Natural satellite

Last updated
Small bodies of the Solar System.jpg
25 solar system objects smaller than Earth.jpg
Moons of solar system v7.jpg
Most of the 194 known natural satellites of the planets and dwarf planets are irregular moons, while only 19 are large enough to be round. Ganymede, followed by Titan, Callisto, Io and Earth's Moon are the largest natural satellites in the Solar System (see List of natural satellites § List).

A natural satellite or moon is, in the most common usage, an astronomical body that orbits a planet or minor planet (or sometimes another small Solar System body).

Orbit gravitationally curved path of an object around a point in outer space; circular or elliptical path of one object around another object

In physics, an orbit is the gravitationally curved trajectory of an object, such as the trajectory of a planet around a star or a natural satellite around a planet. Normally, orbit refers to a regularly repeating trajectory, although it may also refer to a non-repeating trajectory. To a close approximation, planets and satellites follow elliptic orbits, with the central mass being orbited at a focal point of the ellipse, as described by Kepler's laws of planetary motion.

Planet Class of astronomical body directly orbiting a star or stellar remnant

A planet is an astronomical body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.

Minor planet astronomical object in direct orbit around a star that is neither a planet nor originally classified as a comet

A minor planet is an astronomical object in direct orbit around the Sun that is neither a planet nor exclusively classified as a comet. Before 2006 the International Astronomical Union (IAU) officially used the term minor planet, but during that year's meeting it reclassified minor planets and comets into dwarf planets and small Solar System bodies (SSSBs).

Contents

In the Solar System there are six planetary satellite systems containing 185 known natural satellites. [1] [2] Four IAU-listed dwarf planets are also known to have natural satellites: Pluto, Haumea, Makemake, and Eris. [3] As of September 2018, there are 334 other minor planets known to have moons. [4]

Solar System planetary system of the Sun

The Solar System is the gravitationally bound planetary system of the Sun and the objects that orbit it, either directly or indirectly. Of the objects that orbit the Sun directly, the largest are the eight planets, with the remainder being smaller objects, such as the five dwarf planets and small Solar System bodies. Of the objects that orbit the Sun indirectly—the moons—two are larger than the smallest planet, Mercury.

Satellite system (astronomy) collection of objects orbiting around a planetary mass object

A satellite system is a set of gravitationally bound objects in orbit around a planetary mass object or minor planet. Generally speaking, it is a set of natural satellites (moons), although such systems may also consist of bodies such as circumplanetary disks, ring systems, moonlets, minor-planet moons and artificial satellites any of which may themselves have satellite systems of their own. Some bodies also possess quasi-satellites that have orbits gravitationally influenced by their primary, but are generally not considered to be part of a satellite system. Satellite systems can have complex interactions including magnetic, tidal, atmospheric and orbital interactions such as orbital resonances and libration. Individually major satellite objects are designated in Roman numerals. Satellite systems are referred to either by the possessive adjectives of their primary, or less commonly by the name of their primary. Where only one satellite is known, or it is a binary orbiting a common centre of gravity, it may be referred to using the hyphenated names of the primary and major satellite.

International Astronomical Union Association of professional astronomers

The International Astronomical Union is an international association of professional astronomers, at the PhD level and beyond, active in professional research and education in astronomy. Among other activities, it acts as the internationally recognized authority for assigning designations and names to celestial bodies and any surface features on them.

The Earth–Moon system is unique in that the ratio of the mass of the Moon to the mass of Earth is much greater than that of any other natural-satellite–planet ratio in the Solar System (although there are minor-planet systems with even greater ratios, notably the PlutoCharon system). At 3,474 km (2,158 miles) across, the Moon is 0.27 times the diameter of Earth. [5]

Mass Quantity of matter

Mass is both a property of a physical body and a measure of its resistance to acceleration when a net force is applied. An object's mass also determines the strength of its gravitational attraction to other bodies.

Pluto A dwarf planet in the Kuiper belt of the Solar System

Pluto is a dwarf planet in the Kuiper belt, a ring of bodies beyond Neptune. It was the first Kuiper belt object to be discovered and is the largest known plutoid.

Charon (moon) largest natural satellite of the dwarf planet Pluto

Charon, also known as (134340) Pluto I, is the largest of the five known natural satellites of the dwarf planet Pluto. It has a mean radius of 606 km. It was discovered in 1978 at the United States Naval Observatory in Washington, D.C., using photographic plates taken at the United States Naval Observatory Flagstaff Station (NOFS).

Terminology

The first known natural satellite was the Moon, but it was considered a "planet" until Copernicus' introduction of De revolutionibus orbium coelestium in 1543. Until the discovery of the Galilean satellites in 1610, however, there was no opportunity for referring to such objects as a class. Galileo chose to refer to his discoveries as Planetæ ("planets"), but later discoverers chose other terms to distinguish them from the objects they orbited.[ citation needed ]

Moon Earths natural satellite

The Moon, also known as Luna, is an astronomical body that orbits planet Earth and is Earth's only permanent natural satellite. It is the fifth-largest natural satellite in the Solar System, and the largest among planetary satellites relative to the size of the planet that it orbits. The Moon is after Jupiter's satellite Io the second-densest satellite in the Solar System among those whose densities are known.

Nicolaus Copernicus Renaissanse-era mathematician and astronomer who formulated the heliocentric model of the Universe

Nicolaus Copernicus was a Renaissance-era mathematician and astronomer, who formulated a model of the universe that placed the Sun rather than the Earth at the center of the universe, in all likelihood independently of Aristarchus of Samos, who had formulated such a model some eighteen centuries earlier.

<i>De revolutionibus orbium coelestium</i> book by Copernicus

De revolutionibus orbium coelestium is the seminal work on the heliocentric theory of the astronomer Nicolaus Copernicus (1473–1543) of the Polish Renaissance. The book, first printed in 1543 in Nuremberg, Holy Roman Empire, offered an alternative model of the universe to Ptolemy's geocentric system, which had been widely accepted since ancient times.

The first to use of the term satellite to describe orbiting bodies was the German astronomer Johannes Kepler in his pamphlet Narratio de Observatis a se quatuor Iouis satellitibus erronibus ("Narration About Four Satellites of Jupiter Observed") in 1610. He derived the term from the Latin word satelles, meaning "guard", "attendant", or "companion", because the satellites accompanied their primary planet in their journey through the heavens. [6]

Johannes Kepler 17th-century German mathematician, astronomer and astrologer

Johannes Kepler was a German astronomer, mathematician, and astrologer. He is a key figure in the 17th-century scientific revolution, best known for his laws of planetary motion, and his books Astronomia nova, Harmonices Mundi, and Epitome Astronomiae Copernicanae. These works also provided one of the foundations for Newton's theory of universal gravitation.

Latin Indo-European language of the Italic family

Latin is a classical language belonging to the Italic branch of the Indo-European languages. The Latin alphabet is derived from the Etruscan and Greek alphabets and ultimately from the Phoenician alphabet.

The term satellite thus became the normal one for referring to an object orbiting a planet, as it avoided the ambiguity of "moon". In 1957, however, the launching of the artificial object Sputnik created a need for new terminology. Sputnik was created by Soviet Union, and it was the first satellite ever. [6] The terms man-made satellite and artificial moon were very quickly abandoned in favor of the simpler satellite, and as a consequence, the term has become linked primarily with artificial objects flown in space – including, sometimes, even those not in orbit around a planet.[ citation needed ]

Because of this shift in meaning, the term moon, which had continued to be used in a generic sense in works of popular science and in fiction, has regained respectability and is now used interchangeably with natural satellite, even in scientific articles. When it is necessary to avoid both the ambiguity of confusion with Earth's natural satellite the Moon and the natural satellites of the other planets on the one hand, and artificial satellites on the other, the term natural satellite (using "natural" in a sense opposed to "artificial") is used. To further avoid ambiguity, the convention is to capitalize the word Moon when referring to Earth's natural satellite, but not when referring to other natural satellites.

Many authors define "satellite" or "natural satellite" as orbiting some planet or minor planet, synonymous with "moon" – by such a definition all natural satellites are moons, but Earth and other planets are not satellites. [7] [8] [9] A few recent authors define "moon" as "a satellite of a planet or minor planet", and "planet" as "a satellite of a star" – such authors consider Earth as a "natural satellite of the sun". [10] [11] [12]

Definition of a moon

Size comparison of Earth and the Moon Moon, Earth size comparison.jpg
Size comparison of Earth and the Moon

There is no established lower limit on what is considered a "moon". Every natural celestial body with an identified orbit around a planet of the Solar System, some as small as a kilometer across, has been considered a moon, though objects a tenth that size within Saturn's rings, which have not been directly observed, have been called moonlets . Small asteroid moons (natural satellites of asteroids), such as Dactyl, have also been called moonlets. [13]

The upper limit is also vague. Two orbiting bodies are sometimes described as a double planet rather than primary and satellite. Asteroids such as 90 Antiope are considered double asteroids, but they have not forced a clear definition of what constitutes a moon. Some authors consider the Pluto–Charon system to be a double (dwarf) planet. The most common[ citation needed ] dividing line on what is considered a moon rests upon whether the barycentre is below the surface of the larger body, though this is somewhat arbitrary, because it depends on distance as well as relative mass.

Origin and orbital characteristics

Two moons: Saturn's natural satellite Dione occults Enceladus Occulting Enceladus PIA10500.jpg
Two moons: Saturn's natural satellite Dione occults Enceladus

The natural satellites orbiting relatively close to the planet on prograde, uninclined circular orbits (regular satellites) are generally thought to have been formed out of the same collapsing region of the protoplanetary disk that created its primary. [14] [15] In contrast, irregular satellites (generally orbiting on distant, inclined, eccentric and/or retrograde orbits) are thought to be captured asteroids possibly further fragmented by collisions. Most of the major natural satellites of the Solar System have regular orbits, while most of the small natural satellites have irregular orbits. [16] The Moon [17] and possibly Charon [18] are exceptions among large bodies in that they are thought to have originated by the collision of two large proto-planetary objects (see the giant impact hypothesis). The material that would have been placed in orbit around the central body is predicted to have reaccreted to form one or more orbiting natural satellites. As opposed to planetary-sized bodies, asteroid moons are thought to commonly form by this process. Triton is another exception; although large and in a close, circular orbit, its motion is retrograde and it is thought to be a captured dwarf planet.

Temporary satellites

The capture of an asteroid from a heliocentric orbit is not always permanent. According to simulations, temporary satellites should be a common phenomenon. [19] [20] The only observed example is 2006 RH120 , which was a temporary satellite of Earth for nine months in 2006 and 2007. [21] [22]

Tidal locking

Most regular moons (natural satellites following relatively close and prograde orbits with small orbital inclination and eccentricity) in the Solar System are tidally locked to their respective primaries, meaning that the same side of the natural satellite always faces its planet. The only known exception is Saturn's natural satellite Hyperion, which rotates chaotically because of the gravitational influence of Titan.

In contrast, the outer natural satellites of the giant planets (irregular satellites) are too far away to have become locked. For example, Jupiter's Himalia, Saturn's Phoebe, and Neptune's Nereid have rotation periods in the range of ten hours, whereas their orbital periods are hundreds of days.

Satellites of satellites

Artist impression of Rhea's proposed rings Rhean rings PIA10246 Full res.jpg
Artist impression of Rhea's proposed rings

No "moons of moons" or subsatellites (natural satellites that orbit a natural satellite of a planet) are currently known as of 2019. In most cases, the tidal effects of the planet would make such a system unstable.

However, calculations performed after the recent detection [23] of a possible ring system around Saturn's moon Rhea indicate that satellites orbiting Rhea could have stable orbits. Furthermore, the suspected rings are thought to be narrow, [24] a phenomenon normally associated with shepherd moons. However, targeted images taken by the Cassini spacecraft failed to detect rings around Rhea. [25]

It has also been proposed that Saturn's moon Iapetus had a satellite in the past; this is one of several hypotheses that have been put forward to account for its equatorial ridge. [26]

Trojan satellites

Two natural satellites are known to have small companions at both their L4 and L5 Lagrangian points, sixty degrees ahead and behind the body in its orbit. These companions are called trojan moons, as their orbits are analogous to the trojan asteroids of Jupiter. The trojan moons are Telesto and Calypso, which are the leading and following companions, respectively, of the Saturnian moon Tethys; and Helene and Polydeuces, the leading and following companions of the Saturnian moon Dione.

Asteroid satellites

The discovery of 243 Ida's natural satellite Dactyl in the early 1990s confirmed that some asteroids have natural satellites; indeed, 87 Sylvia has two. Some, such as 90 Antiope, are double asteroids with two comparably sized components.

Shape

The relative masses of the natural satellites of the Solar System. Mimas, Enceladus, and Miranda are too small to be visible at this scale. All the irregularly shaped natural satellites, even added together, would also be too small to be visible. Masses of all moons.png
The relative masses of the natural satellites of the Solar System. Mimas, Enceladus, and Miranda are too small to be visible at this scale. All the irregularly shaped natural satellites, even added together, would also be too small to be visible.

Neptune's moon Proteus is the largest irregularly shaped natural satellite. All other known natural satellites that are at least the size of Uranus's Miranda have lapsed into rounded ellipsoids under hydrostatic equilibrium, i.e. are "round/rounded satellites". The larger natural satellites, being tidally locked, tend toward ovoid (egg-like) shapes: squat at their poles and with longer equatorial axes in the direction of their primaries (their planets) than in the direction of their motion. Saturn's moon Mimas, for example, has a major axis 9% greater than its polar axis and 5% greater than its other equatorial axis. Methone, another of Saturn's moons, is only around 3 km in diameter and visibly egg-shaped. The effect is smaller on the largest natural satellites, where their own gravity is greater relative to the effects of tidal distortion, especially those that orbit less massive planets or, as in the case of the Moon, at greater distances.

NameSatellite ofDifference in axes
km
% of mean
diameter
Mimas Saturn 33.4 (20.4 /13.0)8.4 (5.1 /3.3)
Enceladus Saturn16.63.3
Miranda Uranus 14.23.0
Tethys Saturn25.82.4
Io Jupiter 29.40.8
The Moon Earth 4.30.1

Geological activity

Of the nineteen known natural satellites in the Solar System that are large enough to have lapsed into hydrostatic equilibrium, several remain geologically active today. Io is the most volcanically active body in the Solar System, while Europa, Enceladus, Titan and Triton display evidence of ongoing tectonic activity and cryovolcanism. In the first three cases, the geological activity is powered by the tidal heating resulting from having eccentric orbits close to their giant-planet primaries. (This mechanism would have also operated on Triton in the past, before its orbit was circularized.) Many other natural satellites, such as Earth's Moon, Ganymede, Tethys and Miranda, show evidence of past geological activity, resulting from energy sources such as the decay of their primordial radioisotopes, greater past orbital eccentricities (due in some cases to past orbital resonances), or the differentiation or freezing of their interiors. Enceladus and Triton both have active features resembling geysers, although in the case of Triton solar heating appears to provide the energy. Titan and Triton have significant atmospheres; Titan also has hydrocarbon lakes. Four of the largest natural satellites, Europa, Ganymede, Callisto, and Titan, are thought to have subsurface oceans of liquid water, while smaller Enceladus may have localized subsurface liquid water.

Natural satellites of the Solar System

Euler diagram showing the types of bodies in the Solar System. Euler diagram of solar system bodies.svg
Euler diagram showing the types of bodies in the Solar System.

Of the objects within our Solar System known to have natural satellites, there are 76 in the asteroid belt (five with two each), four Jupiter trojans, 39 near-Earth objects (two with two satellites each), and 14 Mars-crossers. [4] There are also 84 known natural satellites of trans-Neptunian objects. [4] Some 150 additional small bodies have been observed within the rings of Saturn, but only a few were tracked long enough to establish orbits. Planets around other stars are likely to have satellites as well, and although numerous candidates have been detected to date, none have yet been confirmed.

Of the inner planets, Mercury and Venus have no natural satellites; Earth has one large natural satellite, known as the Moon; and Mars has two tiny natural satellites, Phobos and Deimos. The giant planets have extensive systems of natural satellites, including half a dozen comparable in size to Earth's Moon: the four Galilean moons, Saturn's Titan, and Neptune's Triton. Saturn has an additional six mid-sized natural satellites massive enough to have achieved hydrostatic equilibrium, and Uranus has five. It has been suggested that some satellites may potentially harbour life. [27]

Among the identified dwarf planets, Ceres has no known natural satellites. Pluto has the relatively large natural satellite Charon and four smaller natural satellites; Styx, Nix, Kerberos, and Hydra. [28] Haumea has two natural satellites, and Eris and Makemake have one each. The Pluto–Charon system is unusual in that the center of mass lies in open space between the two, a characteristic sometimes associated with a double-planet system.

The seven largest natural satellites in the Solar System (those bigger than 2,500 km across) are Jupiter's Galilean moons (Ganymede, Callisto, Io, and Europa), Saturn's moon Titan, Earth's moon, and Neptune's captured natural satellite Triton. Triton, the smallest of these, has more mass than all smaller natural satellites together. Similarly in the next size group of nine mid-sized natural satellites, between 1,000 km and 1,600 km across, Titania, Oberon, Rhea, Iapetus, Charon, Ariel, Umbriel, Dione, and Tethys, the smallest, Tethys, has more mass than all smaller natural satellites together. As well as the natural satellites of the various planets, there are also over 80 known natural satellites of the dwarf planets, minor planets and other small Solar System bodies. Some studies estimate that up to 15% of all trans-Neptunian objects could have satellites.

The following is a comparative table classifying the natural satellites in the Solar System by diameter. The column on the right includes some notable planets, dwarf planets, asteroids, and trans-Neptunian objects for comparison. The natural satellites of the planets are named after mythological figures. These are predominantly Greek, except for the Uranian natural satellites, which are named after Shakespearean characters. The nineteen bodies massive enough to have achieved hydrostatic equilibrium are in bold in the table below. Minor planets and satellites suspected but not proven to have achieved a hydrostatic equilibrium are italicized in the table below.

Mean
diameter
(km)
Satellites of planetsSatellites of dwarf planetsSatellites of
other
minor planets
Non-satellites
for comparison
EarthMarsJupiterSaturnUranusNeptunePlutoMakemakeHaumeaEris
4,000–6,000 Ganymede
Callisto
Titan Mercury
3,000–4,000 Moon Io
Europa
2,000–3,000 Triton Eris
Pluto
1,000–2,000 Rhea
Iapetus
Dione
Tethys
Titania
Oberon
Umbriel
Ariel
Charon Makemake
Haumea
2007 OR10 ,
Quaoar
500–1,000 Enceladus Dysnomia Sedna , Ceres ,
Salacia, Orcus,
Pallas, Vesta
many more TNOs
250–500 Mimas
Hyperion
Miranda Proteus
Nereid
Hiʻiaka Orcus I Vanth
Salacia I Actaea
10 Hygiea
704 Interamnia
87 Sylvia
and many others
100–250 Amalthea
Himalia
Thebe
Phoebe
Janus
Epimetheus
Sycorax
Puck
Portia
Larissa
Galatea
Despina
S/2015 (136472) 1 Namaka S/2005 (82075)  1
Sila–Nunam  I
Ceto  I Phorcys
Patroclus  I Menoetius
~21 more moons of TNOs
3 Juno
15760 Albion
5 Astraea
42355 Typhon
and many others
50–100 Elara
Pasiphae
Prometheus
Pandora
Caliban
Juliet
Belinda
Cressida
Rosalind
Desdemona
Bianca
Thalassa
Halimede
Neso
Naiad
Quaoar I Weywot
90 Antiope  I
Typhon  I Echidna
Logos  I Zoe
5 more moons of TNOs
90 Antiope
58534 Logos
253 Mathilde
and many others
25–50 Carme
Metis
Sinope
Lysithea
Ananke
Siarnaq
Helene
Albiorix
Atlas
Pan
Ophelia
Cordelia
Setebos
Prospero
Perdita
Stephano
Sao
Laomedeia
Psamathe
Hippocamp
Hydra
Nix [29]
Kalliope I Linus 1036 Ganymed
243 Ida
and many others
10–25 Phobos
Deimos
Leda
Adrastea
Telesto
Paaliaq
Calypso
Ymir
Kiviuq
Tarvos
Ijiraq
Erriapus
Mab
Cupid
Francisco
Ferdinand
Margaret
Trinculo
Kerberos
Styx
762 Pulcova I
Sylvia I Romulus
624 Hektor  I Skamandrios
Eugenia I Petit-Prince
121 Hermione  I
283 Emma  I
1313 Berna  I
107 Camilla I
433 Eros
1313 Berna
and many others
< 10 63 moons 36 moons Sylvia II Remus
Ida I Dactyl
and many others
many

Visual summary

Solar System moons
Ganymede g1 true-edit1.jpg
Two Halves of Titan.png
Callisto (cropped)-1.jpg
Io highest resolution true color (non-edit version).jpg
FullMoon2010 (cropped)-1.jpg
Europa-moon.jpg
Triton moon mosaic Voyager 2 (large).jpg
Ganymede
(moon of Jupiter)
Titan
(moon of Saturn)
Callisto
(moon of Jupiter)
Io
(moon of Jupiter)
Moon
(moon of Earth)
Europa
(moon of Jupiter)
Triton
(moon of Neptune)
Titania (moon) color cropped.jpg
PIA07763 Rhea full globe5.jpg
Voyager 2 picture of Oberon.jpg
Iapetus as seen by the Cassini probe - 20071008 (cropped).jpg
Charon in Color (HQ).jpg
PIA00040 Umbrielx2.47.jpg
Color Image of Ariel as seen from Voyager 2.jpg
Titania
(moon of Uranus)
Rhea
(moon of Saturn)
Oberon
(moon of Uranus)
Iapetus
(moon of Saturn)
Charon
(moon of Pluto)
Umbriel
(moon of Uranus)
Ariel
(moon of Uranus)
Dione color south.jpg
PIA18317-SaturnMoon-Tethys-Cassini-20150411.jpg
PIA17202-SaturnMoon-Enceladus-ApproachingFlyby-20151028-cropped.jpg
PIA18185 Miranda's Icy Face.jpg
Proteus Voyager 2 croped.jpg
Mimas PIA12568.jpg
Hyperion true.jpg
Dione
(moon of Saturn)
Tethys
(moon of Saturn)
Enceladus
(moon of Saturn)
Miranda
(moon of Uranus)
Proteus
(moon of Neptune)
Mimas
(moon of Saturn)
Hyperion
(moon of Saturn)
Phoebe cassini.jpg
PIA12714 Janus crop.jpg
Amalthea (moon).png
PIA09813 Epimetheus S. polar region.jpg
Thebe.jpg
Prometheus 12-26-09a.jpg
PIA21055 - Pandora Up Close (cropped).jpg
Phoebe
(moon of Saturn)
Janus
(moon of Saturn)
Amalthea
(moon of Jupiter)
Epimetheus
(moon of Saturn)
Thebe
(moon of Jupiter)
Prometheus
(moon of Saturn)
Pandora
(moon of Saturn)
Hydra (moon) from 231 000 kilometres.jpg
Nix best view-true color.jpg
Leading hemisphere of Helene - 20110618.jpg
Atlas (NASA).jpg
Pan by Cassini, March 2017.jpg
Telesto cassini closeup.jpg
N00151485 Calypso crop.jpg
Hydra
(moon of Pluto)
Nix
(moon of Pluto)
Helene
(moon of Saturn)
Atlas
(moon of Saturn)
Pan
(moon of Saturn)
Telesto
(moon of Saturn)
Calypso
(moon of Saturn)
Phobos colour 2008.jpg
Deimos-MRO.jpg
Daphnis (Saturn's Moon).jpg
Methone PIA14633.jpg
Dactyl-HiRes.jpg
Phobos
(moon of Mars)
Deimos
(moon of Mars)
Daphnis
(moon of Saturn)
Methone
(moon of Saturn)
Dactyl
(moon of Ida)
Comparison of (a part of) Jupiter
and its four largest natural satellites Jupiter.moons2.jpg
Comparison of (a part of) Jupiter
and its four largest natural satellites

See also

Moons of planets

Moons of dwarf planets and small Solar System bodies

Related Research Articles

Double planet

In astronomy, a double planet is a binary system where both objects are of planetary mass. The term is not recognized by the International Astronomical Union (IAU) and is therefore not an official classification. At its 2006 General Assembly, the International Astronomical Union considered a proposal that Pluto and Charon be reclassified as a double planet, but the proposal was abandoned in favor of the current definition of planet. In promotional materials advertising the SMART-1 mission and pre-dating the IAU planet definition, the European Space Agency once referred to the Earth–Moon system as a double planet.

Orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of two small integers

In celestial mechanics, an orbital resonance occurs when orbiting bodies exert a regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Most commonly this relationship is found for a pair of objects. The physical principle behind orbital resonance is similar in concept to pushing a child on a swing, where the orbit and the swing both have a natural frequency, and the other body doing the "pushing" will act in periodic repetition to have a cumulative effect on the motion. Orbital resonances greatly enhance the mutual gravitational influence of the bodies, i.e., their ability to alter or constrain each other's orbits. In most cases, this results in an unstable interaction, in which the bodies exchange momentum and shift orbits until the resonance no longer exists. Under some circumstances, a resonant system can be stable and self-correcting, so that the bodies remain in resonance. Examples are the 1:2:4 resonance of Jupiter's moons Ganymede, Europa and Io, and the 2:3 resonance between Pluto and Neptune. Unstable resonances with Saturn's inner moons give rise to gaps in the rings of Saturn. The special case of 1:1 resonance between bodies with similar orbital radii causes large Solar System bodies to eject most other bodies sharing their orbits; this is part of the much more extensive process of clearing the neighbourhood, an effect that is used in the current definition of a planet.

Icy moons are a class of natural satellites with surfaces composed mostly of ice. An icy moon may harbor an ocean underneath the surface, and possibly include a rocky core of silicate or metallic rocks. It is thought that they may be composed of ice II or other polymorph of water ice. The prime example of this class of object is Europa.

Minor-planet moon A natural satellite of a minor planet

A minor-planet moon is an astronomical object that orbits a minor planet as its natural satellite. As of February 2019, there are 352 minor planets known or suspected to have moons. Discoveries of minor-planet moons are important because the determination of their orbits provides estimates on the mass and density of the primary, allowing insights of their physical properties that is generally not otherwise possible.

Extraterrestrial skies

In astronomy, an extraterrestrial sky is a view of outer space from the surface of an astronomical body other than Earth.

This is a directory of lists of geological features on planets excepting Earth, moons and asteroids ordered by increasing distance from the Sun.

The naming of moons has been the responsibility of the International Astronomical Union's committee for Planetary System Nomenclature since 1973. That committee is known today as the Working Group for Planetary System Nomenclature (WGPSN).

Definition of <i>planet</i> definition of word planet

The definition of planet, since the word was coined by the ancient Greeks, has included within its scope a wide range of celestial bodies. Greek astronomers employed the term asteres planetai, "wandering stars", for star-like objects which apparently moved over the sky. Over the millennia, the term has included a variety of different objects, from the Sun and the Moon to satellites and asteroids.

Outer planets planet in the Solar System beyond the orbits of the its Main-belt asteroids

The outer planets are those planets in the Solar System beyond the asteroid belt, and hence refers to the gas giants and ice giants, which are in order of their distance from the Sun:

Formation and evolution of the Solar System Formation of the Solar System by gravitational collapse of a molecular cloud and subsequent geological history

The formation and evolution of the Solar System began 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. Most of the collapsing mass collected in the center, forming the Sun, while the rest flattened into a protoplanetary disk out of which the planets, moons, asteroids, and other small Solar System bodies formed.

Dwarf planet planetary-mass object

A dwarf planet is a planetary-mass object that is neither a true planet nor a natural satellite. That is, it is in direct orbit of a star, and is massive enough for its gravity to compress it into a hydrostatically equilibrious shape, but has not cleared the neighborhood of other material around its orbit.

IAU definition of <i>planet</i> definition of a planet as a body orbiting the Sun, in hydrostatic equilibrium, having cleared the neighborhood around its orbit; ratified by the IAU in 2006, thereby reclassifying Pluto as a dwarf planet instead

The International Astronomical Union (IAU) defined in August 2006 that, in the Solar System, a planet is a celestial body which:

  1. is in orbit around the Sun,
  2. has sufficient mass to assume hydrostatic equilibrium, and
  3. has "cleared the neighborhood" around its orbit.
Small Solar System body object in the Solar System that is neither a planet, nor a dwarf planet, nor a satellite

A small Solar System body (SSSB) is an object in the Solar System that is neither a planet, a dwarf planet, nor a natural satellite. The term was first defined in 2006 by the International Astronomical Union (IAU) as follows: "All other objects, except satellites, orbiting the Sun shall be referred to collectively as 'Small Solar System Bodies' ".

Discovery and exploration of the Solar System

Discovery and exploration of the Solar System is observation, visitation, and increase in knowledge and understanding of Earth's "cosmic neighborhood". This includes the Sun, Earth and the Moon, the major planets including Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune, their satellites, as well as smaller bodies including comets, asteroids, and dust.

The Solar System — our Sun’s system of planets, moons, and smaller debris — is humankind’s cosmic backyard. Small by factors of millions compared to interstellar distances, the spaces between the planets are daunting, but technologically surmountable

The following outline is provided as an overview of and topical guide to the Solar System:

References

  1. Sheppard, Scott S. "The Jupiter Satellite and Moon Page". Departament of Terrestrial Magnetism at Carniege Institution for science. Retrieved 8 March 2018.
  2. "How Many Solar System Bodies". NASA/JPL Solar System Dynamics. Retrieved 26 January 2012.
  3. "Planet and Satellite Names and Discoverers". International Astronomical Union (IAU) Working Group for Planetary System Nomenclature (WGPSN). Retrieved 27 January 2012.
  4. 1 2 3 Wm. Robert Johnston (30 September 2018). "Asteroids with Satellites". Johnston's Archive. Retrieved 22 October 2018.
  5. Glenday, Craig (2014). Guinness World Records 2014. p. 186. ISBN   978-1-908843-15-9.
  6. 1 2 "Early History – First Satellites". www.jpl.nasa.gov. Retrieved 8 February 2018.
  7. Kenneth R. Lang. "The Cambridge Guide to the Solar System". 2011. p. 15. quote: "Any object that orbits a planet is now called a satellite, and a natural satellite is also now called a moon."
  8. Therese Encrenaz, et. al. "The Solar System". 2004. p. 30.
  9. Tilman Spohn, Doris Breuer, Torrence Johnson. "Encyclopedia of the Solar System". 2014. p. 18.
  10. David Andrew Weintraub. "Is Pluto a Planet?: A Historical Journey Through the Solar System". p. 65 quote: "... the general concept of a "moon" as a satellite of a planet and "planet" as a satellite of a star."
  11. "Satellite". www.merriam-webster.com. Merriam Webster. Retrieved 16 November 2015.
  12. Stillman, Dan. "What Is a Satellite?". www.nasa.gov. NASA. Retrieved 16 November 2015.
  13. F. Marchis, et al. (2005). "Discovery of the triple asteroidal system 87 Sylvia". Nature. 436 (7052): 822–24. Bibcode:2005Natur.436..822M. doi:10.1038/nature04018. PMID   16094362.
  14. Canup, Robin M.; Ward, William R. (30 December 2008). Origin of Europa and the Galilean Satellites. University of Arizona Press. p. 59. arXiv: 0812.4995 . Bibcode:2009euro.book...59C. ISBN   978-0-8165-2844-8.
  15. D'Angelo, G.; Podolak, M. (2015). "Capture and Evolution of Planetesimals in Circumjovian Disks". The Astrophysical Journal. 806 (1): 29–. arXiv: 1504.04364 . Bibcode:2015ApJ...806..203D. doi:10.1088/0004-637X/806/2/203.
  16. Encyclopedia of the Solar System, page 366, Academic Press, 2007, Lucy-Ann Adams McFadden, Paul Robert Weissman, Torrence V. Johnson
  17. Canup, RM & Asphaug, E (2001). "Origin of the Moon in a giant impact near the end of the Earth's formation". Nature. 412 (6848): 708–12. Bibcode:2001Natur.412..708C. doi:10.1038/35089010. PMID   11507633.
  18. Stern, SA; Weaver, HA; Steffl, AJ; Mutchler, MJ; et al. (2006). "A giant impact origin for Pluto's small natural satellites and satellite multiplicity in the Kuiper belt". Nature. 439 (7079): 946–49. Bibcode:2006Natur.439..946S. doi:10.1038/nature04548. PMID   16495992.
  19. Camille M. Carlisle (30 December 2011). "Pseudo-moons Orbit Earth". Sky & Telescope.
  20. Fedorets, Grigori; Granvik, Mikael; Jedicke, Robert (15 March 2017). "Orbit and size distributions for asteroids temporarily captured by the Earth-Moon system". Icarus. 285: 83–94. Bibcode:2017Icar..285...83F. doi:10.1016/j.icarus.2016.12.022.
  21. "2006 RH120 ( = 6R10DB9) (A second moon for the Earth?)". Great Shefford Observatory. 14 September 2017. Archived from the original on 6 February 2015. Retrieved 13 November 2017.
  22. Roger W. Sinnott (17 April 2007). "Earth's "Other Moon"". Sky & Telescope. Archived from the original on 27 August 2012. Retrieved 13 November 2017.
  23. G.H. Jones, E. Roussos, N. Krupp, U. Beckmann, A.J. Coates, F. Crar, I. Dandouras, V. Dikarev & M.K. Dougherty, P. Garnier, C.J. Hansen, A.R. Hendrix, G.B. Hospodarsky, R.E. Johnson, S. Kempf, K.K. Khurana, S.M. Krimigis, H. Krüger, W.S. Kurth, A. Lagg, H.J. McAndrews, D.G. Mitchell, C. Paranicas, F. Postberg, C.T. Russell, J. Saur, M. Seiß, F. Spahn, R. Srama, D.F. Strobel, R. Tokar, J.-E. Wahlund, R.J. Wilson, J. Woch, D. Young (2008). "The Dust Halo of Saturn's Largest Icy Moon, Rhea – Jones et al. 319 (5868): 1380 – Science". Science. 319 (5868): 1380–1384. Bibcode:2008Sci...319.1380J. doi:10.1126/science.1151524. PMID   18323452.CS1 maint: Multiple names: authors list (link) Pdf
  24. Jeff Hecht (6 March 2008). "Saturn satellite reveals first moon rings". New Scientist. Retrieved 8 March 2018.
  25. Tiscareno, Matthew S.; Burns, Joseph A.; Cuzzi, Jeffrey N.; Hedman, Matthew M. (2010). "Cassini imaging search rules out rings around Rhea – Tiscareno – 2010". Geophysical Research Letters – Wiley Online Library. 37 (14): n/a. arXiv: 1008.1764 . Bibcode:2010GeoRL..3714205T. doi:10.1029/2010GL043663.
  26. "How Iapetus, Saturn's outermost moon, got its ridge" . Retrieved 8 March 2018.
  27. Woo, Marcus (27 January 2015). "Why We're Looking for Alien Life on Moons, Not Just Planets". Wired . Retrieved 27 January 2015.
  28. "Hubble Discovers New Pluto Moon". ESA/Hubble Press Release. Retrieved 13 July 2012.
  29. "How Big Is Pluto? New Horizons Settles Decades-Long Debate". NASA.

All moons

Jupiter's moons

Saturn's moons