611 articles
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.
Parker spiral
The Parker spiral is the spiral shape the Sun's magnetic field lines take in interplanetary space, predicted by Eugene Parker in 1958 and confirmed by spacecraft in 1962.
Pebble accretion
Pebble accretion is a planet-formation mechanism in which planetary cores grow by capturing millimeter- to centimeter-sized pebbles, with gas drag boosting accretion rates far above planetesimal accretion.
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.
Perdita (moon)
Perdita is a small inner moon of Uranus, about 30 km across, discovered in 1999 in archived Voyager 2 images and confirmed by Hubble in 2003.
Perseids
The Perseids, also called the Perseid meteor shower, are an annual meteor shower peaking around August 13, caused by debris from comet 109P/Swift-Tuttle and known for bright fireballs.
Perturbation (astronomy)
A perturbation, also called an orbital or gravitational perturbation, is a deviation of an orbit from the ideal Keplerian ellipse, caused by third bodies and other forces.
Phobos (Φόβος) (moon)
Phobos is the larger and innermost of Mars's two moons, an irregular, dark body discovered in 1877 that orbits closer to its planet than any other moon.
Phosphine in the atmosphere of Venus
Phosphine in the atmosphere of Venus is a claimed 2020 detection of the gas phosphine in Venus's clouds, led by Jane Greaves, which remains debated.
Photoevaporation
Photoevaporation is the loss of a planet's atmosphere driven by extreme ultraviolet and X-ray radiation from its host star, and one of two leading explanations for the exoplanet radius valley.
Photosphere
The photosphere is the visible surface of the Sun, the lowest layer of the solar atmosphere, which emits most of the Sun's light at about 5,500 °C.
Planet
A planet, sometimes called a major planet, is a body orbiting the Sun that is nearly round and has cleared its orbital neighborhood, a definition adopted in 2006.
Planet Nine
Planet Nine is a hypothetical planet of five to ten Earth masses proposed in 2016 to orbit the Sun far beyond Neptune and explain the clustering of distant Kuiper Belt object orbits.
Planet Nine hypothesis
The Planet Nine hypothesis, proposed by Caltech's Konstantin Batygin and Mike Brown in 2016, holds that an undiscovered planet of 5 to 10 Earth masses orbits far beyond Neptune.
Planetary and Space Science (journal)
Planetary and Space Science (ISSN 0032-0633) is an Elsevier peer-reviewed planetary science journal founded in 1959 under Pergamon Press, edited by Maria Cristina De Sanctis, hybrid access with a USD 3,460 APC, SCIE/Scopus-indexed, JCR Q3.
Planetary core
A planetary core is the iron-rich central region of a differentiated planet, formed when dense metal sank from the silicate mantle during the body's earliest evolution.
Planetary differentiation
Planetary differentiation is the process by which gravity separates a planet's molten interior into layers of different density: a dense metal core, a silicate mantle, and a crust.
Planetary habitability
Planetary habitability is the study of whether a planetary body can sustain life, extrapolated from Earth and centered on the habitable zone where liquid water can exist.
Planetary migration
Planetary migration is the drift of a forming planet's semi-major axis from tidal interaction with its protoplanetary disk; models like the Nice model explain the Solar System's giant planets.
Planetary mnemonic
A planetary mnemonic is a sentence whose word initials encode the planets in order from the Sun, such as "My Very Educated Mother Just Served Us Noodles."
Planetary objects proposed in religion, astrology, ufology and pseudoscience
Planetary objects proposed in religion, astrology, ufology and pseudoscience, also called planets in religion, ufology and mythology, are unconfirmed bodies like Vulcan, Planet X, and Nibiru.
Planetary parade
A planetary parade is a popular, non-technical name for several planets appearing in Earth's sky at once along a line or arc, a line-of-sight effect along the ecliptic.
Planetary radar
Planetary radar is the study of Solar System bodies, from the Moon to asteroids and comets, by transmitting radio signals and analyzing the returning echoes with large Earth-based dishes.
Planets beyond Neptune
Planets beyond Neptune are hypothetical massive bodies, including the proposed Planet Nine, inferred from the clustered orbits of distant icy objects; only Pluto was ever found, in 1930.
Planets in astrology
In astrology, the planets are the Sun, the Moon, and the solar system bodies, treated as symbolic forces whose chart positions are read as influences on personality and events.
Plutino
A plutino is a trans-Neptunian object locked in a 3:2 resonance with Neptune, orbiting the Sun twice for every three Neptune orbits; Pluto is the largest known member.
Pluto
Pluto is a dwarf planet in the Kuiper Belt beyond Neptune, reclassified from ninth planet in 2006 and explored by NASA's New Horizons flyby of 2015.
Poynting–Robertson effect
The Poynting–Robertson effect, proposed by John Henry Poynting in 1903 and treated relativistically by Howard P. Robertson in 1937, is radiation drag that makes small orbiting dust particles lose momentum and spiral inward toward the Sun.