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Solar System
The solar system is the gravitationally
bound system comprising the sun
and the objects that orbit it.
Formation of the Solar System
• The solar system formed 4.6 billion years ago
• Gravitational collapse of a giant interstellar
molecular cloud.
• Vast majority of the system’s mass (99.86%) is
in the sun, with most of the remaining mass
contained in Jupiter.
Four inner planets
• “terrestrial” planets
• Mercury, Venus, Earth and Mars
• Composed of rock and metal
Four outer planets
• Giant planets
• Much more massive than the terrestrial
• Jupiter and Saturn are gas giants, mostly
hydrogen and helium
• Uranus and Neptune are ice giants, mostly
water, ammonia and methane
Orbits
• Elliptical, but nearly circular
• Flat
• Within a flat disc called “ecliptic”
Smaller Objects
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Asteroid belt between Mars and Jupiter
Kuiper belt beyond Neptune (ices)
Dwart planets (Pluto, Chiron, Ceres, Eris)
Solar wind. A stream of charged particles
flowing outward from the sun.
• Oort cloud. Source for comets. Reservoir of
ices.
Sun
• 99.86% of mass of solar system (332,900
times the mass of the earth)
• Mostly hydrogen and helium
• Fusion of hydrogen into helium.
• Main sequence star on Russell Hertzsprung
• Surface temperature 5500 – 5700 K
• Radiates yellow and yellow-green light
Inner Solar System
• Four terrestrial or inner planets have dense,
rocky compositions, few or no moons and no
ring systems.
• Venus, earth and Mars have atmospheres that
generate weather
• Impact craters, mountains, valleys and
volcanoes
Asteroid belt
• Between Mars and Jupiter
• Rock and metallic minerals with some ice
• Remnants from solar system formation that
failed to coalesce because of the gravity of
Jupiter
• Tens of thousands, perhaps millions, of
objects over one kilometer in diameter.
Outer solar system
• Four outer planets or giant planets
• All four giant planets have rings
• Jupiter and Saturn are hydrogen and helium
gaseous
• Uranus and Neptune are ices of water,
ammonia and methane
Kuiper belt
• Mostly ice
• Dwarf planets
• 100,000 objects with diameter greater than 50
kilometer
• Pluto, Chiron (moon of Pluto)
Oort Cloud
• Trillion icy objects
• Source for comets
• Move very slowly
Solar System in Milky Way
• Milky Way is a spiral galaxy with a diameter of
100,000 light years containing about 100
billion stars (10^(11))
• The sun is on one of the outer spiral arms
between 25,000 and 28,000 light years from
the center of the Milky Way.
• Speed is 220 km/s, so it completes one
revolution every 225-250 million years.