Question

Suppose a satellite has a diameter of $800\mathrm{km}$ and an orbit that lies nearly in the equatorial plane of its parent planet well outside of the planet's ring system. Is the satellite likely to be a regular satellite, a collision fragment, or a captured asteroid?

Short answer

The satellite is likely to be a regular satellite.

Step-by-step solution

Understand Satellite Types

Firstly, understand the types of satellites. Regular satellites typically have nearly circular orbits and lie close to the planet's equatorial plane. Collision fragments are pieces of a larger body that broke apart and might have irregular shapes and more eccentric orbits. Captured asteroids are bodies that were captured by a planet's gravitational pull and generally have more eccentric and inclined orbits.

Analyze Orbit Position

The problem states that the satellite's orbit lies nearly in the equatorial plane of its parent planet and is well outside the planet’s ring system. Regular satellites often have orbits that align closely with the planet's equatorial plane, which is consistent with this description.

Consider Satellite Size

The satellite has a diameter of 800 km. This size is significant, and regular satellites are often large due to their origin near the planet; they are formed from the planetary disk from which the planet itself formed. Collision fragments and captured asteroids tend to be smaller and irregular in size.

Evaluate Satellite Type Likelihood

Given the orbit's alignment with the equatorial plane and the large size of the satellite, these characteristics strongly suggest it is a regular satellite rather than a collision fragment or a captured asteroid. Regular satellites are formed in the planet's equatorial plane and tend to be larger and more spherical than other types.

Key concepts

Regular Satellites

Regular satellites are closely associated with their parent planets. They typically form within the same disk of gas and dust that formed the planet itself.
This means that their orbits naturally align with the planet's equatorial plane, leading to nearly circular paths around their parent bodies. Here are some key characteristics of regular satellites:

• They usually have circular orbits and stay close to the equatorial plane of the planet.
• Their formations are synchronized with the planet's formation and are often spherical due to gravitational forces.
• They can be quite large, as they form from substantial material within the protoplanetary disk.

If a satellite orbits outside of a planet's ring and aligns well with the equatorial plane, it's likely to be a regular satellite. This alignment supports the theory that regular satellites formed alongside their parent planets in stable and predictable orbits.

Collision Fragments

Collision fragments result from cosmic collisions where a larger celestial body loses pieces of itself. These fragments often have irregular shapes and unexpected orbits, sometimes significantly deviating from their parent planet's equatorial plane.
Key features of collision fragments include:

• They generally have chaotic and eccentric (oval-shaped) orbits due to the unpredictable nature of their formation.
• These fragments tend to be smaller and irregularly shaped compared to regular satellites.
• Because of their origins, collision fragments might not conform to the regular patterns exhibited by native satellite bodies.

Thus, if a satellite does not have a near-circular orbit or is situated in an unexpected plane compared to the equator, it might be a collision fragment, born from a violent event in the solar system.

Captured Asteroids

Captured asteroids are celestial bodies that originate elsewhere in the solar system and are caught by the gravitational pull of a planet, transforming into its satellite.
These asteroids typically have more erratic orbits, with greater eccentricity and inclination compared to the planet's equatorial plane. Important aspects of captured asteroids include:

• They tend to have high-inclination orbits and are often quite eccentric.
• Their sizes and shapes are irregular, as they were not formed in the planet's vicinity but rather captured later.
• These orbital characteristics reflect their origins outside the immediate influence of the planet’s gravity.

If you encounter a satellite with an unusual and highly eccentric orbit that does not align with the planet's equatorial plane, it’s likely to be a captured asteroid rather than a regular satellite or a collision fragment.