Imaginary Picture of K2-21 c

Display orbital revolution of K2-21 c around the hoststar K2-21
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Exoplanet Name : K2-21 c
Alternate Name : "2MASS J22411288-1429202 c, EPIC 206011691 c, EPIC 206011691.02, WISE J224112.90-142921.1 c"
Status : Confirmed
Radius (Rjup / Re): 0.2220 (Rjup) 2.4884 (Rearth)
Mass (Mjup / Me): 0.0194 (Mjup) 6.1591 (Mearth)
Semi Major Axis / Orbital Distance Calculated 0.1070 (AU) 0.1070 (AU Est.)
Eccentricity : 0.2100
Orbital Period(Yrs) 0.0424
Orbital Period(Observed/Estimated) 15.50 (Days Obs.) 15.50 (Days Est.)
Surface Gravity (G Earth) 0.9947
Star Radiation at Atmospheric Boundary: 14379.3 (W/m2)
Measured Temperature (K) 0.0 (K)
Blackbody T 0.1(K) 488.7 (K)
Blackbody T 0.3(K) 459.0 (K)
Blackbody T 0.7(K) 371.4 (K)
Tidally Locked Blackbody T 0.1(K) 581.2 (K)
Tidally Locked Blackbody T 0.3(K) 545.8 (K)
Size Class: sub-Neptune-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 : K2-21
Alternate Name : "2MASS 22411288-1429202, 2MASS J22411288-1429202, EPIC 206011691, WISE J224112.90-142921.1"
Star Distance(LY) : 273.5
Stellar Radius(Rsun) : 0.7 (Rsun Measured)
Stellar Mass(Msun) : 0.7 (Msun Measured) 0.7 (Msun Estimated)
Star Age : 0.0 (GY)
Temperature : 4222 (K)
Spectral type : M0.0
UV portion[%]: 0.8
Visible portion[%]: 26.8
IR portion[%]: 72.4
Metalicity : -0.1
Absolute Magnitude: 8.2
Apparent Magnitude: 12.8
Right Ascension(RA) 340.3037
Declination (DEC) -14.4890
Hubble Space Telescope Guide Star Catalog (GSC) ID
Discovered by
Discovery Paper - Authors "Erik A. Petigura, Joshua E. Schlieder, Ian J. M. Crossfield, Andrew W. Howard, Katherine M. Deck, David R. Ciardi, Evan Sinukoff, Katelyn N. Allers, William M. J. Best, Michael C. Liu, Charles A. Beichman, Howard Isaacson, Brad M. S. Hansen, S_bastien L_pine"
Discovery Paper - Title Two Transiting Earth-size Planets Near Resonance Orbiting a Nearby Cool Star
Discovery Paper - Journal 0
Discovery Paper - URL 0
SIMBAD LINK
Open Exoplanet Database Link http://www.openexoplanetcatalogue.com/planet/EPIC%20206011691%20c/
K2-21 c
K2-21 c

  • K2-21 c is an exoplanet orbiting the star K2-21, located about 273.5 light-years (83.8 pc) away from Solar System. Its discovery was publicly announced on 2015.
  • The host star K2-21 has apparent magnitude of 12.8, with absolute magnitude of 8.2.
  • It is 0.7 times more massive and 0.7 times bigger compared with our Sun. The surface temperature is 4222 with its spectral types of M0.0
  • In this planetary system, the extrasolar planet K2-21 c orbits around the star K2-21 every 15.5 days with its orbital distance of 0.11 AU ( 16006972.2 km)
  • (Projected orbit of K2-21 c around its host star K2-21)


  • The Star K2-21 's habitable zone is located at the following distance
  • Inner Boundary (the orbital distance at Venus's Equivalent Radiation ) : 0.251 AU ( 37549825.8 km)
  • Earth Boundary (the orbital distance at Earth's Equivalent Radiation) : 0.347 AU ( 51903672.3 km)
  • Outer Boundary (the orbital distance at Mars's Equivalent Radiation) : 0.529 AU ( 79089710.3 km)
  • Snow Line (the orbital distance at Snow Line Equivalent Radiation) : 0.778 AU ( 116383973.3 km)
  • Radiation at Planetary Boundary of K2-21 c : 14379.27 W/m2

    (Habitable zone calculated based on SEAU(Solar Equivalent Astronomical Unit) around the star K2-21)



  • Kopparapu Recent Venus for Star K2-21 distance : 0.280 AU
  • Kopparapu Runaway Greenhouse for Earth-sized planet for Star K2-21 distance : 0.354 AU
  • Kopparapu Runaway Greenhouse for Super-Earth-sized planet for Star K2-21 distance : 0.342 AU
  • Kopparapu Runaway Greenhouse for Mars-sized planet for Star K2-21 distance : 0.376 AU
  • Kopparapu Outer Boundary for Maximum Greenhouse for Star K2-21 distance : 0.664 AU
  • Kopparapu Outer Boundary for Early Mars for Star K2-21 distance : 0.701 AU

    (Habitable zone calculated based on Kopparapu et al.(2013) around the star K2-21)



  • Original Kopparapu Recent Venus for Star K2-21 distance : 0.276 AU
  • Original Kopparapu Runaway Greenhouse for Star K2-21 distance : 0.366 AU
  • Original Kopparapu Moist Greenhouse for Star K2-21 distance : 0.365 AU
  • Original Kopparapu Outer Boundary for Maximum Greenhouse for Star K2-21 distance : 0.675 AU
  • Original Kopparapu Outer Boundary for Early Mars for Star K2-21 distance : 0.702 AU

    (Habitable zone calculated based on Kopparapu et al.(Original) around the star K2-21)



    (Position in Stellar Map of star K2-21 and its Exoplanet K2-21 c)



    (Zoomed position in Stellar Map of star K2-21 and its Exoplanet K2-21 c (zoom level 3))

    (Synthetic Spectrum of star K2-21*)
    *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