1. Asteroids

• Asteroids are remnants of planetary formation that failed to form a planet due to Jupiter’s strong gravitational pull
• Also called planetoids
• Composition:
  • Rocky and metallic minerals
  • Some ice
• Size:
  • From microscopic particles to hundreds of kilometres
    

2. Asteroid Belt

• A circular zone of asteroids orbiting the Sun
• Located between Mars and Jupiter
• Distance from Sun: 3 AU to 3.3 AU
• Reason for formation:
  • Jupiter’s gravity prevented planet formation
• Mostly contains rocky bodies
• The asteroid belt is NOT between Jupiter and Saturn

  

3. Ceres

• Largest asteroid
• Distance from Sun: 77 AU
• Diameter: 946 km
• Classified as:
  • Dwarf planet
  • Protoplanet
• Only an asteroid large enough to become nearly spherical
• All other asteroids → Small Solar System Bodies
• Ceres is to the asteroid belt what Pluto is to the Kuiper Belt

4. Kuiper Belt

• A ring of icy objects beyond Neptune
• Extends from 30 AU to 50 AU
• Composition:
  • Mostly ice + rocky material
• Similar to the asteroid belt, but:
  • Farther
  • Icy instead of rocky

5. Pluto and Charon

• Pluto:
  • Distance: 39 AU
  • Largest known Kuiper Belt Object
  • Diameter: 2,377 km
  • Declared Dwarf Planet (2006)
• Charon:
  • The largest moon of Pluto

IAU Definition of a Planet

A planet must:

• Orbit the Sun
• Be nearly spherical
• Not be a satellite
• Clear its orbital neighbourhood

Pluto fails the last condition

Dwarf Planet

• Meets all criteria except clearing debris
• Examples:
  • Ceres
  • Pluto
  • Eris (2,326 km)

6. Comets

• Made of:
  • Frozen gases (water, ammonia, methane, CO₂)
  • Rocky and metallic material
• Orbits:
  • Highly elliptical
• When near the Sun:
  • Solar wind causes heating
  • Forms coma and tail
    

Types of Comets

• Short-period comets
  • Origin: Kuiper Belt
  • Period: a few hundred years
• Long-period comets
  • Origin: Oort Cloud
  • Period: thousands of years

7. Oort Cloud

• A giant spherical shell of icy bodies
• Surrounds the solar system
• Distance:
  • 5,000 AU to 100,000 AU
• Source of long-period comets
  
  

8. Halley’s Comet

• One of the largest known comets
• Orbital period: 76 years
• Last visited Earth: 1986
  
  

9. Meteoroid, Meteor & Meteorite

Meteoroid

• Small solid debris from:
  • Asteroids
  • Comets
• Moves in interplanetary space

Meteor

• When a meteoroid enters Earth’s atmosphere
• Burns due to friction in the mesosphere (~200 km)
• Appears as:
  • Shooting star / falling star

Meteorite

• Part of a meteoroid that:
  • Survives atmospheric burning
  • Reaches Earth’s surface

10. Meteorite Craters

• Circular depressions formed by a meteorite impact
• Common on:
  • Moon and Mercury
  • Reason: negligible atmosphere + geological inactivity

Largest Meteor Crater (World)

• Arizona, USA
• Depth: 1,300 m
• Age: over 10,000 years

11. Chicxulub Crater

• Location: Yucatan Peninsula, Mexico
• Cause:
  • Massive meteor impact
• Impact:
  • Mass extinction of dinosaurs
  • End of the Cretaceous period (65 million years ago)

12. Meteorite Craters in India

• Lonar Lake (Maharashtra)
  • Diameter: 8 km
  • Ramsar Site
• Dhala Crater (Madhya Pradesh)
  • Diameter: 14 km
• Ramgarh Crater (Rajasthan)
  • Diameter: 5 km
  • Potential meteorite crater