Satellite Formation in Our Solar System

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  • 0:03 How the Planets Got…
  • 0:49 Regular and Irregular…
  • 2:11 Collision Fragments &…
  • 3:16 Captured Asteroids and…
  • 4:28 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson will describe regular, irregular, collision fragments, captured asteroids, and other types of satellites orbiting around the planets of the solar system.

How the Planets Got Their Moons

With the exception of Mercury and Venus, which have no moons, there are over 145 officially recognized moons in our solar system orbiting the other planets. There are some moons-to-be awaiting confirmation and more that will be discovered in the future as our technology improves.

But not all moons look like our planet's moon, be it in their size, color, or shape, and while a lot of that is owed to the fact that these moons formed at very different distances from the sun, the way they formed also influences their properties.

The four different ways by which planets in our solar system got their satellites, or moons, bodies orbiting around a larger parent body, will be described in this lesson.

Regular and Irregular Satellites

Some satellites are known as regular satellites. These are moons that likely formed as their parent planets formed from the solar nebula long ago.

These moons exhibit important properties:

  • Regular satellites tend to be large and bright. Hence, they have been known to us for a long time because they're so easy to detect.
  • They usually orbit close to their parent planet. Remember, these little guys were born right alongside their planets and don't want to stray too far away from them because they're so close to one another. Pun fully intended.
  • Their orbits are regularly spaced around their planets. That is to say, they are spaced away from their planets sort of like the planets are spaced around our sun.
  • Furthermore, their orbits are basically circular.
  • Their orbits are nearly in the equatorial plane of their planet.
  • They move in the prograde direction. That is to say, they rotate or revolve in the same direction as their parent planet.

Unlike the regular satellites, the irregular satellites are moons that are likely captured objects that:

  • May be smaller than the regular satellites
  • Might have retrograde and/or very inclined orbits
  • Are typically far away from their planets

Collision Fragments & Shepherd Moons

The Jovian planets, in particular, have a lot of small and irregularly shaped satellites that nonetheless have orbits similar to that of the regular satellites. Such satellites are most likely collision fragments, or satellites that are fragments of once larger satellites that were torn apart when they collided with a meteoroid.

If you were to take a rock and smash it against another rock, bits and pieces would go in every direction. In space, a planet's gravity would keep these fragments in orbit around the planet, and thus they will become satellites of that planet.

Some of these collision fragments orbit close to their parent planet, so much so that they are known as shepherd satellites, satellites that attract and confine particles into a planetary ring by their gravitational attraction. They are like shepherd dogs that collect and confine sheep into a small area, except these satellites attract dust, rocks, and ice and corral it all into a planet's ring system.

Captured Asteroids & Our Moon

Other types of moons orbiting around a planet may simply be captured asteroids that came too close to a planet and got ensnared in its gravitational field. Actually, these types of satellites are just about as far away as they can be from a planet without being whisked away from the planet's gravitational field by the sun's more powerful gravitational forces.

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