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

first according to Genesis, followed by other objects. This is a counter-intuitive process in Genesis that makes mankind the focus of God’s creative activity. 2. Limitations of the Computer Models The Grand Tack and Nice models are based entirely on computer simulations that are constructed to attempt to show how a planetary system like our own could arise by natural physical processes. These models are built on a number of assumptions that determine a specific sequence of processes. Though real physics is put into the computer programs used, these models have been arrived at through much trial and error, varying the initial conditions and parameters input into the simulations. Many observations about our own solar system as well as extrasolar planetary systems have been in view in the development of these new migration theories. The Grand Tack and Nice models therefore do not predict characteristics of our solar system, rather they attempt to adapt to the observed characteristics of the solar system. These models assume a specific history of our solar system. This history cannot be verified by observations. But scientists who are advocating these new theories would say that this new paradigm incorporating planet migration is more successful than other approaches used in the past. Computer simulations of planet formation itself begin assuming that planetesimals and planetary embryos already exist. Yet the formation of these solid objects has not been explained. The planetesimals are often assumed to be 1 km in diameter and sometimes are assumed to be as large as 10 km diameter at the start of the simulation. Planet embryos are assumed to be of a variety of sizes, generally ranging from approximately the mass of our Moon to the mass of Mars. It is usually assumed that there are many more planetesimals than embryos. Fragmentation of solid objects in collisions is usually ignored in the simulations. All collisions with a planetary embryo (both planetesimal to embryo and embryo to embryo) are assumed to result in a merging of the two objects onto the embryo. This is thought to be a valid approximation considering that the mass of the embryos is much greater than the mass of the planetesimals. The author would question this assumption. It is interesting to note that the proposed origin of our Moon by an impact involves a case where a planetary embryo collides with Earth and does not completely merge with the Earth. Then the ejecta reforms into our Moon. This type of impact scenario is not considered as a general case across the solar system in the Grand Tack or Nice simulations, though this theory for the formation of our Moon is widely accepted. The computer simulations make many simplifying assumptions regarding what happens in a disk which consists of a mixture of gas, dust, and larger solid objects. When simulations examine the migration of planets in a gaseous disk, accretion of gas onto the planet at the same time is usually neglected. Accretion of the planet during this process could change what happens in the migration. Raymond and Morbidelli (2014) mentioned this limitation, “Hydrodynamical simulations of planet migration do not have the requisite resolution to realistically include gas accretion, yet these two are intimately coupled in the Grand Tack model. This is a key uncertainty for the Grand Tack; it is unclear whether long-term outward migration of Jupiter and Saturn is possible given the stringent mass ratio requirement”(p.197). The mass ratio requirement here refers to the ratio of the mass of Jupiter to the mass of Saturn. Simulations consistently show that this mass ratio has a major effect on the migration of Jupiter and Saturn. This suggests many outcomes would be possible, if the masses of Jupiter and Saturn had been sufficiently different. Several aspects of the Grand Tack and Nice models seem to require special timing in order for the desired result to be obtained in the end of the simulations. One ongoing question regarding timing is around the question of when did Jupiter form in the protoplanetary disk? Jupiter must reach nearly it’s full mass before the inward migration of Jupiter begins in the Grand Tack. This becomes important because the gas in the disk is required to remain available until Jupiter and Saturn have completed their outward migration in the Grand Tack. Thus, the gas in the disk must last long enough for Jupiter and Saturn to migrate through it twice. This tends to necessitate Jupiter’s formation being rather rapid. If the gas in the disk dissipated too quickly, Jupiter and Saturn might not migrate outward far enough. Not only would this lead to different orbits for the outer planets, it could affect the orbits of Earth and Mars due to their proximity to Jupiter and it could prevent the Nice scenario from occurring. Other issues of timing could affect the Nice model. The resonance between Jupiter and Saturn during their outward migration in the Grand Tack is assumed to be a 2:3 resonance. But the start of the Nice model is usually implemented with Jupiter and Saturn crossing their 1:2 resonance. It is not clear how the transition between these two resonances would take place. In the Grand Tack, Jupiter and Saturn clear objects out of the asteroid belt as they migrate inward. Then as they migrate back out again, they scatter planetesimals outward. The outward migration in the Nice model depends on the availability of planetesimals in the outer disk. The outer part of the disk is assumed to start with a large mass of planetesimals, on the order of 20 to 35 Earth masses in planetesimals. In the Nice model, resonances between Saturn, Uranus, and Neptune can lead to many outcomes for the final state of the planets. Simulations have shown that if the initial positions of the outer planets are closer together this tends to make their influence on each other via resonance greater and migration is more rapid. But if they are farther apart at the start then they migrate less because they reach stability sooner. Multiple resonances such as this are imposed on the simulations as starting conditions or by varying the disk properties. In a forming planetary system these resonances may or may not occur. Furthermore, the simulations presuppose resonances that do not actually exist among the real planets in our solar system. Another question of timing regarding the Nice model is a point of ongoing debate, the cause of the Late Heavy Bombardment of impacts in the inner solar system. One of the extensions to the Nice model is to modify the parameters of the simulation to delay when Saturn crosses the 1:2 resonance with Jupiter. This makes Neptune reach the inner edge of the outer planetesimal belt at a later time so as to be able to cause the Late Heavy Bombardment (LHB) impacts. In the original Nice model Neptune would reach the inner edge of the planetesimal disk at approximately 100 MY after the start of the Nice migration. Later modifications to the model push this time to approximately 700 MY after the start of Spencer ◀ Origin of our solar system with planet migration ▶ 2018 ICC 78