III. The Solar System

A. Solar System Inventory

1. Planetsa. Terrestrial Planets (Earth-like)

- The First Four Planets: Mercury, Venus Earth and Mars

- All are found within 1.5au of the Sun and have similar chemical properties.

- All are low-mass, with atmospheres and rocky surfaces.

- Have relatively long rotations (for their size) & short revolutions.

Similarities

1. Terrestrial Planets Continued..

Atmospheres – Mercury has almost none Venus has the Densest Earth is the only planet with Oxygen Mars has a thin atmosphere of CO

2.

Rotations – Earth and Mars both take roughly 24 hours

Venus and Mercury take months to complete one rotation. In fact Venus rotates very slowly in the opposite direction of all other planets.

Moons – Earth and Mars both have moons

Mercury and Venus have none

Distances from the Sun:Mercury: .4au Earth: 1auVenus: .72au Mars: 1.5au

b. Jovian Planets: (Jupiter-like)

- The Last Four Planets: Jupiter, Saturn, Uranus, Neptune

- VERY widely spaced out (5au to 40au away)

- All are high mass, mostly consisting of hydrogen & helium gases, with no rocky surface.

- Have relatively short rotations and long revolutions.

- All have large systems of rings and moons

Distances from the Sun:Jupiter: 5 au Uranus: 20auSaturn: 10au Neptune: 30au

2. Jovian Planets Continued..

Atmospheres – Jupiter and Saturn are mostly Helium

Uranus and Neptune have large amounts of methane.

Rotations – All have rotations that are shorter then one earth day, but Uranus actually rotates sideways.

Moons – Have many moons made mostly of ice and small amounts of rock.

- Jupiter: 32+ moons, plus 4 of the largest

- Saturn: Many moons. Largest is Titan

- Uranus: The moons orbit at the same inclination as the planet rotates.

Why no Pluto?

Recently scientists have discovered many objects of similar size and composition to Pluto (some even larger). So they came up with a definition for the word planet:

a. Orbits a star

b. Has sufficient gravity to pull itself into a spherical shape.

c. Has cleared the area of its orbit of other debris

d. Is not undergoing nuclear fusion.

Pluto has been therefore defined as a dwarf planet.

c. Terrestial Planets in Detail1. Mercury

A. 0.4au from the sun B. Temperature extremes from 700 K during the day and 100 K at night. C. The smallest planet (in both diameter and mass)

D. The high daytime temperature and low gravity means that Mercury cannot hold onto any appreciable atmosphere.

E. The interior of Mercury is a large Iorn Core. This causes it to have a weak (100 times less then earth) magnetic feild.

c. Terrestial Planets in Detail2. Venus

A. About 0.7au from the sun

B. Has the hottest average surface temperature, 730 K.

C. Very close in mass to the Earth.

D. Has an atmosphere of 96.5% Carbon Dioxide. This has lead to a runaway greenouse effect which is why it is so much hotter then any other planet.

E. Venus has no known magnetic field.

c. Terrestial Planets in Detail 3. Mars

A. Roughly 1.5au from the sun

B. Only 1/3 the mass of the earth

C. Average temperature on Mars is about 50 K cooler then the Earth. D. Has an atmosphere of 95.6% Carbon Dioxide, but it is 13,000 times thinner then Venus

E. No magnetic field has ever been detected on Mars. This is likely because its core has cooled and become soild or because it does not contain enough metalic material.

d. The jovian planets1. Jupiter

A. About 5au from the sun

B. By far the most massive of all the planets.

C. More then 28 moons discovered so far. Some are larger then the planet Mercury.

D. Known for it's distinct banding of clouds at different latitudes.

E. Has a very thin system of rings.

d. The jovian planets1. Saturn

A. About 10au from the sun

B. Second most massive planet. C. Also has a vast system of moons D. Does not have many distinct

bands in it's clouds.. E. best known for it's spectacular

ring system.

d. The jovian planets1. Uranus

A. About 20au from the sun

B. Contains no visible cloud banding.

C. Also has a vast system of moons D. Has a small system of rings. E. best known for rotating 98o

compared to the ecliptic.F. This gives Uranus the most extreme seasons of any

planet in the solar system

d. The jovian planets1. Neptune

A. About 30au from the sun

B. Known for having the fastest winds in the solar system. Clocked

at over 2000 km/hr.. C. Also has a vast system of moons D. Does not have many distinct

bands in it's clouds.. E. The only outer planet to have an

interior source of heat. It radiates 2.7 times more heat then it receives from the sun.

2. Solar System Debris

a. Asteroids: Masses of rocky material that is not part of a planet or moon.

- Most are found 2.1au to 3.3au from the sun. Between the orbits of Mars and Jupiter. This is known as the Asteroid Belt.

- In addition to Main belt asteroids there are two “packs” of asteroids that share Jupiter's orbit. 60o ahead and behind the planet. These are known as the Trojan asteroids.

2. Solar System Debrisa. Comets: Masses of icy material that travel from the

outermost reaches of the solar system to very close to the sun. VERY elliptical orbits.

- Made mostly of frozen water, ammonia and some rocky material. Think of a dirty snowball. This is known as the nucleus of the comet.

- When the comet approaches the sun many of these materials vaporize. The cloud of vapor around the nucleus is called the coma.

- The gas and dust trailing the comet is called the tail. The tail always points away from the sun.

Anatomy of a comet

Tail

Nucleus

Coma