# Kepler-12b

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Exoplanet in the constellation Draco

Kepler-12b Discovery Discovered by Fortney et al.[1] Discovery site Kepler spacecraft Discovery date Published September 5, 2011[1] Detection method radial velocity/transit[1] Orbital characteristics Semi-major axis 0.0556 (± 0.0007)[2] AU Eccentricity 0.01[2] Orbital period (sidereal) 4.4379637 (± 0.0007)[2] d Inclination 88.76 (±0.08)[2] Star Kepler-12 Physical characteristics Mean radius 1.695 +0.028 −0.032[2] RJ Mass 0.431 (± 0.041)[2] MJ Mean density 0.111 +0.011 −0.009[1] g cm−3 Temperature 1711±223 K.[3]

**Kepler-12b** is a [hot Jupiter](/source/Hot_Jupiter) that orbits G-type star [Kepler-12](/source/Kepler-12) some 900 parsecs (2,900 ly) away. The planet has an anomalously large radius that could not be explained by standard models at the time of its discovery, almost 1.7 times Jupiter's size while being 0.4 times Jupiter's mass. The planet was detected by the [Kepler](/source/Kepler_(spacecraft)) spacecraft, a [NASA](/source/NASA) project searching for planets that [transit](/source/Transit_method) (cross in front of) their host stars. The discovery paper was published on September 5, 2011.

## Discovery

[NASA](/source/NASA)'s [Kepler](/source/Kepler_(spacecraft)) spacecraft continuously observes a region of the night sky, searching for signs of [transiting planets](/source/Transit_method). While orbiting their host stars, such transiting planets cross in front of host stars as seen from Earth. The slight and periodic dimming in the star's brightness is used to determine whether or not the dimming was caused by a planet and not by a [false positive](/source/False_positive). Analysis of Kepler's early data yielded evidence of a transit signal around a star designated as KIC 11804465, later known as Kepler-12. The transit signal was designated KOI-20.[1]

The Keck Observatory collected observations to prove that Kepler-12b's signal was not actually caused by an eclipsing binary.

The [Kepler Follow-up Program](/source/Kepler_Follow-up_Program) (KFOP) worked to verify the existence of the planet. KFOP used the [W.M. Keck Observatory](/source/W.M._Keck_Observatory)'s Keck I telescope to prove that Kepler-12 was not an [eclipsing binary](/source/Eclipsing_binary) star (a possible false positive that mimics the transit signal). The [WIYN Observatory](/source/WIYN_Observatory), which was used for [speckle imaging](/source/Speckle_imaging), supported Keck's findings and verified that the signal caused by KOI-20 was not caused by a nearby background star's interference. [Adaptive optics](/source/Adaptive_optics) imaging in the near-infrared was obtained on September 9, 2009 with the [Palomar Observatory](/source/Palomar_Observatory)'s PHARO camera on the [Hale Telescope](/source/Hale_Telescope) confirmed both the WIYN and Keck findings.[1]

Keck's HIRES instrument measured Kepler-12's [radial velocity](/source/Radial_velocity), which was used to find more of Kepler-12's characteristics (and, by extension, deduce the characteristics of KOI-20 itself). The radial velocity measurements eventually led to the confirmation of Kepler-12b as a planet.[1] Kepler's data in its first 1.5 years of operation was processed and analyzed, yielding Kepler-12b's radius, mass and density.[1]

The [Spitzer Space Telescope](/source/Spitzer_Space_Telescope)'s IRAC infrared adaptive optics camera was used to carry out program #60028, which observed the [occultations](/source/Occultation) by several giant planets detected by Kepler behind their host stars. The Kepler team, using the observations, tentatively concluded that Kepler-12b most likely did not experience a [temperature inversion](/source/Temperature_inversion), in which the day-side temperature of the planet is lower than the night-side. Kepler-12b's discovery paper was published in the *[Astrophysical Journal](/source/Astrophysical_Journal)* on September 5, 2011.[1]

## Host star

Main article: [Kepler-12](/source/Kepler-12)

Kepler-12, known also as KIC 11804465 in the [Kepler Input Catalog](/source/Kepler_Input_Catalog), is an early [G-type](/source/Stellar_classification#Class_G) to late [F-type](/source/Stellar_classification#Class_F) star. This corresponds strongly with a sunlike [dwarf star](/source/Dwarf_star) nearing the end of the [main sequence](/source/Main_sequence), and is about to become a [red giant](/source/Red_giant).[1] Kepler-12 is located approximately 900 [parsecs](/source/Parsec) (2,950 [light years](/source/Light_year)) away from Earth. The star also has an [apparent magnitude](/source/Apparent_magnitude) of 13.438, which means that it cannot be seen from Earth with the unaided eye.[4]

The star is slightly more massive, slightly more iron-rich and slightly hotter than the Sun. However, Kepler-12 is larger, with a radius of 1.483 times the [Sun's radius](/source/Solar_radius).[4]

## Characteristics

Kepler-12b is a [Hot Jupiter](/source/Hot_Jupiter), and (at the time of its discovery) was the least-irradiated of four Hot Jupiters experiencing a [radius anomaly](https://en.wikipedia.org/w/index.php?title=Radius_anomaly&action=edit&redlink=1) of approximately 1.7 times or more the [mass of Jupiter](/source/Jupiter_mass). This radius anomaly entails Hot Jupiters experiencing massive radius increases for a reason not explained by scientific models. Although Kepler-12 is the least-irradiated of the four Hot Jupiters, its radius is just as large, suggesting that multiple mechanisms influencing the planet's inflation are at work.[1] Kepler-12b was compared to [HD 209458 b](/source/HD_209458_b) in its discovery paper because both planets appear to release similar amounts of energy ([flux](/source/Flux)); it was also compared to [TrES-4b](/source/TrES-4b) because of the similar radius of the planet.[1]

Kepler-12b has a mass of 0.431 Jupiters. Its radius of 1.695 [Jupiter radii](/source/Jupiter_radius), however, indicates that the planet is almost 70% more than the size of Jupiter. With an orbit of 0.0556 [AU](/source/Astronomical_unit), Kepler-12b's [average orbit](/source/Semimajor_axis) is approximately 5% the average distance between the Earth and Sun. The orbit lasts 4.4379637 days. Kepler-12b has an [orbital inclination](/source/Orbital_inclination) of 88.86º, indicating that the planet is seen as nearly edge-on with respect to the Earth and to its host star.[2] According to Kepler's official website, the mass and radius of the planet can be compared to 137 Earths (in mass) and 19 Earths (for its radius). The planet's density is 0.111 grams/cm3, about a tenth of the density of water, and its [equilibrium temperature](/source/Thermal_equilibrium) is 1481 [K](/source/Kelvin_scale) (some 5.8 times greater than Jupiter's equilibrium temperature). Additionally, Kepler-12b has an almost totally circular orbit, with an [orbital eccentricity](/source/Orbital_eccentricity) of less than 0.01.[4]

The planet is likely to be tidally locked to the parent star. In 2015, the planetary nightside temperature was estimated to be equal to 1711±223 [K](/source/Kelvin).[3] The brightest spot in the planetary atmosphere is shifted westward from the substellar point, indicating a strong winds.[5]

## References

1. ^ [***a***](#cite_ref-Fortney2011_1-0) [***b***](#cite_ref-Fortney2011_1-1) [***c***](#cite_ref-Fortney2011_1-2) [***d***](#cite_ref-Fortney2011_1-3) [***e***](#cite_ref-Fortney2011_1-4) [***f***](#cite_ref-Fortney2011_1-5) [***g***](#cite_ref-Fortney2011_1-6) [***h***](#cite_ref-Fortney2011_1-7) [***i***](#cite_ref-Fortney2011_1-8) [***j***](#cite_ref-Fortney2011_1-9) [***k***](#cite_ref-Fortney2011_1-10) [***l***](#cite_ref-Fortney2011_1-11) Fortney, Jonathan J.; et al. (2011). "Discovery and Atmospheric Characterization of Giant Planet Kepler-12b: An Inflated Radius Outlier". *The Astrophysical Journal Supplement Series*. **197** (1). 9. [arXiv](/source/ArXiv_(identifier)):[1109.1611](https://arxiv.org/abs/1109.1611). [Bibcode](/source/Bibcode_(identifier)):[2011ApJS..197....9F](https://ui.adsabs.harvard.edu/abs/2011ApJS..197....9F). [doi](/source/Doi_(identifier)):[10.1088/0067-0049/197/1/9](https://doi.org/10.1088%2F0067-0049%2F197%2F1%2F9). [S2CID](/source/S2CID_(identifier)) [688362](https://api.semanticscholar.org/CorpusID:688362).

1. ^ [***a***](#cite_ref-EPE_2-0) [***b***](#cite_ref-EPE_2-1) [***c***](#cite_ref-EPE_2-2) [***d***](#cite_ref-EPE_2-3) [***e***](#cite_ref-EPE_2-4) [***f***](#cite_ref-EPE_2-5) [***g***](#cite_ref-EPE_2-6) Jean Schneider (2011). ["Notes for star Kepler-12"](https://web.archive.org/web/20111005040129/http://exoplanet.eu/star.php?st=Kepler-12#a_publi). *[Extrasolar Planets Encyclopaedia](/source/Extrasolar_Planets_Encyclopaedia)*. Archived from [the original](http://www.exoplanet.eu/star.php?st=Kepler-12#a_publi) on 5 October 2011. Retrieved 12 September 2011.

1. ^ [***a***](#cite_ref-Angerhausen2015_3-0) [***b***](#cite_ref-Angerhausen2015_3-1) [A Comprehensive Study of Kepler Phase Curves and Secondary Eclipses:Temperatures and Albedos of Confirmed Kepler Giant Planets](https://iopscience.iop.org/article/10.1086/683797/pdf)

1. ^ [***a***](#cite_ref-datatable_4-0) [***b***](#cite_ref-datatable_4-1) [***c***](#cite_ref-datatable_4-2) ["Datatable of Kepler Discoveries"](https://web.archive.org/web/20100527104316/http://kepler.nasa.gov/Mission/discoveries/). *[Ames Research Center](/source/Ames_Research_Center)*. [NASA](/source/NASA). 2011. Archived from [the original](https://kepler.nasa.gov/Mission/discoveries/) on 2010-05-27. Retrieved 12 September 2011.

1. **[^](#cite_ref-5)** Shporer, Avi; Hu, Renyu (2015), "Studying Atmosphere-Dominated Hot Jupiter Kepler Phase Curves: Evidence That Inhomogeneous Atmospheric Reflection is Common", *The Astronomical Journal*, **150** (4): 112, [arXiv](/source/ArXiv_(identifier)):[1504.00498](https://arxiv.org/abs/1504.00498), [Bibcode](/source/Bibcode_(identifier)):[2015AJ....150..112S](https://ui.adsabs.harvard.edu/abs/2015AJ....150..112S), [doi](/source/Doi_(identifier)):[10.1088/0004-6256/150/4/112](https://doi.org/10.1088%2F0004-6256%2F150%2F4%2F112), [S2CID](/source/S2CID_(identifier)) [33182939](https://api.semanticscholar.org/CorpusID:33182939)

v t e Constellation of Draco List of stars in Draco Draco in Chinese astronomy Stars Bayer α (Thuban) β (Rastaban) γ (Eltanin) δ (Altais) ε (Tyl) ζ (Aldhibah) η (Athebyne) θ ι (Edasich) κ λ (Giausar) μ (Alrakis) ν (Kuma) ξ (Grumium) ο π ρ σ (Alsafi) τ υ φ χ ψ1 (Dziban) ψ2 ω Flamsteed 4 6 7 (Tianyi) 8 (Taiyi) 10 (i) 15 (A) 18 (g) 19 (h) 26 36 39 (b) 42 (Fafnir) 45 (d) 50 59 64 (e) 68 Variable TW YY AG BY CL CM CX DO EK HP V581 HR 3751 4126 4934 5811 6237 6518 6618 (Alruba) 6817 7137 7783 HD 109246 (Funi) 101364 128717 147379 156279 158259 176693 191939 Other 2MASS 1237+6526 2MASS J17554042+6551277 G 240-72 GD 356 Gliese 420 Gliese 625 Gliese 687 GRW +70 8247 Kepler-4 Kepler-10 Kepler-12 Kepler-90 Kepler-296 KOI-256 LP 71-82 Qatar-1 SDSS J1240+6710 Struve 2398 TOI-1136 WD 1856+534 WISE 1647+5632 WISE 1841+7000 Exoplanets HD 139357 b HD 167042 b ι Dra b (Hypatia) Kepler-4b Kepler-10b c Kepler-12b Kepler-90e f g h i Kepler-296b c d e f TOI-1452 b TrES-2b Star clusters LAMOST 1 Nebulae Cat's Eye Nebula NGC 6742 Galaxies NGC 3147 3197 3735 4121 4125 4221 4236 4319 4331 4332 4363 4441 4513 4545 4589 5678 5777 5866 5866B 5879 5905 5907 5949 5963 5965 5982 5985 6090 6248 6285 6286 6338 6340 6365 6373 6394 6412 6503 6505 6566 6621 6622 6670 6676 6786 6789 Other 1ES 1927+654 1ES 1959+650 3C 249.1 3C 305 3C 319 3C 343 3C 343.1 3C 351 3C 356 3C 371 3C 380 3C 390.3 3C 401 4C +72.26 4C 73.08 8C 1241+735 Abell 2218 BCG Bean galaxy Beaver galaxy BZQ J1727+5510 Draco Dwarf Draco II GB 1508+5714 Goldfish galaxy H1821+643 HFLS3 IERS B1946+708 IRAS F17179+5444 IRAS 18580+6527 J120011.1+680924.8 KKR 25 Markarian 817 Markarian 876 Original TRG PGC 39058 Porphyrion QSO B1823+568 RGZ J172749.5+534647 S5 1803+784 S5 2007+777 SDSS J1715+6008 Tadpole Galaxy UGC 9391 UGC 9405 UGC 11241 UGC 11411 WISEA J145223.62+611707.5 WN B1851+5707 Galaxy clusters Abell 2218 CL1358+62 Draco Supercluster NGC 5866 Group Astronomical events SN 2003jb SN 2005B SN 2016aps Swift J1644+57 Category

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Adapted from the Wikipedia article [Kepler-12b](https://en.wikipedia.org/wiki/Kepler-12b) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Kepler-12b?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.