Скачать или смотреть Formation of Comets / Halley's Comets [ How it is formed ]

Comets are essentially icy leftovers from the early solar system's formation, about 4.6 billion years ago. Here's a step-by-step breakdown:  

1. Birth in the Cold Outer Disk:

The early solar system had a spinning disk of gas and dust called the solar nebula.  
In the cold outer regions, beyond the "frost line," water and other volatile gases froze into ice grains.
2. Dusty Snowballs Forming:

These ice grains collided and stuck together, also incorporating dust particles present in the disk.
Over time, these small clumps grew larger through more collisions and accretion.  
3. Building Blocks: Cometesimals:

Eventually, kilometer-sized bodies called cometesimals formed. These were the initial "dirty snowballs" of ice, dust, and rock.  
4. Scattered by Giants:

The gravity of the large, newly formed giant planets (Jupiter, Saturn, Uranus, Neptune) flung many of these cometesimals into the far reaches of the solar system.
5. Forming the Reservoirs:

Kuiper Belt: Some scattered cometesimals settled into a donut-shaped region beyond Neptune (30-55 astronomical units from the Sun). This is the source of many short-period comets.
Oort Cloud: Many more were thrown into a vast, spherical cloud much farther out (2,000 to 200,000 AU from the Sun). This is thought to be the origin of most long-period comets.
6. Dormant Icy Bodies:

In these distant, cold regions, comets exist as inactive nuclei – frozen mixtures of ice, dust, and rock.
7. Awakening Near the Sun:

When a gravitational disturbance nudges a comet from these reservoirs into the inner solar system, the Sun's heat causes its ices to sublimate (turn directly into gas).
This creates the comet's atmosphere (coma) and its characteristic tails (gas and dust).