Our Solar System Chapter 28

Formation of the Solar System 28.1

A collapsing interstellar cloud Stars and planets form from interstellar clouds They appear dark because of dust blocking out the light The light can cause it to glow, or even become heated Starts and solar systems are “born” this way Collapse accelerates The collapse of this cloud is slow, but it accelerates and becomes denser at the center

This collapse and spin results in a flattening at the equatorial plane Matter condenses Our solar system may hav eformed this way when temperature and pressure cause hydrogen to fuse into helium The temperature differential allowed for different elements to concentrate in different areas around the sun This is why the inner planets are rocky and have a higher melting point Outer ones are less dense and made of ice and gas

Planetesimals Much like coalescence, the planetesimals combined to get larger in many cases to become the known planets. Gas giants form Jupiter was the first to form Icy planetesimals combined to form it Its mass (gravity) caused it to collect much of the debris The others formed the same way, but Jupiter took most of the extraneous material

Terrestrial planets form the merging of planetesimals in the inner portion of the disk Made of materials that resist vaporization Most of the gaseous material and “smaller stuff” consumed by the sun, hence fewer satellites. Debris All of the “junk” left over Some became comets Some ejected from solar system or destroyed in collisions The asteroid belt between mars and Jupiter is the rest

Modeling the Solar system Initially the geocentric theory stated that everything moved around the earth. Retrograde motion led astronomers to find a different explanation The heliocentric model (Copernicus) put the sun at the center and planets in orbit around it. Proximity to the sun caused planets to move at different speeds This explained retrograde

Kepler’s Laws 1st law is that planets move in elliptical orbits The sun was at 1 focus The semi-major axis (half the length of the major axis) is where we get the AU (astronomical unit) distance many distances are measured in This is more math that I want to get into! The eccentricity of the orbit is how “squashed” the orbit is 2nd law is an equal area is swept out in equal amounts of time (although the orbital distance may be different) 3rd law he defined the size of the ellipse and the orbital period (year)

Gravity Gravity is the attractive force between 2 objects It is affected by mass and distance Gravity is what determines the orbit planets follow Newton’s explanation of gravity supported Kepler’s laws of planetary motion.

The Inner Planets 28.2

Terrestrial Planets these are the 4 inner planets similar densities to Earth solid rocky surfaces

Mercury closest to the sun 1/3 Earth’s size no moons 2 Mercury Years is 3 Mercury days Atmosphere O2 and Sodium replenished daily by the sun

Surface Interior covered with craters and plains the plains formed much like the maria on the moon the craters are smaller with less ejecta Interior the density suggests a dense core similar to the Earth the magnetic field suggests its partially molten

Venus Has no moons the brightest planet because of proximity and albedo 75% Thick atmosphere doesn’t allow for direct observation probes and satellites have provided radar images of 98% of the surface

The Outer Planets 28.3

The Gas Giants These planets include: Jupiter, Saturn, Uranus and Neptune All larger than Earth by 15-300 times

Jupiter The largest planet 1/10 of the sun and 11X Earth’s Better than 70% of the planetary mass of the solar system 52% albedo Has a banded appearance “the great spot” is a storm that has lasted for better than 300 years

Density is relatively low for its size The is because of it composition (H and He in gas or liquid form. Rotation Shortest day in the solar system about 10hrs This fast spin distorts the shape This also contributes to its banded appearance Belts are low lying dark-colored clouds Zones are high light-colored clouds Moons More than 60, but some are very small

Mostly composed of ice and rock Gravity assist

Saturn Second largest planet in the solar system Atmosphere and interior Slightly smaller than Jupiter Density less than water… it would float! Rings Much broader and brighter than other planets’ 7 major rings made up of ringlets Gravity keeps the rings in place

Moons 55 moons Titan, the largest is bigger than Mercury Odd among moons because of content with dense atmosphere and methane’s existence in 3 states

Uranus 4x larger and 15Xmass of the Earth Atmosphere Moons and Rings Bluish appearance cause by methane gas Clouds are similar in appearance to the surface Liquid surface with a small solid core Moons and Rings At least 27 moons and faint rings

Rotation The rings are dark and almost not observed Almost a top to bottom rotation Poles vacillate between 42 years of darkness and light

Neptune Atmosphere Moons and Rings Smaller and denser than Uranus but 4XEarth Similar in color to Uranus (twins??) but does have some color variation on surface Belts and zones give it texture Moons and Rings 13 moons Triton being the largest Triton has retrograde orbit Also has nitrogen geysers when heated by the sun Rings are invisible from Earth but exist