The Layout

• Inner Rocky Planets

• Asteroid Belt

• Outer Gas Giants

• Kuiper Belt

• Oort Cloud

Planets

• “Wandering Stars” or “Wanders” (Greek)

• Discovery of Uranus (1781) and Neptune (1846)

• Discovery of Pluto (1930) later reclassified as a dwarf planet

• Discovery of Eris (2003) later reclassified as a dwarf planet

Planets

• International Astronomical Union (IAU) 2006 definition:

• a planet is a celestial body that– is in orbit around the Sun, – has sufficient mass to assume hydrostatic

equilibrium (a nearly round shape), and – has cleared the neighbourhood around its

orbit.

Rocky Planets

• Mercury

• Venus

• Earth

• Mars

Images: www.nasa.gov

Asteroids

• Orbit between Mars and Jupiter

• Rocky objects too small to be called planets

Images: www.nasa.gov

Gas Giant Planets

• Jupiter

• Saturn

• Uranus

• Neptune

Images: www.nasa.gov

Kuiper Belt

• Disk-shaped region past Neptune 30-50 AU from the Sun

• Similar to asteroid belt, but much larger—20 times as wide and 20–200 times as massive

• Kuiper Belt Objects (KBOs): Icy “asteroids”

Poor Pluto?

Images: http://web.gps.caltech.edu/~mbrown/dwarfplanets/

Dwarf Planets

• A "dwarf planet" is a celestial body that – is in orbit around the Sun, – has sufficient mass for its self-gravity to

overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape,

– has not cleared the neighbourhood around its orbit, and

– is not a satellite.International Astronomical Union (IAU) 2006

Dwarf Planets

• Orbits in the Asteroid Belt:– Ceres

• Orbits in the Kuiper Belt:– Pluto– Eris – MakeMake – Haumea

Image: www.nasa.gov

Comets

• “dirty snowballs”• Highly elliptical orbits

around the Sun• As they get close to

the Sun, the ices “melt” and trail out behind the comet making a “tail”

• “tails” always point away from the Sun

Image: http://spaceplace.jpl.nasa.gov/en/kids/phonedrmarc/2004_january.shtml

Images: www.nasa.gov

Oort Cloud

• Proposed in 1950 by Dutch astronomer Jan Oort

• Spherical shell of icy bodies surrounding the solar system

• Origin of “long period” comets (200+ years)