Definition
A long-period comet is a celestial object composed of ice and dust, whose orbit around the Sun exceeds two centuries. These comets originate from very distant regions located beyond the planets.
Structure
Their nucleus is a solid mixture of volatile ices and mineral particles. As they approach the Sun, the surface sublimates, releasing gas and dust that form the coma and tails.
Origin and Orbit
Most long-period comets come from distant reservoirs such as the hypothetical Oort Cloud. Their orbits are often highly inclined and can be oriented in any direction.
Orbital Behavior
Their trajectory sometimes brings them into the inner Solar System, where solar heating triggers cometary activity. After perihelion, they recede again to immense distances.
Evolution
Subjected to repeated passages, they may gradually lose their volatile substances or break apart. For those with extremely long periods, only one passage may occur during human history.
Limits
Their observation is rare and unpredictable, as their return exceeds the lifespan of civilizations. Their study relies on orbital calculations and observation of exceptional trajectories.