Imaginary Picture of Kepler-21 b

Display orbital revolution of Kepler-21 b around the hoststar Kepler-21
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Exoplanet Name : Kepler-21 b
Alternate Name : "Kepler-21 b, 2MASS J19092683+3842505 b, BD+38 3455 b, HD 179070 b, HIP 94112 b, K00975.01, KIC 3632418 b, KOI-975 b, KO
Status : Confirmed
Radius (Rjup / Re): 0.1460 (Rjup) 1.6365 (Rearth)
Mass (Mjup / Me): 0.0160 (Mjup) 5.0806 (Mearth)
Semi Major Axis / Orbital Distance Calculated 0.0427 (AU) 0.0427 (AU Est.)
Eccentricity : 0.0200
Orbital Period(Yrs) 0.0076
Orbital Period(Observed/Estimated) 2.79 (Days Obs.) 2.72 (Days Est.)
Surface Gravity (G Earth) 1.8971
Star Radiation at Atmospheric Boundary: 3761573.7 (W/m2)
Measured Temperature (K) 0.0 (K)
Blackbody T 0.1(K) 1965.6 (K)
Blackbody T 0.3(K) 1845.9 (K)
Blackbody T 0.7(K) 1493.5 (K)
Tidally Locked Blackbody T 0.1(K) 2337.5 (K)
Tidally Locked Blackbody T 0.3(K) 2195.1 (K)
Size Class: super-Earth-size
Mass Class:
Detection Type : Primary Transit
Mass Detection :
Radius Detection : Primary Transit
Habitability by Solar Eq. Astronomical Unit: Not habitable
Habitability by Kopparapu: Not habitable
Star Name : Kepler-21
Alternate Name : "Kepler-21, 2MASS J19092683+3842505, BD+38 3455, HD 179070, HIP 94112, KIC 3632418, KOI-975, Kepler-21 A, SAO 67891, TYCJ
Star Distance(LY) : 353.9
Stellar Radius(Rsun) : 1.9 (Rsun Measured)
Stellar Mass(Msun) : 1.4 (Msun Measured) 1.3 (Msun Estimated)
Star Age : 3.0 (GY)
Temperature : 6202 (K)
Spectral type : F6 IV
UV portion[%]: 7.8
Visible portion[%]: 44.8
IR portion[%]: 47.4
Metalicity : -0.0
Absolute Magnitude: 3.1
Apparent Magnitude: 8.3
Right Ascension(RA) 287.3618
Declination (DEC) 38.7140
Hubble Space Telescope Guide Star Catalog (GSC) ID 03120-00963
Discovered by
Discovery Paper - Authors 0
Discovery Paper - Title Kepler-21b: A 1.6 R Earth Planet Transiting the Bright Oscillating F Subgiant Star HD 179070
Discovery Paper - Journal 0
Discovery Paper - URL 0
SIMBAD LINK http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=Kepler-21+&submit=SIMBAD+search
Open Exoplanet Database Link http://www.openexoplanetcatalogue.com/planet/Kepler-21%20b/
Kepler-21 b
Kepler-21 b

  • Kepler-21 b is an exoplanet orbiting the star Kepler-21, located about 353.9 light-years (108.5 pc) away from Solar System. Its discovery was publicly announced on 2012.
  • The host star Kepler-21 has apparent magnitude of 8.3, with absolute magnitude of 3.1.
  • It is 1.4 times more massive and 1.9 times bigger compared with our Sun. The surface temperature is 6202 with its spectral types of F6 IV
  • In this planetary system, the extrasolar planet Kepler-21 b orbits around the star Kepler-21 every 2.8 days with its orbital distance of 0.04 AU ( 6390372.2 km)
  • (Projected orbit of Kepler-21 b around its host star Kepler-21)


  • The Star Kepler-21 's habitable zone is located at the following distance
  • Inner Boundary (the orbital distance at Venus's Equivalent Radiation ) : 1.621 AU ( 242460637.1 km)
  • Earth Boundary (the orbital distance at Earth's Equivalent Radiation) : 2.240 AU ( 335143963.0 km)
  • Outer Boundary (the orbital distance at Mars's Equivalent Radiation) : 3.414 AU ( 510685232.3 km)
  • Snow Line (the orbital distance at Snow Line Equivalent Radiation) : 5.023 AU ( 751495691.1 km)
  • Radiation at Planetary Boundary of Kepler-21 b : 3761573.74 W/m2

    (Habitable zone calculated based on SEAU(Solar Equivalent Astronomical Unit) around the star Kepler-21)



  • Kopparapu Recent Venus for Star Kepler-21 distance : 1.637 AU
  • Kopparapu Runaway Greenhouse for Earth-sized planet for Star Kepler-21 distance : 2.073 AU
  • Kopparapu Runaway Greenhouse for Super-Earth-sized planet for Star Kepler-21 distance : 2.002 AU
  • Kopparapu Runaway Greenhouse for Mars-sized planet for Star Kepler-21 distance : 2.194 AU
  • Kopparapu Outer Boundary for Maximum Greenhouse for Star Kepler-21 distance : 3.625 AU
  • Kopparapu Outer Boundary for Early Mars for Star Kepler-21 distance : 3.824 AU

    (Habitable zone calculated based on Kopparapu et al.(2013) around the star Kepler-21)



  • Original Kopparapu Recent Venus for Star Kepler-21 distance : 1.654 AU
  • Original Kopparapu Runaway Greenhouse for Star Kepler-21 distance : 2.127 AU
  • Original Kopparapu Moist Greenhouse for Star Kepler-21 distance : 2.189 AU
  • Original Kopparapu Outer Boundary for Maximum Greenhouse for Star Kepler-21 distance : 3.690 AU
  • Original Kopparapu Outer Boundary for Early Mars for Star Kepler-21 distance : 3.838 AU

    (Habitable zone calculated based on Kopparapu et al.(Original) around the star Kepler-21)



    (Position in Stellar Map of star Kepler-21 and its Exoplanet Kepler-21 b)



    (Zoomed position in Stellar Map of star Kepler-21 and its Exoplanet Kepler-21 b (zoom level 3))

    (Synthetic Spectrum of star Kepler-21*)
    *Yamashiki YA et al. 2019 ApJ 881 114
    MUSCLES Paper I - France et al. 2016 ApJ 820 89
    MUSCLES Paper II- Youngblood et al. 2016 ApJ 824 101
    MUSCLES Paper III- Loyd et al. 2016 ApJ 824 102