Download Public Lecture - Our Solar System

OUR SOLAR SYSTEM
James Martin
Facebook.com/groups/AstroLSSC
Twitter.com/AstroLSSC
“It’s time for the human race to enter the
solar system.”
-Dan Quayle
Structure of the Solar System
• Our Solar System
contains a star, planets,
dwarf planets, and other
objects!
• Orbits of the planets are
within a few degrees of
each other and move in
the same direction
around the Sun
The Sun
• Sun’s energy comes from nuclear fusion
within its core
• A star’s temperature determines its
“color”
– Coldest stars are red (as low as ~1,000oF)
– Hottest stars are blue (as high as ~62,500oF)
– Our Sun’s surface temperature = ~10,000oF
Defining a Planet
• A planet is defined as a celestial body that:
– Orbits the Sun
– Is nearly spherical due to its own gravity
– Travels along an orbital path free of most debris
• Dwarf planets meet the first two conditions only
Planet Sizes & Compositions
• Inner Planets
– Terrestrial planets composed of rocky materials with dense iron
cores and high average densities
• Outer Planets
– Jovian planets composed primarily of lighter elements, such as
H and He, with low average densities
Mercury
• Revolution period of 88 days
• Extreme temperature
fluctuations ranging from
800oF to -270oF
• No moons 
Venus
• Thick CO2, H20 and H2SO4 (sulfuric
acid) atmosphere traps sunlight
and broils the planet’s surface
– Maximum surface temperature
reaches up to 900oF
• Revolution period of 225 days, but
one rotation is 243 days
– In other words, 1 day on Venus is
longer than 1 year!
• No moons 
Earth
• Only planet known to support
living organisms
• 71% surface is composed of
water
– Oceans help to maintain stable
temperatures
• O & Nitrogen rich atmosphere is
layered trap sunlight to heat the
surface (greenhouse effect)
• One Moon orbits Earth
Mars
• Water on Mars!
– Most water is frozen in the polar caps
or as subsurface permafrost
– Subsurface liquid water recently
discovered
• Appears red due to iron oxide (rust)
in its soil
• One revolution takes about 2 yrs
• 2 moons orbit the planet
Jupiter
• Great Red Spot is a complex storm raging for the last ~400 years
• Largest and most massive planet
– Diameter is 11x bigger than that of Earth’s
• One revolution
takes about 12
years
• Composed mostly
of H and He
• 67 known moons!
Io and Europa
over Jupiter disk
Saturn
• Mostly composed of H and He
• Complex ring structure A-G
– Only A, B and C rings can be readily seen from
Earth!
– Rings are less than 1 mile thick, but extend to ~
260,000 miles from the surface
• One revolution takes ~30 years
• 62 known moons!
Uranus
• Bluish color is a result of methane in the
atmosphere (absorbs red and green light)
• One revolution takes ~84 years
• Cloud top temperatures measured to be
about -350oF over most of the planet
• Planet is tilted 60o and appears to rotate
on its side
• 5 known moons
Neptune
• Also blue due to methane in the
atmosphere
• One revolution takes ~165 years
• Several large storm systems
similar to Jupiter’s G.R.S.
– Great Dark Spot is the size of Earth!
• Fastest winds in the solar system
(~1200 mph)
• 14 known moons
Dwarf Planets
Video: What is a dwarf planet?
Asteroids
• Asteroid sizes range from
100m to about 1000km
• 100,000+ rocky objects
within the orbit of Jupiter
(2-3.5 AU)
– Orbit the Sun in the same
direction as the planets
Meteoroids
• Interplanetary rocky material smaller
than 100m (down to grain size)
– Called a meteor as it burns in Earth’s
atmosphere
– If it makes it to the ground, it is a meteorite
• Most meteor showers are the result of
the Earth passing through the orbit of a
comet which has left debris along its
path
Trans-Neptunian Objects
• 1,000+ small bodies orbiting beyond Neptune in the same
direction as the planets
– Most are in the Kuiper Belt at 30-50 AU
– Pluto orbits at an avg. 39 AU!
Comets
• Kuiper Belt collisions cause
fragmented objects to change
orbits
• Sun’s radiation vaporizes ices,
producing gas and dust tails
• Some comets from the Oort Cloud
(~50,000 AU)
Scale of the Solar System
FOR ASTRONOMY
NEWS + EVENTS…
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