The Inner and Outer Planets

A solar story

Astronomical Unit1 AU = 149,597,870.691 kilometers

(93,000,000 miles)

Definition: An Astronomical Unit is approximately the mean distance between the Earth and the Sun.

Why is it the mean distance?

Answer: Because orbits are elliptical

•Jupiter is 5.2 AU’s away from the sun

Mercury

• Smallest terrestrial planet closest to the sun

• No moons

• Surface consists of flat plains and craters

• Very little atmosphere

• Greatest temp. difference 860 F to –274F

Venus

• Similar to Earth in Size

• Takes 8 months to rotate on it’s axis and 7.5 months to revolve around the sun.

• Planet rotates from east to west.

Earth

• Unique because it has liquid water (70%)

• Has enough gravity to hold an atmosphere

• Atmosphere is made out of nitrogen, oxygen and carbon dioxide.

• Has one moon

Mars• Red because of the iron rich

rocks on the surface• Atmosphere is more than

95% CO2• Surface temps. range from –

140 to 20 C.• There may have been

flowing water• Has seasons because of its

tilted axis• Has two moons

The Outer Planets

• Known as the gas planets

• All the gas planets have rings

• Rings are mostly ice but are also composed of rock and dust

Jupiter

• Largest most massive planet• Thick atmosphere of H and

He• Great red spot the size of

Earth• Prob. has a dense core of

rock• Atmospheric pressure at the

core is 30 million X that of Earth.

• Many moons most famous are the Galileon moons (4)

Saturn

• Thick atmosphere of H and He

• The density of Saturn is less than water!

• Rings made of chunks of rock and ice.

• Saturn’s largest moon is titian

Uranus

• Blue green color because atmosphere is made up of methane

• Discovered in 1781 by William Herschel

• Axis is tilted at 90 deg. and rotates in about 17 hours

• Has at least 27 moons

Neptune

• Cold blue planet

• Discovered by mathematical prediction based on the orbit of Uranus

• Dark spots are prob. storms on the surface

• 13 moons

• Internal heat source. Slowly shrinking

Pluto?(The roman god of the underworld)

• Three moons• Revolves around the

sun 1x every 248 Earth years

• Not considered a planet today

So why isn’t Pluto a planet?Is Pluto a planet? Does it qualify? For an object to be a planet, it needs to meet these three requirements defined by the IAU:

•It needs to be in orbit around the Sun – Yes, so maybe Pluto is a planet.

•It needs to have enough gravity to pull itself into a spherical shape – Pluto…check

•It needs to have “cleared the neighborhood” of its orbit – Uh oh. Here’s the rule breaker. According to this, Pluto is not a planet.

What does “cleared its neighborhood” mean? As planets form, they become the dominant gravitational body in their orbit in the Solar System. As they interact with other, smaller objects, they either consume them, or sling them away with their gravity. Pluto is only 0.07 times the mass of the other objects in its orbit. The Earth, in comparison, has 1.7 million times the mass of the other objects in its orbit.

Any object that doesn’t meet this 3rd criteria is considered a dwarf planet. And so, Pluto is a dwarf planet. There are still many objects with similar size and mass to Pluto jostling around in its orbit. And until Pluto crashes into many of them and gains mass, it will remain a dwarf planet. Eris suffers from the same problem.

Size comparison of planets

The next slide shows The Relative Sizes of the Largest Solar System Objects - in the following order (to scale): Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars, Ganymede, Titan, Mercury, Callisto, Io, the Moon,

Europa, Triton, Eris, Pluto

Size comparison of planets

Size comparison of planets compared to the Sun

100 Largest objects in the solar system