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

(MMSN) were byWeidenschilling (1977) and Hayashi (1981). The protosolar disk theory in these early models has not been modified very significantly until very recent years. Some recent revisions of these disk models will be discussed below. The general concept is to derive a mathematical representation describing how the density of the disk would vary as a function of distance from the Sun. The density is determined by estimating a “feeding zone” in the vicinity of each planet based on their current positions. The planets are assumed to have accreted in their present locations with no migration in these disk models. These models also assume that all the solids in the vicinity of each planet accreted onto the planet. Hayashi (1981) indicates the initial mass of the protosolar disk is in the range of 0.01 – 0.04 times the mass of the Sun (p.114). Solar system origins theories from the 1980’s thought of planet formation of the inner and outer planets to be essentially concurrent but that the inner planets formed more slowly due to the higher temperatures at their orbital positions. However, today in the light of the new Grand Tack and Nice Models the gas giant planets in the outer solar system form first and the inner planets form later. Today the outer planets would be understood to reach most of their current mass within 10 million years but then continue to accrete material at a slower rate for perhaps 100 million years or more. The inner planets do not accrete large gas concentrations early but they grow by the oligarchic process described above from impacts of planetesimals and collisions with planetary embryos. Volatile elements and compounds in the inner planets, including water, are believed to be delivered to the growing inner planets primarily from planetesimal impacts. The “end” of planet formation is generally taken to be the end of the Late Heavy Bombardment and the proposed impact that is thought to have formed our Moon. The timing of the Moon-forming impact is debated but it is taken as sometime from approximately 30 to 120 million years after the beginning of the formation of Earth. Today the research on extrasolar planets has convinced many scientists that our solar system could have lost planets and that the current planets may not be in the same orbits in which they formed. There have been some observations of so-called “rogue” or “free-floating” exoplanets using infrared telescopes (Liu, 2013) or gravitational microlensing (Clanton and Gaudi, 2016). There are some uncertainties regarding these objects and there is some on-going debate over whether they should be viewed as planets or as small dwarf stars. The apparent existence of planets separated from their stars has led to planetary scientists proposing that the planet formation process can involve planet orbit migration and planet-planet scattering events that can sometimes eject planets away from their stars. Simulations do sometimes show planets being ejected. Thus, planet formation is viewed as a process in which some planets survive and some do not. 3. Planetary Migration Planet orbit migration is now a well-accepted process that is thought to have happened in many extrasolar planetary systems as well as in our own solar system. Today extrasolar planets are detected by radial velocity redshift measurements, by transits of their star, by direct infrared imaging, and by other methods (Spencer, 2011, 2017). Planetary migration is a theoretical concept that is thought to explain the origin of planetary systems. In many observed extrasolar planetary systems there are planets quite close to the star, which places them at temperatures where it would be impossible for gases to condense. Thus, it was proposed that these “hot Jupiter” planets actually formed farther from the star where temperatures would allow gases to condense onto the planet, then as the planet formed or perhaps later from other events, it migrated inward toward the star. Note that this migration is assumed, not observed. To date, no researchers have claimed to have direct observational evidence of migrating exoplanets. Not all extrasolar planets are “hot Jupiters” near their star. Extrasolar planetary systems are known to have a variety of orbital configurations. It is understood that planet migration can be either inward or outward depending on the conditions in the system being studied. Planet migration theories have been developed through many theoretical studies. Planet migration is believed to have multiple possible physical mechanisms which can be theoretically compared considering their causes: • Caused by the disk of gas and dust (migration Types I, II, or III) • Caused by solid planetesimals in the system • Caused by planet-planet gravitational interactions and orbit resonances Migration caused by the protosolar disk involves an interaction between the disk and a forming planet. This encompasses at least three modes of migration referred to in the scientific literature as Types I, II, and III. These three migration modes have been applied in models of our solar system. There are certain prerequisites to these migration processes to be possible. First, these modes of migration all require a planet to be of at least several Earth masses while gases have not dissipated in the disk. The distance scales where the models are applicable depends on the star and the characteristics of the disk. Torques are produced on the planetary embryo by gases that stream past it moving near the planet. Gases just inside or just outside the planet’s orbital position enter what are known as Lindblad resonances with the orbiting planet that lead to a tidal interaction with the planet. Streamlines of gas can come to follow what are called horseshoe streamlines that exert a torque tangential to the orbit of the planet. These modes of migration are distinguished by the relative mass of the planet in comparison to the mass of the disk, and the rate of orbit migration. In Type I migration the disk is massive and dense enough that the presence of the planet has little effect on the distribution of gas. Thus, Type I migration tends to be more applicable in earlier stages when the disk has not dissipated and the planet is well below its final mass. In Type II migration the planet is larger and the disk material is significantly affected by the presence of the planet. Normally this means that a gap forms in the disk in the vicinity of the planet’s orbit. The planet clears away a zone on either side but a density wave forms in the disk such that a stream of gas forms that passes by the planet. Type II migration can be considered a slow gradual type of change in the orbit. Type I migration is more rapid than Type II. It is believed that a planetary system can undergo a transition from Type I to Type II as a planet grows and as the disk changes. This transition can be important for explaining how the migration process can stop and allow the planet or planets to not spiral into the star. Type III migration is another mode that is sometimes described as “runaway” migration. Spencer ◀ Origin of our solar system with planet migration ▶ 2018 ICC 73