The Solar System

The Solar System Contains:

• One star (the sun).• Nine planets (well now there’s eight planets and

3 dwarf planets).• 157 moons (at last count) orbiting the planets.• Eight large asteroids.• More than 100 Kuiper belt objects larger than

300 km in diameter.• Tens of thousands of smaller asteroids, myriad

comets a few km in diameter, and countless meteoroids less than 100 m across.

Planetary Properties

• From closest to the sun, we have Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto (My Very Educated Mother Just Served Us Nine Pizzas).

• All planets orbit Sun counterclockwise as seen from Earth’s north pole and in nearly the same plane as the earth (only Mercury and Pluto deviate slightly).

Planetary Properties

• Earth’s radius is known using conventional surveying techniques as well as satellite observations. Radii of the other planets are determined by measuring their angular radii (size as seen on the sky) and using geometry to compute the physical radii.

• Mass is determined by observing a planet’s gravitational influence on some nearby object and applying Newton’s laws of motion and gravity (used to use planets’ moons, now can also use artificial satellites).

Planetary Properties

• 99.9 % of the mass in the solar system is contained in the sun, whose gravity dominates the motion of everything else.

• Density is a measure of the compactness of an object (mass / volume).

Planetary Properties

Lecture Tutorial: Sun Size (p. 105)

• Work with a partner!• Read the instructions and questions

carefully.• Discuss the concepts and your answers

with one another. Take time to understand it now!!!!

• Come to a consensus answer you both agree on.

• If you get stuck or are not sure of your answer, ask me or another group.

Terrestrial and Jovian Planets

• Inner planets - small, dense, and rocky in composition. Called “terrestrial” planets since the composition is similar to Earth’s. They are Mercury, Venus, Earth, and Mars.

• Outer planets - large, low density, and gaseous. Called “jovian” planets after Jupiter. They are Jupiter, Saturn, Uranus, and Neptune.

• Note - Pluto does not fit into either of the above categories! It has more in common with the icy jovian moons than with any terrestrial or jovian planet.