What is our little corner of the Milky Way Galaxy like? The Solar System What is our little corner of the Milky Way Galaxy like?

Composition of the Solar System The sun = 99.85% of all the matter in the solar system. Jupiter contains more than twice the matter of all the other planets combined. Star/Sun = 1 Planets = 8 Dwarf Planets = 5

Size Comparisons

Solar System Structure All planets orbit the sun in a counter-clockwise fashion. Orbits are contained within a very narrow disk or plane. Most orbits are very nearly circular with the exception of Mercury and Pluto.

Solar System Structure The spin axes of most planets and moons are perpendicular to the orbital plane (Venus and Uranus are notable counter examples). Thus, solar system is basically disk shaped with the Sun near the center.

Small Rocky Worlds Terrestrial/Rocky Planets – Small, dense, rocky worlds with less atmosphere than the other type of planet. Craters, no rings, very few moons. Mercury Venus Earth Mars

Jovian/Gaseous Planets Jovian Planets – Large, gaseous, low density worlds. Thick gaseous mostly hydrogen atmospheres, rings, lots of moons, and very large in comparison to terrestrial planets. Jupiter Saturn Neptune Uranus

Pluto Pluto – Does not fit the current definition of a “planet”. Pluto is a small icy world clearly different from either the Jovian and Terrestrial worlds. Since its discovery by Clyde Tombaugh in 1930, it has been a unique mystery mostly because of its great distance from the Earth and is peculiar orbit.

Pluto’s Orbit

Space Debris Asteroids  (minor planets) are small rocky worlds. Most (not all) orbit between Mars and Jupiter—Asteroid Belt . Most are irregular in shape, crated, and dense.

Comets An impressive glowing object that is illuminated by the Sun as it sweeps through the inner solar system. Dirty snowball theory. (Water and CO2 ices)

Meteor  falling “shooting star” – bits of rock and metal falling into the Earth’s atmosphere and bursting into vibrant light as they drastically heat because of the friction created between them and the Earth’s atmosphere. These bits are, on average, tiny – specks of dust, sand grain size, small pebbles – NOT large. Meteoroid  in space before its fiery collision with the Earth’s atmosphere. Meteorite  fallen piece that survived the fall. Most “shooting stars” are less than 1 gram of material.

Age of the Solar System Oldest rocks dated on Earth ~ 3.9 billion years; however, the Earth’s own volcanism and plate-tectonics erase most of the evidence!! Lunar rocks are dated to 4.48 billion years. Meteorites ~ 4.6 billion years Sun estimated age is based on all the circumstantial evidence ~ 4.5 - 5 billion years. It has about a 10 billion-year life.

Solar Nebula Theory A large massive slowly rotating cloud of interstellar material begins to collapse under the influence of gravity. A star forming nebula begins to grow warm and grow denser. The warming center is becoming a “protostar” of mostly hot hydrogen gas. Further out in the nebula other clumps of dust and debris are gathering into asteroid sized objects and “planetesimals”.

Solar Nebula Theory When nuclear fusion begins we have a new star! The star will vaporize the inner regions of the cloud and begin to drive off the gaseous and dusty material As the star continues to shine and produce energy the nebula is driven off revealing the surviving material; planets, comets, and asteroids.