Structure Formation of the Solar System SUN INVENTORY

Structure & Formation of the Solar System

SUN INVENTORY

Mass Fraction One Star (“Sun”) 99. 85% Nine (? ) Planets 0. 135% 80 (? ) Satellites (“Moons”) 1 million (? ) Asteroids 1011 (? ) Comets Meteoroids + Dust + Gas

SUN

Sun 865, 000 mi (1. 39 x 106 km) ·

SUN PLANETS

p. 122 * * Orbits almost in same plane Orbit sense same Orbits nearly circular Rotation sense same (almost!)

* Composition gradient Solid: Metallic, rocky: high density (3. 9 – 5. 5 g/cm 3) Fluid: Hydrogen & Helium: Low density (0. 7 – 1. 6 g/cm 3)

SUN MOONS

Most (mainly) orbit in same sense as planets

* Inner moons rocky; outer moons (mainly) icy!

SUN ASTEROIDS

Main Asteroid Belt Rocky Chunks

Some asteroids are found elsewhere. . . Earth Asteroid Near-Earth Asteroids

SUN COMETS

Kuiper Belt Icy Chunks

Oort Cloud 100, 000 AU * Orbits in every possible plane!

SUN SOLAR SYSTEM FORMATION: NEBULAR THEORY

Star Formation

Collapsing ‘Solar Nebula” Collapse of an Interstellar Cloud p. 127

Cloud contracts & heats Gravitational potential energy Heat (thermal) energy

. . . And spins faster & flattens as it contracts Small diameter, rapid spin Large diameter, slow spin

Slow Fast

‘Difficult’ collapse ‘Easy’ collapse ~ 200 AU

Protosun Protoplanetary Disk

. . . Leading to arrangement of planet’s orbits.

‘Circumstellar’ disks in Orion

Disk surrounding star Beta Pictoris 600 AU

SUN MAKING PLANETS

98% H & He Gas begins to condense to solid particles. . . p. 128

Temp (K) Temp. in the Solar Nebula Only rocky & metallic materials solidify. Ices can form (in large amounts) Distance from Sun (AU)

Cosmic Abundance of the Elements Abundance icy stuff Atomic Number

Planetesimals . . . Eventually gravity aids assembly. Particles begin to accrete into larger chunks. . .

Small planetesimals (asteroid-like) Large planetesimals (planet-like)

Inner (terrestrial) planets small: little rocky/metallic material available

‘Nebular Capture’ Outer (Jovian) Planets: Large icy core planetesimals gathered-in abundant H & He Big planets! p. 130

SUN THE LEFTOVERS

Asteroids form here Comets form here

Small bodies that get too close to big planets may get ejected to far reaches of solar system.

Many leftover planetesimals collided with the planets. p. 132

Craters, craters everywhere. . . Mercury Moon Mars Callisto (a moon of Jupiter)

Bombardment History

Comets/Asteroids probably delivered most water!