Our Planetary System

Chapter 7

Key Concepts for Chapter 7 and 8

Inventory of the Solar System

Origin of the Solar System

What does the Solar System consist of?

• The Sun: It has 99.85% of the mass of the solar system

• Eight planets. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune

• Several dwarf planets. Pluto is one of them

• There are around 169 satellites (moons). Except for three satellites orbiting the Earth and Mars (Moon, Phobos and Deimos) all the rest are in orbit around the Jovian planets.

• A bunch of other smaller object (comets, asteroids, Kuiper Belt Objects etc.)

What does the solar system look like?

The scale of solar system (distances between planets are not to scale)

A way to remember the order of the planets:

My Very Excellent Mother Just Sent Us Nine Pizzas

Where is everything?

J S U N P

1 AU is the mean Sun-Earth distance = 150 million km

For comparison: The nearest star (Proxima Centauri) is 4.2 LY=265,000 AU

KB

Outer solar system

Me V E Ma

Note log scales!

Inner solar system

1.5 AU

Note logarithmic scales!

Me V Ma E

Jovian or giants planets Terrestrial planets

The Sun An image in the visible light. The dark spots are sunspots

The Sun •Provides most of the energy received by the Earth and other planets

•Radius: 696,000 km (108 radius of Earth)

•Mass: 333,000 mass of Earth

•It contains 99.8% of the mass of the solar system

•Composition (by mass): 70% H2, 28% He, ~2% of heavier elements

•Surface temperaure:5,800 K

•Core temperature; 15 million K

•Source of energy: Conversion (Fusion) of H into He

•It is a nuclear fusion power plant

•Each second, it converts 600 million tons of H into 596 million tons of

He

•What happens with the missing 4 million tons of matter?

• That matter is converted into energy according the Einstein equation

•E = mc2

• Its gravity determines the orbit of all the planets

•It is the closest Star

The four terrestrial (inner) planets • Sizes to scale

• Small in size and mass

• Composed primarily of rock and metals

• High density

• Only 3 satellites. Earth (Moon), Mars (Phobos and Deimos)

• No rings

Mercury • Average distance from Sun: 0.39 AU

•Radius: 2440 km, 0.38 Earth radius

•Mass: 0.055 Earth mass

•Average density: 5.43 g/cm^3. This suggest an iron core

•No atmosphere

•Composition: made of metal and rock; large iron core

•Average surface temperature: 700K (day), 100 K (night)

•The smallest of all planets

• Surface: heavily cratered; long, tall, steep cliffs

• Because of lack of atmosphere: very hot and very cold: 425°C (day), –150°C (night)

• Rotational period: 58.6 days, orbital period: 87.9 days. Resonance 2/3

•No satellites

•Messenger spacecraft in orbit around the planet. First orbiting spacecraft.

Venus •Average distance from Sun: 0.72 UA

•Radius: 6051 km, 0.95 earth radius

•Mass:0.82 earth mass

•Average density; 5.24 g/cm^3

•Average surface temperature: 740 K

•Nearly identical in size to Earth; surface hidden by thick clouds of droplets of sulfuric acid.

•Dense atmosphere composed mainly of carbon dioxide

• Extreme greenhouse effect:

• Even hotter than Mercury: 470°C (880°F) both day and night

• Atmospheric pressure equiv. to pressure 1 km deep in oceans

• No oxygen, no water, …

• No satellites

•Spacecraft in orbit to study the planet : Magellan (radar surface imaging), Venus Express

Earth • Our home planet, the blue planet

•Average distance from sun; 1AU

•Radius: 6378 km. 1 Earth radius

•Mass; 1 Earth mass

•Average density:5.52 g/cm^3

•Average surface temperature: 290 K

• The only object with surface liquid water in the solar system; about 3/4 of surface covered by

water

• A surprisingly large moon. The most accepted theory for the formation of the Moon: The

result of an impact with a large body (Mars-size)

Earth and Moon

to scale

(distance not to

scale)

Mars • Average distance from Sun:1.52 AU

• Radius: 3397 km, 0.53 Earth radius

•Mass: 0.11 Earth mass

•Average density: 3.93 g/cm^3

•Average surface temperature:220 K

•Satellites: two small ones ,Phobos and Deimos). Probably two asteroids captured

• Looks almost Earth-like, but don’t go there without a spacesuit!

•The atmospheric pressure is low, 1/150 of the Earth.

•Temperature well below freezing

•No enough oxygen, in the atmosphere, just traces

• Giant volcanoes, a huge canyon, polar caps made of frozen carbon dioxide (dry ice) and

water

• Water flowed in the distant past; maybe more recent as well…

• Could there have been life?

The four Jovian (outer) planets • They are large in comparison with the Earth and all the terrestrial planets

• Composed primarily of gases (mostly hydrogen and helium), liquids, and ices

• All of them have low density

• 169 known satellites

• All the four Jovian planets have rings

Jupiter

•Average distance from the Sun: 5.2 AU

•Radius: 71,492 km (11.2 Earth radius)

•Mass: 318 Earth mass

•Average density: 1.33 g/cm^3

•Composition: Mainly H and He

•Cloud top temperature: 125 K

•Satellites: at least 67

•Four large satellites discovered by Galileo

(Galilean satellites): Io, Europa, Ganymede

and Callisto

•The volume of Jupiter is more than 1000

of Earth volume

•Long-lived storm: The Great Red Spot

•No solid surface

• It has rings, too faint to see them from

ground-based telescopes. Discovered by

Voyager spacecraft

•Spacecrafts: Pioneer 10 and 11 (1970”s),

Voyager 1 and 2,(1980’s) Galileo (orbit),

Cassini

The Galilean satellites • Io (shown here) has several active volcanoes. The most volcanic active body

in the solar system

• Europa has an icy crust with a subsurface ocean. Is a candidate for

the search of life in the subsurface ocean

• Ganymede is the largest moon in solar system — larger than Mercury

• Callisto: a large, cratered “ice ball” with unexplained surface features

Saturn •Average distance from the sun: 9.54 AU

•Radius: 60,268 km, 9.4 radius of Earth

•Mass: 95.2 mass of Earth

•Average density: 0.70 g/cm^3

•Composition: Mostly H and He

•Cloud-top temperature: 95K

• Satellites: At least 62

•It is a giant and gaseous planet like Jupiter

• It has the most spectacular ring system . Easily visible even in small

telescopes

• Large number of satellites

• The largest is the cloud-covered Titan. This is another body targeted for

search life in the solar system. It has high content of hydrocarbons.

•Titan has lakes and small oceans of liquid methane and ethane

• Currently under study by the Cassini spacecraft in orbit around the planet

Saturn’s rings

The rings are NOT

solid; they are made

of countless small

chunks of ice and

rock, each orbiting

like a tiny satellite.

Uranus • Average distance from Sun: 19.2 AU

•Radius: 25,559 km, 4.0 radius of Earth

•Mass: 14.5 Mass of Earth

•Average density: 1.32 g/cm^3

•Composition: H, He, water, ammonia, methane

•Cloud-top temperature: 60K

•Satellites: at least 27

•Orbital period: 84 years

•Sidereal rotation period: -72 earth days

•Much smaller than Jupiter and Saturn, but much

larger than Earth

• Made of H, He gas, hydrogen compounds (gas

and ices of H2O, NH3, CH4)

•The bluish green color is due to the presence of

methane in the atmosphere. Methane absorb the

red part of spectrum and reflect the blue.

•Extreme axis tilt, 97 degrees — nearly tipped on

its “side” — makes extreme seasons during its

84-year orbit.

• The satellites and ring system also tipped in

their orbits around 97 degrees

• The extreme tilt probably caused by a collision

with a large body

Neptune •Average distance from Sun: 30.1 AU

•Radius: 24,764 km, 3.9 earth radius

•Mass: 17.1 Earth mass

•Average density: 1.64 g/cm^3

•Composition: H, He, water, ammonia,

methane

•Cloud-top temperature: 60K

•Satellites: at least 13

•Orbital period: 165 years

•Rotational period: 16 hours

•Absorption of red due to methane

content in the atmosphere make it

appear blue

• The largest satellite Triton (shown

here) orbits the planets in “backward”

direction. Triton is probably a captured

body. It is larger than Pluto.

•Triton has “geysers” of nitrogen gas

Pluto Pluto is one of the largest dwarf planets (Eris is slightly larger). They are

located farther than Neptune

Average distance from Sun: 39.5 AU

Radius: 1160 km, 0.18 Earth radius

Orbital period: 248 years

Mass: 0.0022 Mass of Earth

Average density: 2.0 g/cm^3

Average temperature: 40K

Satellites: 5

Pluto and four of its satellites: Charon, Nix, Hydra and P4

(Image by Hubble Space Telescope)

Pluto and its 5 satellites P5 discovered in 2012

(Hubble telescope image)