300 articles
Meteorite
A meteorite, also called an aerolite, is a natural solid object from space that survives its fiery passage through an atmosphere. Most come from asteroids, with a few from the Moon and Mars.
Methane on Mars
Methane on Mars refers to trace methane gas reported in the Martian atmosphere since 2004, from Curiosity and Mars Express, whose origins, geological or biological, remain debated.
Methone (moon)
Methone (Saturn XXXII) is a small moon of Saturn about 3 kilometers across that orbits between Mimas and Enceladus and was discovered in Cassini images in 2004.
Minor Planet Electronic Circulars
Minor Planet Electronic Circulars (MPECs) are electronic bulletins issued by the Minor Planet Center, generally daily since 1993, announcing discoveries, orbits, and identifications of minor planets and comets.
Minor-planet designation
Minor-planet designation, also called asteroid designation, is the formal identifier for an asteroid, consisting of a provisional designation, a permanent number, and optionally a name.
Miranda (moon)
Miranda (Uranus V) is the smallest and innermost of Uranus's five major moons, discovered in 1948 and found by Voyager 2 in 1986 to have unique patchwork terrain called coronae.
Mneme
Mneme (Jupiter XL, S/2003 J 21) is a small retrograde irregular moon of Jupiter in the Ananke group, discovered February 9, 2003 by Sheppard and Gladman at Mauna Kea; about 1 km in radius, orbiting ~21 million km away in ~620 days, named for the Muse of memory.
Moment of inertia factor
The moment of inertia factor, or normalized polar moment of inertia, is a dimensionless measure of how mass is distributed inside a planet, equal to 0.4 for a uniform sphere.
Moon
The Moon is Earth's only natural satellite, a rocky body about one-fourth Earth's size that orbits 384,400 km away. It likely formed from debris of a giant collision with Earth.
Moonquake
A moonquake is a seismic event on the Moon, driven by Earth's tidal pull, global contraction as the Moon cools, and impacts, recorded by Apollo seismometers between 1969 and 1977.
Moons of Jupiter
The moons of Jupiter, also called Jupiter's satellites, are natural satellites ranging from the four planet-sized Galilean moons to small captured bodies, with 115 recognized as of 2026.
Moons of Mars
The moons of Mars, Phobos and Deimos, are two small, dark, tidally locked satellites discovered by Asaph Hall in 1877, whose origin, captured asteroids or impact debris, remains unresolved.
Moons of Neptune
Neptune's moons are the 16 known natural satellites of Neptune, led by captured Kuiper Belt object Triton, with Nereid, Hippocamp, and six moons revealed by Voyager 2's 1989 flyby.
Moons of Pluto
The moons of Pluto are five: large Charon, discovered in 1978, and the small satellites Styx, Nix, Kerberos, and Hydra, discovered between 2005 and 2012, orbiting the Pluto–Charon pair.
Moons of Saturn
Saturn's moons are the natural satellites of Saturn, the most of any planet at 285 confirmed, ranging from Titan, larger than Mercury, to tiny irregular fragments.
Moons of Uranus
The moons of Uranus are its natural satellites, 29 recognized as of 2026, with five major moons named for characters from Shakespeare, visited only by Voyager 2 in 1986.
Murchison meteorite
The Murchison meteorite is a carbonaceous chondrite that fell near Murchison, Victoria, Australia, in September 1969, becoming one of the most studied meteorites for its organic compounds.
Naming of moons
Naming of moons, or naming of natural satellites, is the process by which newly found moons get provisional designations and permanent names approved by the IAU, arbiter since 1919.
Natural satellite
A natural satellite, also called a planetary satellite or moon, is a celestial body that orbits a planet, dwarf planet, or other larger non-stellar body.
Nemesis (hypothetical star)
Nemesis, or the Nemesis star, is a hypothetical dim companion of the Sun proposed in 1984 to explain a 26-million-year cycle in mass extinctions; infrared surveys have ruled it out.
Neptune
Neptune is the eighth and most distant planet of the solar system, an ice giant found in 1846 through mathematical prediction and flown past by Voyager 2 in 1989.
Nereid (moon)
Nereid, also known as Neptune II, is the third-largest moon of Neptune, discovered by Gerard Kuiper in 1949 and famous for one of the most eccentric orbits of any moon.
Neso
Neso (Neptune XIII, S/2002 N 4) is a small retrograde irregular moon of Neptune discovered in 2002 with the Blanco telescope. It orbits about 48.4 million km out with a 9,374-day period, eccentricity 0.495, and may be a fragment of a broken larger moon.
Nibiru cataclysm
The Nibiru cataclysm, also called the Nibiru collision, is a claimed doomsday scenario in which planet Nibiru destroys civilization; astronomers say no such object exists.
Olokun Vallis
Olokun Vallis is a 150 km sinuous channel (vallis) on Venus at 81.5°N, 269.0°E, named by the IAU in 1997 for the Bini sea and river deity Olokun; one of 72 named Venusian valles.
Orgueil meteorite
The Orgueil meteorite is a carbonaceous chondrite that fell as an observed fall near Orgueil, France, in 1864, and its composition is the reference standard for the solar system.
Pallene (moon)
Pallene, designated Saturn XXXIII, is a small moon of Saturn about 4 kilometers across, discovered by the Cassini imaging team in 2004 and orbited by a faint dusty ring.
Pan (moon)
Pan (Saturn XVIII, S/1981 S13) is a small moon of Saturn that keeps the A ring's Encke Gap open, discovered by Mark Showalter in 1990.
Pan-STARRS
Pan-STARRS, the Panoramic Survey Telescope and Rapid Response System, is a pair of University of Hawaii survey telescopes on Haleakalā, Maui, known for asteroid searches and discovering ʻOumuamua, the first known interstellar object, in 2017.
Percival Lowell
Percival Lowell (1855–1916) was an American astronomer and businessman from Boston who founded Lowell Observatory in Flagstaff, Arizona, in 1894 and promoted the theory of Martian canals.