Jupiter formation

Jin and Copper, 2000, GSC 117847, dorsal and lateral views, upper Goeland Member, Jupiter Formation (16,17) Stricklandia planirostrata Jin and Copper, 2000, GSC 59182, dorsal and lateral views, Ferrum Member, Jupiter Formation (18,19) Stricklandia lens (Sowerby, 1839), GSC I 17872, normal and oblique views of dorsal interior, Merrimack Formation (20) Stricklandia gwelani jin and Copper, 2000, GSC 117834, acetate peel section of spondylium, 4.4 mm from apex. Scale bar= I cm except for Fig. 19.2(20). 

Figure 19.3 Morphology of dorsal adductor muscle fields in stricklandiid brachiopods. (A) Sttickhndia gwelani, GSC 85097, upper Gun River Formation (B) Ehlersella davidsonii (Billings, 1868), GSC 117853, Ferrum Member, Jupiter Formation (C) Microcardinalia (Chiastodoca) saherii (Billings, 1868), GSC 59198, Ferrum Member, Jupiter Formation. Scale bar = 2 mm.

Irradiation of ethyleneimine (341,342) with light of short wavelength ia the gas phase has been carried out direcdy and with sensitization (343—349). Photolysis products found were hydrogen, nitrogen, ethylene, ammonium, saturated hydrocarbons (methane, ethane, propane, / -butane), and the dimer of the ethyleneimino radical. The nature and the amount of the reaction products is highly dependent on the conditions used. For example, the photoproducts identified ia a fast flow photoreactor iacluded hydrocyanic acid and acetonitrile (345), ia addition to those found ia a steady state system. The reaction of hydrogen radicals with ethyleneimine results ia the formation of hydrocyanic acid ia addition to methane (350). Important processes ia the photolysis of ethyleneimine are nitrene extmsion and homolysis of the N—H bond, as suggested and simulated by ab initio SCF calculations (351). The occurrence of ethyleneimine as an iatermediate ia the photolytic formation of hydrocyanic acid from acetylene and ammonia ia the atmosphere of the planet Jupiter has been postulated (352), but is disputed (353). 

The giant planets possess low surface temperatures and have atmospheres that extend several thousand miles. The markings on Jupiter, the largest planet, consist of cloud formations composed of methane containing a small amount of ammonia. The atmosphere of Jupiter absorbs the extreme red and infrared portions of the spectrum. These absorptions correspond to the absorption spectra of ammonia and methane, suggesting the presence of these gases in Jupiter s... 

Fig. 1. Evolution of 3He/H in the solar neighborhood, computed without extra-mixing (upper curve) and with extra-mixing in 90% or 100% of stars M < 2.5 M (lower curves). The two arrows indicate the present epoch (assuming a Galactic age of 13.7 Gyr) and the time of formation of the solar system 4.55 Gyr ago. Symbols and errorbars show the 3He/H value measured in meteorites (empty squares) Jupiter s atmosphere (errorbar) the local ionized ISM (filled triangle) the local neutral ISM (filled circle) the sample of simple Hll regions (empty circles). Data points have been slightly displaced for clarity. The He isotopic ratios has been converted into abundances relative to hydrogen assuming a universal ratio He/H= 0.1. See text for references.

The formation of the planets around the proto-sun initially started as a simple accretion process, aggregating small particles to form larger particles. This process was common to all planets, even the gas giants Jupiter and Saturn and to a lesser extent Neptune and Uranus. The planetesimals form at different rates and as soon as Jupiter and Saturn had reached a critical mass they were able to trap large amounts of hydrogen and helium from the solar nebula. The centres of Jupiter... 

A new reservoir of comets may have formed at around 5 AU in a local orbit around Jupiter or at least perturbed by its gravitational attraction. A comet close to Jupiter would simply have been captured, delivering its chemical payload to the ever-increasing gas giant. Some comets would merely have been deflected towards the inner terrestrial planets, delivering a similar payload of water and processed molecules. Cometary impacts such as the spectacular collision of the comet Shoemaker-Levy 9 with Jupiter would have been common in the early formation phase of the solar system but with a much greater collision rate. Calculations of the expected collision rate between the Earth and potential small comets deflected from the snow line may have been sufficient to provide the Earth with its entire... 

The short-orbit comet 67P has been influenced by two close encounters with the gravitational field of Jupiter in the same way as comets in the snow line may have been deflected during the formation of the Earth. Prior to 1840 its perihelion distance was 4.0 AU when the Jovian encounter reduced it to 3.0 AU or 450 million kilometres. It decreased steadily until a further brush with the Jovian gravitational field in 1959 knocked its perihelion distance to 1.29 AU, which is its present-day value. The properties of the comet are summarised in Table 6.5. 

It is tempting to take a tour of the solar system, stopping off at each planet to look at the chemistry from the origin of the red colour in Jupiter s great red spot to the volcanic activity of Io, but this would be another book for each planet. Instead, we will generalise the study to the formation of Earth-like planets in order to focus on the possibilities for life. 

The next most likely possibility is cometary delivery of the atmosphere but again there are some problems with the isotope ratios, this time with D/H. The cometary D/H ratios measured in methane from Halley are 31 3 x 10-5 and 29 10 x 10-5 in Hayuatake and 33 8 x 10-5 in Hale-Bopp, whereas methane measurements from Earth of the Titan atmosphere suggest a methane D/H ratio of 10 5 x 10-5, which is considerably smaller than the ratio in the comets. The methane at least in Titan s atmosphere is not exclusively from cometary sources. Degassing of the rocks from which Titan was formed could be a useful source of methane, especially as the subnebula temperature around Saturn (100 K) is somewhat cooler than that around Jupiter. This would allow volatiles to be more easily trapped on Titan and contribute to the formation of a denser atmosphere. This mechanism would, however, apply to all of Saturn s moons equally and this is not the case. 

Polymerisation of HCN species is also possible once the initial monomers have been formed by the reactions with nitrogen HCN polymers have been postulated in many places in the solar system, from the clouds of Jupiter and Saturn to the dark colour of the surface of comet Halley, not to mention its possible role in the formation of the prebiotic molecule adenine. Photolysis of HCN produces CN and then the formation of nitrile polymers ... 

The dissociation reaction predicted by Umemoto et al. s calculations has important implications for creating good models of planetary formation. At the simplest level, it gives new information about what materials exist inside large planets. The calculations predict, for example, that the center of Uranus or Neptune can contain MgSiC>3, but that the cores of Jupiter or Saturn will not. At a more detailed level, the thermodynamic properties of the materials can be used to model phenomena such as convection inside planets. Umemoto et al. speculated that the dissociation reaction above might severely limit convection inside dense-Satum, a Saturn-like planet that has been discovered outside the solar system with a mass of 67 Earth masses. 

Chemically, the methylene imino radical (H2CN) is of interest, e.g., by its importance as a chemical intermediate in some ballistic propellants and in the formation of HCN in the clouds of Jupiter. A discussion of recent theoretical... 

Planet formation unfolds differently beyond the snowline, where water condensation enhances the surface density. Here massive cores (> 5-10 MEarth) may form rapid enough to accrete directly and retain nebular gas. These massive cores, if formed prior to the dispersal of the gas disk, rapidly reach Jupiter masses, forming giant planets. An alternative mechanism that may be responsible for the formation of some giant planets is gravitational instability in a massive, marginally unstable disk (e.g. Boss 2007 Mayer etal. 2007). 

The initial mass and lifetime of gas in circumstellar disks affect both the formation of giant planets as well as the formation of terrestrial planets. According to the widely accepted scenario of giant-planet formation, rocky cores need to reach several M before being able to accumulate a substantial amount of gas from the protoplanetary disk. Current models require from a few to 10 million years to form Jupiter-like planets at 5AU (see e.g. Lissauer Stevenson 2007), meaning that primordial... 

Planet formation followed the planetesimal and protoplanet formation in the final stage of the disk evolution (Chapter 10). Gas giants, Jupiter and Saturn, captured disk gas due to their large gravities, and other planets, including Earth, may also have some evidence of disk-gas capture. In the second part of this section, we will seek constraints on the timing of dust and gas dispersal in the proto-solar disk from planets (Section 9.3.2). 

Studies of the gas content of protoplanetary disks with ages between 1 and 30 Myr are necessary to determine how rapidly the gas disperses and make a more direct comparison to the evolution and dispersal of dust in disks. As we discussed in Section 9.1.2, the dispersal of gaseous disks also provides an upper limit for the formation time of giant planets that can be compared to the time necessary to form Jupiter and Saturn in our Solar System. From a Solar System perspective it is interesting to expand on the constraints placed on the gas dispersal from the age determination of meteorites with implantation of solar wind, which provide us a... 

The giant planets, especially Jupiter and Saturn, significantly influenced accretion in the inner Solar System, with important consequences for the properties of the terrestrial planets, described in Section 10.4.1. The influence of the giant planets is especially strong in the Asteroid Belt. Given that meteorites are our primary samples of primitive Solar System material, understanding the role of dynamical and collisional processes in the formation and evolution of the Asteroid Belt is of fundamental importance for theories of planet formation (Section 10.4.2). 

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