Did You Know There Are Over 200 Other Moons in our Solar System?
Our Solar System is teeming with small worlds orbiting more massive planets. You may be familiar with one of these worlds, our Moon. We now know of more than 200 other “moons” in our Solar System alone. Eighteen of these moons are rounded into a spherical shape, just like our Moon.
Galileo Galilei was the first person to discover moons orbiting another planet in 1610 when he discovered the four Galilean moons, Ganymede, Callisto, Io, and Europa orbiting Jupiter. These moons are visible with binoculars or a telescope with a few completing orbits around Jupiter in the same night. Along with these Jovian moons, Saturn’s seven large moons are also visible via telescope, although they are a little harder to spot.
How Moons are Named
One of my favorite characteristics of these moons is their names. Most moons are named after mythological characters with a subordinate relationship with the mythological characters their planet was named after. The only exception to this rule is Uranus’ moons, which were named after characters from Shakespearean plays.
Types of Moons
Regular moons have prograde orbits (an orbit that follows the direction of the primary planet’s rotation) and usually orbits the planet close to the planet’s equatorial plane. For reference, the Moon is unusual as it orbits the Earth closer to the Earth’s ecliptic plane than it’s the equatorial plane.
The Earth’s equatorial plane is the imaginary plane that extends out into space from the Equator. The Earth’s ecliptic plane is the imaginary plane in which the Earth and most other planets orbit the Sun. This plane is also the apparent path the Sun travels through the sky throughout the year if you mark the Sun’s location in the sky at the same time every day over a period of time.
Irregular moons orbit their planets or “primary” in retrograde orbits. A retrograde orbit is a moon’s orbit that moves in the opposite direction as the planet’s rotation. Retrograde orbits are similar to observational retrograde motion, which is the apparent change in a celestial body’s movement, usually a backward direction. These moons are typically tiny, non-spherical, orbit their primary at extreme angles and most likely captured minor planets of the Solar System.
Moons of Each Planet
Inner Solar System Moons
The Earth has one Moon with a couple of co-orbitals, or quasi-satellites: the asteroids 3753 Cruithne and 2002 AA29.
Mars has two moons, Phobos and Deimos. These names mean “fear” and “dread” respectively and are the attendants of Ares, the god of war in Greek mythology.
Jupiter has the largest number of known moons in our Solar System coming in at 79. Of these moons, 52 have been named. 8 of these moons are regular moons which include Galilean moons and the smaller Amalthea group. Jupiter’s moons were named after lovers of Zeus, the Greek equivalent of Jupiter. Jupiter’s moons can be classified in several ways.
There are 5 groups based on their origins and the way they orbit the planet. These groups consist of the Galilean moons, and the Himalia, Carme, Ananke, and Pasiphae groups. The Galilean moons, the Himalia group, and three moons without a group are regular moons. The Carme, Ananke, and Pasiphae groups are irregular moons.
Saturn has 62 moons with orbits. There may be more as that number continues to climb every few years. Seven moons of these moons are large enough to reach hydrostatic equilibrium. Saturn’s moon, Titan is the second-largest moon in our Solar System. 24 of Saturn’s moons are regular and are named after the mythological Titans or other characters associated with the Roman god, Saturn.
Identifying moons of Saturn can be tricky since Saturn’s rings are composed of millions of small rocks and icy material that can otherwise be classified as a moon. At least 150 “moonlets” have been identified. Moonlets are smaller, minor satellites and usually serve as “shepherd moons”. Shepard moons clear gaps in planetary-ring material and keep particles within a ring contained.
Saturn’s moons are grouped into the following groups: Shepherd Moons, Norse moons, Tethys Trojans, Inuit group, the Gallic group, the Dione Trojan moons, the Alkyonides group and two subgroups of the Norse moons, Narvi and Skathi. Trojan moons are moons that share an orbit of a larger moon.
Trojan moons orbit their planet in a stable orbit approximately 60° ahead or behind the main moon. The points at 60° ahead or behind the other orbiting body are referred too as Lagrangian points L4 and L5. The term “trojan” also applies to planetary objects other than moons as well.
Uranus has 27 moons. These moons are divided into three groups, the 5 major moons, 13 inner moons, and 9 irregular moons. Uranus’ moons are named after characters from the works of Shakespeare and Alexander Pope’s work: The Rape of the Lock. Titania, Uranus’s largest moon is the eighth-largest moon in the Solar System and is slightly larger than Pluto. All of Uranus’s moons orbit Uranus in a coplanar fashion, parallel to Uranus’s equator, which is tilted 98° to its orbit.
Neptune has 14 moons with one large moon, Triton. Triton is unique for a large moon in that it orbits Neptune a retrograde orbit. Neptune’s smaller moons can be classified into 7 inner, regular satellites and 6 outer, irregular satellites. Neptune’s moon Neso has an orbital period of about 26 years and orbits further from its planet than any other known moon in the Solar System.
Dwarf Planet Moons
Pluto has five moons with its largest moon, Charon, being more than half the size of Pluto. Pluto and Charon are a binary or double dwarf planetary system, since Charon and Pluto orbit a point outside of Pluto’s mass. The only other system close to this configuration is the Earth-Moon system. The Moon orbits a point miles away from the Earth’s center. Pluto’s four other moons are Nix, Hydra, Kerberos, and Styx. These moons are far smaller and orbit the Pluto–Charon system.
Haumea has two moons, Hiʻiaka and Namaka, named after Hawaiian goddesses since Haumea was named after the Hawaiian goddess of childbirth. Haumea and its moons are thought to be a part of a collision family. A collision family is a group of objects that may share their origin in a historical collision. A collision in Haumea’s past would explain both Haumea’s usual shape, rotation, and the extremely eccentric orbits of its moons.
Eris has one moon, Dysnomia. Dysnomia was named after the daughter of the Greek goddess Eris, in which Eris is named.
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