Primordial Matter in the Solar System
• Solar system formed out of cold, dense hydrogen gas cloud , but containing ALL other heavy elements
• Sun too young to have synthesized any other elements, still in the H  He production stage
(about half-way)

Planetesimals or Minor Planets
• In addition to the Sun and 8 planets and we have
-Asteroid Belt , rocky/metallic bodies (also called minor planets or planetesimals ) up to 1000 Kms in diameter,
-- Planet never formed, or broken up by Jupiter ’ s tidal effect
-- Pluto and Kuiper Belt Objects (KBOs)

‘ Debris ’ of the Solar System
• The ice/rock dichotomy is most starkly evident in comets and asteroids
• Meteoroids in space; meteors or meteorites when they enter the Earth ’ s atmosphere
 Comets/Meteors are mainly ice(snow) balls, and
 Asteroid/Meteorites are rocky/metallic objects
• Comets would have been a source of water on the
Earth
• Comets originate in either (i) the Oort Cloud at the edge of the solar system, or (ii) the Kuiper Belt beyond the orbit of Pluto

Planetesimals etc.
• Minor planets or asteroids, comets, and other objects orbiting the Sun obey
Kepler ’ s laws
• Kuiper Belt Objects (KBO ’ s) are planetesimals beyond Pluto ’ s orbit
• Recently discovered (at least) two
“ planets ” comparable to Pluto, named
Xena and Sedna

Asteroids
• Over 5000 found between 2.8-3.2 AU
• Keplerian orbits, e.g. P 2 = a 3
• Gaps, such as the Kirkwood Gap, due to orbital resonance with Jupiter and other asteroids (like the Cassini Division in Saturn ’ s rings)
• Jupiter maintains the asteroid belt, although may have prevented planet formation
• Families of asteroids: Floras, Trojans, and the AAA objects -- Amors Appolos, Atems – that could come close to Earth (Dinosaurs !)

Asteroids (Contd.)
• Small albedo ~ 0.1-0.2
• Masses: Largest about 1/20,000 of the mass of the Earth; all asteroids combined would still be only about 1/1000 of M(E)
• Composition of Asteroids  Meteorites ; metallic and silicates mixed with organic carbon compounds

Meteorites
• “ Stones from Heaven ”  Excalibur, Ka ’ aba
(black) stone, etc.; survive atmospheric friction and land on Earth)
• Metallic ones with pure iron; surprising ?
• Extraterrestrial origin since Iron never occurs in pure form on the Earth but as iron ore compounds
• Stones (silicates), Irons (iron and nickel),
Stony-irons (silicates and metals)
• Largest meteorite (Namibia): 7m 3 , 60 tons
• Ages from radioactivity  4.6 Gyrs

Typical asteroids

Meteorite damage!

Barringer Crater (Flagstaff, AZ)

Stony Carbonaceous chondrites
(Allende Meteorite)

Stony Iron Meteorite
Glassy nodules on exterior. Why?

Iron Meteorite
(Interlocking crystal pattern)

Comets

Comets: Head and Tail
Where is the Sun (which direction) ?

Orbits of comets

Altering orbits of comets
Long-period comet
Short-period comet

The Tale of Two Tails!
Gaseous and Ionic Tails

ice/dust tail (white)
Ion tail (blue)
Ice/dust tail: Evaporating mattter as the comet approaches the Sun
Ion tail: charged particles
Electrons, protons, ions pushed directly away by charged particles in the
Solar Wind

Structure of comets

The vaporizing nucleus

Cometary Orbit Around the Sun

Comets
• Ancient remnants of the Solar nebula
• Long period comets from the Oort Cloud; short period ones from the Kuiper Belt
• Total number about 10 trillion !
• Structure  Nucleus, Coma, H-cloud, Tail
• Tail(s): Gaseous and Ionic
• Nucleus  ~ 5-10 Kms diameter, less than ten billionth of the mass of the Earth
• Total mass in comets about 1000 times
Earth ’ s mass (all the planets combined)

Comets (Contd.)
• Formed out of the building blocks of the
Solar System: Ices (H2O, CO2), like the outer planets
• Large eccentricity
• Evaporate while approaching the Sun; the tail gets longer
• Sometimes break up , e.g. Comet
Shoemaker-Levy in 1993
• Meteor Showers , e.g. Leonid shower in 2001

Meteors
• “ Shooting Stars ”
• Icy/Dusty pieces like cometary material, or small pieces from comets
• Burn up completely in the atmosphere
• Meteor showers appear to originate at a common point  optical illusion like parallel rail tracks meeting in the distance