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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?
Note logarithmic scales!
Me
V E
Ma
Terrestrial planets
J
S
U
N P
KB
Jovian or giants planets
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
Me V E Ma
Inner solar system
1.5 AU
Note
log scales!
Outer solar system
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 and Moon
to scale
(distance not to
scale)
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)
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)