how many planets are there orbiting the sun
Heliocentric orbit


A heliocentric orbit (also called circumsolar orbit) is an orbit around the barycenter of the Solar System, which is usually located within or very near the surface of the Sun. All planets, comets, and asteroids in the Solar System, and the Sun itself are in such orbits, as are many artificial probes and pieces of debris. The moons of planets in the Solar System, by contrast, are not in heliocentric orbits, as they orbit their respective planet (although the Moon has a convex orbit around the Sun
11319165
Definition of planet


that the timing of the Moon's orbit is in tandem with the Earth's own orbit around the Sun—looking down on the ecliptic, the Moon never actually loops back on itself, and in essence it orbits the Sun in its own right. Also many moons, even those that do not orbit the Sun directly, often exhibit features in common with true planets. There are 19 moons in the Solar System that have achieved hydrostatic equilibrium and would be considered planets if only the physical parameters are considered. Both Jupiter's
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Retrograde and prograde motion


if so described. In our Solar System, the orbits about the Sun of all planets and most other objects, except many comets, are prograde, i.e. in the same direction as the Sun rotates. The rotations of most planets, except Venus and Uranus, are also prograde. Most natural satellites have prograde orbits about their planets. Prograde satellites of Uranus orbit in the direction Uranus rotates, which is retrograde to the Sun. Retrograde satellites are generally small and distant from their planets, except Neptune's satellite Triton, which
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List of Firefly planets and moons


". The fourth star Kalidasa and its planets orbit next. After that, the fifth and last star Blue Sun and its planets orbit. Worlds orbiting these last two stars comprise "The Rim". Planets too far away from the biozones of the main stars are sustained for habitability by a series of protostars. The protostars Qin Shi Huang and Lux orbit the White Sun. Murphy orbits Georgia. Himinbjørg and Heinlein orbit the Red Sun, Penglai orbits Kalidasa, and Burnham orbits the Blue Sun. The number of terraformed worlds
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Mercury (planet)


many years it was thought that Mercury was synchronously tidally locked with the Sun, rotating once for each orbit and always keeping the same face directed towards the Sun, in the same way that the same side of the Moon always faces Earth. Radar observations in 1965 proved that the planet has a 3:2 spin–orbit resonance, rotating three times for every two revolutions around the Sun. The eccentricity of Mercury's orbit makes this resonance stable—at perihelion, when the solar tide is strongest, the Sun is nearly still in
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Orbit


orbital speed of each planet is not constant, as had previously been thought, but rather that the speed depends on the planet's distance from the Sun. Third, Kepler found a universal relationship between the orbital properties of all the planets orbiting the Sun. For the planets, the cubes of their distances from the Sun are proportional to the squares of their orbital periods. Jupiter and Venus, for example, are respectively about 5.2 and 0.723 AU distant from the Sun, their orbital periods respectively about 11.86 and 0.615 years.
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Quasi-satellite


A quasi-satellite is an object in a specific type of co-orbital configuration (1:1 orbital resonance) with a planet where the object stays close to that planet over many orbital periods. A quasi-satellite's orbit around the Sun takes exactly the same time as the planet's, but has a different eccentricity (usually greater), as shown in the diagram on the right. When viewed from the perspective of the planet, the quasi-satellite will appear to travel in an oblong retrograde loop around the planet
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Circumstellar habitable zone


CHZ planet, including some systems that consist of multiple CHZ planets. Most such planets, being super-Earths or gas giants, are more massive than Earth, because such planets are easier to detect. On November 4, 2013, astronomers reported, based on "Kepler" data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarfs in the Milky Way. 11 billion of these may be orbiting Sun-like stars. Proxima Centauri
2294441
Perturbation theory


as taking place along Kepler's orbits, which are defined by the equations of the two-body problem, the two bodies being the planet and the Sun. Since astronomic data came to be known with much greater accuracy, it became necessary to consider how the motion of a planet around the Sun is affected by other planets. This was the origin of the three-body problem; thus, in studying the system Moon–Earth–Sun the mass ratio between the Moon and the Earth was chosen as the small parameter
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Drake equation


the exception; and that there are one or more bound planets per Milky Way star. In November 2013, astronomers reported, based on "Kepler" space mission data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of sun-like stars and red dwarf stars within the Milky Way Galaxy. 11 billion of these estimated planets may be orbiting sun-like stars. Since there are about 100 billion stars in the galaxy, this implies is roughly 0.4. The nearest planet
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K2-3d


, or how bright it appears from Earth's perspective, is 12.168. Therefore, it is too dim to be seen with the naked eye. K2-3d orbits its host star, which has about 6% of the Sun's luminosity, with an orbital period of 44 days and an orbital radius of about 0.2 times that of Earth (compared to the distance of Mercury from the Sun, which is about 0.38 AU). The planet orbits on the edge of the inner (empirical) habitable zone, a region
2330126
K2-33b


The star's apparent magnitude, or how bright it appears from Earth's perspective, is 14.3. Therefore, it is too dim to be seen with the naked eye. K2-33b orbits its host star with an orbital period of 5.424 days at a distance of 0.049 AU (compared to the distance of Mercury from the Sun, which is about 0.38 AU). The planet likely receives about 125 times as much sunlight that Earth does from the Sun. The planet is best known for its remarkably young age, which
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Planet Nine


in the orbits of Sedna and and several other eTNOs. They proposed that an unknown planet in a circular orbit between 200 and 300 AU was perturbing their orbits. Later, in 2015, Raúl and Carlos de la Fuente Marco argued that two massive planets in orbital resonance were necessary to produce the similarities of so many orbits. In early 2016, California Institute of Technology's Batygin and Brown described how the similar orbits of six eTNOs could be explained by Planet Nine and proposed a possible orbit for the planet. This hypothesis could
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Planet Nine


also explain eTNOs with orbits perpendicular to the inner planets and others with extreme inclinations, and had been offered as an explanation of the tilt of the Sun's axis. Planet Nine is hypothesized to follow an elliptical orbit around the Sun with an eccentricity of to . The planet's semi-major axis is estimated to be to , roughly 13 to 26 times the distance from Neptune to the Sun. It would take the planet between 10,000 and 20,000 years to make one full orbit around the Sun. Its inclination to the ecliptic
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Mercury (planet)


Mercury is the smallest and innermost planet in the Solar System. Its orbital period around the Sun of 87.97 days is the shortest of all the planets in the Solar System. It is named after the Roman deity Mercury, the messenger of the gods. Like Venus, Mercury orbits the Sun within Earth's orbit as an "inferior planet", and never exceeds 28° away from the Sun when viewed from Earth. This proximity to the Sun means the planet can only be seen near the western or eastern horizon during the
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Planetary habitability


November 2013, astronomers reported, based on "Kepler" space mission data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarfs within the Milky Way. 11 billion of these estimated planets may be orbiting Sun-like stars. The nearest such planet may be 12 light-years away, according to the scientists. An understanding of planetary habitability begins with the host star. The classical HZ is defined for surface conditions only; but a
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Flight dynamics (spacecraft)


) the departure planet's orbital velocity around the Sun. The desired heliocentric transfer orbit to a superior planet will have its perihelion at the departure planet, requiring the hyperbolic excess velocity to be applied in the posigrade direction, when the spacecraft is away from the Sun. To an inferior planet destination, aphelion will be at the departure planet, and the excess velocity is applied in the retrograde direction when the spacecraft is toward the Sun. For accurate mission calculations, the orbital elements of the planets must be obtained from an ephemeris
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Exploration of Mercury


MESSENGER" and "BepiColombo" are intended to gather complementary data to help scientists understand many of the mysteries discovered by "Mariner 10"s flybys. Compared to other planets, Mercury is difficult to explore. The increased speed required to reach it is relatively high, and due to the proximity to the Sun, orbits around it are rather unstable. "MESSENGER" was the first probe to orbit Mercury. Mercury has not been a primary focus of many space programs. Because the planet is so close to the Sun and spins on
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Nibiru cataclysm


any scientific evidence and has been rejected by astronomers and planetary scientists as pseudoscience and an Internet hoax. Such an object would have destabilised the orbits of the planets to the extent that their effects would be easily observable today. Astronomers have hypothesized many planets beyond Neptune, and though many have been disproved, there are some that remain viable candidates such as Planet Nine. All the current candidates are in orbits that keep them well beyond Neptune throughout their orbit, even when they are closest to the Sun. The idea of the Nibiru
6830939
Exoplanetology


and Saturn in the Solar System. Giant planets with substantially larger orbits are now known to be rare, at least around Sun-like stars. The distance of the habitable zone from a star depends on the type of star and this distance changes during the star's lifetime as the size and temperature of the star changes. The eccentricity of an orbit is a measure of how elliptical (elongated) it is. All the planets of the Solar System except for Mercury have near-circular orbits (e<0.1). Most exoplanets
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Solar System


size of Earth's orbit, whereas Earth's volume is roughly one millionth (10) that of the Sun. Jupiter, the largest planet, is from the Sun and has a radius of , whereas the most distant planet, Neptune, is from the Sun. With a few exceptions, the farther a planet or belt is from the Sun, the larger the distance between its orbit and the orbit of the next nearer object to the Sun. For example, Venus is approximately 0.33 AU farther out from the Sun than
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Laplace plane


coplanar with, and between, (a) the polar axis of the parent planet's spin, and (b) the orbital axis of the parent planet's orbit around the Sun. The Laplace plane arises because the equatorial oblateness of the parent planet tends to cause the orbit of the satellite to precess around the polar axis of the parent planet's equatorial plane, while the solar perturbations tend to cause the orbit of the satellite to precess around the polar axis of the parent planet's orbital plane around the Sun. The
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Terrestrial planet


Kepler-102b, Kepler-102d, Kepler-113b, Kepler-131b, Kepler-131c, Kepler-138c, Kepler-406b, Kepler-406c, Kepler-409b. The Neptune-mass planet Kepler-10c also has a density 5 g/cm and is thus very likely terrestrial. In 2013, astronomers reported, based on "Kepler" space mission data, that there could be as many as 40 billion Earth- and super-Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarfs within the Milky Way. 11 billion of these estimated planets may be orbiting Sun-
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HD 69830 d


orbital period. The star has a mass of 0.86 and a radius of 0.90 . It has a surface temperature of 5394 K and is 10.6 billion years old. In comparison, the Sun is 4.6 billion years old and has a surface temperature of 5778 K. The star's apparent magnitude, or how bright it appears from Earth's perspective, is 5.47. Therefore, HD 69830 is visible to the naked eye. The planet's orbit has a low orbital eccentricity, like most of the planets in the Solar System. The
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Laplace plane


) or to the plane of the primary planet's orbit around the Sun (if the satellite is far away from its planet). This is because the strength of the planet's perturbation on the satellite's orbit is much stronger for orbits close to the planet, but drops below the strength of the Sun's perturbation for orbits farther away. Examples of satellites whose Laplace plane is close to their planet's equatorial plane include the satellites of Mars and the inner satellites of the giant planets. Examples of satellites whose Laplace plane
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List of Firefly planets and moons


is a desert world orbited by Niska's Skyplex. Mal tries to sell medical supplies here. Named in the script for "War Stories" The third planet orbiting the Red Sun with a strong Alliance presence. Said to be located at times to be 10 hours away from Jiangyin. Mentioned in "Safe" as a location likely to have medical facilities. The fourth planet orbiting the Red Sun. Higgin's Moon is one of its two moons. The fifth planet orbiting the Blue Sun. It has one moon, Perth
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Earth analog


data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarf stars within the Milky Way galaxy. 11 billion of these estimated planets may be orbiting Sun-like stars. The nearest such planet may be 12 light-years away. Scientific findings since the 1990s have greatly influenced the scope of the fields of astrobiology, models of planetary habitability and the search for extraterrestrial intelligence (SETI). Scientists estimate that there may be billions of Earth
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Rare Earth hypothesis


within the habitable zones of their stars"; 8.8 billion of them therefore exist in the Milky Way galaxy alone. On 4 November 2013, astronomers reported, based on "Kepler" space mission data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of sun-like stars and red dwarf stars within the Milky Way Galaxy. 11 billion of these estimated planets may be orbiting sun-like stars. The requirement for a system to have a Jovian planet as protector (Rare
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Sun-synchronous orbit


A Sun-synchronous orbit (SSO, also called a heliosynchronous orbit) is a nearly polar orbit around a planet, in which the satellite passes over any given point of the planet's surface at the same local mean solar time. More technically, it is an orbit arranged so that it precesses through one complete revolution each year, so it always maintains the same relationship with the Sun. A Sun-synchronous orbit can place a satellite in constant sunlight, which allows the solar panels to work continually. This orbit is
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Planet


trans-Neptunian object discovered), that were once considered "planets" by the scientific community, are no longer viewed as planets under the current definition of "planet". Planets in astrology have a different definition. The planets were thought by Ptolemy to orbit Earth in deferent and epicycle motions. Although the idea that the planets orbited the Sun had been 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. About the
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Temporary satellite


planet's (co-orbital configuration) and are captured most often when the planet is closest to the Sun (in the case of the Earth, in January) or furthest from the Sun (Earth: in July). In strict sense, only bodies that complete a full orbit around a planet are considered temporary satellites, also called temporarily captured orbiters (TCO). However, asteroids not in a tight co-orbital configuration with a planet can be temporarily captured for less than a full orbit; such objects have
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Red giant


lasts from 10 years for a planet with an orbit similar to that of Mars to for one that orbits at Saturn's distance to the Sun, the maximum time () corresponding for planets orbiting at the distance of Jupiter. However, for planets orbiting a star in equivalent orbits to those of Jupiter and Saturn they would be in the habitable zone for and respectively; for stars more massive than the Sun, the times are considerably shorter. As of June 2014, 50 giant planets have been discovered around giant stars. However
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Superflare


stars had violent outbursts, up to 10,000 times as powerful as the strongest flares known on the Sun. In many cases there were multiple events on the same star. Younger stars were more likely to flare than old ones, but strong events were seen on stars as old as the Sun. The flares were initially explained by postulating giant planets in very close orbits, such that the magnetic fields of the star and planet were linked. The orbit of the planet would warp the field lines until the instability released magnetic field energy
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Gliese 832 c


dense atmosphere, which could make it much hotter and more like the planet Venus. The planet orbits a (M-type) star named Gliese 832, orbited by a total of two known planets. The star has a mass of 0.45 and a radius of 0.48 . It has a temperature of 3620 K and is estimated to be about 9.54 billion years old. In comparison, the Sun is 4.6 billion years old and has a temperature of 5778 K. The star's apparent magnitude, or how bright it appears from Earth
7431606
Exploration of Mercury


the planet on account of its proximity to the Sun, which causes the Sun's gravitational field to pull on any satellite that would be set into Mercury's orbit. The planet's orbit is inclined to the ecliptic by 7°, and its orbital velocity varies from at aphelion to almost at perihelion. Spacecraft would be even faster, because they accelerate as they approach the greater gravitational pull of the Sun, but must slow down for orbit insertion, so this entails considerable fuel requirements. This is different with superior planets beyond
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Asteroid


this article, the term "asteroid" refers to the minor planets of the inner Solar System including those co-orbital with Jupiter. There exist millions of asteroids, many thought to be the shattered remnants of planetesimals, bodies within the young Sun's solar nebula that never grew large enough to become planets. The vast majority of known asteroids orbit within the main asteroid belt located between the orbits of Mars and Jupiter, or are co-orbital with Jupiter (the Jupiter trojans). However, other orbital families exist with
218045
Orbiter (simulator)


and interplanetary travel is supported, including orbital and sub-orbital flight, although only vessel-ground collisions are supported. Docking and attachment systems allow the user to simulate docking with a space station or other spacecraft and rendezvous with and retrieval of satellite. Users can also build space stations in orbit. The solar system presented in "Orbiter" consists of the Sun, the eight planets and their major moons. Many dwarf planets, asteroids (except Vesta), and comets not included in the simulator are available as add-
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Sun-synchronous orbit


oblate planet is given by where An orbit will be Sun-synchronous when the precession rate equals the mean motion of the Earth about the Sun, which is 360° per sidereal year (), so we must set , where is the orbital period. As the orbital period of a spacecraft is where is the semi-major axis of the orbit and is the standard gravitational parameter of the planet ( for Earth); as for a circular or almost circular orbit, it follows that or when is 360° per year
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Gliese 832 c


's perspective, is 10.19. Therefore, it is too dim to be seen with the naked eye. The planet orbits its host star with about 3% of the Sun's luminosity approximately every 36 days and an orbital radius 0.16 times that of Earth (compared to Mercury's orbital distance of 0.38 AU). The planet is a super-Earth mass planet orbiting in its star's habitable zone. Although it orbits its star much closer than the Earth orbits the Sun, it orbits a red dwarf, receiving approximately as
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TRAPPIST-1


TRAPPIST-1, also designated 2MASS J23062928-0502285, is an ultra-cool red dwarf star that is slightly larger, but much more massive, than the planet Jupiter; it is located from the Sun in the constellation Aquarius. Seven temperate terrestrial planets have been detected orbiting the star, a larger number than detected in any other planetary system. A study released in May 2017 suggests that the stability of the system is not particularly surprising if one considers how the planets migrated to their present orbits through a protoplanetary disk. A team
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List of Firefly planets and moons


to around 1G (Earth standard) and hold surface water and atmosphere necessary to sustain life. The system has five stars and seven brown dwarf/protostars. All the stars orbit the White Sun, which is a class A0 giant, 2.5 times bigger than Sol and 80 times as bright. The "Central Planets" are the terrestrial worlds that orbit the White Sun. Farther out in this system the Red Sun and Georgia share an orbit, along with the worlds orbiting these stars, referred to as "Border Planets
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Elongation (astronomy)


In astronomy, a planet's elongation is the angular separation between the Sun and the planet, with Earth as the reference point. The greatest elongation of a given inferior planet occurs when this planet's position, in its orbital path around the Sun, is at tangent to the observer on Earth. Since an inferior planet is well within the area of Earth's orbit around the Sun, observation of its elongation should not pose that much a challenge (compared to deep-sky objects, for example). When a planet
14029094
Solar System


its "perihelion", whereas its most distant point from the Sun is called its "aphelion". The orbits of the planets are nearly circular, but many comets, asteroids, and Kuiper belt objects follow highly elliptical orbits. The positions of the bodies in the Solar System can be predicted using numerical models. Although the Sun dominates the system by mass, it accounts for only about 2% of the angular momentum. The planets, dominated by Jupiter, account for most of the rest of the angular momentum due to
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Apsis


image below-left features the "inner" planets: their orbits, orbital nodes, and the points of perihelion (green dot) and aphelion (red dot), as seen from above Earth's northern pole and Earth's ecliptic plane, which is coplanar with Earth's orbital plane. From this orientation, the planets are situated outward from the Sun as Mercury, Venus, Earth, and Mars, with all planets travelling their orbits counterclockwise around the Sun. The "reference" Earth-orbit is colored yellow and
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Planet Nine


high inclination orbit at 1,500 AU. Another process such as a passing star would be required to account for the absence of objects with arguments of perihelion near 180°. These simulations showed the basic idea of how a single large planet can shepherd the smaller TNOs into similar types of orbits. They were basic proof of concept simulations that did not obtain a unique orbit for the planet as they state there are many possible orbital configurations the planet could have. Thus they did not fully formulate a model that successfully incorporated all the clustering
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Giovanni Alfonso Borelli


the orbits of the planets. Borelli believed that the planets were revolving as a result of three forces. The first force involved the planets' desire to approach the sun. The second force dictated that the planets were propelled to the side by impulses from sunlight, which is corporeal. Finally, the third force impelled the planets outward due to the sun’s revolution. The result of these forces is similar to a stone’s orbit when tied on a string. Borelli's measurements of the orbits of satellites of Jupiter are mentioned
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Planet Nine


Planet Nine is a hypothetical planet in the outer region of the Solar System. Its gravitational effects could explain the unusual clustering of orbits for a group of extreme trans-Neptunian objects (eTNOs), bodies beyond Neptune that orbit the Sun at distances averaging more than 250 times that of the Earth. These eTNOs tend to make their closest approaches to the Sun in one sector, and their orbits are similarly tilted. These improbable alignments suggest that an undiscovered planet may be shepherding the orbits of the most distant known Solar System objects
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Aries (constellation)


sequence star, slightly larger than the Sun, with two orbiting planets. One planet is 2.3 times the mass of Jupiter, and the other is 1.57 times the mass of Jupiter. HD 20367 is a G0 type star, approximately the size of the Sun, with one orbiting planet. The planet, discovered in 2002, has a mass 1.07 times that of Jupiter and orbits every 500 days. In 2019, scientists conducting the CARMENES survey at the Calar Alto Observatory announced evidence of two Earth-mass exoplanets orbiting the star
218176
Extraterrestrial life


the most likely places for life to exist. Numerous discoveries of such zones since 2007 have generated numerical estimates of many billions of planets with Earth-like compositions. , only a few planets had been discovered in these zones. Nonetheless, on 4 November 2013, astronomers reported, based on "Kepler" space mission data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarfs in the Milky Way, 11 billion of which may be orbiting
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Flight dynamics (spacecraft)


orbit occurs at the planet's sphere of influence radius relative to the Sun, as defined above in Orbital flight. Given the Sun's mass ratio of 333,432 times that of Earth and distance of , the Earth's sphere of influence radius is (roughly 1,000,000 kilometers). The transfer orbit required to carry the spacecraft from the departure planet's orbit to the destination planet is chosen among several options: The required hyperbolic excess velocity "v" (sometimes called "characteristic velocity") is the difference between the transfer orbit's
16661487
Early life of Isaac Newton


and supposing the orbits of the planets to be circles with the sun at the centre, had already proved that the force of the Sun acting upon the different planets must vary as the inverse square of the distances of the planets from the Sun. He was therefore led to inquire whether, if the Earth's attraction extended to the Moon, the force at that distance would be of the exact magnitude necessary to retain the Moon in its orbit. He found that the Moon by its motion in its orbit was deflected from the
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Kepler-41


Kepler-41 or KOI-196 is a star in the constellation Cygnus. It is a G-type main-sequence star, like the Sun, and it is located about 3,680 light-years (1130 parsecs) away. It is fairly similar to the Sun, with 115% of its mass, a radius of 129% times that of the Sun, and a surface temperature of 5,750 K. There is one known extrasolar planet orbiting Kepler-41. In 2011, the planet Kepler-41b was discovered in orbit around the star. The planet orbits
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14 Herculis


percent of the luminosity of the Sun. The star appears to be 2.7 times as enriched with elements heavier than hydrogen (based on its abundance of iron), in comparison to the Sun. In 1998 a planet was discovered orbiting 14 Herculis. The planet's eccentric orbital period is 4.8 years. In 2005, a possible second planet was proposed, designated 14 Herculis c. The parameters of this planet are uncertain, but a recent analysis suggests it may lie in the 4:1 resonance with the inner planet, with an orbital period
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List of Firefly planets and moons


. It is probably named after the London borough of Highgate A moon of Whittier. The crew of the "S.S. Walden" was returning from a salvage mission here before they discovered "Serenity"'s distress signal in the episode "Out of Gas". Fourth planet orbiting Georgia. Named after County Kerry, Ireland. A core world and fourth planet orbiting the White Sun. Londinium is one of the two major planets of the 'verse (the other being Sihnon). It is the second planet orbiting the White Sun
20183844
Orbit of Venus


Venus has an orbit with a semi-major axis of , and an eccentricity of 0.007. The low eccentricity and comparatively small size of its orbit give Venus the least range in distance between perihelion and aphelion of the planets: 1.46 Gm. The planet orbits the Sun once every 225 days and travels in doing so, giving an average orbital speed of . When the geocentric ecliptic longitude of Venus coincides with that of the Sun, it is in conjunction with the Sun – inferior if Venus is nearer and superior if farther.
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Red dwarf


V), Wolf 359 (M6 V), Van Biesbroeck 8 (M7 V), VB 10 (M8 V), LHS 2924 (M9 V). Many red dwarfs are orbited by exoplanets, but large Jupiter-sized planets are comparatively rare. Doppler surveys of a wide variety of stars indicate about 1 in 6 stars with twice the mass of the Sun are orbited by one or more Jupiter-sized planets, versus 1 in 16 for Sun-like stars and only 1 in 50 for red dwarfs.
11476493
Earth analog


is that it should orbit a solar analog, that is, a star much like our Sun, similar photometrically or in terms of spectral type. It follows that the composition of a planet around a solar twin with similar metallicity might have a similar composition to Earth. Also, this would help eliminate stellar extremes and variability that may be applicable to other types of stars. While planets have been discovered orbiting similar stars to the Sun, most are gas giant or super-Earth sized, and many of these planetary systems have
21304830
Nebular hypothesis


from the Sun. Thousands of exoplanets have been identified in the last twenty years. The orbits of many of these planets and systems of planets differ significantly from the planets in the Solar System. The exoplanets discovered include hot-Jupiters, warm-Jupiters, super-Earths, and systems of tightly packed inner planets. The hot-Jupiters and warm-Jupiters are thought to have migrated to their current orbits during or following their formation. A number of possible mechanisms for this migration have been proposed. Type I or Type
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Jupiter


that moon. Along with the Sun, the gravitational influence of Jupiter has helped shape the Solar System. The orbits of most of the system's planets lie closer to Jupiter's orbital plane than the Sun's equatorial plane (Mercury is the only planet that is closer to the Sun's equator in orbital tilt), the Kirkwood gaps in the asteroid belt are mostly caused by Jupiter, and the planet may have been responsible for the Late Heavy Bombardment of the inner Solar System's history. Along with its moons, Jupiter
17937560
Outline of the Solar System


The following outline is provided as an overview of and topical guide to the Solar System: Solar System – gravitationally bound system comprising the Sun and the objects that orbit it, either directly or indirectly. Of those objects that orbit the Sun directly, the largest eight are the planets (including Earth), with the remainder being significantly smaller objects, such as 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. History of
225299
Solar System


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. The Solar System formed 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud.
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Double planet


binary planet. See the Path of Earth and Moon around Sun section in the "Orbit of the Moon" article for a more detailed explanation. This definition of double planet depends on the pair's distance from the Sun. If the Earth–Moon system happened to orbit farther away from the Sun than it does now, then Earth would win the tug of war. For example, at the orbit of Mars, the Moon's tug-of-war value would be 1.05. Also, several tiny moons discovered since
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Planet Nine


closest to the Sun. Trujillo and Sheppard proposed that this alignment was caused by a massive unknown planet beyond Neptune via the Kozai mechanism. For objects with similar semi-major axes the Kozai mechanism would confine their arguments of perihelion to near 0 or 180 degrees. This confinement allows objects with eccentric and inclined orbits to avoid close approaches to the planet because they would cross the plane of the planet's orbit at their closest and farthest points from the Sun, and cross the planet's orbit when they are well above or below
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Planet Nine


orbit; an unmodeled mass in the Solar System, such as a small planet in the range of 60– (potentially explaining the Kuiper cliff); or a planet more massive or closer to the Sun instead of the planet predicted by Batygin and Brown. An analysis of the orbits of comets with nearly parabolic orbits identifies five new comets with hyperbolic orbits that approach the nominal orbit of Planet Nine described in Batygin and Brown's initial article. If these orbits are hyperbolic due to close encounters with Planet Nine the analysis estimates that
17368992
Methods of detecting exoplanets


are observable only when the planet's orbit happens to be perfectly aligned from the astronomers' vantage point. The probability of a planetary orbital plane being directly on the line-of-sight to a star is the ratio of the diameter of the star to the diameter of the orbit (in small stars, the radius of the planet is also an important factor). About 10% of planets with small orbits have such an alignment, and the fraction decreases for planets with larger orbits. For a planet orbiting a Sun
20321884
Definition of planet


a planet is a body that orbits the Sun, is massive enough for its own gravity to make it round, and has "cleared its neighbourhood" of smaller objects around its orbit. Under this new definition, Pluto and the other trans-Neptunian objects do not qualify as planets. The IAU's decision has not resolved all controversies, and while many scientists have accepted the definition, some in the astronomical community have rejected it outright. In particular, some favor a strictly geophysical definition of a planet. While knowledge of
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Orbital period


The orbital period is the time a given astronomical object takes to complete one orbit around another object, and applies in astronomy usually to planets or asteroids orbiting the Sun, moons orbiting planets, exoplanets orbiting other stars, or binary stars. For objects in the Solar System, this is often referred to as the sidereal period, determined by a 360° revolution of one celestial body around another, e.g. the Earth orbiting the Sun. The term "sidereal" denotes that the object returns to the same position relative to the fixed
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Tidal acceleration


in 1 day) in 210 million years. The sun-planet system has two tidal friction effects. One effect is that the sun creates a tidal friction in the planet, which decreases its spinning angular momentum and hence also increases its orbital angular momentum around the sun, hence increasing its distance and reducing its angular velocity (assuming the orbital angular velocity of the sun is smaller than that of the planet spinning; otherwise directions of change are opposite). If "M" is the sun mass and "D" is
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Gravity assist


its relative speed because it is falling toward the Sun, and a spacecraft traveling from Earth to an outer planet will decrease its speed because it is leaving the vicinity of the Sun. Although the orbital speed of an inner planet is greater than that of the Earth, a spacecraft traveling to an inner planet, even at the minimum speed needed to reach it, is still accelerated by the Sun's gravity to a speed notably greater than the orbital speed of that destination planet. If the spacecraft's purpose is only to fly
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List of nearest terrestrial exoplanet candidates


light-years from our Solar System (64 of them are yellow-orange "G" stars like our Sun). As many as 15% of them can have Earth-sized planets in the habitable zones. On November 4, 2013, astronomers reported, based on "Kepler" space mission data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of sun-like stars and red dwarf stars within the Milky Way Galaxy. 11 billion of these estimated planets may
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Planetary mass


of the mass of the Earth can overcome its compressive strength and achieve hydrostatic equilibrium: it will be roughly spherical, and since 2006 has been classified as a dwarf planet if it orbits around the Sun (that is, if it is not the satellite of another planet). Smaller bodies like asteroids are classified as "small Solar System bodies". A dwarf planet, by definition, is not massive enough to have gravitationally cleared its neighbouring region of planetesimals: it is not known quite how large a planet must be before
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Meteor shower


of some repeating comets, and meteoroids leaving them, are in resonant orbits with Jupiter or one of the other large planets – so many revolutions of one will equal another number of revolutions of the other. This creates a shower component called a filament. A second effect is a close encounter with a planet. When the meteoroids pass by Earth, some are accelerated (making wider orbits around the Sun), others are decelerated (making shorter orbits), resulting in gaps in the dust trail in the next return (like
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Moon


period). Unlike most satellites of other planets, the Moon orbits closer to the ecliptic plane than to the planet's equatorial plane. The Moon's orbit is subtly perturbed by the Sun and Earth in many small, complex and interacting ways. For example, the plane of the Moon's orbit gradually rotates once every 18.61 years, which affects other aspects of lunar motion. These follow-on effects are mathematically described by Cassini's laws. The Moon is exceptionally large relative to Earth: Its diameter is more than a
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Orrery


224.7 days to orbit the Sun, will take 37 seconds to complete an orbit on an orrery, and Jupiter will take 11 minutes, 52 seconds. Some planetariums have taken advantage of this to use orreries to simulate planets and their moons. Thus Mercury orbits the Sun in 0.24 of an Earth year, while Phobos and Deimos orbit Mars in a similar 4:1 time ratio. Planetarium operators wishing to show this have placed a red cap on the Sun (to make it resemble Mars) and turned off all the planets but Mercury
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2012 VP113


could indicate a similar formation mechanism for these bodies. was the first such object discovered. It is currently unknown how acquired a perihelion distance beyond the Kuiper belt. The characteristics of its orbit, like those of Sedna's, have been explained as possibly created by a passing star or a trans-Neptunian planet of several Earth masses hundreds of astronomical units from the Sun. The orbital architecture of the trans-Plutonian region may signal the presence of more than one planet. could even be captured from another planetary system. However
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Mass


carob seeds) to a Roman pound (1728 carob seeds) was: In 1600 AD, Johannes Kepler sought employment with Tycho Brahe, who had some of the most precise astronomical data available. Using Brahe's precise observations of the planet Mars, Kepler spent the next five years developing his own method for characterizing planetary motion. In 1609, Johannes Kepler published his three laws of planetary motion, explaining how the planets orbit the Sun. In Kepler's final planetary model, he described planetary orbits as following elliptical paths with the
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Gravity


mass of the Sun, and details of quasars; even the existence of dark matter is inferred using Newton's law of gravity. Although we have not traveled to all the planets nor to the Sun, we know their masses. These masses are obtained by applying the laws of gravity to the measured characteristics of the orbit. In space an object maintains its orbit because of the force of gravity acting upon it. Planets orbit stars, stars orbit galactic centers, galaxies orbit a center of mass in clusters, and clusters orbit
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HD 73526 c


HD 73526 c is an extrasolar planet orbiting about 97 million miles (1.05 AU) away from its parent star. Based on its mass, this planet is likely to be a gas giant. At the distance this planet orbits from its star, which is more luminous than our Sun, HD 73526 c would receive insolation 84% that of Venus. HD 73526 c is in a 2:1 orbital resonance with HD 73526 b. Every time planet b goes around its sun twice, planet c goes around once, a similar configuration to
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List of possible dwarf planets


; currently there are no other bodies that meet this criterion. All other bodies are named by the minor-planet naming committee alone, and the IAU has not stated how or if they will be accepted as dwarf planets. Beside directly orbiting the Sun, the qualifying feature of a dwarf planet is that it "has sufficient mass for its self-gravity to overcome rigid-body forces so that it assumes a hydrostatic equilibrium (nearly round) shape". Current observations are generally insufficient for a direct determination as to whether
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List of Solar System objects by greatest aphelion


Because they are typically discovered close to the Sun, it will take some time even thousands of years for them to actually travel out to great distances. The "Whipple" proposal might be able to detect Oort cloud objects at great distances, but probably not a particular object. A large number of trans-Neptunian objects (TNOs) – minor planets orbiting beyond the orbit of Neptune – have been discovered in recent years. Many TNOs have orbits with an aphelion (farthest distance to the Sun) far beyond Neptune's orbit
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HD 74156


giant planets were announced orbiting the star. The first planet HD 74156 b orbits the star at a distance closer than Mercury is to our Sun, in an extremely eccentric orbit. The second planet HD 74156 c is a long-period, massive planet (at least 8 times the mass of Jupiter), which orbits the star in an elliptical orbit with a semimajor axis of 3.90 astronomical units. Given the two-planet configuration of the system under the assumption that the orbits are coplanar and have masses equal to their minimum
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Paul Wittich


Paul Wittich (c.1546 – 9 January 1586) was a German mathematician and astronomer whose Capellan geoheliocentric model, in which the inner planets Mercury and Venus orbit the sun but the outer planets Mars, Jupiter and Saturn orbit the Earth, may have directly inspired Tycho Brahe's more radically heliocentric geoheliocentric model in which all the 5 known primary planets orbited the Sun, which in turn orbited the stationary Earth. Wittich was born in Breslau (Wrocław), Silesia, and studied at the universities of Leipzig, Wittenberg and Frankfurt/Oder
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Two-body problem in general relativity


mass of the Sun is much larger than those of the planets, the force acting on each planet is principally due to the Sun; the gravity of the planets for each other can be neglected to first approximation. If the potential energy between the two bodies is not exactly the 1/"r" potential of Newton's gravitational law but differs only slightly, then the ellipse of the orbit gradually rotates (among other possible effects). This apsidal precession is observed for all the planets orbiting the Sun, primarily due to the oblateness of
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HD 175541 b


HD 175541 b is a jovian planet located approximately 410 light-years away in the constellation of Serpens, orbiting the star HD 175541. This planet was discovered in April 2007. Despite the distance of planet to star slightly more than Earth to the Sun, the period is less than 300 days that orbits in an eccentric orbit, because the parent star is 65% more massive than our Sun. The discovery of this planet and two others: HD 192699 b and HD 210702 b around intermediate-mass stars provide clues about
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HD 28185 b


HD 28185 b is an extrasolar planet approximately 128.6 light-years away from Earth in the constellation of Eridanus. The planet was discovered orbiting the Sun-like star HD 28185 in April 2001 as a part of the CORALIE survey for southern extrasolar planets, and its existence was independently confirmed by the Magellan Planet Search Survey in 2008. HD 28185 b orbits its sun in a circular orbit that is at the inner edge of its star's habitable zone. HD 28185 b was discovered by detecting small periodic variations in the radial velocity
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Gravity assist


which is approximately the same), but because the planet orbits the Sun the spacecraft is affected by this motion during the maneuver. To increase speed, the spacecraft flies with the movement of the planet, acquiring some of the planet's orbital energy in the process; to decrease speed, the spacecraft flies against the movement of the planet to transfer some of its own orbital energy to the planet - in both types of maneuver the energy transfer compared to the planet's total orbital energy will be negligible. The sum of the
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List of natural satellites


The Solar System's planets and officially recognized dwarf planets are known to be orbited by 194 natural satellites, or moons. 19 moons in the Solar System are large enough to be gravitationally rounded, and thus would be considered planets or dwarf planets if they were in direct orbit around the Sun. Moons are classed in two separate categories according to their orbits: regular moons, which have prograde orbits (they orbit in the direction of their planets' rotation) and lie close to the plane of their equators, and irregular moons
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Kepler-1652b


9 times shorter than Earth's year of 365 days. It has a semi-major axis, or average orbital radius, of 0.1654 AU, also much lower than Earth's. Despite its close proximity to the star, Kepler-1652b is still temperate, due to how small Kepler-1652 is compared to our Sun. The planet's eccentricity is believed to be near or at 0. Kepler-1652b orbits the red dwarf star Kepler-1652, also designated KOI-2626. It is 0.404 times the mass and 0.382 times the radius of the Sun, with
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Planetary phase


Sun and the Earth. (Sometimes they appear to cross the solar disk, which is called a transit of the planet.) At intermediate points on their orbits, these planets exhibit the full range of crescent and gibbous phases. The superior planets, orbiting outside the Earth's orbit, do not exhibit the full range of phases as they appear almost always as gibbous or full. However, Mars often appears significantly gibbous, when it is illuminated by the Sun at a very different angle than it is seen by an observer
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Kepler space telescope


probability of a random planetary orbit being along the line-of-sight to a star is the diameter of the star divided by the diameter of the orbit. For an Earth-size planet at 1 AU transiting a Sun-like star the probability is 0.47%, or about 1 in 210. For a planet like Venus orbiting a Sun-like star the probability is slightly higher, at 0.65%; If the host star has multiple planets, the probability of additional detections is higher than the probability of initial detection
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HD 40307


by the radial velocity method, using the HARPS spectrograph system. In 2012, an independent analysis carried out by a team of astronomers led by Mikko Tuomi of the University of Hertfordshire confirmed the existence of these planets and found an additional three planets in the systems. Five of the planets orbit very close to the star, with the farthest of them located twice as close to HD 40307 than is the planet Mercury is to the Sun. The outermost planet orbits at a distance similar to the distance of Venus to the Sun and
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Formation and evolution of the Solar System


entirely of degenerate carbon and oxygen, but will never reach temperatures hot enough to fuse these elements. Thus the white dwarf Sun will gradually cool, growing dimmer and dimmer. As the Sun dies, its gravitational pull on the orbiting bodies such as planets, comets and asteroids will weaken due to its mass loss. All remaining planets' orbits will expand; if Venus, Earth, and Mars still exist, their orbits will lie roughly at , , and . They and the other remaining planets will become dark, frigid hulks
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Gliese 317


Gliese 317 is a red dwarf approximately 50 light-years away in the constellation of Pyxis. , two extrasolar planets have been confirmed to be orbiting the star. Photometric calibrations and infrared spectroscopic measurements indicate that the star is enriched in heavy elements compared to the Sun. In 2007, a jovian planet (designated Gliese 317 b) was announced to orbit the star. The planet orbits about 95% the distance between Earth to the Sun. Despite of this, it takes about 1.9 years, due to the lower mass of
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Planets in science fiction


considered as an object in space: the interest of the fiction depends upon its astronomical characteristics, such as its mass, its geological composition, its atmosphere, how many moons it has and what size they are, how close it is to its sun (or suns) and how hot they are. Such considerations are found prominently though not exclusively in the hard science fiction genre. In other stories, a planet is considered as a world or setting. Such a planet will be described from the point of view of a
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Torque multiplier


The outside casing of the multiplier is also engaged with the planet gear teeth, but is prevented from rotating by means of a reaction arm, causing the planet gears to orbit around the sun gear. The planet gears are held in a ‘planet carrier' which also holds the output drive shaft. As the planet gears orbit around the sun gear, the carrier and the output shaft rotate together. Without the reaction arm to prevent rotation of the outer casing, the output shaft cannot apply torque. Along with the multiplication
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Kepler-33b


Kepler-33b is an extrasolar planet orbiting Kepler-33 in the constellation Cygnus. It is one of five planets orbiting Kepler-33. Kepler-33b was, along with twenty-six other planets in eleven different planetary systems, confirmed to be a planet on January 26, 2012. Kepler-33b orbits its host star with 4 other planets. All five planets orbit its star closer than Mercury does to the Sun. Of those five, Kepler-33b is closest. All Kepler-33 planets are too close to be in the habitable zone. List of planets discovered by the Kepler
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List of Solar System objects by greatest aphelion


are thought to orbit the Sun at great distances, but then be perturbed by passing stars and the galactic tides. As they come into or leave the inner Solar System they may have their orbit changed by the planets, or alternatively be ejected from the Solar System. It is also possible they may collide with the Sun or a planet. The exact furthest distance from the Sun (aphelion) can be very different depending on the object's position in its orbit, as well as the epoch. An incoming asteroid could be
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Solar System


asteroids, and comets) together comprise less than 0.002% of the Solar System's total mass. Most large objects in orbit around the Sun lie near the plane of Earth's orbit, known as the ecliptic. The planets are very close to the ecliptic, whereas comets and Kuiper belt objects are frequently at significantly greater angles to it. All the planets, and most other objects, orbit the Sun in the same direction that the Sun is rotating (counter-clockwise, as viewed from above Earth's north pole)
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William Samuel Henson


system formed from cold dust and gas, and discussed how it could condense into meteors and comets, and further condense into planets, moons and the sun, in the process heating up. He also discusses how this would lead to the planets orbiting in the ecliptic and rotating in the same general plane. Henson created inventions in other areas as well. Among them were ice-making machines (1870), fabric waterproofing, and cistern-cleaning. He patented and submitted a proposal for an improved low-recoil breech-
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Earth's orbit


Earth orbits the Sun at an average distance of 149.60 million km (92.96 million mi), and one complete orbit takes  days (1 sidereal year), during which time Earth has traveled 940 million km (584 million mi). Earth's orbit has an eccentricity of 0.0167. Since the Sun constitutes 99.76% of the mass of the Sun–Earth system, the center of the orbit is extremely close to the center of the Sun. As seen from Earth, the planet's orbital prograde motion makes the Sun appear
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