Download Wednesday, March 27

The Solar System
Contents of the Solar System
• Sun
• Planets – 9 known (now: 8)
– Mercury, Venus, Earth, Mars (“Terrestrials”)
– Jupiter, Saturn, Uranus, Neptune (“Jovians”)
– Pluto (a Kuiper Belt object?)
• Natural satellites (moons) – over a hundred
• Asteroids and Meteoroids
– 6 known that are larger than 300 km across
– Largest, Ceres, is about 940 km in diameter
• Comets
• Rings
• Dust
Size matters: radii of the Planets
The Astronomical Unit
• A convenient unit of length for discussing
the solar system is the Astronomical Unit
(A.U.)
• One A.U. is the average distance between
the Earth and Sun
– About 1.5  108 km or 8 light-minutes
• Entire solar system is about 80 A.U. across
The Terrestrial Planets
• Small, dense and rocky
Mercury
Mars
Venus
Earth
The Jovian Planets
• Large, made out of gas, and low density
Saturn
Jupiter
Uranus
Neptune
Asteroids, Comets and
Meteors
Debris in the Solar System
Asteroids
Asteroid Discovery
• First (and largest) Asteroid Ceres
discovered New Year’s 1801 by G. Piazzi,
fitting exactly into Bode’s law: a=2.8 A.U.
• Today more than 100,000 asteroids known
• Largest diameter 960 km, smallest: few km
• Most of them are named
• about 20 of them are visible with binoculars
Comets - Traveling Dirty Snowballs
• Small icy bodies, “dirty snowballs”
• Develops a “tail” as it approaches the Sun
Comet Anatomy
• Tail may be up to 1 A.U. long
Comet Tail
• Two kinds of tails:
• Dust
• Ion (charged
particles)
Shapes
Comet GiacobiniZinner (1959)
• Ion tail 500,000 km long
• Coma: 70,000 km across
Comet Hale-Bopp
(1997)
• Tail 40° long as seen
from earth
Halley’s Comet – a typical Comet
Meteor Showers
Radiant
Quadrantids (QUA)
Lyrids (LYR)
Eta Aquarids
Beta Taurids
Delta Aquarids
Perseids (PER)
Draconids
Orionids (ORI)
Taurids
Leonids (LEO)
Geminids (GEM)
Duration
Dec. 28-Jan. 7
Apr. 16-25
Apr. 21-May 12
June 30
July 25-31
Aug. 10-14
Oct. 6-10
Oct. 15-29
Oct.12- Dec 2
Nov. 14-20
Dec. 6-19
Meteors, Meteroids and Meteorites
• A Meteor is a sudden strike of light in the
night sky
• A Meteoroid is a small asteroid, less than
100 m in diameter
• A Meteorite is any piece of interplanetary
matter that survives the passage through
Earth’s atmosphere and lands on Earth’s
surface
Meteors and Meteorites
• Small particles that strike the atmosphere
• Come from fragments of asteroids, Moon, Mars,
comets
• Strike the earth all the time (“meteorites”)
– High speed means lots of energy released on impact
Impact Craters
• Barringer Crater, AZ
0.8 mi diameter, 200
yd deep; produced
by impact about
25,000 years ago
• Quebec's Manicouagan
Reservoir. Large
meteorite landed about
200 million years ago. The
lake, 45 miles in diameter,
now fills the ring.
Tunguska
• ~30 m body
struck Siberia
in 1908
• Energy equal
to that of a 10
Megaton
bomb!
• Detonation
above ground;
several craters
Frequency of Impact Events
Formation of the Solar System
• Features to explain:
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–
–
–
–
–
–
–
–
planets are far apart, not bunched together
orbits of planets are nearly circular
orbits of planets lie mostly in a single plane
directions of revolution of planets about Sun is the same, and is
the same as the direction of the Sun's rotation
directions of rotation of planets about their axes is also mostly in
the same direction as the Sun's (exceptions: Venus, Uranus, Pluto)
most moons revolve around their planets in the same direction as
the rotation of the planets
differentiation between inner (terrestrial) and outer (Jovian)
planets
existence and properties of the asteroids
existence and properties of the comets
Formation of the Solar System
• Condenses from a
rotating cloud of gas
and dust
– Conservation of angular
momentum flattens it
• Dust helps cool the
nebula and acts as
seeds for the clumping
of matter
Formation of Planets
• Orbiting dust – planitesimals
• Planitesimals collide
• Different elements form in
different regions due to
temperature
• Asteroids
• Remaining gas
Structure of the Planets explained
Temperature and density of materials drop with distance to sun