(a planet's natural satellite, such as Earth's)
A moon is a natural satellite of a planet.
(A satellite is an object orbiting a planet,
and can either be natural, like the Moon,
or artificial, like HST.)
the Earth's natural satellite is called The Moon.
Tidal locking keeps the Moon's same face toward the Earth,
and it rotates roughly perpendicular to the ecliptic,
so its poles have shadows that receive no light from the Sun.
Places cold enough to keep water ice frozen are called
Lunar cold traps.
Current theory on the origin of the Moon (Moon formation) favors the
giant-impact hypothesis, that the Moon coalesced from
orbiting debris from an impact between Earth and a
Mars-sized planet. Characteristics of lunar material show a
striking similarity to that of Earth in abundances and
radioactivity, as compared to other planets such as Mars.
This supports the giant impact hypothesis, yet it is
too much like Earth, providing no evidence of different
material from the presumed impacting planet.
The Moon is thought to have a relatively small iron core.
The Moon does not have the type of magnetic field
that suggests a current dynamo and it is thought the Moon
is solid (unlike Earth), but the Moon's magnetic rocks might
reveal its early thermal history, before it cooled.
Other well-known solar system moons:
| Planet || Well-known moons || 6/2018 total|
| Mars || Deimos, Phobos || 2 |
| Jupiter || Io, Europa, Ganymede, Callisto (the Galilean Moons) || 69 |
| Saturn || Titan, Mimas, Enceladus, Tethys, Dione, Rhea, Iapetus, Hyperion || 62 |
| Uranus || Miranda, Ariel, Umbriel, Oberon, Titania || 27 |
| Neptune || Triton || 14 |
| Pluto || Charon || 5 |
Moons of the planets are still being discovered.
None are known for Mercury or Venus,
but they have been found for more than 300 minor planets.
| || |
Arecibo Occultation Survey (AO)
apparent magnitude (m)
atmospheric temperature profile
astronomical unit (AU)
chemical equilibrium (CE)
circular polarization ratio (CPR)
Carl Sagan Institute (CSI)
Enceladus Life Finder (ELF)
escape velocity (Ve)
47 Tucanae (47 Tuc)
general circulation model (GCM)
internal gravity wave
intertropical convergence zone (ITCZ)
late heavy bombardment (LHB)
Lunar Reconnaissance Orbiter (LRO)
moment of inertia factor
solar mass (MSun)
polycyclic aromatic hydrocarbon (PAH)
standard gravitational parameter (μ)
stellar radius determination
TiNy Titans (TNT)