Hello ATS,
I have been a long time lurker on ATS, this forum never fails to amaze me and to expand my horizon. Now this will be my first thread about moons in
our Solar System and the different kinds that exist.
While researching Europa and Phobos I stumbled upon a site that has a list of moons in our solar system, to my surprise there were more than I
expected, a total of 172 known natural moons orbiting planets in our Solar System. Wow, that's a lot!
The following list gives you perspective of how many there are:
Mercury - 0 Moons
Venus - 0 Moons
Earth - 1 Moon
Mars - 2 Moons
Jupiter - 63 Moons
Saturn - 60 Moons
Uranus - 27 Moons
Neptune - 13 Moons
Dwarf Planets:
Pluto - 3 Moons
Haumea - 2 Moons
Eris - 1 Moon
You will find the complete list
here
And the list is not close of being finished. So what makes a moon a moon? Well the definition of a moon has become unclear over the last years, some
scientists refer to it as "natural satellites" some others prefer the term "moon". But no matter what you choose to say, a moon/natural satellite
is a trapped object in orbit around a planet. So they can be any size or shape to be referred as a moon? So far, yes!
Several interviews with moon hunters and top theorists reveal that the definition of a moon is not clear and that there has been almost no discussion,
professional or casual, about whether there should be any lower size limits set to separate real moons from miniature imposters. And nobody is in a
rush to do anything about it.
Some take long, elliptical paths and stray far above and below the planet's plane of rotation. Few are round.
Space.com
So we have moons like our own:
And we have moons of different shape, for example Phobos:
So how can we really differentiate them from another? Well there are four distinct kinds of moons/natural satellites, a regular moon, an irregular
moon, inner moons, and outcast moons.
Regular Moons:
While irregular moons define the outer orbital reaches of a planet's domain in space, the next region in is dominated by regular moons. Examples
include Saturn's moon Titan and Jupiter's Galilean satellites: Io, Europa, Ganymede and Callisto. These classic, large and round moons tend toward
entirely stable, simple, nearly circular orbits. All move through a plane in space that is roughly equal to the planet's equatorial plane. This
conformity leads theorists to believe the moons formed out of the same nebula of gas and dust that built the planet.
Irregular Moons:
Irregular moons are of unknown origin. They might be captured asteroids or comets, or perhaps they're pieces of young planetary hopefuls that didn't
survive to orbit at the big table of nine, researchers believe. Many irregulars travel in packs that indicate they were once parts of larger objects.
The irregulars are typically small and orbit at great distances and often on odd trajectories. Their orbits are stretched and tilted in just about
every way you can imagine. They soar high above and below the plane in which regular moons orbit. They come close to the planet and then zoom far away
on elliptical trajectories. More often than not their orbits are retrograde -- opposite the direction of regular moons and of the planet's spin.
Inner Moons:
Inner moons, sometimes called ring moons because they often travel amidst other debris, are almost surely the youngest. They're also the most likely
to disappear.
Outcast Moons:
Outside the traditional categories of satellites are two sorts of objects that really stretch definitions. Ahead of and behind Jupiter are two packs
of asteroids -- tens of thousands of them -- that orbit the Sun but are also gravitationally bound to Jupiter. Astronomers call them Trojan
asteroids.
Visit the article (
Space.com) for more information.
I hope you found this informative.
[edit on 7-11-2009 by Clairaudience]
