How did the Solar System form?

1. How did the Solar System form? • Before we can investigate this fundamental issue of all of science we need some general information about science and the Solar System.

2. How did the Solar System form? • Where is our Solar System located?

5. How did the Solar System form? 2. What must occur first for the Solar System to form?

6. How did the Solar System form: Sun and Clouds? • Our Solar System’s formation is the by-product of the formation of our star, the Sun. • The Sun rules the Solar System. It is the largest object in our system. • It makes up ~ 99.85% of the mass of the Solar System and is composed mainly of H2 and He. • The Sun is the closest star to Earth. • It is somewhat of a mystery that the Sun is alone.

7. How did the Solar System form: Sun and Clouds? Therefore, the Sun must form first. But how?

8. How did the Solar System form: Sun and Clouds? • In the beginning… …a molecular cloud existed in the vicinity of our solar system. Stars are formed within molecular clouds.

11. How did the Solar System form: Sun and Clouds? • A molecular cloud is a dark interstellar cloud where stars and hence Solar Systems are born. • They are composed mostly of molecular hydrogen (H2) with carbon monoxide (CO) and organic compounds. • They contain dust that likely acts as shields so that molecules exist. • They are cold, ~10K (0K is absolute 0, -273C) • They have masses from a few times the mass of our star up to 107 times the mass of our star.

12. How did the Solar System form: Sun and Clouds? • The Nebular Contraction Theory: a large cloud of interstellar gas or molecular cloud collapses under the influence of its own gravity or due to a super nova shock wave. • It becomes denser and hotter during contraction, forming a star or young stellar object (YSO) at the center. A disk of gas is produced around the young stellar object. Planets are then formed within this disk. • This object is known as a solar nebula and within it a protoplanetary disk or accretion disk forms. • We see them!

18. How did the Solar System form: Sun and Clouds? • How is a star formed? • Most of the mass of the nebula becomes concentrated into one or more areas that become hot enough for nuclear fusion to start and thus a protosun is formed. The internal temperature reaches some 1,000,000 K. • The number of atoms required to have accumulated is nearly 1057 atoms-more than all the sand on all the beaches of the world and all the atoms on our entire planet! • At this point most of the collapse or contraction stops and a star is born. This is called a protostar. • This protostar evolves over a relatively short time, contracting and getting hotter until about 30 million years pass and finally the star is ‘main sequence’ burning at 15,000,000 K in the core.

19. How did the Solar System form: Sun and Clouds? • How is a star formed? • Star formation is usually discussed as having 7 stages. • Stage 1 = Interstellar cloud • Stage 2 = Collapsing cloud fragment • Stage 3 = Fragmentation ceases • Stage 4 = Protostar • Stage 5 = Protostellar evolution • Stage 6 = A newborn star • Stage 7 = The main sequence

20. How did the Solar System form: Sun and Clouds?

21. How did the Solar System form: Sun and Clouds?

22. How did the Solar System form: Sun and Clouds?

23. How did the Solar System form: Sun and Clouds? • How does the disk form and why? • As the cloud continues to contract, gravity become greater and greater. But, the cloud does not contract into a single mass. • The collapse towards the center of the cloud proceeds very slowly due to several other effects, including turbulence and magnetic fields, but the most important is the conservation of angular momentum.

24. How did the Solar System form: Sun and Clouds? • As the cloud continues to contract it begins to spin or orbit the center, which contains a YSO. The more it contracts the faster it spins. • Thus, a decrease in the size of a rotating mass must be balanced by an increase in its rotational speed. This concept is known as angular momentum and was first determined by Pierre Simon de Laplace, 1796.

27. How did the Solar System form: Sun and Clouds? • What is angular momentum? • Well, first we must understand momentum. • Linear momentum = mass x velocity (or acceleration) • Run into a wall slowly, now run into the wall very fast OR increase the size of the person running into the wall.

28. How did the Solar System form: Sun and Clouds? Angular momentum = mass x angular speed x radius2 • It is a measure of an object’s tendency to keep spinning, or how much effort must be expended to stop spinning. • Both types of momentum, according to Newton’s laws of motion, must be conserved at all times. As long as no external forces is active, momentum must remain constant before, during, and after a physical change in any object.

31. How did the Solar System form: Sun and Clouds? • The fact is, dust also exists within a molecular cloud and the contraction theory does not account for gas-dust, dust-gas, or dust-dust interactions. • We know from observations that dust is found as a component of disks.

32. How did the Solar System form: Sun and Clouds? • A more up-to-date theory - Nebular Condensation Theory. This theory incorporates most of the Nebular Contraction Theory and it adds one critical component, dust from the interstellar medium. • This dust is known as interstellar dust, similar and in some cases the same as, circumstellar dust.

33. How did the Solar System form: Sun and Clouds? • Dust is important because it helps to cool warm matter by radiating its heat away, thus reducing pressure and allowing the gas portion to collapse more easily under the influence of gravity. • It also acts as nuclei for the formation of larger grains by condensation and accretion.