the merging of the objects, regardless of whether the “impactor” is another embryo or a planetesimal. In the early solar system while Saturn is still growing the “snow line” would be located at approximately 3 A.U. from the Sun. Today this point would be at approximately 5 A.U. distance from the Sun. This is the distance at which water ice could exist at an equilibrium temperature below freezing and not evaporate. When Jupiter migrates in to 1.5 A.U. it pulls planetesimals from the region beyond the snow line inward. Jupiter will also scatter planetesimals that formed in the near-Sun region outward. So, an important effect of Jupiter’s inward and outward migrations is to mix small bodies in the solar system. The current asteroid belt, located roughly from 2 to 3.5 A.U. is understood as having formed after Jupiter’s outward migration. Though planetesimals (or asteroids) could have formed early before Jupiter’s inward migration, those objects would have been scattered as a result of Jupiter and Saturn’s migration episodes. The current asteroid belt has several characteristics that are difficult to explain in traditional no-migration models of the formation of the solar system. First, the asteroids have a range of orbit eccentricities and orbit inclinations that are unlike those of the planet orbits. Though many known asteroid orbits have eccentricities of roughly 0.2 or less, some go as high as 0.4 or more. Orbit inclinations of most of the asteroids are 20 degrees or less but some have orbits inclined up to 42 degrees in angle (Lewis, 2004, p. 70). The scattering associated with the migrations of Jupiter and Saturn are taken as supporting the Grand Tack because the planetesimals would be scattered into a variety of orbits. Secondly, the asteroid belt is somewhat “zoned by composition” and this is taken as support for the Grand Tack model as well (Walsh, et. al., 2012, pp.1943-1944). For example, of the various spectral classes of asteroids, Class S, consisting of metals and minerals such as olivine and pyroxene is most prevalent at a distance of about 2.5 A.U. But Class P asteroids have spectra indicating carbon and various organics and are most abundant at about 4 A.U. (Lewis, 2004, p.401). The Class S and Class P asteroids are both spread over a wide region but their regions overlap only slightly. Other classes of asteroids have their own characteristics and regions as well. Thirdly, the asteroid orbits strongly cluster around a number of orbit resonances with Jupiter. This is also taken as support for the Grand Tack, since Jupiter’s migration is thought to be a natural explanation of this. 2. The Nice Model The Nicemodel begins after the end of the GrandTack and addresses several aspects of the outer solar system. Traditional solar system theories without planet orbit migration have had some difficulties addressing certain questions that are addressed in the Nice model. The Nice model addresses the following: 1) how the outer planets came to their present orbits, 2) how the Trojan asteroids in the outer solar system came into their orbital configurations, and 3) The Nice model also suggests that the migration of the outer planets caused an instability among small bodies that caused the Late Heavy Bombardment, generating many impacts throughout the solar system. To understand how the Nice model addresses the above issues, we must consider the scenario it proposes. The Nice model begins with Jupiter located at approximately 5.45 A.U. from the Sun (slightly outside its current position). The four outer planets, Jupiter, Saturn, Uranus, and Neptune begin the Nice scenario much nearer to each other than their current orbital configurations. The Spencer ◀ Origin of our solar system with planet migration ▶ 2018 ICC 75