Moons are natural satellites that revolve around planets or asteroids. They come in many shapes, sizes and types. The largest moons are spherical, but others may have an irregular shape or texture. Although they vary in size, each moon is much smaller than its planet. Moons are generally solid bodies, and a few have atmospheres or even hidden oceans.
A total of 214 known moons orbit planets and dwarf planets in our solar system. This includes confirmed moons and tentative ones that are about to become official. When moons are provisional, they are named with a letter followed by a year. Once confirmed, they are given an official name. Many moons are named after mythological characters.
Terrestrial planets: The four planets closest to the sun are mostly made of rocky material and are known as terrestrial planets. These planets have few or no moons.
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Proximity to the sun: Mercury and Venus are unable to hold their own moons due to their proximity to the sun’s gravity.
Distance from Earth: 233,535 miles
Rotation and Orbit: The rotations of the Moon and Earth are so synchronized that we only see one side of the Moon at any time. It takes 27 Earth days for the Moon to orbit the Earth.
Structure: The moon has a core, a mantle and a crust. The surface is covered with many craters. It also has a very thin atmosphere.
Cut: Earth’s moon is 3.7 times smaller than Earth. If the Earth were the size of an American nickel, the moon would be the size of a green pea.
Moon names: Deimos and Phobos
Discovered by: Aspa room
Orbit: Of all known moons, Phobos orbits closest to its planet at just 3,700 miles above the surface. It orbits Mars three times a day. The more distant Deimos takes 30 hours for each orbit.
Structure: Both of Mars’ moons are lumpy, heavily cratered, and covered in dust and loose rock. They are among the darkest objects in the solar system. The dominant feature of Phobos is a six-mile-wide crater.
Cut: The moons of Mars are among the smallest in the solar system. Phobos is 14 miles in diameter, while Deimos is only 7 miles.
First discovery: 1610
Jovian Planets: Ice and gas planets in the outer solar system can have many moons due to their size.
Galilean satellites: Of all Jupiter’s moons, the four largest – Io, Europa, Ganymede and Callisto – have generated the most scientific interest.
The biggest: Not only is Ganymede the largest moon of Jupiter, but it is also the largest moon in the solar system.
Structure: Like Earth, Io, Europa and Ganymede have a layered structure. Callisto is less defined and appears to be a mix of mostly ice and rock.
Cassino: Four spacecraft have visited the Saturn system, but NASA’s Cassini is the only one orbiting the planet. That gave the spacecraft more than a decade to study Saturn’s moons.
The biggest: Titan is Saturn’s largest moon and the only one with clouds and a substantial atmosphere. It is also the only known world other than Earth that has liquid on its surface.
Jets: Enceladus has a geyser that sprays water vapor, ice particles, and simple organic matter into space. It is the source material for one of Saturn’s rings.
Names: The moons of Uranus are named after characters from the works of William Shakespeare and Alexander Pope.
Single system: Uranus has a region of eight small satellites unlike any other planetary moon system. There are so many people that astronomers still don’t know how they avoided crashing into each other.
Structure: All of Uranus’ inner moons appear to be composed of roughly half water ice and half rock. The composition of the moons outside Oberon’s orbit remains unknown, but they are likely captured asteroids.
First discovery: 1846 (17 days after the discovery of Neptune)
Names: In keeping with Neptune’s maritime name, most of its moons are named after sea gods and nymphs from Greek mythology.
Triton: It is Neptune’s largest moon. It is also one of the coldest objects in the solar system. Its icy surface reflects what little sunlight reaches it, making the moon about -400 degrees Fahrenheit.
Proteus: It is Neptune’s second largest moon. It is slightly non-spherical and is thought to be just on the edge of an object’s mass before its gravity pulls it into a sphere.
Moon names: Charon, Nix, Hydra, Kerberos and Styx
Wheelwright: It is the largest of Pluto’s moons. It’s almost half the size of the planet itself. Charon and Pluto are sometimes called a double planet.
Structure: Pluto’s other four moons are each less than 100 miles wide. They are also irregularly shaped instead of spherical.
Twirl: Unlike many other moons in the solar system, Nix, Hydra, Kerberos and Styx all rotate and do not keep the same side towards Pluto.
Moon names: Namaka and Hi’iaka
Discovery: The two moons of Haumea were discovered by a team from the California Institute of Technology. Namaka is the inner moon and Hi’iaka is the outer moon.
Cut: Namaka is about 105 miles in diameter and Hi’iaka is about 193 miles.
Distance: Namaka is about 24,000 miles from Haumea, while Hi’iaka is about 31,000 miles.
Temporary name: S/2015 (nicknamed MK 2)
Discovery: In 2015, the Hubble Space Telescope discovered a moon orbiting the dwarf planet Makemake.
Cut: Makemake’s moon is estimated to be 100 miles in diameter.
Distance: MK 2 was seen about 13,000 miles from Makemake.
Visibility: MK 2 is over 1300 times weaker than Makemake.
Cut: The moon of Eris is estimated to be around 200 miles in diameter.
Orbit: Dysnomia has an almost circular orbit that lasts about 16 days. It orbits Eris at an average distance of 2,300 miles.
Visibility: The moon is about 60 times weaker than Eris.
Total number of dwarf planet moons: 9
By measuring the orbit of a small moon, astronomers can calculate the mass of the parent body. This technique was used with Dysnomia (the moon of Eris). Dysnomia also played a role in determining the comparison between Pluto and Eris.
The biggest: Jupiter’s moon Ganymede is 3,270 miles in diameter. It is larger than the planet Mercury.
Largest relative to the parent body: Charon, the moon of Pluto
Smaller : The title is competed by tentative moons around Saturn and Jupiter. There can be moons as small as a mile in diameter.
Contrast orbit: Neptune’s moon Triton is the only large moon that orbits its planet in the opposite direction of the planet’s rotation.
Humans set foot: earth’s moon
The most active volcanoes: Io, the moon of Jupiter
The most reflective surface: Saturn’s moon Enceladus
Most heavily cratered: Callisto, the moon of Jupiter
Consequent atmosphere: Titan, Saturn’s moon
Own magnetic field: Ganymede, the moon of Jupiter
Liquids on the surface: Titan, Saturn’s moon