Question

What is the eventual fate of most short-period and long-period comets?

Short answer

Most comets disintegrate, become inactive, or collide with the Sun or planets.

Step-by-step solution

Understanding Short-Period Comets

Short-period comets, also known as periodic comets, have orbits that take less than 200 years to complete. Over time, as they get close to the Sun in their elliptical orbits, they lose material due to sublimation (transition of ice directly to gas), becoming less massive. Eventually, they can disintegrate entirely, collide with a planet or the Sun, or become inactive and indistinguishable from asteroids.

Understanding Long-Period Comets

Long-period comets have orbits that take more than 200 years to complete, often originating from the Oort Cloud. Like short-period comets, they lose material with each pass close to the Sun. However, due to their longer orbits, their periodicity means they have less frequent solar encounters. The eventual fate of these comets may be similar: disintegration, ejection from the Solar System, or collisions with celestial bodies.

Summarizing Comet Fates

The eventual fate of both short-period and long-period comets is largely governed by similar processes of gravitational interactions and sublimation. Many continue to shrink and disintegrate over time until they either vanish from disintegration or collision, or become inactive.

Key concepts

Short-Period Comets

Short-period comets are often the familiar comets we hear about in the news. They have relatively short orbits, taking less than 200 years to travel around the Sun. This means they frequently fanfare through our inner solar system.
They originate from the Kuiper Belt, a region just beyond Neptune filled with icy bodies. Because they travel around the Sun more often, they are subject to repeated heating.

• Each time they near the Sun, their icy composition starts to sublimate.
• Sublimation is the process where ice turns directly into gas, releasing dust and gas into space.

Over thousands of years, this repeated sublimation can result in a short-period comet losing considerable mass.
Their fate typically ends in one of these outcomes:

• Complete disintegration due to mass loss.
• Collision with a planet or the Sun.
• Gradually losing all their ice and becoming inactive, resembling asteroids.

Long-Period Comets

Long-period comets are the less frequent visitors from the outermost parts of our solar system. Their immense orbits take more than 200 years to complete. Unlike their short-period counterparts, these comets usually emerge from the distant Oort Cloud. This cloud is a shell of icy objects marking the solar system's boundary.
Because these comets are rarely near the Sun, they don’t undergo sublimation as frequently. When they do make their way towards the Sun, they, like short-period comets, gradually lose material.

• This is also due to sublimation when they come close to the Sun.
• Occasionally, they gain speed, potentially leaving the solar system!

The fate of long-period comets can lead to various outcomes:

• They might eventually disintegrate over many solar passes.
• Curiously, some may even be flung out from the solar realm due to gravitational forces.
• They can also strike a planet or the Sun, disappearing in a fiery demise.

Sublimation

Understanding sublimation is crucial to understanding how comets evolve over time. Sublimation is the process where a solid turns directly into a gas without becoming a liquid first.
In space, this occurs due to low pressure and high temperatures, especially when a comet passes close to the Sun.

• The intense sunlight causes ices in the comet to heat up rapidly.
• This process releases gas and dust, creating a glowing coma and sometimes a tail.

As a result, comets lose mass with each solar passage. This transformation, which doesn’t solely affect comet size, is visibly spectacular and contributes to their eventual fate:

• Repeated sublimation reduces the core size of comets significantly.
• When this mass loss is extensive, comets may disintegrate completely.
• The gradual depletion can also make them become inactive resembling barren asteroids.

Sublimation is not just a scientific concept but offers a mesmerizing space spectacle witnessed from Earth.