1. The Solar System
all planets orbit in same direction (ccw as seen from above the north pole)
all orbits lie nearly in a single plane (Mercury (7deg) and Pluto (17deg) being most notable exceptions)
inner planets are small, dense, rocky (Terrestrial); outer planets are large, gaseous, low density (Jovian)
density = mass/volume
inner planets close together, outer planets further apart

2. 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
Some of this debris lands on earth as meteorites
Most of the solar system is a better vacuum than we can produce in the laboratory on earth!
Meteoroids = bodies < 100 m across

3. Size matters: radii of the Planets

4. 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
Size of solar sys ~ 1/1000 lyr; distance to nearest star ~ 4.3 lyr

5. The Terrestrial Planets
Small, dense and rocky
Mercury
Mars
Venus
Earth

6. The Jovian Planets Large, made out of gas, and low density Saturn
Terrestrial-type cores
Jupiter
Neptune
Uranus

7. Asteroids, Comets and Meteors
Debris in the Solar System
Some of this debris lands on earth as meteorites
Most of the solar system is a better vacuum than we can produce in the laboratory on earth!
Meteoroids = bodies < 100 m across

8. Asteroids
mostly in orbits that lie between that of Mars and Jupiter in the asteroid belt; probably just junk that never formed a planet
some have elongated orbits that cross orbits of Mars and Earth: some occasionally collide with Earth (Maybe 3 every Myrs or so)
Asteroids are also found locked into Jupiter's orbit (Trojan asteroids)
Too small and far away for surface to be visible from Earth, but close-up pictures have been returned by Galileo. Size can be estimated from brightness (assuming reflectivity is known), or from occultation of stars.
The moons of Mars, Phobos and Deimos, photographed by Viking, may have originally been asteroids.
At least one asteroid (Ida) has a moon (Dactyl)!

9. 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

10. Comets - Traveling Dirty Snowballs
Small icy bodies, “dirty snowballs”
Develops a “tail” as it approaches the Sun
Whipple's dirty snowball theory
Some rock, water ice, ammonia, methane, other junk
Not very dense, ~ 100 kg/m^3, masses typically about the same as smaller asteroids
Highly elliptical orbits
Halley's comet: orbit stretches from Earth's orbit to Neptune's; period 76 years, return predicted by Edmund Halley in 1705.
during 1986, Halley was photographed by spacecraft from USSR, western European consortium and Japan. Pictures show that surface of Halley is dark (covered with dirt) and that gas escapes from cracks in the surface
Tycho showed that they are celestial bodies, not weather phenomena.

11. Comet Anatomy Tail may be up to 1 A.U. long Parts of a comet:
• nucleus: icy core
• coma: sphere of gas evaporated from nucleus when it approaches the sun
• tail: ice and gas that streams away from comet.
NOTE: direction of tail is opposite to sun, not opposite to motion of comet; streaming is due to solar wind (a wind of charged particles emitted by the Sun)

12. Comet Tail
Two kinds of tails:
Dust
Ion (charged particles)

13. Shapes Comet Giacobini-Zinner (1959) Comet Hale-Bopp (1997)
Ion tail 500,000 km long
Coma: 70,000 km across
Comet Hale-Bopp (1997)
Tail 40° long as seen from earth

14. Halley’s Comet – a typical Comet

15. Meteor Showers Radiant Duration Quadrantids (QUA) Dec. 28-Jan. 7
Lyrids (LYR) Apr
Eta Aquarids Apr. 21-May 12
Beta Taurids June 30
Delta Aquarids July 25-31
Perseids (PER) Aug
Draconids Oct. 6-10
Orionids (ORI) Oct
Taurids Oct.12- Dec 2
Leonids (LEO) Nov
Geminids (GEM) Dec. 6-19
Some meteorites come from breakup of comets.
meteor showers occur when Earth passes through former comet's orbit.
radiant: the meteors appear to come from the direction of the original comet
an extreme example: Shoemaker-Levy strikes Jupiter, 1994

16. 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
before Apollo missions, these were the only extraterrestrial materials we could analyze!
extraterrestrial origin not established until 1803 (Biot)
come from fragments of asteroids (this explains stony and iron meteorites: they come from core and mantle of original body), some apparently come from the Moon, and some perhaps from Mars! (based on chemical analysis). Small ones are the remains of broken-up comets
some 4.5 billion years old, give clues to origin of solar system
If less than 1m across they generally burn up before hitting the ground

17. 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
before Apollo missions, these were the only extraterrestrial materials we could analyze!
extraterrestrial origin not established until 1803 (Biot)
come from fragments of asteroids (this explains stony and iron meteorites: they come from core and mantle of original body), some apparently come from the Moon, and some perhaps from Mars! (based on chemical analysis). Small ones are the remains of broken-up comets
some 4.5 billion years old, give clues to origin of solar system
If less than 1m across they generally burn up before hitting the ground

18. 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.

19. Tunguska ~30 m body struck Siberia in 1908
Energy equal to that of a 10 Megaton bomb!
Detonation above ground; several craters

20. Frequency of Impact Events

21. Formation of the Solar System
Features to explain:
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

22. 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

23. Formation of Planets Orbiting dust – planitesimals
Planitesimals collide
Different elements form in different regions due to temperature
Asteroids
Remaining gas

24. Structure of the Planets explained
Temperature and density of materials drop with distance to sun