Ch5_Heavy_Const

Ch5_Heavy_Const - The Heavy Construction 1 Chapter Five The...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
The Heavy Construction 1 Chapter Five The Heavy Construction Our Solar System has many characteristics that show that all the objects in it formed as part of a coherent process. The planets all rotate in the same direction and in the same plane around the sun, they are regularly spaced and there are systematic and regular differences between the inner and outer planets. The ages of formation of primitive solar system objects we can date are nearly identical. Therefore formation of the solar system was a co-genetic event, and not the result of a random collection of materials by the gravitational F eld of the sun. We hypothesize that solar system creation took place in an interstellar cloud of gas and dust, which served as a “stellar incubator.” There is evidence that other larger stars formed in the same vicinity, creating supernovae that seeded the solar nebula with short-lived radionuclides. Such clouds are common in the universe, and we can observe new star systems forming elsewhere in the universe. There is also evidence for the existence of planets around other stars, indicating that creation of planetary systems is a normal and common event in the universe. The various objects in the Solar System formed from a complex series of processes, understood well in general terms but about which many details remain to be clariF ed. Most of the material in the cloud was drawn to its center to form the Sun; therefore our Sun has a composition very close to that of the original cloud. It consists of 99 percent hydrogen and helium. The remaining 1 percent is made up by 90 elements. A small amount of the matter in the cloud ended up in a nebular disk around the newly formed Sun. A small percentage of this material condensed to solid form and then aggregated to form planets, moons, asteroids and comets. The remaining gas was blown away by a violent solar wind. ±ragments of these materials which occasionally reach the earth are known as meteorites. They provide us with direct samples of solar system materials. The composition of most of these materials is very different from the Sun. This difference is largely the result of “differential volatility” where the temperature boundary between gas and solid varies for the different elements. In those parts of the disk closest to the hot Sun, only the least volatile elements such as ±e, Mg, Al and Si were in solid form and therefore could collect together to form rocky planets. In the most distant reaches of the disk, ices crystallized and almost all the elements except hydrogen and helium were in solid form, leading to large planets with small proportions of rock and metal, surrounded by gassy atmospheres. Because of this the comets and planets of the outer solar system have a chemical composition very different from the asteroids and planets of the inner solar system. Huge numbers of comets are likely to have impacted the earth early in its history, likely bringing with them volatile components and organic molecules that are essential for
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 18

Ch5_Heavy_Const - The Heavy Construction 1 Chapter Five The...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online