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★ Planet - outer space ..



Venus is the second planet from the Sun. It is ...


Mercury (planet)

Mercury is the smallest and innermost planet of...



Jupiter, the fifth planet from the Sun and larg...



Earth is the third planet from the Sun and the ...



Mars is the fourth planet from the Sun and the ...



Neptune is the eighth and farthest known planet...


★ Planet

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

The term planet is ancient, associated with the history of astrology, science, mythology and religion. Five planets in the Solar system visible to the naked eye. These are considered by many early cultures as divine, or as emissaries of the gods. As scientific knowledge advanced, human perception of the planets changed, incorporating a number of disparate objects. In 2006, the international astronomical Union the international astronomical Union officially adopted a resolution defining planets within the Solar system. This definition is controversial because it excludes many objects of planetary mass based on where or how they orbit. Although eight of the planetary bodies discovered before 1950 remain "planets" under this definition, some celestial bodies, such as Ceres, Pallas, Juno and Vesta, every object in the Solar asteroid belt and Pluto, the first TRANS-Neptunian object discovered, which were once considered planets by the scientific community, more not considered as planets under the current definition of a planet.

Planets in astrology have a different definition.

The planets were thought by Ptolemy to orbit Earth in deferent and epicycles motion. Although the idea that planets move in orbits around the Sun, it was suggested many times, it was not until the 17th century that this view was supported by evidence from the first telescopic astronomical observations, performed by Galileo Galilei. Around the same time, by a careful analysis of pre-telescopic observational data collected by Tycho Brahe, Johannes Kepler found the planets orbits are elliptical, not circular. As observational tools improved, astronomers saw that, like Earth, each planet rotates around an axis that is tilted relative to its orbit pole, and some shared such features as ice caps and seasons. With the dawn of the space age, close observation by space probes has found that Earth and other planets of the same characteristics, such as volcanism, hurricanes, tectonics, and even hydrology.

Planets of the Solar system are divided into two main types: large low-density giant planets and the small rocky earthlings. There are eight planets in the Solar system. In order of increasing distance from the sun, they are the four bodies, mercury, Venus, Earth, Mars, and the four giant planets, Jupiter, Saturn, Uranus and Neptune. Six planets, around which revolve one or more satellites.

A few thousand planets around other stars "extrasolar planets" or "exoplanets" have been discovered in the milky Way. As at 1 Feb 2020, 4.173 planets in known extrasolar planetary systems 3.096, including 678 several planetary systems, ranging in size from just above the size of the moon of the gas giants is about two times the size of Jupiter was discovered, of which more than 100 planets the same size as Earth, nine of which are located at the same relative distance from its star as earth is from the Sun, i.e. in the circumstellar habitable zone. 20 Dec 2011, the space telescope Kepler team reported the discovery of the first earth-sized extrasolar planets, Kepler-20E and Kepler-20F, orbiting a sun-like star Kepler-20. A 2012 study, analyzing gravitational microlensing data, estimates the average at least 1.6 bound planets for every star in the milky Way. About one in five sun-like stars are believed to be a planet the size of Earth in habitable zone.


1. History. (История)

The idea of planets has evolved over its history, from the Divine light of antiquity to the earthly objects of the scientific age. The concept has expanded to include worlds not only in the Solar system, but hundreds of other extrasolar systems. The ambiguities inherent in defining planets have led to scientific debate.

The five classical planets visible to the naked eye, were known since ancient times and has had a significant impact on mythology, religious cosmology, and ancient Astronomy. In ancient times, astronomers noted how certain lights moved across the sky, unlike the "fixed stars", which maintained a constant relative position in the sky. The ancient Greeks called these lights πλάνητες ἀστέρες planētes asteres, "wandering stars" or just πλανῆται planētai, "strangers", from which todays word "planet" has occurred. In Ancient Greece, China, Babylon and indeed all modern civilizations, it was almost universally believed that the earth was the center of the Universe and that all the "planets" circled the Earth. The reasons for this perception were that stars and planets appeared to revolve around the Earth every day, and apparently common-sense perceptions that Earth was solid and stable, and that he was not moving but at rest.


1.1. History. Babylon. (Вавилон)

The first civilization known to have a functional theory of the planets were the Babylonians who lived in Mesopotamia in the first and second millennia BC. The oldest surviving planetary astronomical text is the Babylonian Venus tablet of Ammisaduqa, a 7th-century BC copy of a list of observations of the movement of the planet Venus that probably dates as early as the second Millennium BC. LMU.A couple of APIN cuneiform tablets that date back to the 7th century BC, which describes the motion of the Sun, moon and planets during the year. The Babylonian astrologers also laid the foundations of what will eventually become Western Astrology. In Enuma Anu Enlil, written during the Neo-Assyrian period in the 7th century BC, comprises a list of omens and their relationships with various celestial phenomena including the motions of the planets. Venus, mercury and the outer planets Mars, Jupiter and Saturn have been defined by Babylonian astronomers. These remain the only known planets until the invention of the telescope in early modern times.


1.2. History. Greco-Roman astronomy. (Греко-римской астрономии)

The ancient Greeks initially did not attach any significance to the planets as the Babylonians. The Pythagoreans, in the 6th and 5th centuries BC appear to have developed their own independent planetary theory, which consisted of Earth, Sun, moon, and planets revolving around the "Central fire" at the center of the Universe. Pythagoras or Parmenides was the first to identify Hesperus the evening star and the Morning star Phosphoros as the same Aphrodite, Greek corresponding to Latin Venus, although it was long known among the Babylonians. In the 3rd century BC Aristarchus of Samos proposed a heliocentric system, according to which the Earth and planets revolve around the Sun. The geocentric system remained dominant until the scientific revolution.

In the 1st century BC, In the Hellenistic period, the Greeks began to develop their own mathematical schemes for predicting planetary positions. These schemes are based on geometry rather than arithmetic of the Babylonians, eventually darkening of the theory of the Babylonians complexity and comprehensiveness, and account for most of the astronomical movements observed from Earth with the naked eye. These theories would reach their fullest expression in the Almagest written by Ptolemy in the 2nd century ad. So complete was the domination of Ptolemys model that it replaces all previous works on astronomy and remained the definitive astronomical text in the Western world for 13 centuries. For the Greeks and Romans there were seven known planets, each is presumed to be circling Earth according to the complex laws set forth by Ptolemy. They were ascending from the Earth in order of the Ptolemies and using modern names: the Moon, mercury, Venus, Sun, Mars, Jupiter and Saturn.

Cicero, in his De Natura Deorum, these planets known in the 1st century BC with names for their use at the time:

"But there is most matter for wonder in the movements of the five stars which are falsely called wandering, falsely, because nothing wanders which through all eternity preserves its forward and retrograde courses, and its other movements, constant and unaltered. For instance, the star which is farthest from the earth, which is known as the star of Saturn, and is called by the Greeks Φαίνων Phainon, accomplishes its course in about thirty years, and though in that course it does much that is wonderful, first preceding the sun, and then falling off in speed, becoming invisible at the hour of evening, and returning to view in the morning, it never through the unending ages of time makes any variation, but performs the same movements at the same times. Beneath it, and nearer to the earth, moves the planet of Jupiter, which is called in Greek Φαέθων Phaethon, it completes the same round of the twelve signs in twelve years, and performs in its course the same variations as the planet of Saturn. The circle next below it is held by Πυρόεις Pyroeis, which is called the planet of Mars, and traverses the same round as the two planets above it in four and twenty months, all but, I think, six days. Beneath this is the planet of Mercury, which is called by the Greeks Στίλβων Stilbon, it traverses the round of the zodiac in about the time of the year’s revolution, and never withdraws more than one sign’s distance from the sun, moving at one time in advance of it, and at another in its rear. The lowest of the five wandering stars, and the one nearest the earth, is the planet of Venus, which is called Φωσϕόρος Phosphoros in Greek, and Lucifer in Latin, when it is preceding the sun, but Ἕσπερος Hesperos when it is following it, it completes its course in a year, traversing the zodiac both latitudinally and longitudinally, as is also done by the planets above it, and on whichever side of the sun it is, it never departs more than two signs’ distance from it."


1.3. History. India. (Индия)

In 499 ad, the Indian astronomer Aryabhata proposed a planetary model that explicitly incorporated earths rotation about its axis, which he explains as the reason that clearly there was a West motion of the stars. He also believed that the orbits of the planets are elliptical. Followers Aryabhatas was particularly strong in South India, where his principles of the diurnal rotation of the Earth, in particular, was carried out and a number of secondary works based on them.

In 1500, Nilakantha Somayaji of the Kerala school of astronomy and mathematics, in his Tantrasangraha, revised model Aryabhatas. In his Aryabhatiyabhasya, review Aryabhatas Aryabhatiya, he developed a planetary model where mercury, Venus, Mars, Jupiter and Saturn revolve around the Sun which in turn orbits earth, similar to the Tychonic System later proposed by Tycho Brahe in the late 16th century. Most astronomers of the Kerala school who followed him accepted his planetary model.


1.4. History. Medieval Muslim astronomy. (Средневековой мусульманской астрономии)

In the 11th century, the transit of Venus over the solar disk was observed by Avicenna, who established that Venus was, at least sometimes, below the sun. In the 12th century, Ibn Bajjah observed "two planets as black spots on the face from the Sun", which was later identified as a transit of mercury and Venus by the Maragha astronomer Qotb al-DIN Shirazi in the 13th century. Ibn Bajjah could not observe a transit of Venus across the disk of the Sun, because that did not happen in his life.


1.5. History. European Renaissance. (Европейский Ренессанс)

With the advent of technological revolution, the use of the term "planet" has changed from what moves across the sky relative to the stars, to the fact that the orbit of the Earth, or that was considered at the time, and by the 18th century to something that directly orbited the Sun when the heliocentric model of Copernicus, Galileo and Keplers understanding.

Thus, Earth became included in the list of the planets and the Sun and Moon were excluded. First, When the first satellites of Jupiter and Saturn was discovered in the 17th century, the terms "planet" and "satellite" were used interchangeably, although the latter gradually began to prevail in the next century. Until the mid-19th century, the number of "planets" rose rapidly because any newly discovered object orbiting the Sun was listed as a planet by the scientific community.


1.6. History. 19th century. (19 века)

In the 19th century astronomers began to realize that recently discovered bodies that have been classified as planets for almost half a century was very different from the traditional. These bodies shared the same region of space between Mars and Jupiter the asteroid belt, and had a much smaller mass, as a result they were reclassified as "asteroids". In the absence of any formal definition, came to the planet should be understood as any "large" body that orbited the Sun. Because there has been a sharp gap between asteroids and planets, as well as a series of new discoveries, it would seem, has ended after the discovery of Neptune in 1846, there was no obvious need to have a formal definition.


1.7. History. 20th century. (20-го века)

In the 20th century, Pluto was discovered. After initial observations led to the conclusion that it was more than Earth, the object was immediately recognized as the ninth planet. Further monitoring found the body was actually much smaller: in 1936, Ray lyttleton suggested that Pluto may be an escaped satellite of Neptune, and Fred Whipple suggested in 1964 that Pluto may be a comet. As it was still more than all known asteroids and seemingly did not exist in most of the population, it kept its status until 2006.

In 1992, astronomers Alexander Wolszczan and Dale frail announced the discovery of planets around pulsar PSR B1257 12. This discovery is considered the first definitive detection of a planetary system around another star. Then, on 6 October 1995, Michel Mayor and Didier Queloz of Geneva Observatory announced the first definitive detection of an exoplanet orbiting an ordinary main sequence star 51 peg.

The discovery of extrasolar planets led to another ambiguity in defining a planet: the points at which a planet becomes a star. Many known extrasolar planets are many times the mass of Jupiter, approaching that of stellar objects known as brown dwarfs. Brown dwarfs are generally considered stars due to their ability to burn deuterium, a heavy isotope of hydrogen. Although objects more massive than 75 times that of Jupiter fuse hydrogen objects of only 13 Jupiter masses can fuse deuterium. Deuterium is quite rare, and most brown dwarfs would have ceased fusing deuterium long before their discovery, making them virtually indistinguishable from supermassive planets.


1.8. History. 21st century. (21-го века)

With the opening in the second half of the 20th century a few objects within the Solar system and large objects around other stars, disputes arose over what should constitute a planet. There were particular disagreements over whether an object should be considered a planet if it was part of a unique population such as a belt, or if it was large enough to generate energy by thermonuclear synthesis of deuterium.

A growing number of Astronomers argued for Pluto to be declassified as a planet because many similar objects approaching its size were found in the same region of the Solar system the Kuiper belt during the 1990s and early 2000-ies. Pluto was just one small body in a population of thousands.

Some of them, such as Quaoar, Sedna and Eris, were perceived in the popular press as the tenth planet, has not received wide scientific recognition. After the announcement of Eris in 2005, the project is considered as 27% more massive than Pluto, created the need and desire for an official definition of planet.

Recognizing the problem, the IAU set about creating the definition of planet, and produced in August 2006. The number of planets dropped to the eight significantly larger bodies that had cleared their orbit, and a new class of dwarf planets was created, initially containing three objects, Ceres, Pluto and Eris.


1.9. History. Extrasolar planets. (Внесолнечных планет)

There is no formal definition of exoplanets. In 2003, the international astronomical Union IAU working group on extrasolar planets issued a statement, but the statement was not offered as an official resolution of MAS was never voted on by the members of the IAU. The Position statement includes the following guidelines are mainly centered on the boundary between planets and brown dwarfs:

  • Substellar objects with true masses above the limiting mass for thermonuclear fusion of deuterium are several "brown dwarfs", no matter how they are formed and where they are.
  • Free-floating objects in young star clusters with masses below the limiting mass for thermonuclear fusion of deuterium are not "planets", but "sub-brown dwarfs," or whatever name would be most appropriate.
  • Objects with true masses below the limiting mass for thermonuclear fusion of deuterium, currently estimated at 13 times the mass of Jupiter for objects with the same isotopic abundance as the Sun, orbit stars or stellar remnants "of the planet" regardless of how they were formed. The minimum mass and size required for the facility extrasolar planet is supposed to be the same as in the Solar system.

This working definition has since been widely used by astronomers when publishing discoveries of exoplanets in academic journals. Although temporary it remains an effective working definition until a more permanent is officially accepted. It does not address the dispute over the lower mass limit, so he avoided the controversy regarding objects within the Solar system. This definition also makes no comment on the planetary status of objects orbiting brown dwarfs, such as 2M1207b.

One of the definitions of sub-brown dwarf is a planet-mass object that formed through cloud collapse and not by accretion. This difference in education between a sub-brown dwarf and a planet is not aligned, astronomers have divided into two camps as whether to consider the formation of planets in the composition of its division in classification. One of the reasons for the disagreement lies in the fact that it is often impossible to determine the process of formation. For example, planets were formed by accretion around a star may get ejected from the system to become free-floating, and sub-brown dwarfs that formed in a star cluster through the cloud collapse can be captured into orbit around the star.

One study suggests that the objects above 10 m Jup was formed by gravitational instability and should not be considered as a planet.

At 13 Jupiter-mass cutoff is the average weight, rather than a precise threshold. Large objects fuse most of their deuterium and smaller fuse just a little and 13 m J a value somewhere in the middle. In fact, calculations show that the object fuses 50% of its initial content of deuterium, when the total weight varied between 12 and 14 m j the amount of deuterium fused depends not only on mass but also on the composition of the objects, the amount of helium and deuterium present. As of 2011 the extrasolar planets ENCYCLOPAEDIA includes objects up to 25 Jupiter masses, saying, "that is no special feature around 13 m JUP in the observed mass spectrum confirms the choice to forget this mass limit". In 2016, this limit was increased to 60 Jupiter masses based on the study of the mass-density relations. The exoplanet data Explorer includes objects up to 24 Jupiter masses with the Advisory: "the 13 Jupiter-mass distinction by the working group of the IAU is physically unmotivated for planets with rocky cores and experimentally problematic due to the sin I ambiguity". The NASA exoplanet archive includes objects with a mass or minimum mass equal to or less than 30 Jupiter masses.

Another criterion for separating planets and brown dwarfs, not deuterium fusion, formation process or location is whether the core pressure is dominated by Coulomb pressure or electron degenerate pressure.


1.10. History. The definition the IAU 2006 planet. (Определение планеты ИнАУ 2006)

Question about the lower boundary was raised at the meeting of the General Assembly of 2006 internal audit. After much debate and a failed proposal, the vast majority of those who remained at the meeting voted to adopt a resolution. The 2006 resolution, determines the planets within the Solar system, as follows:

At the planet, differ from planets in that they can collide with each other and with the planets".

The definition the IAU 2006 presents some problems for exoplanets, because the language is specific to the Solar system, and because the criteria for the roundness and orbital design of areas not currently observed. The astronomer Jean-Luc Margot proposed a mathematical criterion that determines whether an object can clear its orbit during the life of its star host, based on the mass of the planet, its semimajor axis and mass of its host star. This formula produces the value of π greater than 1 for the planets. Eight known planets and all the known exoplanets have π values of above 100, while Ceres, Pluto and Eris have values of 0.1 π or less. Objects with values of π 1 or more, is expected to be approximately spherical, so that the objects that correspond to the orbital requirement for the clearance zone automatically fulfill the requirement of roundness.


1.11. History. Once considered a planet. (Как считать планету)

The table below lists Solar system bodies considered planets.

Beyond the scientific community, Pluto still has cultural significance for many in the General public due to its historic classification as a planet from 1930 to 2006.


2. Mythology and naming. (Мифология и именования)

The names of the planets in the Western world are derived from the naming practices of the Romans, which ultimately derive from those of the Greeks and the Babylonians. In Ancient Greece, the two great luminaries-the moon and the Sun were Helios and Selene, the furthest planet Saturn was called Phainon, the Shiner, then Phaeton "Jupiter", "bright", the Red planet Mars was known as Pyroeis, "fiery", Venus is the brightest was known as Phosphoros, the light bringer, and the fleeting final planet was called mercury stilbon, the gleamer in. The Greeks also made each planet sacred to one of their Pantheon of gods, the Olympians: Helios and Selene were the names of both planets and gods, Phainon was sacred to Kronos, the Titan who fathered the Olympians, Phaethon was sacred to Zeus, Cronuss son who deposed him as king, Pyroeis was given to Ares, son of Zeus and the God of war, Phosphoros was ruled by Aphrodite, the goddess of love, Hermes, the messenger of the gods and God of learning and wit, ruled over Stilbon.

The Greek practice of grafting of their gods names onto the planets was almost certainly borrowed from the Babylonians. The Babylonians called Phosphoros after their goddess of love, Ishtar, Pyroeis after their God of war, Nergal, Stilbon after their God of wisdom NABU, and Phaethon after their chief God Marduk. Too many matches between Greek and Babylonian naming conventions for them to have arisen separately. The translation was not perfect. For instance, the Babylonian Nergal-God of war, and therefore the Greeks identified him with Ares. Unlike Ares, Nergal was also God of plague and the underworld.

Today, most people in the Western world know the planets by names derived from the Olympian Pantheon of gods. While modern Greeks still use their ancient names for the planets, other European languages, because of the influence of the Roman Empire and, later, the Catholic Church, use the Roman-Latin names, not Greek. The Romans, like the Greeks, were Indo-Europeans, shared with them a common Pantheon under different names but not the rich narrative traditions of Greek poetic culture had given their gods. In the late period of the Roman Republic, Roman writers borrowed much of the Greek narratives and applied them to your Pantheon, to the point where they became virtually indistinguishable. When the Romans studied Greek astronomy, they gave the planets the names of their own gods: mercury for Hermes, Aphrodite Venus, Mars, Ares, Zeus and Iuppiter Kronos Saturnus. When subsequent planets were discovered in the 18th and 19th centuries, the naming practice was retained with Neptūnus of Poseidon. Uranus is unique in that it is named after the Greek deity, not his Roman counterpart.

Some Romans, following a belief possibly originating in Mesopotamia but developed in Hellenistic Egypt, believed that the seven gods after whom the planets were named took hourly shifts in the situation on the Ground. The order of shifts went Saturn, Jupiter, Mars, Sun, Venus, mercury, Moon-from the farthest to the nearest planet. So the first day was started by Saturn the 1st hour, the second day in the sun, 25th hour, followed by the 49th hour of the moon, Mars, mercury, Jupiter and Venus. Because each day was named by the God that started it all, this is also the order of the days of the week in the Roman calendar after the Nundinal cycle was rejected – and still preserved many modern languages. In English, Saturday, Sunday and Monday are straightforward translations of these Roman names. The other days were renamed after the Tiv on Tuesday, setting the environment, Monorom Thursday and Friday refrigerator, the Anglo-Saxon gods considered similar or equivalent to Mars, mercury, Jupiter and Venus, respectively.

The earth is the only planet whose name in English is not derived from Greco-Roman mythology. Because it was only generally accepted as a planet in the 17th century, no tradition of naming it in honor of God. The name comes from the 8th to the Anglo-Saxon century the word Erda, which means ground or soil and was first used in writing in the name of the sphere of the Earth perhaps around 1300. Like its equivalents in other Germanic languages, it receives ultimately from the proto-Germanic word ertho, "ground", as seen in the English earth, the German "song of the earth", the Dutch whale route and the Scandinavian Jord. Many of the romance languages retain the old Roman word Terra or some variation of that, which was used in the meaning "land" and not "sea". Non-romance languages use their own native words. The Greeks retain their original name, Γή GE.

Non-European cultures use other planetary naming systems. India uses a system based on Navagraha which includes seven traditional planets and the ascending and descending lunar nodes Rahu and Ketu.

China and the countries of Eastern Asia historically subject to Chinese cultural influence, such as Japan, Korea and Vietnam, use a naming system based on the five Chinese elements: water, mercury, metal, Venus, Mars fire, wood and Earth Jupiter Saturn.

In traditional Hebrew astronomy, the seven traditional planets are for the most part descriptive names – the Sun-חמה Hammah or "beauty," Luna לבנה Livani or "white," Venus כוכב נוגה kokhav legs, or "bright planet" mercury כוכב kokhav or "planet" given the lack of distinguishing features, Mars מאדים Maadim or "red,"and" Saturn - שבתאי Shabbatai or "resting" with reference to their slow movement compared to the other visible planets. Strange is Jupiter, called Tzedeq צדק or "justice". Stiglitz suggests that it may be a euphemism for the original name of the kokhav כוכב בעל Baal or "the Baals planet", seen as idolatrous and commuted by analogy with Ishbosheth II Samuel.

In Arabic, the mercury عُطَارِد ʿUtārid, cognate with Ishtar / Astarte, Venus الزهرة, Earth الأرض al-ʾArd, from the same root as the land, Mars اَلْمِرِّيخ al-Mirrīkh, which means "featherless arrow" because of its retrograde motion of Jupiter and Saturn المشتري زُحَل Zuhal, "output".


3. The formation of. (Формирование)

It is not known with certainty how planets are formed. The prevailing theory is that they are formed during the collapse of a nebula into a thin disk of gas and dust. A protostar forms at the core, surrounded by a rotating protoplanetary disk. Through the accretion process of sticky collisions of dust particles in the disk steadily gaining ground in great body shape. Local concentrations of mass known as planetesimals form, and these accelerate the accretion process, drawing in additional material by their gravitational attraction. These concentrations become denser until they collapse inward under gravity to form protoplanets. After a planet reaches a mass slightly larger than the mass of Mars, it begins to accumulate in the atmosphere, greatly increasing the capture rate of planetesimals by aerodynamic drag. Depending on the history of accretion of solid particles and the gas giant planet, an ice giant or a terrestrial planet may lead.

When the protostar has grown such that it ignites to form a star, the surviving disk is removed from the inside out photoevaporation, the solar wind, Poynting–Robertson drag and other effects. After that, there still may be many protoplanets orbiting the star or each other, but over time many will collide, either to form a single larger planet or release material for other larger protoplanets or planets to absorb. Those objects that have become massive enough will capture most important in their orbital neighborhoods to become planets. Protoplanetary, to avoid collisions may become natural satellites of planets through a process of gravitational capture, or remain in belts of other objects to become either dwarf planets and small bodies.

Energy impact of small planetesimals, as well as radioactive decay will heat up the growing planet, causing it to at least partially melt. The interior of the planet begins to differentiate by mass, developing a denser core. Smaller terrestrial planets lose most of their atmospheres because of this accretion, but the lost gases can be replaced by outgassing from the mantle and from the subsequent impact of comets. Smaller planets will lose the atmosphere they gain through various escape mechanisms.

With the discovery and observation of planetary systems around stars other than the Sun, it becomes possible to elaborate, revise or even replace this account. The level of metallicheski is an astronomical term describing the abundance of chemical elements with atomic number greater than 2 helium - now thought to determine the probability that stars have planets. Therefore, it is believed that the metal-rich population I star will likely have a more substantial planetary system than a metal-poor population of the second star.


4. The Solar System. (Солнечной Системы)

There are eight planets in the Solar system, which as the distance from the Sun:

  • ♆ Neptune. (♆ Нептун)
  • ⊕ The earth. (⊕ Земли)
  • ♀ Venus. (♀ Венера)
  • ♃ Jupiter. (♃ Юпитер)
  • ♂ Mars. (♂ Марс)
  • ☿ Mercury. (☿ Меркурий)
  • ♅ Uranus. (♅ Уран)
  • ♄ Saturn. (♄ Сатурн)

Jupiter is the largest, at 318 Earth masses, while mercury is smallest, at 0.055 Earth masses.

The planets of the Solar system can be divided into categories depending on their composition:

  • Earthlings: the planet, similar to Earth, with the body mostly consist of rocks: mercury, Venus, Earth and Mars. At 0.055 Earth masses, mercury is the smallest terrestrial planet and the smallest planet in the Solar system. Earth is the largest terrestrial planet.
  • The ice giants, Uranus and Neptune, which are primarily composed of low-boiling materials such as water, methane and ammonia, with a thick atmosphere of hydrogen and helium. They are much less massive than gas giants, only 14 and 17 Earth masses.
  • Gas giants, Jupiter and Saturn, the giant planets consist mainly of hydrogen and helium, the most massive planet in the Solar system. Jupiter at 318 Earth masses is the largest planet in the Solar system, and Saturn the third massive, at 95 Earth masses.
  • Giant terrestrial planets: solid planets much more massive than Earthmen: Jupiter, Saturn, Uranus, Neptune.

5. Exoplanets. (Экзопланеты)

Exoplanet an exoplanet is a planet outside the Solar system. As at 1 Feb 2020, there is 4.173 confirmed exoplanets in systems 3.096, with 678 systems with more than one planet.

In early 1992, radio astronomers Alexander Wolszczan and Dale frail announced the discovery of two planets orbiting the pulsar PSR 1257 12. This discovery was confirmed, and, as a rule, is considered the first definitive detection of exoplanets. These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation, either the remaining rocky cores of giant planets that survived the supernova and then decayed into their current orbits.

The first confirmed discovery of extrasolar planets orbiting around a normal main sequence star occurred on 6 October 1995, when Michel Mayor and Didier Queloz of University of Geneva announced the discovery of planet around 51 Pegasus. From then until the Kepler mission most known extrasolar planets are gas giants comparable in mass to Jupiter or larger as they were easily detected. Directory of candidates of Kepler planets consists mostly of planets the size of Neptune and smaller, down to less than mercury.

There are several types of planets that do not exist in the Solar system: super-earths and mini-Neptune, which could be rocky like Earth or a mixture of volatiles and gas like Neptune - a radius of 1.75 times that of the earth can be the dividing line between the two types of planet. There are hot Jupiters that orbit very close to their star and may evaporate to become a chthonic planets that are remnants of the cores. Another possible type of planet is carbon planets, which form in systems with a high percentage of carbon than in the Solar system.

A 2012 study, analyzing gravitational microlensing data, estimates the average at least 1.6 bound planets for every star in the milky Way.

20 Dec 2011, the space telescope Kepler team reported the discovery of the first Earth-size exoplanets, Kepler-20E and Kepler-20F, orbiting a sun-like star Kepler-20.

Around 1 in 5 sun-like stars have an "Earth-sized" planet in the habitable zone, so the nearest expected to be within 12 light-years distance from Earth. The frequency of occurrence of such terrestrial planets is one of the variables in the Drake equation, which estimates the number of intelligent, communicating civilizations exist in the milky Way galaxy.

There are exoplanets that are much closer to their parent star than any planet in the Solar system is the Sun, and also exoplanets that are much farther away from its star. Mercury, the closest planet to the Sun at 0.4 AU, takes 88 days to orbit, but the shortest known orbits of exoplanets will only take a few hours, see ultra-short period planets. On the Kepler-11 system has five of its planets in shorter orbits than the Mercurys, they are all much more massive than mercury. Neptune is 30 AU from the Sun and takes 165 years to orbit, but there are exoplanets that are hundreds of AU from their star and take more thousands of years to orbit, e.g. 1RXS1609 b.


6. Planetary-mass objects. (Планетарно-массовые объекты)

Planetary-mass object, PMO planemo, or planetary body is a celestial object with a mass in the range definition of a planet: massive enough to achieve hydrostatic equilibrium to be rounded by its own gravity, but not enough to support the core synthesis as a star. By definition all planets are planetary-mass objects but the purpose of this term to refer to objects that do not conform to typical expectations for a planet. These include dwarf planets, which are surrounded by their own gravity but not massive enough to clear its own orbit large satellites, and free-floating planemos, which could be ejected from the system rogue planets or formed through cloud-collapse and not by accretion, sometimes called brown dwarfs.


6.1. Planetary-mass objects. Dwarf planet. (Карликовая планета)

A dwarf planet is a planetary-mass object that is neither true, nor a planet, natural satellite, it is in direct orbit around the star and is massive enough for its gravity to compress it into a hydrostatically equilibrious form, generally spheroid, but has not cleared neighborhood of other material in its orbit. Alan stern, who coined the term dwarf planet, says that the location doesnt matter and that only geophysical attributes to take into account the geophysical definition of planet, and dwarf planet is a subtype of planet. However, the IAU dwarf planets klassificeret as a separate category. The number of dwarf planets in the Solar system is unknown. The MAC recognized the three Ceres, Pluto and Eris has the names of two additional candidates, Haumea and Makemake, IAU dwarf planet naming Committee.


6.2. Planetary-mass objects. Rogue planets. (Изгои планет)

Several computer models of stellar and planetary system formation suggest that some objects of planetary mass would be ejected into interstellar space. Some scientists have argued that such objects found roaming in deep space should be classed as "planets", although others suggested that they should be called low-mass brown dwarfs.


6.3. Planetary-mass objects. Sub-brown dwarfs. (Суб-коричневые карлики)

Stars form through gravitational collapse of gas clouds, but smaller objects can also form via cloud-collapse. Planetary-mass objects formed this way are sometimes called sub-brown dwarfs. Sub-brown dwarfs may be free-floating such as Cha 110913-773444, and OTS 44, or orbiting a larger object, such as 2МАСС J04414489 2301513.

A binary system of sub-brown dwarfs are theoretically possible, 162225-240515 OPH was initially thought to be a binary brown dwarf of 14 Jupiter masses, and the sub-brown dwarf is 7 Jupiter masses, but further observations have revised the estimate of the mass up to more than 13 Jupiter masses, which makes them brown dwarfs according to the IAU working definitions.


6.4. Planetary-mass objects. Former star. (Бывшая звезда)

In close binary star systems one of the stars can lose a lot heavier companion. Accretion-powered pulsars can result in massive losses. On the shrinking star can become a planetary mass object. For example, Jupiter-mass object orbiting the pulsar PSR J1719-1438. These shrunken white dwarfs may be a helium planet, or the carbon of the planet.


6.5. Planetary-mass objects. A satellite of the planet. (Спутник планеты)

Some large satellites are of the same size or larger than the planet mercury, e.g. Jupiters Galilean satellites and Titan. Alan stern has argued that location doesnt matter and that only geophysical attributes will be taken into account in the definition of a planet, and proposes the term satellite planet for a planet-sized satellite.


6.6. Planetary-mass objects. Captured planets. (Захваченных планетах)

Rogue planets in star clusters have similar speed to the stars and so can be recaptured. They are usually fixed on wide orbits between 100 and 10 5 AC. Capture efficiency decreases with increasing cluster volume and the cluster size increases with the node and the bulk. It is almost independent of the mass of the planet. Single and multiple planets can be captured in random orbit misaligned, not coplanar with each other and with the host star spin or the already existing planetary systems.


7. Attributes. (Атрибутами)

Although each planet has unique physical characteristics, a number of broad commonalities do exist between them. Some of these characteristics, such as rings or natural satellites, only are not observed on the planets in the Solar system, while other commonly observed in extrasolar planets.


7.1. Attributes. Orbit. (Орбиты)

According to current definitions, all planets must revolve around stars, so any potential "rogue planets" are excluded. In the Solar system all the planets revolve around the Sun in the same direction as the Sun rotates counterclockwise as seen from above the Suns North pole. At least one exoplanet, Wasp-17B were found to orbit in the direction opposite to the direction of rotation of the star. The period of one revolution of the planet in its orbit is called the sidereal period or year. The planets year depends on its distance from its star, the further a planet is from its star, not only the longer the distance it must travel, but also the slower its speed, because it is less affected by its stars gravity. The orbits of the planets are not perfectly round, and therefore the distance from each of them varies during the year. The closest approach to its star is called perihelion of periastron in the Solar system, while its farthest separation from the star is called its apastron aphelion. As a planet approaches periastron, its speed increases as it trades gravitational potential energy to kinetic energy, just as a falling object on Earth accelerates as it falls, as the planet reaches apastron, its speed decreases, just as an object thrown upwards on Earth slows down when he reaches the top of its trajectory.

Each planets orbit is determined by the set of elements:

  • The semimajor axis distance from the planet to the halfway point along the longest diameter of its elliptical orbit Fig. This distance is not the same as its apastron, because there are no planets orbits its star at its exact centre.
  • The inclination of a planet tells how far above or below the established reference plane its orbit lies. In the Solar system, the reference plane is the plane of earths orbit, called the Ecliptic. For extrasolar planets, the plane, known as the sky plane or plane of the sky, is the plane perpendicular to the line of sight of an observer on Earth. Eight planets of the Solar system are very close to the Ecliptic, comets and Kuiper belt objects like Pluto are at far more extreme angles to it. The point at which a planet crosses above and below the reference plane, called the ascending and descending nodes. The longitude of the ascending node is the angle between the reference planes 0 and planets the longitude of the ascending node. Argument of periapsis or perihelion in the Solar system is the angle between the planets ascending node and its closest approach to its star.
  • The eccentricity of an orbit describes how elongated a planets orbit. Planets with low eccentricities have more circular orbits, while planets with high eccentricities have more elliptical orbits. Planets of the Solar system very low eccentricities, and thus nearly circular orbits. Comets and Kuiper belt objects, as well as several extrasolar planets have very high eccentricities, and thus exceedingly elliptical orbits.

7.2. Attributes. The inclination of the axis. (Наклон оси)

Planets also have varying degrees of axial tilt, they lie at an angle to the plane of their equator of the star. In this case, the amount of light received in each hemisphere to vary over the year, when the Northern hemisphere points away from its star, the southern hemisphere points to her, and Vice versa. So each planet has seasons, climate changes throughout the year. The time at which each hemisphere point far or close from its star is called the solstice. Each planet has two in the field of its orbit when one hemisphere its the summer solstice, when the day is longest and the other the winter solstice, when the day is short. Varying amounts of light and heat received each hemisphere creates annual changes in weather conditions for each half of the planet. Jupiters axial tilt is very small, so its seasonal changes are minimal, Uranium, on the other hand, has a tilt so extreme it is virtually on its side, which means that its hemispheres are either constantly in the sun or kept in the dark during your solstice. Among extrasolar planets, axial tilts are not known, though most hot Jupiters is considered to be negligible to the tilt axis as a result of their proximity to their stars.


7.3. Attributes. Rotation. (Вращение)

Planets rotate around invisible axes through their centres. The rotation period of the planet is called stellar day. Most planets in the Solar system rotate in the same direction around the Sun, which is counterclockwise as seen from above the Suns North pole, the exceptions being Venus and Uranus which rotate clockwise, though Uranuss extreme axial tilt means there are different conventions on which of its poles is "North", and so whether it rotates clockwise or anti-clockwise. Regardless of the Convention, Uranus has a retrograde rotation relative to its orbit.

The rotation of the planet can be caused by several factors in the process of formation. The net angular momentum can be caused by certain moments of the contributions to the dynamics of objects increase. In accretion, gas giant planets can also contribute to angular momentum. Finally, in the last stages of planet building, a stochastic process of protoplanetary accretion can randomly change the axis of rotation of the planet. There is a large variation in the length of day between the planets, with Venus taking 243 days to rotate, and the giant planets only a few hours. The rotational periods of extrasolar planets are not known. However, for hot Jupiters, their proximity to their stars mean that they are tidal locked, that is, their orbits are in sync with their rotations. This means that they always show one face to their stars, with one side in perpetual day, the other in eternal night.


7.4. Attributes. Orbital clearing. (Орбиталь поляне)

Determination of dynamic characteristics of the planet is that it has cleared its neighborhood. A planet that has cleared its neighborhood has accumulated enough mass to gather and sweep away all the planetesimals in its orbit. In fact, it orbits its star in isolation and not share its orbit with lots of similar sized objects. This feature was approved as part of the official definition of internal audit of the planet in August 2006. This criterion excludes such planetary bodies as Pluto, Eris and Ceres from full-fledged planethood, making them instead dwarf planets. Although to date this criterion only applies to the Solar system, a number of young extrasolar systems have been found in which evidence suggests orbital clearing is about to occur in their circumstellar disk.


7.5. Attributes. Weight. (Вес)

The planets define the physical characteristics is that it is massive enough for its own gravity to dominate over the electromagnetic forces binding its physical structure, leading to a state of hydrostatic equilibrium. This effectively means that all planets have a spherical or spheroidal shape. Up to a certain mass, an object can be irregular in shape, but also links to, which varies depending on the chemical composition of the object, gravity begins to pull an object towards its own centre of mass until then, until the object collapses into a sphere.

Mass is also the Prime attribute by which planets are distinguished from stars. The upper limit for planethood mass about 13 times Jupiter masses for objects with solar-type isotopic content, for which it achieves conditions suitable for nuclear fusion. In addition to the Sun, no objects of such mass exist in the Solar system but there are exoplanets of this size. 13-Jupiter-mass limit is not agreed upon and the extrasolar planets ENCYCLOPAEDIA includes objects up to 60 Jupiter masses, and the exoplanet data Explorer up to 24 Jupiter masses.

The smallest known planet is PSR B1257 12A, one of the first exoplanets discovered, which was found in 1992 in orbit around a pulsar. Its mass is about half of the planet mercury. The smallest known planets orbiting main sequence stars than our Sun, Kepler-37B, with a Mass and radius slightly higher than that of the moon.


7.6. Attributes. Internal differentiation. (Внутренней дифференциации)

Every planet began its existence in a completely liquid state, in the early formation, the denser, heavier materials sank to the center, leaving the lighter materials near the surface. Therefore, each has a differentiated interior consisting of a dense planetary core surrounded by a mantle, which is or has been liquid. The terrestrial planets are sealed in hard crusts, but in giant planets mantle just goes into the upper layers of the cloud. The terrestrial planets possess cores of elements such as iron and Nickel, and mantles of silicates. Jupiter and Saturn are believed to have cores of rock and metal surrounded by a mantle of metallic hydrogen. Uranus and Neptune, which are smaller, have rocky cores surrounded by mantles of water, ammonia, methane and other ICES. The fluid action within these planets cores creates a geodynamo that generates a magnetic field.


7.7. Attributes. The atmosphere. (Атмосфера)

All the planets in the Solar system except mercury have no significant atmospheres because their gravity is strong enough to keep gases close to the surface. Larger planets massive enough to keep large quantities of light gases hydrogen and helium, while the smaller planets lose these gases into space. The composition of Earths atmosphere different from other planets because the various life processes that have occurred on the planet have introduced free molecular oxygen.

Planetary atmospheres depends on the different insolation or internal energy, leading to the formation of dynamic weather systems such as hurricanes, on Earth, on the planet of dust storms on Mars, more than an Earth-sized anticyclone on Jupiter called the Great red Spot, and a hole in the atmosphere of Neptune. At least one exoplanet system HD 189733 b, which was argued that the weather system that is similar to the Great Red Spot but twice.

Hot Jupiters, due to their extreme proximity to their host stars, have been shown to lose its atmosphere to space due to stellar radiation, like the tails of comets. These planets may have vast differences in temperature between day and night sides that produce supersonic winds, although the day and night sides of the system HD 189733 b appear very similar temperatures, indicating that planets atmosphere effectively redistributes the stars energy around the planet.


7.8. Attributes. The magnetosphere. (Магнитосфера)

One of the important characteristics of the planets is their intrinsic magnetic moments which in turn give rise to magnetospheres. The presence of a magnetic field indicates that the planet is still geologically alive. In other words, magnetized planets have flows of electrically conducting material in their interiors, which generate their magnetic field. These fields significantly change the interaction of the planet and solar wind. This is a magnetized planet creates a cavity in the solar wind around itself called magnetosphere, which the wind cannot penetrate. The magnetosphere can be much larger than the planet itself. In contrast, non-magnetized planets have only small magnetospheres induced by interaction of the ionosphere with the solar wind, which cannot effectively protect the planet.

Of the eight planets in the Solar system only Venus and Mars lack such a magnetic field. In addition, the moon of Jupiter Ganymede also has one. Of the magnetized planets the magnetic field of mercury is the weakest, and is barely able to deflect the solar wind. Ganymedes magnetic field is several times larger, and Jupiter is the strongest in the Solar system so strong that it poses a serious health risk to future manned missions to its moons. The magnetic fields of other planets roughly similar in strength on Earth but their magnetic moments are much larger. The magnetic fields of Uranus and Neptune are strongly tilted relative to the axis of rotation and offset from the center of the planet.

In 2004 a team of astronomers in Hawaii observed an exoplanet around the star HD 179949, which appeared to create a sunspot on the surface of their parent stars. The team suggested that the magnetosphere of the planet were to transfer energy to the stellar surface, increasing its already high 7.760 °C temperature even at 400 °C.


7.9. Attributes. Secondary characteristics. (Второстепенные характеристики)

Several planets or dwarf planets in the Solar system such as Neptune and Pluto have orbital periods that are in resonance with each other or with smaller bodies, it is also common in satellite systems. All, except mercury and Venus have natural satellites, often called "moons". Earth has one, Mars two, and the giant planets have numerous moons in complex planetary systems. Many satellites of the giant planets have many characteristics similar to the terrestrial planets and dwarf planets, and some of them have been studied as possible abodes of life, especially Europe.

Four giant planets and the orbit of the planetary rings of varying size and complexity. The rings are made mostly of dust and debris, but can accommodate tiny moonlets whose gravity shapes and maintains their structure. Although the origins of planetary rings is not precisely known, they are considered to be the result of natural satellites that fell below their parent planets, the Roche limit and was torn apart by tidal forces.

No secondary signs are not observed around extrasolar planets. Outdoor brown dwarf Cha 110913-773444, which has been described as a rogue planet, is considered the orbit of a tiny protoplanetary disc and open the brown dwarf OTS 44 was shown that surrounded by a substantial protoplanetary disk of at least 10 Earth masses.

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Encyclopedic dictionary

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