Origin of Solar System Lecture 15

Key Properties of our Solar System Any theory of the origin of the solar system must be able to explain following key properties in the simplest manner. 1.Sizes and compositions of terrestrial planets versus Jovian planets 2.Direction and orientations of planetary orbits 3.Sizes of terrestrial planet orbits versus Jovian planet orbits

There are 103 elements known to exist. Yet, all known life forms are mainly based on C, H, O, & N, and most advanced organisms are using H 2 O! Why? Why shouldn’t there be life forms with iron skeleton and using methanol?

Origin of the Elements After Big Bang, lightest elements (H, He, Li, Be) were created, but only for a limited time period (3 to 20 minutes). 92% H + 8% He and almost no other elements.

Creation of the Elements (Nuclear Synthesis) Hydrogen “burning” = the main energy source of stars over long, long time (e.g., for Sun, 10 billion years). Hydrogen “burning” = the main energy source of stars over long, long time (e.g., for Sun, 10 billion years). Hydrogen burning : 4 Hydrogens  Helium + energy 4 Hydrogens  Helium + energy US yearly energy consumption: 1.107×10 20 Joules = can light Sanford stadium for 100 billion years! = can be produced from a fusion of mere 80lb of Hydrogen!

Cosmic abundance Later stages of Nuclear fusions in Stars Later stages of Nuclear fusions in Stars Not much Li (H+He), Be, B (Be+H or He+Li)…

Lots of clouds in the Galaxy

Angular Momentum Conservation Spinning sphere Spinning Figure Skater

Formation of Planetary System (nebular theory) Contraction and disk formation Contraction and disk formation Once the collapse begins, nebula would heat up, spin faster, and flatten… Conservation of Energy (heating up) : gravitational potential energy  heat energy Conservation of angular momentum (spinning up) collapsed to a nearly 1/1,000,000 of the initial size

Composition of Clouds

Formation of Planetary System Condensation (opposite of melting) : Condensation (opposite of melting) : High temperatures in the inner region  materials only with high condensation temperatures can turn to solids (metals and rocks). Outer region is much cooler  materials with lower condensation temperatures can turn to solids also (ices, rocks and metals)  more solids than the inner region! Hydrogen and Helium remain as gas everywhere in the disk.

Formation of Planetary System Accretion of solids Accretion of solids Pebbles  rocks  boulders  …  planetesimals (~100 km size) … this process over a few million years… Collisions b/w planetesimals (some stuck, some shatter) Collisions b/w planetesimals (some stuck, some shatter) Formation of rocky planets (inner) and some ice-rocky planets (outer) Formation of rocky planets (inner) and some ice-rocky planets (outer) Gas accretion in the outer area (why not inner?)  Jovian planets! Gas accretion in the outer area (why not inner?)  Jovian planets!

Formation of Planetary System Moon formations around Jovian planets Moon formations around Jovian planets  in a disk surrounding a Jovian planet (similar to the way planets are formed)…

Formation of Planetary System Clearing the Disk Clearing the Disk Remaining gas will be blown away by solar wind… Rocks remain, but gradually being cleared by planets or collide among themselves…

Is this happening at other stars? Young stars in their early formation showing a disk (dark shade) Y E S !

Planetary system formation simulation

In summary… Important Concepts Planet formation (nebular hypothesis) Conservation of Energy Conservation of angular momentum Ordered structure of planets is a natural outcome of planet formation. Important Terms cosmic abundance solar nebula condensation protoplanetary disk Chapter/sections covered in this lecture : sections 8-1,8-2, & 8-4