# The Solar System An Inventory.

## Presentation on theme: "The Solar System An Inventory."— Presentation transcript:

The Solar System An Inventory

What is the Solar System?
Answer: The system of objects in the solar neighborhood (near the Sun) What are these objects? One Star Nine Planets Six Planets Dozens of moons Thousands of asteroids Trillions of comets

The Discovered Planets
All planets through Saturn known since the ancients – all you have to do is look up to see them Uranus discovered in 1781 by William Herschel He wanted to name the planet “Georgium Sidus” after his king and patron, George III of England Neptune was first seen in 1846 by Johann Galle using predictions by Urbain Jean Joseph Leverrier and John Couch Adams Pluto was discovered in 1930 by Clyde Tombaugh at Lowell observatory

Size and Scale

Planets The first step to studying planets? Compare and contrast
What are important quantities? You have: A stick A tree A car A house What are the important quantities?

Planetary Properties

Density and Mass What is mass? What is density?
Mass is similar to weight, it measures how much stuff an object is made of Example: A bowling ball and a soccer ball are about the same size, but have different masses What is density? Density is mass per volume. It helps to tell you what kind of stuff an object is made of Example: A log and a tree have different masses (and sizes), but the same density because they are made of the same stuff

Terrestrial Planets Close to the sun Small High density
Mass Radius High density Primarily rocky Solid surface Weak magnetic field Few moons No rings

Jovian Planets Far from the sun Large Low density
Mass Radius Low density Primarily gaseous No solid surface Strong magnetic fields Many moons Many rings

What About Pluto? Pluto does not easily fit into either category
Far from the sun (jovian) Small (terrestrial) Neither rocky nor gaseous (icy) One moon No rings It is similar is composition to some moons in the outer solar system and its orbit is similar to a group of objects called “Kuiper Belt Objects” or KBOs

Pluto Only planet in our Solar System that has not been visited by a NASA (or any other) spacecraft

Charon Largest of any moon in relation to the planet it orbits (1/2 the size of Pluto) Pluto and Charon are tidally locked to each other (always show the same face) Charon discovered in 1978 by astronomers at the US Naval Observatory

Formation Where did the Solar System come from?
First, what observations can we make that will constrain the origin of the Solar System?

Model Requirements Planet’s are isolated
Planetary orbits are nearly circular All planetary orbits lie in the same plane All planets orbit in the same direction as the Sun’s rotation All planets rotate in the same direction as the Sun Most moons rotate in the same direction as the planet they orbit The planetary system is highly differentiated

Differentiation In general, planets get less dense as they get further from the Sun They go from being composed of metals, to rocks, to ices, to gases In other words, they go from being made of things with high melting temperatures to things with low melting temperatures

Highlights of the current theory
Nebular contraction Mutual gravity causes contraction Conservation of momentum increases speed Planetary formation (accretion)

Differentiation revisited
As the solar nebula contracted, the center became hotter than the rest of the cloud As elements condensed out of the nebulae, temperature determined which could form

Clearing of the nebula After the planets formed, some small debris still remained. All of these small objects were affected by the gravity of the much larger planets. The debris either: Hit a planet Hit the Sun Was thrown out of the area near the planets – becoming KBOs

Explaining observation
Matching model requirements: Point (1) is due to planetesimal growth Points (2), (3), (4), (5), and (6) are due to conservation of angular momentum and gravitational collapse Point (7) is due to the heating in the nebula Anomalies: Retrograde rotation of Venus Uranus’ axial tilt The Earth’s moon All can be explained by impacts of protoplanets into the planet soon after its formation