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{{short description|Binary star in the constellation Cygnus}}
{{good article}}
{{good article}}
{{Starbox begin
{{Starbox begin
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| epoch = J2000
| epoch = J2000
| constell= [[Cygnus (constellation)|Cygnus]]
| constell= [[Cygnus (constellation)|Cygnus]]
| ra = {{RA|19|41|11.4985}}<ref name="cdsportal"/>
| ra = {{RA|19|41|11.49832}}<ref name="GaiaDR3"/>
| dec = {{DEC|+46|55|13.705}}<ref name="cdsportal"/>
| dec = {{DEC|+46|55|13.7073}}<ref name="GaiaDR3"/>
| appmag_v = 15.4<ref name="APASS"/>
| appmag_v = 15.4<ref name="APASS"/>
}}
}}
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{{Starbox astrometry
{{Starbox astrometry
| radial_v =
| radial_v =
| prop_mo_ra = {{val|−3.494|0.057}}<ref name="cdsportal"/>
| prop_mo_ra = {{val|−3.383}}
| prop_mo_dec = {{val|−10.065|0.055}}<ref name="cdsportal"/>
| prop_mo_dec = {{val|−10.212}}
⚫
| pm_footnote = <ref name="GaiaDR3"/>
| parallax = 0.9476
| p_error = 0.0289
| parallax = 0.9540
| p_error = 0.0208
⚫
| parallax_footnote = <ref name="cdsportal"/>
| parallax_footnote = <ref name="GaiaDR3"/>
| dist_pc = 1055
| dist_ly =3442
| absmag_v =
| absmag_v =
}}
}}
{{Starbox orbit
{{Starbox orbit
| source = <ref name=discovery/><ref name="predicting"/>
| reference = <ref name="thirdtransiting"/>
| primary = Kepler-47A
| primary = Kepler-47A
| name = Kepler-47B
| name = Kepler-47B
| period_unitless = {{val|7.44837695|0.00000021}} days
| period_unitless = {{val|7.4483648|0.0000038|0.0000270|ul=d}}
| axis_unitless = {{val|0.0836|0.0014}} [[astronomical unit|AU]]
| axis_unitless = {{val|0.08145|0.00036|0.00037|ul=AU}}
| eccentricity = {{val|0.0234|0.001}}
| eccentricity = {{val|0.0288|0.0015|0.0013}}
| inclination = {{val|89.34|0.12}}
| inclination = {{val|89.613|0.045|0.040}}
| periarg = {{val|212.3|4.4}}
| periarg = {{val|226.3|2.8|2.6}}
}}
}}
{{Starbox detail
{{Starbox detail
| source = <ref name=discovery/><ref name=NASA/>
| source = <ref name=discovery/><ref name="thirdtransiting"/>
| component1 = Kepler-47A
| component1 = Kepler-47A
| mass = 1.043 ± 0.055
| mass = {{val|0.957|0.013|0.015}}
| radius = 0.964 ± 0.017
| radius = {{val|0.936|0.005}}
| density = 1.163 ± 0.025
| density = {{val|1.65|0.02|0.01}}
| gravity = 4.488 ± 0.01
| gravity = 4.488 ± 0.01
| luminosity = 0.840 ± 0.067
| luminosity = 0.840 ± 0.067
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| age_gyr = 4–5
| age_gyr = 4–5
| component2 = Kepler-47B
| component2 = Kepler-47B
| mass2 = 0.362 ± 0.013
| mass2 = {{val|0.342|0.003}}
| radius2 = 0.3506 ± 0.0063
| radius2 = {{val|0.338|0.002}}
| density2 = 8.41 ± 0.2
| density2 = {{val|12.42|0.11}}
| gravity2 = 4.9073 ± 0.0067
| gravity2 = 4.9073 ± 0.0067
| luminosity2 = 0.014 ± 0.002
| luminosity2 = 0.014 ± 0.002
| temperature2 = 3357 ± 100
| temperature2 = 3357 ± 100
| metal_fe2 = ?
| metal_fe2 =
| rotational_velocity2 =
| rotational_velocity2 =
| age_gyr2 = 4–5
| age_gyr2 = 4–5
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{{Starbox end}}
{{Starbox end}}


'''Kepler-47''' is a [[binary star system]] with three [[exoplanet]]s in orbit around the pair of stars located about 1055 [[parsec]]s (3,442 [[light year]]s) away from Earth. The first two planets announced are designated [[Kepler-47b]], and [[Kepler-47c]]. Kepler-47 is the first [[Circumbinary planet|circumbinary]] multi-planet system discovered by the [[Kepler (spacecraft)#Objectives and methods|Kepler mission]].<ref name=NASA/> The outermost of the planets is a [[gas giant]] orbiting within the [[habitable zone]] of the stars.<ref name="ScienceDaily2012"/> Because most stars are binary, the discovery that multi-planet systems can form in such a system has impacted previous theories of planetary formation.<ref name=binarycommon/><ref name=NASA/>
'''Kepler-47''' is a [[binary star system]] in the [[constellation]] [[Cygnus (constellation)|Cygnus]] located about {{convert|3420|ly|pc|lk=on|abbr=off}} away from Earth. The stars have three [[exoplanets]], all of which orbit both stars at the same time, making this a circumbinary system. The first two planets announced are designated [[Kepler-47b]], and [[Kepler-47c]], and the third, later discovery is [[Kepler-47d]]. Kepler-47 is the first [[Circumbinary planet|circumbinary]] multi-planet system discovered by the [[Kepler (spacecraft)#Objectives and methods|Kepler mission]].<ref name=NASA/> The outermost of the planets is a [[gas giant]] orbiting within the [[habitable zone]] of the stars.<ref name="ScienceDaily2012"/> Because most stars are binary, the discovery that multi-planet systems can form in such a system has impacted previous theories of planetary formation.<ref name=binarycommon/><ref name=NASA/>


A group of astronomers led by Jerome Orosz at [[San Diego State University]], including astronomers from [[Tel-Aviv University]] in [[Israel]], discovered the planetary system via [[NASA]]'s Kepler space telescope in 2012.<ref name=TTOI/> In November 2013, evidence of a third planet orbiting between the planets b and c, Kepler-47d, was announced.<ref name="3rd"/> Later analyses of transit data from the Kepler space telescope confirmed the existence of Kepler-47d.<ref name="fillout"/>
A group of astronomers led by Jerome Orosz at [[San Diego State University]], including astronomers from [[Tel-Aviv University]] in [[Israel]], [[discovered]] the planetary system via [[NASA]]'s Kepler space telescope in 2012.<ref name=TTOI/> In November 2013, evidence of a third planet orbiting between the planets b and c, Kepler-47d, was announced.<ref name="3rd"/> Later analyses of transit data from the Kepler space telescope confirmed the existence of Kepler-47d.<ref name="fillout"/>


==Nomenclature and history==
==Nomenclature and history==
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Prior to Kepler observation, Kepler-47 had the [[2MASS]] catalogue number 2MASS J19411149+4655136. In the Kepler Input Catalog it has the designation of KIC 10020423, and when it was found to have transiting planet candidates it was given the [[Kepler object of interest]] number of KOI-3154.<ref name=discovery/>
Prior to Kepler observation, Kepler-47 had the [[2MASS]] catalogue number 2MASS J19411149+4655136. In the Kepler Input Catalog it has the designation of KIC 10020423, and when it was found to have transiting planet candidates it was given the [[Kepler object of interest]] number of KOI-3154.<ref name=discovery/>


Planetary candidates were detected around the pair of stars by [[NASA]]'s [[Kepler Mission]], a mission tasked with discovering planets in [[transit method|transit]] around their stars.<ref name="kepler">{{cite web|title=Mission overview|url=https://www.nasa.gov/mission_pages/kepler/overview/index.html|publisher=NASA|accessdate=17 April 2019}}</ref> The discoverers referred the pair of stars as Kepler-47, which is the normal procedure for naming stars with exoplanets discovered by the spacecraft.<ref name="discovery"/> Hence, this is the name used by the public to refer to the pair of stars and its planets. Candidate planets that are associated with stars studied by the Kepler Mission are known as [[Kepler object of interest|Kepler objects of interest]] (KOI) and are assigned the designations ".01", ".02", ".03" etc. after the star's name, in the order of discovery.<ref name="Borucki2011"/> If planet candidates are detected simultaneously, then the ordering follows the order of orbital periods from shortest to longest.<ref name="Borucki2011"/> Following these rules, two candidate planets were detected, with orbital periods of 49.51 and 303.158 days.<ref name=discovery/> Upon confirmation, the planets of Kepler-47 are designated by letters, with the first planet being designated ''b'' and so on. The ordering of designations are identical to the latter designations for candidate planets.<ref name="planetnaming"/>
Planetary candidates were detected around the pair of stars by [[NASA]]'s [[Kepler Mission]], a mission tasked with discovering planets in [[transit method|transit]] around their stars.<ref name="kepler">{{cite web|title=Mission overview|date=13 April 2015 |url=https://www.nasa.gov/mission_pages/kepler/overview/index.html|publisher=NASA|access-date=17 April 2019}}</ref> The discoverers referred the pair of stars as Kepler-47, which is the normal procedure for naming stars with exoplanets discovered by the spacecraft.<ref name="discovery"/> Hence, this is the name used by the public to refer to the pair of stars and its planets. Candidate planets that are associated with stars studied by the Kepler Mission are known as [[Kepler object of interest|Kepler objects of interest]] (KOI) and are assigned the designations ".01", ".02", ".03" etc. after the star's name, in the order of discovery.<ref name="Borucki2011"/> If planet candidates are detected simultaneously, then the ordering follows the order of orbital periods from shortest to longest.<ref name="Borucki2011"/> Following these rules, two candidate planets were detected, with orbital periods of 49.51 and 303.158 days.<ref name=discovery/> Upon confirmation, the planets of Kepler-47 are designated by letters, with the first planet being designated ''b'' and so on. The ordering of designations are identical to the latter designations for candidate planets.<ref name="planetnaming"/>


==Stellar characteristics==
==Stellar characteristics==
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The primary star is somewhat metal-poor, with a [[metallicity]] ([Fe/H]) of about −0.25, or about 56% of the amount of iron and other heavier metals found in the Sun.<ref name="discovery"/> Both of the stars' luminosities are typical for their kind, with a luminosities of around 84% and 1% of that of the solar [[luminosity]], respectively.<ref name="discovery"/>
The primary star is somewhat metal-poor, with a [[metallicity]] ([Fe/H]) of about −0.25, or about 56% of the amount of iron and other heavier metals found in the Sun.<ref name="discovery"/> Both of the stars' luminosities are typical for their kind, with a luminosities of around 84% and 1% of that of the solar [[luminosity]], respectively.<ref name="discovery"/>


The [[apparent magnitude]] of the star system, or how bright it appears from Earth's perspective, is about 15.4.<ref name="APASS"/> It is too dim to be seen with the naked eye, which can typically detect objects with a [[magnitude (astronomy)|magnitude]] less than 6.5.<ref>{{cite web|title=University Lowbrow Astronomers Naked Eye Observer's Guide|url=http://umich.edu/~lowbrows/guide/eye.html|first=Dave|last=Snyder|work=University Lowbrow Astronomers|date=September 2005|accessdate=18 September 2019}}</ref>
The [[apparent magnitude]] of the star system, or how bright it appears from Earth's perspective, is about 15.4.<ref name="APASS"/> It is too dim to be seen with the naked eye, which can typically detect objects with a [[magnitude (astronomy)|magnitude]] less than 6.5.<ref>{{cite web|title=University Lowbrow Astronomers Naked Eye Observer's Guide|url=http://umich.edu/~lowbrows/guide/eye.html|first=Dave|last=Snyder|work=University Lowbrow Astronomers|date=September 2005|access-date=18 September 2019}}</ref>


==Planetary system==
==Planetary system==
[[File:Kepler-47 System Artist-Impression Overhead.jpg|thumb|upright=1.5|Orbital diagram of the Kepler-47 system. The outermost planet is Kepler-47c while the innermost planet is Kepler-47b. The largest planet, Kepler-47d, orbits between Kepler-47 b and c.]]
[[File:Kepler-47 System Artist-Impression Overhead.jpg|thumb|upright=1.5|Orbital diagram of the Kepler-47 system. The outermost planet is Kepler-47c while the innermost planet is Kepler-47b. The largest planet, Kepler-47d, orbits between Kepler-47 b and c.]]


Prior to the discovery of the Kepler-47 planetary system by Jerome Orosz, his colleagues, as well as astronomers from [[Tel-Aviv University]] in 2012,<ref name=TTOI/> it was thought that binary stars with multiple planets could not exist.<ref name=NASA/> It was believed that gravitational [[Perturbation (astronomy)|perturbation]]s caused by the orbiting parent stars would cause any circumbinary planets to collide with each other or be ejected out of orbit, either into one of the parent stars or away from the system.<ref name=NASA/> However, this discovery demonstrates that multiple planets can form around binary stars, even in their [[habitable zone]]s; and while the planets in the Kepler-47 system are unlikely to harbor life, other planets orbiting around binary star systems may be habitable and could support life.<ref name=NASA/> Because most stars are binary, the discovery that multi-planet systems can form in such a system has impacted previous theories of planetary formation, and could provide more opportunities for finding potentially habitable exoplanets.<ref name=binarycommon/><ref name=NASA/>
Prior to the discovery of the Kepler-47 planetary system by Jerome Orosz, his colleagues, as well as astronomers from [[Tel-Aviv University]] in 2012,<ref name=TTOI/> most scientists thought that binary stars with multiple planets could not exist.<ref name=NASA/> It was believed that gravitational [[Perturbation (astronomy)|perturbation]]s caused by the orbiting parent stars would cause any circumbinary planets to collide with each other or be ejected out of orbit, either into one of the parent stars or away from the system.<ref name=NASA/> However, this discovery demonstrates that multiple planets can form around binary stars, even in their [[habitable zone]]s; and while the planets in the Kepler-47 system are unlikely to harbor life, other planets orbiting around binary star systems may be habitable and could support life.<ref name=NASA/> Because most stars are binary, the discovery that multi-planet systems can form in such a system has impacted previous theories of planetary formation, and could provide more opportunities for finding potentially habitable exoplanets.<ref name=binarycommon/><ref name=NASA/>


The binary system is known to host three planets, all orbiting close to each other and larger than Earth, with no solid surface.<ref name="thirdtransiting"/> All three of the planets in the Kepler-47 system have a very low density, less than that of Saturn.<ref name="discoveryalert"/><ref name="MikeWall2019"/> The densities of the planets are estimated to be around {{val|0.26|u=g/cm3}} to {{val|0.68|u=g/cm3}}.<ref name="thirdtransiting"/> The low densities of the planets are unusual for their relatively mild temperatures; planets with such low densities are typically [[hot jupiter]]s that orbit close to their host stars, being known as so-called puffy planets.<ref name="MikeWall2019"/><ref name="discoveryalert"/> Low density planets with such mild temperatures are thought to be uncommon.<ref name="discoveryalert"/>
The binary system is known to host three planets, all orbiting close to each other and larger than Earth, with no solid surface.<ref name="thirdtransiting"/> All three of the planets in the Kepler-47 system have a very low density, less than that of Saturn.<ref name="discoveryalert"/><ref name="MikeWall2019"/> The densities of the planets are estimated to be around {{val|0.26|u=g/cm3}} to {{val|0.68|u=g/cm3}}.<ref name="thirdtransiting"/> The low densities of the planets are unusual for their relatively mild temperatures; planets with such low densities are typically [[hot jupiter]]s that orbit close to their host stars, being known as so-called puffy planets.<ref name="MikeWall2019"/><ref name="discoveryalert"/> Temperate low-density planets like these are thought to be uncommon.<ref name="discoveryalert"/>
{{clear|right}}
{{clear|right}}
{{OrbitboxPlanet begin
{{OrbitboxPlanet begin
| name = Kepler-47
| name = Kepler-47
| table_ref=<ref name=discovery/><ref name="thirdtransiting"/><ref name="exoplanet.eu-K47d"/>
| table_ref = <ref name="thirdtransiting"/>
}}
}}
{{OrbitboxPlanet
{{OrbitboxPlanet
| exoplanet = [[Kepler-47b|b]]
| exoplanet = [[Kepler-47b|b]]
| mass_earth = 8.427 ± 0.62
| mass_earth = {{val|2.07|23.70|2.07}}
| period = 49.51 ± 0.04
| period = {{val|49.4643|0.0081|0.0074}}
| semimajor = 0.2956 ± 0.0047
| semimajor = {{val|0.2877|0.0014|0.0011}}
| radius_earth = 3.03 ± 0.12
| radius_earth = {{val|3.05|0.04}}
| eccentricity = <0.035
| eccentricity = {{val|0.0210|0.0025|0.0022}}
| inclination = 89.59 ± 0.5
| inclination = {{val|89.752|0.063|0.045}}
}}
}}
{{OrbitboxPlanet
{{OrbitboxPlanet
| exoplanet = d
| exoplanet = d
| mass_earth = 25 ± 18<ref name="fillout" />
| mass_earth = {{val|19.02|23.84|11.67}}
| period = 187.35 ± 0.15
| period = {{val|187.366|0.069|0.051}}
| semimajor = 0.6992 ± 0.0033
| semimajor = {{val|0.6992|0.0031|0.0033}}
| radius_earth = {{val|7.04|-0.49|+0.66}}
| radius_earth = {{val|7.04|0.66|0.49}}
| eccentricity = {{val|0.024|-0.017|+0.025}}
| eccentricity = {{val|0.024|0.025|0.017}}
| inclination = ≈90
| inclination = {{val|90.395|0.009|0.012}}
}}
}}
{{OrbitboxPlanet
{{OrbitboxPlanet
| exoplanet = [[Kepler-47c|c]]
| exoplanet = [[Kepler-47c|c]]
| mass_earth = 23.17 ± 1.97
| mass_earth = {{val|3.17|2.18|1.25}}
| period = 303.158 ± 0.072
| period = {{val|303.227|0.062|0.027}}
| semimajor = 0.989 ± 0.016
| semimajor = {{val|0.9638|0.0041|0.0044}}
| radius_earth = 4.61 ±  0.20
| radius_earth = {{val|4.65|0.09|0.07}}
| eccentricity = <0.411
| eccentricity = {{val|0.044|0.029|0.019}}
| inclination = 89.825 ± 0.010
| inclination = {{val|90.1925|0.0055|0.0042}}
}}
}}
{{Orbitbox end}}
{{Orbitbox end}}
[[File:Kepler-47 Artist-Impression 20190416.jpg|thumb|upright=1|Artist's depiction of the relative sizes of the three planets in the Kepler-47 system. From the left: Kepler-47b; Kepler-47d; and Kepler-47c.]]
[[File:Kepler-47 Artist-Impression 20190416.jpg|thumb|upright=1|Artist's depiction of the relative sizes of the three planets in the Kepler-47 system. From the left: Kepler-47b; Kepler-47d; and Kepler-47c.]]
=== Kepler-47b ===

{{main|Kepler-47b}}
Kepler-47b is a [[super-Earth]] and the innermost planet of the Kepler-47 system. It resides close to its parent stars, at a distance of 0.2956&nbsp;AU.<ref name=discovery/><ref name="thirdtransiting"/> It completes one full orbit around its parent stars in less than 50 days.<ref name=NASA/> The [[equilibrium temperature]] of Kepler-47b is 442&nbsp;K, therefore being inhospitable to life.<ref name="discoveryalert">{{cite news|title=Discovery Alert: A Third Planet in Kepler-47 System|url=https://exoplanets.nasa.gov/news/1568/discovery-alert-a-third-planet-in-kepler-47-system/|publisher=NASA|website=exoplanets.nasa.gov|date=17 April 2019|accessdate=17 April 2019}}</ref> Due to the high equilibrium temperature of Kepler-47b, [[methane]] gas in its atmosphere would be broken into other compounds, leading to a thick haze that would cover the planet's atmosphere.<ref name=NASA/> It is the smallest planet of the Kepler-47 system, being 3.1 times the [[Earth radius|size of Earth]].<ref name="discoveryalert"/>
Kepler-47b is a [[Neptune]] class planet and the innermost planet of the Kepler-47 system. It resides close to its parent stars, at a distance of 0.2956&nbsp;AU.<ref name=discovery/><ref name="thirdtransiting"/> It completes one full orbit around its parent stars in less than 50 days.<ref name=NASA/> The [[equilibrium temperature]] of Kepler-47b is 442&nbsp;K, therefore being inhospitable to life.<ref name="discoveryalert">{{cite news|title=Discovery Alert: A Third Planet in Kepler-47 System|url=https://exoplanets.nasa.gov/news/1568/discovery-alert-a-third-planet-in-kepler-47-system/|publisher=NASA|website=exoplanets.nasa.gov|date=17 April 2019|access-date=17 April 2019}}</ref> Due to the high equilibrium temperature of Kepler-47b, [[methane]] gas in its atmosphere would be broken into other compounds, leading to a thick haze that would cover the planet's atmosphere.<ref name=NASA/> It is the smallest planet of the Kepler-47 system, being 3.1 times the [[Earth radius|size of Earth]].<ref name="discoveryalert"/>

=== Kepler-47c ===
{{main|Kepler-47c}}
The second planet discovered, Kepler-47c, is a [[Neptune]] class planet and the outermost planet, orbiting its parent stars from a distance of 0.989&nbsp;AU, nearly the distance from Earth to the [[Sun]].<ref name=discovery/> It completes one full orbit around its parent stars in about 300 days.<ref name=NASA/> Kepler-47c is situated within the habitable zone, with an equilibrium temperature of 241&nbsp;K.<ref name=NASA/><ref name="discoveryalert"/> The radius of Kepler-47c is 4.7 times that of Earth, comparable in size to [[Neptune]].<ref name=NASA/><ref name="discoveryalert"/> Although it is assumed Kepler-47c is not capable of harboring life, it could possibly have a dense atmosphere of water vapor.<ref name=NASA/>
The second planet discovered, Kepler-47c, is a [[Neptune]] class planet and the outermost planet, orbiting its parent stars from a distance of 0.989&nbsp;AU, nearly the distance from Earth to the [[Sun]].<ref name=discovery/> It completes one full orbit around its parent stars in about 300 days.<ref name=NASA/> Kepler-47c is situated within the habitable zone, with an equilibrium temperature of 241&nbsp;K.<ref name=NASA/><ref name="discoveryalert"/> The radius of Kepler-47c is 4.7 times that of Earth, comparable in size to [[Neptune]].<ref name=NASA/><ref name="discoveryalert"/> Although it is assumed Kepler-47c is not capable of harboring life, it could possibly have a dense atmosphere of water vapor.<ref name=NASA/>
=== Kepler-47d ===

[[File:Artist's concept illustrates Kepler-47, the first transiting circumbinary system.jpg|thumb|upright=1|An artist’s rendition of Kepler-47d.]]
The most recently discovered planet in the system, Kepler-47d, was announced as being discovered by astronomer Jerome Orosz and his colleagues at [[San Diego State University]] in November 2013.<ref name="3rd"/><ref name="discoveryalert"/> From transit data of the Kepler-47 system from the Kepler space telescope, Orosz's team had noticed one orphan transit signal that lasted for 4.15 hours,<ref name=discovery/><ref name="predicting"/> and was not attributed to the two previously known planets.<ref name="discoveryalert"/><ref name="3rd"/> Due to the weak transit signals of Kepler-47d, it was not detected earlier in 2012.<ref name="discoveryalert"/><ref name="thirdtransiting"/> Only one noticeable transit of Kepler-47d has been detected,<ref name="predicting"/> thus an additional transit of the planet was needed to confirm its existence.<ref name="fillout"/> From dynamical simulations, the orbit of Kepler-47d was shown to [[precession|precess]] over time, resulting in a four-year period without transits from Kepler-47d.<ref name=discovery/><ref name="3rd"/> Later studies of the Kepler-47 system led to the confirmation of Kepler-47d, which was announced in April 2019.<ref name="fillout"/> The discovery of Kepler-47d was unexpected for Orosz's team, as they had expected to find additional planets with more distant orbits.<ref name="discoveryalert"/><ref name="MikeWall2019">{{cite web|title=Discovery! 3rd Planet Found in Two-Star 'Tatooine' Star System|url=https://www.space.com/third-alien-planet-in-tatooine-system-kepler-47.html|first=Mike|last=Wall|publisher=Space.com|date=16 April 2019|accessdate=16 April 2019}}</ref> Kepler-47d is the largest planet of the Kepler-47 system, with a radius at least 7 times the radius of Earth.<ref name="thirdtransiting"/> It orbits between the planets Kepler-47b and c at a distance of about 0.7 AU, completing an orbit every 187.35 days.<ref name="3rd"/><ref name="exoplanet.eu-K47d">{{cite web|title=Planet Kepler-47 (AB) d|url=http://exoplanet.eu/catalog/kepler-47_(ab)_d/|website=exoplanet.eu|date=17 April 2019|accessdate=18 April 2019}}</ref> Its equilibrium temperature is around 283&nbsp;K.<ref name="discoveryalert"/>
The most recently discovered planet in the system, Kepler-47d, was announced as being discovered by astronomer Jerome Orosz and his colleagues at [[San Diego State University]] in November 2013.<ref name="3rd"/><ref name="discoveryalert"/> From transit data of the Kepler-47 system from the Kepler space telescope, Orosz's team had noticed one orphan transit signal that lasted for 4.15 hours,<ref name=discovery/><ref name="predicting"/> and was not attributed to the two previously known planets.<ref name="discoveryalert"/><ref name="3rd"/> Due to the weak transit signals of Kepler-47d, it was not detected earlier in 2012.<ref name="discoveryalert"/><ref name="thirdtransiting"/> Only one noticeable transit of Kepler-47d has been detected,<ref name="predicting"/> thus an additional transit of the planet was needed to confirm its existence.<ref name="fillout"/> From dynamical simulations, the orbit of Kepler-47d was shown to [[precession|precess]] over time, resulting in a four-year period without transits from Kepler-47d.<ref name=discovery/><ref name="3rd"/> Later studies of the Kepler-47 system led to the confirmation of Kepler-47d, which was announced in April 2019.<ref name="fillout"/> The discovery of Kepler-47d was unexpected for Orosz's team, as they had expected to find additional planets with more distant orbits.<ref name="discoveryalert"/><ref name="MikeWall2019">{{cite web|title=Discovery! 3rd Planet Found in Two-Star 'Tatooine' Star System|url=https://www.space.com/third-alien-planet-in-tatooine-system-kepler-47.html|first=Mike|last=Wall|publisher=Space.com|date=16 April 2019|access-date=16 April 2019}}</ref> Kepler-47d is the largest planet of the Kepler-47 system, with a radius at least 7 times the radius of Earth (almost the size of Saturn, though its mass is comparable to that of Neptune).<ref name="thirdtransiting"/> It orbits between the planets Kepler-47b and c at a distance of about 0.7 AU, completing an orbit every 187.35 days.<ref name="3rd"/><ref name="exoplanet.eu-K47d">{{cite web|title=Planet Kepler-47 (AB) d|url=https://exoplanet.eu/catalog/kepler_47_ab_d--1469/|date=17 April 2019|work=[[Extrasolar Planets Encyclopaedia]]|access-date=18 April 2019}}</ref> Its equilibrium temperature is around 283&nbsp;K.<ref name="discoveryalert"/>


==See also==
==See also==
Line 136: Line 139:
* [[Kepler mission]]
* [[Kepler mission]]
* [[NN Serpentis]], an eclipsing binary system hosting two exoplanets
* [[NN Serpentis]], an eclipsing binary system hosting two exoplanets
* [[List of exoplanets]]
* [[Lists of exoplanets]]
* [[List of extrasolar planet firsts]], including Kepler-47 with the most circumbinary planets
* [[List of extrasolar planet firsts]], including Kepler-47 with the most circumbinary planets


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{{reflist|refs=
{{reflist|refs=


<ref name="GaiaDR3">{{Cite Gaia DR3|2080506523540902912}}</ref>
⚫
<ref name=binarycommon>{{cite journal|title=Terrestrial planet formation surrounding close binary stars|display-authors=1|last1=Quintana|first1=Elisa V.|last2=Lissauer|first2=Jack J.|journal=Icarus|volume=185|issue=1|pages=1–20|date=November 2006|doi=10.1016/j.icarus.2006.06.016|bibcode=2006Icar..185....1Q|arxiv=astro-ph/0607222}}</ref>

⚫
<ref name=binarycommon>{{cite journal|title=Terrestrial planet formation surrounding close binary stars|display-authors=1|last1=Quintana|first1=Elisa V.|last2=Lissauer|first2=Jack J.|journal=Icarus|volume=185|issue=1|pages=1–20|date=November 2006|doi=10.1016/j.icarus.2006.06.016|bibcode=2006Icar..185....1Q|arxiv=astro-ph/0607222|s2cid=17611721}}</ref>


<ref name="cdsportal">{{cite web|url=http://cdsportal.u-strasbg.fr/?target=Kepler-47|title=Kepler-47|website=CDS Portal}}</ref>
<ref name="cdsportal">{{cite web|url=http://cdsportal.u-strasbg.fr/?target=Kepler-47|title=Kepler-47|website=CDS Portal}}</ref>


<ref name="APASS">{{cite web|url=http://vizier.u-strasbg.fr/viz-bin/VizieR-5?-ref=VIZ5cb67eb442ca&-out.add=.&-source=I/322A/out&UCAC4===685-070595&-out.orig=o|title=UCAC4 685-070595|publisher=VizieR|year=2012|accessdate=16 April 2019}}</ref>
<ref name="APASS">{{cite web|url=http://vizier.u-strasbg.fr/viz-bin/VizieR-5?-ref=VIZ5cb67eb442ca&-out.add=.&-source=I/322A/out&UCAC4===685-070595&-out.orig=o|title=UCAC4 685-070595|publisher=VizieR|year=2012|access-date=16 April 2019}}</ref>


<ref name="Fraser2008">{{cite web |url=https://www.universetoday.com/18847/life-of-the-sun/ |title=What is the Life Cycle Of The Sun? |first=Matt |last=Williams |date=22 December 2015 |publisher=[[Universe Today]] |accessdate=16 September 2019}}</ref>
<ref name="Fraser2008">{{cite web |url=https://www.universetoday.com/18847/life-of-the-sun/ |title=What is the Life Cycle Of The Sun? |first=Matt |last=Williams |date=22 December 2015 |publisher=[[Universe Today]] |access-date=16 September 2019}}</ref>


<ref name=discovery>{{Cite journal|author-link= |arxiv= 1208.5489 |title= Kepler-47: A Transiting Circumbinary Multi-Planet System|journal= Science|volume= 337|issue= 6101|pages= 1511–4|last1= Orosz|first1= Jerome A.|last2= Welsh|first2= William F.|last3= Carter|first3= Joshua A.|last4= Fabrycky|first4= Daniel C.|last5= Cochran|first5= William D.|last6= Endl|first6= Michael|last7= Ford|first7= Eric B.|last8= Haghighipour|first8= Nader|last9= MacQueen|first9= Phillip J.|last10= Mazeh|first10= Tsevi|last11= Sanchis-Ojeda|first11= Roberto|last12= Short|first12= Donald R.|last13= Torres|first13= Guillermo|last14= Agol|first14= Eric|last15= Buchhave|first15= Lars A.|last16= Doyle|first16= Laurance R.|last17= Isaacson|first17= Howard|last18= Lissauer|first18= Jack J.|last19= Marcy|first19= Geoffrey W.|last20= Shporer|first20= Avi|last21= Windmiller|first21= Gur|last22= Barclay|first22= Thomas|last23= Boss|first23= Alan P.|last24= Clarke|first24= Bruce D.|last25= Fortney|first25= Jonathan|last26= Geary|first26= John C.|last27= Holman|first27= Matthew J.|last28= Huber|first28= Daniel|last29= Jenkins|first29= Jon M.|last30= Kinemuchi|first30= Karen|display-authors= 29|year= 2012|doi= 10.1126/science.1228380 |pmid=22933522|bibcode = 2012Sci...337.1511O }}</ref>
<ref name=discovery>{{Cite journal|arxiv= 1208.5489 |title= Kepler-47: A Transiting Circumbinary Multi-Planet System|journal= Science|volume= 337|issue= 6101|pages= 1511–4|last1= Orosz|first1= Jerome A.|last2= Welsh|first2= William F.|last3= Carter|first3= Joshua A.|last4= Fabrycky|first4= Daniel C.|last5= Cochran|first5= William D.|last6= Endl|first6= Michael|last7= Ford|first7= Eric B.|last8= Haghighipour|first8= Nader|last9= MacQueen|first9= Phillip J.|last10= Mazeh|first10= Tsevi|last11= Sanchis-Ojeda|first11= Roberto|last12= Short|first12= Donald R.|last13= Torres|first13= Guillermo|last14= Agol|first14= Eric|last15= Buchhave|first15= Lars A.|last16= Doyle|first16= Laurance R.|last17= Isaacson|first17= Howard|last18= Lissauer|first18= Jack J.|last19= Marcy|first19= Geoffrey W.|last20= Shporer|first20= Avi|last21= Windmiller|first21= Gur|last22= Barclay|first22= Thomas|last23= Boss|first23= Alan P.|last24= Clarke|first24= Bruce D.|last25= Fortney|first25= Jonathan|last26= Geary|first26= John C.|last27= Holman|first27= Matthew J.|last28= Huber|first28= Daniel|last29= Jenkins|first29= Jon M.|last30= Kinemuchi|first30= Karen|display-authors= 29|year= 2012|doi= 10.1126/science.1228380 |pmid=22933522|bibcode = 2012Sci...337.1511O |s2cid= 44970411 }}</ref>


<ref name=NASA>{{cite news|url=http://www.nasa.gov/mission_pages/kepler/news/kepler-47.html|title=NASA's Kepler Discovers Multiple Planets Orbiting a Pair of Stars|date=28 August 2012|publisher=[[NASA]]|website=exoplanets.nasa.gov|quote=Kepler mission has discovered multiple transiting planets orbiting two suns for the first time|accessdate=2 September 2012}}</ref>
<ref name=NASA>{{cite news|url=http://www.nasa.gov/mission_pages/kepler/news/kepler-47.html|title=NASA's Kepler Discovers Multiple Planets Orbiting a Pair of Stars|date=28 August 2012|publisher=[[NASA]]|website=exoplanets.nasa.gov|quote=Kepler mission has discovered multiple transiting planets orbiting two suns for the first time|access-date=2 September 2012|archive-date=31 October 2012|archive-url=https://web.archive.org/web/20121031024345/http://www.nasa.gov/mission_pages/kepler/news/kepler-47.html|url-status=dead}}</ref>


<ref name="ScienceDaily2012">{{cite journal|url=https://www.sciencedaily.com/releases/2012/08/120828190127.htm |title=NASA's Kepler discovers multiple planets orbiting a pair of stars |doi=10.1126/science.1228380 |publisher=[[Sciencedaily.com]] |date=28 August 2012 |accessdate=4 November 2012|arxiv = 1208.5489 |bibcode = 2012Sci...337.1511O |last1=Orosz |first1=Jerome A. |last2=Welsh |first2=William F. |last3=Carter |first3=Joshua A. |last4=Fabrycky |first4=Daniel C. |last5=Cochran |first5=William D. |last6=Endl |first6=Michael |last7=Ford |first7=Eric B. |last8=Haghighipour |first8=Nader |last9=MacQueen |first9=Phillip J. |last10=Mazeh |first10=Tsevi |last11=Sanchis-Ojeda |first11=Roberto |last12=Short |first12=Donald R. |last13=Torres |first13=Guillermo |last14=Agol |first14=Eric |last15=Buchhave |first15=Lars A. |last16=Doyle |first16=Laurance R. |last17=Isaacson |first17=Howard |last18=Lissauer |first18=Jack J. |last19=Marcy |first19=Geoffrey W. |last20=Shporer |first20=Avi |last21=Windmiller |first21=Gur |last22=Barclay |first22=Thomas |last23=Boss |first23=Alan P. |last24=Clarke |first24=Bruce D. |last25=Fortney |first25=Jonathan |last26=Geary |first26=John C. |last27=Holman |first27=Matthew J. |last28=Huber |first28=Daniel |last29=Jenkins |first29=Jon M. |last30=Kinemuchi |first30=Karen |journal=Science |volume=337 |issue=6101 |pages=1511–4 |pmid=22933522 |displayauthors=29 }}</ref>
<ref name="ScienceDaily2012">{{cite journal|url=https://www.sciencedaily.com/releases/2012/08/120828190127.htm |title=NASA's Kepler discovers multiple planets orbiting a pair of stars |doi=10.1126/science.1228380 |publisher=[[Sciencedaily.com]] |date=28 August 2012 |access-date=4 November 2012|arxiv = 1208.5489 |bibcode = 2012Sci...337.1511O |last1=Orosz |first1=Jerome A. |last2=Welsh |first2=William F. |last3=Carter |first3=Joshua A. |last4=Fabrycky |first4=Daniel C. |last5=Cochran |first5=William D. |last6=Endl |first6=Michael |last7=Ford |first7=Eric B. |last8=Haghighipour |first8=Nader |last9=MacQueen |first9=Phillip J. |last10=Mazeh |first10=Tsevi |last11=Sanchis-Ojeda |first11=Roberto |last12=Short |first12=Donald R. |last13=Torres |first13=Guillermo |last14=Agol |first14=Eric |last15=Buchhave |first15=Lars A. |last16=Doyle |first16=Laurance R. |last17=Isaacson |first17=Howard |last18=Lissauer |first18=Jack J. |last19=Marcy |first19=Geoffrey W. |last20=Shporer |first20=Avi |last21=Windmiller |first21=Gur |last22=Barclay |first22=Thomas |last23=Boss |first23=Alan P. |last24=Clarke |first24=Bruce D. |last25=Fortney |first25=Jonathan |last26=Geary |first26=John C. |last27=Holman |first27=Matthew J. |last28=Huber |first28=Daniel |last29=Jenkins |first29=Jon M. |last30=Kinemuchi |first30=Karen |journal=Science |volume=337 |issue=6101 |pages=1511–4 |pmid=22933522 |s2cid=44970411 |display-authors=29 }}</ref>


<ref name=TTOI>{{cite news|last=Shamah|first=David|title=New worlds discovered, courtesy of US-Israel team|url=http://www.timesofisrael.com/new-worlds-discovered-courtesy-of-us-israel-team/|accessdate=30 August 2012|newspaper=[[The Times of Israel]]|date=30 August 2012}}</ref>
<ref name=TTOI>{{cite news|last=Shamah|first=David|title=New worlds discovered, courtesy of US-Israel team|url=http://www.timesofisrael.com/new-worlds-discovered-courtesy-of-us-israel-team/|access-date=30 August 2012|newspaper=[[The Times of Israel]]|date=30 August 2012}}</ref>


<ref name="3rd">{{cite web|title=The Confirmation of a Third Planet in the Kepler-47 Circumbinary System|url=http://nexsci.caltech.edu/conferences/KeplerII/abstracts_talks/Orosz.pdf|year=2013}}</ref>
<ref name="3rd">{{cite web|title=The Confirmation of a Third Planet in the Kepler-47 Circumbinary System|url=http://nexsci.caltech.edu/conferences/KeplerII/abstracts_talks/Orosz.pdf|year=2013}}</ref>
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<ref name="planetnaming">{{cite arXiv |title=On the naming convention used for multiple star systems and extrasolar planets |date=2010 |last1=Hessman |first1=F. V. |last2=Dhillon |first2=V. S. |last3=Winget |first3=D. E. |last4=Schreiber |first4=M. R. |last5=Horne |first5=K. |last6=Marsh |first6=T. R. |last7=Guenther |first7=E. |last8=Schwope |first8=A. |last9=Heber |first9=U. |eprint=1012.0707|class=astro-ph.SR }}</ref>
<ref name="planetnaming">{{cite arXiv |title=On the naming convention used for multiple star systems and extrasolar planets |date=2010 |last1=Hessman |first1=F. V. |last2=Dhillon |first2=V. S. |last3=Winget |first3=D. E. |last4=Schreiber |first4=M. R. |last5=Horne |first5=K. |last6=Marsh |first6=T. R. |last7=Guenther |first7=E. |last8=Schwope |first8=A. |last9=Heber |first9=U. |eprint=1012.0707|class=astro-ph.SR }}</ref>


<ref name="SunFactSheet">{{cite web|title=Sun Fact Sheet|url=https://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html|work=NASA Space Science Data Coordinated Archive|publisher=NASA|date=23 February 2018|accessdate=18 September 2019}}</ref>
<ref name="SunFactSheet">{{cite web|title=Sun Fact Sheet|url=https://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html|work=NASA Space Science Data Coordinated Archive|publisher=NASA|date=23 February 2018|access-date=18 September 2019}}</ref>


<ref name="thirdtransiting">{{cite journal|title=Discovery of a Third Transiting Planet in the Kepler-47 Circumbinary System|first1=Jerome A.|last1=Orosz|first2=William F.|last2=Welsh|first3=Nader|last3=Haghighipour|first4=Billy|last4=Quarles|first5=Donald R.|last5=Short|first6=Sean M.|last6=Mills|first7=Suman|last7=Sutyal|first8=Guillermo|last8=Torres|first9=Eric|last9=Agol|first10=Daniel C.|last10=Fabrycky|journal=The Astronomical Journal|doi=10.3847/1538-3881/ab0ca0|volume=157|issue=5|page=174|arxiv=1904.07255|date=16 April 2019}}</ref>
<ref name="thirdtransiting">{{cite journal|title=Discovery of a Third Transiting Planet in the Kepler-47 Circumbinary System|first1=Jerome A.|last1=Orosz|first2=William F.|last2=Welsh|first3=Nader|last3=Haghighipour|first4=Billy|last4=Quarles|first5=Donald R.|last5=Short|first6=Sean M.|last6=Mills|first7=Suman|last7=Sutyal|first8=Guillermo|last8=Torres|first9=Eric|last9=Agol|first10=Daniel C.|last10=Fabrycky|journal=The Astronomical Journal|doi=10.3847/1538-3881/ab0ca0|volume=157|issue=5|page=174|arxiv=1904.07255|date=16 April 2019|bibcode=2019AJ....157..174O |s2cid=118682065 |doi-access=free }}</ref>


<ref name="predicting">{{cite journal|title=Predicting a third planet in the Kepler-47 circumbinary system|first1=Tobias C.|last1=Hinse|journal=The Astrophysical Journal|doi=10.1088/0004-637X/799/1/88|arxiv=1409.1349|date=15 January 2015|volume=799|pages=88|bibcode=2015ApJ...799...88H}}</ref>
<ref name="predicting">{{cite journal|title=Predicting a third planet in the Kepler-47 circumbinary system|first1=Tobias C.|last1=Hinse|journal=The Astrophysical Journal|doi=10.1088/0004-637X/799/1/88|arxiv=1409.1349|date=15 January 2015|volume=799|issue=1|pages=88|bibcode=2015ApJ...799...88H|s2cid=118358830}}</ref>


<ref name="Borucki2011">{{cite journal| last=Borucki |first=William J. | display-authors=etal | title=Characteristics of planetary candidates observed by Kepler, II: Analysis of the first four months of data | journal=The Astrophysical Journal | volume=736 | issue=1 | pages=19 | url=http://kepler.nasa.gov/files/mws/FebDataRelease_revised_020211.pdf | date=1 February 2011 |accessdate=18 September 2019| bibcode=2011ApJ...736...19B | arxiv=1102.0541 | doi=10.1088/0004-637X/736/1/19 }}</ref>
<ref name="Borucki2011">{{cite journal| last=Borucki |first=William J. | display-authors=etal | title=Characteristics of planetary candidates observed by Kepler, II: Analysis of the first four months of data | journal=The Astrophysical Journal | volume=736 | issue=1 | pages=19 | url=http://kepler.nasa.gov/files/mws/FebDataRelease_revised_020211.pdf | archive-url=https://web.archive.org/web/20110721051047/http://kepler.nasa.gov/files/mws/FebDataRelease_revised_020211.pdf | url-status=dead | archive-date=21 July 2011 | date=1 February 2011 |access-date=18 September 2019| bibcode=2011ApJ...736...19B | arxiv=1102.0541 | doi=10.1088/0004-637X/736/1/19 |s2cid=15233153 }}</ref>


}}
}}
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[[Category:Eclipsing binaries]]
[[Category:Eclipsing binaries]]
[[Category:Articles containing video clips]]
[[Category:Articles containing video clips]]
[[Category:Circumbinary planets]]
[[Category:G-type main-sequence stars]]
[[Category:G-type main-sequence stars]]
[[Category:M-type main-sequence stars]]

Latest revision as of 06:23, 22 December 2023

Kepler-47
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus
Right ascension 19h 41m 11.49832s[1]
Declination +46° 55′ 13.7073″[1]
Apparent magnitude (V) 15.4[2]
Characteristics
Evolutionary stage Main sequence
Spectral type G6V / M4V
Astrometry
Proper motion (μ) RA: −3.383 mas/yr[1]
Dec.: −10.212 mas/yr[1]
Parallax (π)0.9540 ± 0.0208 mas[1]
Distance3,420 ± 70 ly
(1,050 ± 20 pc)
Orbit[3]
PrimaryKepler-47A
CompanionKepler-47B
Period (P)7.4483648+0.0000038
−0.0000270 d
Semi-major axis (a)0.08145+0.00036
−0.00037 AU
Eccentricity (e)0.0288+0.0015
−0.0013
Inclination (i)89.613+0.045
−0.040°
Argument of periastron (ω)
(secondary)		226.3+2.8
−2.6°
Details[4][3]
Kepler-47A
Mass0.957+0.013
−0.015 M☉
Radius0.936±0.005 R☉
Luminosity0.840 ± 0.067 L☉
Surface gravity (log g)4.488 ± 0.01 cgs
Temperature5636 ± 100 K
Metallicity [Fe/H]−0.25 ± 0.08 dex
Rotational velocity (v sin i)4.1+0.5
−0.35 km/s
Age4–5 Gyr
Kepler-47B
Mass0.342±0.003 M☉
Radius0.338±0.002 R☉
Luminosity0.014 ± 0.002 L☉
Surface gravity (log g)4.9073 ± 0.0067 cgs
Temperature3357 ± 100 K
Age4–5 Gyr
Other designations
2MASS J19411149+4655136, KOI-3154, KIC 10020423
Database references
SIMBADdata
KICdata

Kepler-47 is a binary star system in the constellation Cygnus located about 3,420 light-years (1,050 parsecs) away from Earth. The stars have three exoplanets, all of which orbit both stars at the same time, making this a circumbinary system. The first two planets announced are designated Kepler-47b, and Kepler-47c, and the third, later discovery is Kepler-47d. Kepler-47 is the first circumbinary multi-planet system discovered by the Kepler mission.[5] The outermost of the planets is a gas giant orbiting within the habitable zone of the stars.[6] Because most stars are binary, the discovery that multi-planet systems can form in such a system has impacted previous theories of planetary formation.[7][5]

A group of astronomers led by Jerome Orosz at San Diego State University, including astronomers from Tel-Aviv University in Israel, discovered the planetary system via NASA's Kepler space telescope in 2012.[8] In November 2013, evidence of a third planet orbiting between the planets b and c, Kepler-47d, was announced.[9] Later analyses of transit data from the Kepler space telescope confirmed the existence of Kepler-47d.[10]

Nomenclature and history

[edit]
The Kepler Space Telescope search volume, in the context of the Milky Way Galaxy.

Prior to Kepler observation, Kepler-47 had the 2MASS catalogue number 2MASS J19411149+4655136. In the Kepler Input Catalog it has the designation of KIC 10020423, and when it was found to have transiting planet candidates it was given the Kepler object of interest number of KOI-3154.[4]

Planetary candidates were detected around the pair of stars by NASA's Kepler Mission, a mission tasked with discovering planets in transit around their stars.[11] The discoverers referred the pair of stars as Kepler-47, which is the normal procedure for naming stars with exoplanets discovered by the spacecraft.[4] Hence, this is the name used by the public to refer to the pair of stars and its planets. Candidate planets that are associated with stars studied by the Kepler Mission are known as Kepler objects of interest (KOI) and are assigned the designations ".01", ".02", ".03" etc. after the star's name, in the order of discovery.[12] If planet candidates are detected simultaneously, then the ordering follows the order of orbital periods from shortest to longest.[12] Following these rules, two candidate planets were detected, with orbital periods of 49.51 and 303.158 days.[4] Upon confirmation, the planets of Kepler-47 are designated by letters, with the first planet being designated b and so on. The ordering of designations are identical to the latter designations for candidate planets.[13]

Stellar characteristics

[edit]

Kepler-47 is a binary star system located about 1,055 parsecs (3,440 light-years) away from Earth.[14] The binary system is composed of a G-type main sequence star (Kepler-47A) and a red dwarf star (Kepler-47B). The stars orbit each other around their barycenter, or center of mass between them, completing one full orbit every 7.45 days.[4] The stars orbit their barycenter from a distance of about 0.084 AU.[4] The stars have 104% and 35% of the Sun's mass, and 96% and 35% of the Sun's radius, respectively.[4] They have surface temperatures of 5636 K and 3357 K.[4] Based on the stellar characteristics and orbital dynamics, an estimated age of 4–5 billion years for the system is possible.[4] In comparison, the Sun is about 4.6 billion years old,[15] and has a temperature of 5772 K.[16]

The primary star is somewhat metal-poor, with a metallicity ([Fe/H]) of about −0.25, or about 56% of the amount of iron and other heavier metals found in the Sun.[4] Both of the stars' luminosities are typical for their kind, with a luminosities of around 84% and 1% of that of the solar luminosity, respectively.[4]

The apparent magnitude of the star system, or how bright it appears from Earth's perspective, is about 15.4.[2] It is too dim to be seen with the naked eye, which can typically detect objects with a magnitude less than 6.5.[17]

Planetary system

[edit]
Orbital diagram of the Kepler-47 system. The outermost planet is Kepler-47c while the innermost planet is Kepler-47b. The largest planet, Kepler-47d, orbits between Kepler-47 b and c.

Prior to the discovery of the Kepler-47 planetary system by Jerome Orosz, his colleagues, as well as astronomers from Tel-Aviv University in 2012,[8] most scientists thought that binary stars with multiple planets could not exist.[5] It was believed that gravitational perturbations caused by the orbiting parent stars would cause any circumbinary planets to collide with each other or be ejected out of orbit, either into one of the parent stars or away from the system.[5] However, this discovery demonstrates that multiple planets can form around binary stars, even in their habitable zones; and while the planets in the Kepler-47 system are unlikely to harbor life, other planets orbiting around binary star systems may be habitable and could support life.[5] Because most stars are binary, the discovery that multi-planet systems can form in such a system has impacted previous theories of planetary formation, and could provide more opportunities for finding potentially habitable exoplanets.[7][5]

The binary system is known to host three planets, all orbiting close to each other and larger than Earth, with no solid surface.[3] All three of the planets in the Kepler-47 system have a very low density, less than that of Saturn.[18][19] The densities of the planets are estimated to be around 0.26 g/cm3 to 0.68 g/cm3.[3] The low densities of the planets are unusual for their relatively mild temperatures; planets with such low densities are typically hot jupiters that orbit close to their host stars, being known as so-called puffy planets.[19][18] Temperate low-density planets like these are thought to be uncommon.[18]

The Kepler-47 planetary system[3]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
b 2.07+23.70
−2.07 M🜨 		0.2877+0.0014
−0.0011 		49.4643+0.0081
−0.0074 		0.0210+0.0025
−0.0022 		89.752+0.063
−0.045° 		3.05±0.04 R🜨
d 19.02+23.84
−11.67 M🜨 		0.6992+0.0031
−0.0033 		187.366+0.069
−0.051 		0.024+0.025
−0.017 		90.395+0.009
−0.012° 		7.04+0.66
−0.49 R🜨
c 3.17+2.18
−1.25 M🜨 		0.9638+0.0041
−0.0044 		303.227+0.062
−0.027 		0.044+0.029
−0.019 		90.1925+0.0055
−0.0042° 		4.65+0.09
−0.07 R🜨
Artist's depiction of the relative sizes of the three planets in the Kepler-47 system. From the left: Kepler-47b; Kepler-47d; and Kepler-47c.

Kepler-47b

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Main article: Kepler-47b

Kepler-47b is a Neptune class planet and the innermost planet of the Kepler-47 system. It resides close to its parent stars, at a distance of 0.2956 AU.[4][3] It completes one full orbit around its parent stars in less than 50 days.[5] The equilibrium temperature of Kepler-47b is 442 K, therefore being inhospitable to life.[18] Due to the high equilibrium temperature of Kepler-47b, methane gas in its atmosphere would be broken into other compounds, leading to a thick haze that would cover the planet's atmosphere.[5] It is the smallest planet of the Kepler-47 system, being 3.1 times the size of Earth.[18]

Kepler-47c

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Main article: Kepler-47c

The second planet discovered, Kepler-47c, is a Neptune class planet and the outermost planet, orbiting its parent stars from a distance of 0.989 AU, nearly the distance from Earth to the Sun.[4] It completes one full orbit around its parent stars in about 300 days.[5] Kepler-47c is situated within the habitable zone, with an equilibrium temperature of 241 K.[5][18] The radius of Kepler-47c is 4.7 times that of Earth, comparable in size to Neptune.[5][18] Although it is assumed Kepler-47c is not capable of harboring life, it could possibly have a dense atmosphere of water vapor.[5]

Kepler-47d

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An artist’s rendition of Kepler-47d.

The most recently discovered planet in the system, Kepler-47d, was announced as being discovered by astronomer Jerome Orosz and his colleagues at San Diego State University in November 2013.[9][18] From transit data of the Kepler-47 system from the Kepler space telescope, Orosz's team had noticed one orphan transit signal that lasted for 4.15 hours,[4][20] and was not attributed to the two previously known planets.[18][9] Due to the weak transit signals of Kepler-47d, it was not detected earlier in 2012.[18][3] Only one noticeable transit of Kepler-47d has been detected,[20] thus an additional transit of the planet was needed to confirm its existence.[10] From dynamical simulations, the orbit of Kepler-47d was shown to precess over time, resulting in a four-year period without transits from Kepler-47d.[4][9] Later studies of the Kepler-47 system led to the confirmation of Kepler-47d, which was announced in April 2019.[10] The discovery of Kepler-47d was unexpected for Orosz's team, as they had expected to find additional planets with more distant orbits.[18][19] Kepler-47d is the largest planet of the Kepler-47 system, with a radius at least 7 times the radius of Earth (almost the size of Saturn, though its mass is comparable to that of Neptune).[3] It orbits between the planets Kepler-47b and c at a distance of about 0.7 AU, completing an orbit every 187.35 days.[9][21] Its equilibrium temperature is around 283 K.[18]

See also

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Wikimedia Commons has media related to Kepler-47.

References

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  1. ^ a b c d Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
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  4. ^ a b c d e f g h i j k l m n o Orosz, Jerome A.; Welsh, William F.; Carter, Joshua A.; Fabrycky, Daniel C.; Cochran, William D.; Endl, Michael; Ford, Eric B.; Haghighipour, Nader; MacQueen, Phillip J.; Mazeh, Tsevi; Sanchis-Ojeda, Roberto; Short, Donald R.; Torres, Guillermo; Agol, Eric; Buchhave, Lars A.; Doyle, Laurance R.; Isaacson, Howard; Lissauer, Jack J.; Marcy, Geoffrey W.; Shporer, Avi; Windmiller, Gur; Barclay, Thomas; Boss, Alan P.; Clarke, Bruce D.; Fortney, Jonathan; Geary, John C.; Holman, Matthew J.; Huber, Daniel; Jenkins, Jon M.; et al. (2012). "Kepler-47: A Transiting Circumbinary Multi-Planet System". Science. 337 (6101): 1511–4. arXiv:1208.5489. Bibcode:2012Sci...337.1511O. doi:10.1126/science.1228380. PMID 22933522. S2CID 44970411.
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  6. ^ Orosz, Jerome A.; Welsh, William F.; Carter, Joshua A.; Fabrycky, Daniel C.; Cochran, William D.; Endl, Michael; Ford, Eric B.; Haghighipour, Nader; MacQueen, Phillip J.; Mazeh, Tsevi; Sanchis-Ojeda, Roberto; Short, Donald R.; Torres, Guillermo; Agol, Eric; Buchhave, Lars A.; Doyle, Laurance R.; Isaacson, Howard; Lissauer, Jack J.; Marcy, Geoffrey W.; Shporer, Avi; Windmiller, Gur; Barclay, Thomas; Boss, Alan P.; Clarke, Bruce D.; Fortney, Jonathan; Geary, John C.; Holman, Matthew J.; Huber, Daniel; Jenkins, Jon M.; et al. (28 August 2012). "NASA's Kepler discovers multiple planets orbiting a pair of stars". Science. 337 (6101). Sciencedaily.com: 1511–4. arXiv:1208.5489. Bibcode:2012Sci...337.1511O. doi:10.1126/science.1228380. PMID 22933522. S2CID 44970411. Retrieved 4 November 2012.
  7. ^ a b Quintana, Elisa V.; et al. (November 2006). "Terrestrial planet formation surrounding close binary stars". Icarus. 185 (1): 1–20. arXiv:astro-ph/0607222. Bibcode:2006Icar..185....1Q. doi:10.1016/j.icarus.2006.06.016. S2CID 17611721.
  8. ^ a b Shamah, David (30 August 2012). "New worlds discovered, courtesy of US-Israel team". The Times of Israel. Retrieved 30 August 2012.
  9. ^ a b c d e "The Confirmation of a Third Planet in the Kepler-47 Circumbinary System" (PDF). 2013.
  10. ^ a b c "Scientists Fill Out A Circumbinary Planetary System". Institute For Astronomy. 16 April 2019.
  11. ^ "Mission overview". NASA. 13 April 2015. Retrieved 17 April 2019.
  12. ^ a b Borucki, William J.; et al. (1 February 2011). "Characteristics of planetary candidates observed by Kepler, II: Analysis of the first four months of data" (PDF). The Astrophysical Journal. 736 (1): 19. arXiv:1102.0541. Bibcode:2011ApJ...736...19B. doi:10.1088/0004-637X/736/1/19. S2CID 15233153. Archived from the original (PDF) on 21 July 2011. Retrieved 18 September 2019.
  13. ^ Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
  14. ^ "Kepler-47". CDS Portal.
  15. ^ Williams, Matt (22 December 2015). "What is the Life Cycle Of The Sun?". Universe Today. Retrieved 16 September 2019.
  16. ^ "Sun Fact Sheet". NASA Space Science Data Coordinated Archive. NASA. 23 February 2018. Retrieved 18 September 2019.
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  19. ^ a b c Wall, Mike (16 April 2019). "Discovery! 3rd Planet Found in Two-Star 'Tatooine' Star System". Space.com. Retrieved 16 April 2019.
  20. ^ a b Hinse, Tobias C. (15 January 2015). "Predicting a third planet in the Kepler-47 circumbinary system". The Astrophysical Journal. 799 (1): 88. arXiv:1409.1349. Bibcode:2015ApJ...799...88H. doi:10.1088/0004-637X/799/1/88. S2CID 118358830.
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