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Iodine may be retained by certain condensing solids, such as sulfides. However, if the time elapsed between the last r-process production of radioiodine and the condensation of mineral grains was more than a few half-lives long, the iodine would have decayed to xenon. Because xenon does not condense to form minerals, the amount of radio genic 129Xe trapped in the grains can be used as a measure of the time gap between the end of nucleosynthesis and the formation of solid presolar grains. This...

Horizontal Structure and Atmospheric Circulation

The visual appearance of Jupiter has for three centuries provided a fascinating and puzzling stream of observations. Rapid and extensive changes often take place, with areas larger than Earth sometimes changing markedly in color and morphology in a few days. Day-to-day changes are often visible, even though the practical limit of resolution (1) corresponds to 3000 km on Jupiter at opposition and to 450 km at superior conjunction. Seasonal variations are not seen or expected, because of the very...

X B Joc2 Ic2Et

But we are neglecting E fields, and currents tend to be very small in the magnetosphere hence V x B 0. This is true if B is the gradient of some magnetic potential V B VV. This potential can generally be expressed as a spherical harmonic expansion of form where 90 - lmag is the colatitude (angle from the magnetic pole) and is the magnetic longitude. The Pnm (cos ) are the associated Legendre polynomials. For the simple and often useful case of a pure dipole field, V becomes independent of...

Energy Transport in the

In order to develop a steady-state model for the structure of the Sun, it is first necessary to examine the mechanisms by which heat may be transported from the site of nuclear reactions in the deep interior out to the radiating surface, the photosphere. Because of the obvious importance of radiation in the Sun, we shall first briefly consider radiative transport of energy. Following the nomenclature of Eq. (IV.6) and the accompanying definition of the mean free path, we have where the...

Geochemical Classification of the Elements

We have now discussed the main features of the equilibrium chemistry of 20 of the 23 most abundant elements in the Sun, plus the heavy rare gases krypton and xenon. If the principle of equal time were applied to the remainder of the periodic table, we would become obliged to convert this chapter into a book in its own right. Instead, we shall recognize that, because there is a periodic chart, there are certain important familial resemblances in chemical and geochemical behavior. To date we have...

Mass and Density of the Solar Nebula

We have seen from our discussion of the chemistry of solar material that the fraction of the total mass of a solar-composition gas that is rocky is very small, only about 0.4 of the total mass. About 98.2 of the mass is accounted for by the permanent gases, and 1.4 by ices. This means that the minimum mass of raw solar material required to make the terrestrial planets is about 100 0.4 times their present total mass, for a grand total of 500 Earth masses. This is more than the total mass of all...

Classification of Stars

Historically, stars were first classified solely on the basis of their apparent brightness, ignoring their easily observed color differences. However, we have seen that the spectral distribution of energy versus frequency Eq. (II. 9) or wavelength contains a maximum. Here BA is the radiation field intensity in ergcm 1 s 1 per centimeter of wavelength. Differentiating with respect to wavelength, we find that the maximum in B occurs where dBA dA 0 or 5(1 e hc kAm T ) - , (II.42) where Am is the...

Exercises The

111.1 The escape velocity from the photospheric ''surface'' of the Sun is 618 km s 1. At what temperature would a gas of hydrogen atoms have a mean thermal speed equal to the Sun's surface escape velocity 111.2 The vis viva equation (III.30) describes the variation of orbital velocity with distance from the central mass. Using the normal symbols for perihelion distance (q) and aphelion distance (Q), note that Figure III.2 tells us that q a(1 e) and Q a(1 + e). Also note that is proportional to...

Galaxy and Star Formation

Spiral Barred Galaxy

A relatively dense gas cloud may collapse if its own gravitational potential energy is greater than its internal thermal energy. This condition, known as Jeans' criterion, after its discoverer, the famous British astronomer Sir James Jeans, is given by where G is the universal constant of gravitation, is the mass of the cloud, rc is the critical unstable radius, and p is the density of the cloud. In effect, a molecule in a cloud larger than rc will have a thermal velocity that is too low for it...

Sodium and Potassium

Atomic sodium and potassium vapor, Na and K, remain in the gas phase until completion of the condensation of enstatite. At slightly lower temperatures it becomes possible for the alkali metal vapors to react with aluminum-bearing minerals to produce alkali alu-minosilicates. A simple conceptual example would be However, pure solid Al2O3 and SiO2 cannot coexist, and quartz is never a stable phase at equilibrium in a solarcomposition system. A better description of the process would be MgAl2O4...

Magnesium and Silicon

Traces of SiO and SiS gases can be found even at temperatures of 3000 to 4000 K. Near 2000 K the dominant gaseous species are Mg, SiO, SiS, and Si. At very high pressures SiH4 (silane) gas is also important. Condensation of these elements begins with the formation of solid forsterite, Mg2SiO4, near 1400 K, followed at most pressures by the formation of enstatite, MgSiO3, at only slightly lower temperatures. The major reactions are SiS + H2O SiO + h2s Si + H2O SiO + h2 SiO + Mg2SiO4(s)+ H2O...

P0 AP Pp0 Ap

Then K AP Ap (dP d p)p0, (V.121) where the constant K is the proportionality constant between AP and Ap. The position of a volume element of the medium before encountering the sound wave is x, and the displacement caused by the sound wave arriving at time t is X(x,t), so that the new position is x + X(x, t). A neighboring volume element, originally at x + Ax, will be displaced by the sound wave to a new position, x + Ax + X(x + Ax, t), at the same instant. The...

Visible and Infrared Radiative Transfer

The transmission, absorption, emission, and scattering behavior of light constitute the area of study called radiative transfer theory. Our purpose here shall be to draw together in a qualitative way the main ideas and phenomena subsumed under this name as they relate to planetary atmospheres. First, in the simplest case, we consider a gas interacting with light of a frequency far removed from the resonant frequencies of the gas, such as visible or infrared radiation in helium. The interaction...

The Major Planets

The outer Solar System presents an astoundingly diverse panorama. The four giant planets subdivide naturally into two classes, Jovian and Uranian. The Jovian planets, Jupiter and Saturn, which are not very far from the composition of the Sun or of other Population I stars, together have more than 100 times the combined masses of the terrestrial planets. The Uranian planets, Uranus and Neptune, are far denser than solar material and present strong but ambiguous evidence regarding large-scale...

O3

Temperature Dependence Stars Fusion

Where Xq is the mass fraction of carbon and the other symbols are as before. Note the dependence of the reaction rate on the 20.3 power of the temperature. This enormously strong dependence of rate on temperature means that the CC process will be negligible in rate compared with the pp rate at T6 15, but strongly dominant at T6 20. For Pop I stars, in which the carbon atomic abundance is about 10-3 of the hydrogen abundance, the two processes produce comparable amounts of energy for stars near...