The Unique Compositional Characteristics of the Solar System

How did the elements constituting the planets and the Sun originate? Did the planets originate from the Sun or the Sun and the planets had a common parentage and a simultaneous origin. This kind of the possible origin of the Solar System is referred to as the ‘nebular hypothesis’, initially conceived towards the end of the 18th Century, and later contributed to by many astrophysicists and geochemists (Hoyle, 1946, 1950; Urey, 1952). Hoyle (1946) was perhaps the first to observe that the composition of the terrestrial planets was far too dense compared to the Sun to have supplied it all. As such, he proposed that the Sun once had a companion star that underwent a supernova explosion, giving rise to the planetary nebulae which were caught in the Sun’s gravitational field to ultimately condense first as planetsimals and then coalescing as planets.
During the latter two centuries, the thoughts, arguments, observations, and calculations put forward by several scientists representing different disciplines, but devoted to the Earth and planetary sciences, have enabled substantial progress in modeling the events that should have preceded the formation of the Earth, as a member of the Solar System (Berlage, 1968).
The basic premise for the nebular hypothesis is that the compositions of planets inherited the pattern of compositions that are achieved in stellar interiors. The massive stars in the sky support proton-proton fusion reactions, referred to as the nucleosynthesis, continuously manufacture the chemical elements. It is the most widely accepted model interconnecting the composition of the solar system with the stellar compositions. It simultaneously explains the planetary compositions and densities, planetary distances and orbits, and the origin and evolution of the entire Solar System. The supernova explosion that expelled a large parental nebula that condensed to form the Sun (star (Sun) and its planets, the moons, the asteroids, comets and the interplanetary dust should have preceded about a couple of billion years prior to the calculated age of the Earth (4.5 b.y.). The Solar System is estimated to have appeared about 8–12 b.y. after the explosive beginning of the Universe, the Big Bang. Thus, all the planetary bodies of the Solar System, including the Sun had a common nebular parentage.
The Hubble space telescope has recently spotted the birth of new stars in the Orion nebula and at least half of the new born stars appear accompanied with nebulae that eventually should form a planetary system. A great probability also exists for locating stars and planetary systems in other galaxies if not in the Milky Way galaxy to which our Solar System belongs.
1.9 COMPOSITION OF THE SOLAR SYSTEM
The Solar System shows some unusual compositional characteristics which relate well it to the nucleosynthesis reactions accomplished in massive stars. The elemental composition shows a steep or rapid decline in abundance of elements as the atomic number increases. Significantly, the elements H, He, C, N, O, Ne, Na, Mg, Al, Si, P and S with Z 16 dominate over elements with higher Z (Table 1.2). The decline in abundance becomes less steep beyond the atomic number 40 of Zr, and the range of difference in abundance becomes narrow between the abundances of elements with even and odd Z.. It is also seen in the compositions of all planetary bodies, which accreted directly from the solar nebulae, that the element Fe (Z = 26) shows remarkably higher abundance than even those elements next to it, namely Mn and Co, in the Periodic Table.
Detailed chemical data gathered on meteorites (stones from the sky) further confirmed the pattern of abundance of elements in the Solar System. When plotted on a logarithmic scale, the abundance pattern distinctly revealed much greater abundance of elements with even Z over those with odd Z. The regularity of this pattern was recognized by two astrophysicists Oddo and Harkins independently in the second decade of the 20th Century. Since then this pattern of abundance has been referred to as the Oddo-Harkins rule. Even the stability of isotopes is governed by the same rule; isotopes with even Z (multiples of 4) and even N are mre stable than those with odd Z and odd N which are the least stble.

Illustrations : Dr A M Patwardhan & Ajay Pacharne
Recorded, Mixed and Produced at 'unpluggedmee' studio by Rohit Patwardhan
Contact : 8806747788

[vimalkantdave]

I must admit that the talk by Professor Patwardhan is very absorbing and a mature attempt to explain the elemental abundance.