Imaginary Picture of K2-138 b

Display orbital revolution of K2-138 b around the hoststar K2-138
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Exoplanet Name : K2-138 b
Alternate Name : "2MASS J23154776-1050590 b, EPIC 245950175 b, WISE J231547.76-105059.0 b"
Radius (Rjup / Re): 0.1400 (Rjup) 1.5693 (Rearth)
Mass (Mjup / Me): 0.0098 (Mjup) 3.1158 (Mearth)
Semi Major Axis / Orbital Distance Calculated 0.0338 (AU) 0.0338 (AU Est.)
Eccentricity : 0.4030
Orbital Period(Yrs) 0.0064
Orbital Period(Observed/Estimated) 2.35 (Days Obs.) 2.35 (Days Est.)
Surface Gravity (G Earth) 1.2653
Star Radiation at Atmospheric Boundary: 664127.6 (W/m2)
Measured Temperature (K) 0.0 (K)
Blackbody T 0.1(K) 1274.1 (K)
Blackbody T 0.3(K) 1196.5 (K)
Blackbody T 0.7(K) 968.1 (K)
Tidally Locked Blackbody T 0.1(K) 1515.2 (K)
Tidally Locked Blackbody T 0.3(K) 1422.9 (K)
Size Class: super-Earth-size
Mass Class:
Detection Type : Primary Transit
Mass Detection : Spectrum
Radius Detection : Primary Transit
Habitability by Solar Eq. Astronomical Unit: Not habitable
Habitability by Kopparapu: Not habitable
Star Name : K2-138
Alternate Name : "EPIC 245950175, 2MASS J23154776-1050590, WISE J231547.76-105059.0"
Star Distance(LY) : 596.9
Stellar Radius(Rsun) : 0.9 (Rsun Measured)
Stellar Mass(Msun) : 0.9 (Msun Measured) 0.9 (Msun Estimated)
Star Age : 0.0 (GY)
Temperature : 5378 (K)
Spectral type : K1 V
UV portion[%]: 6.3
Visible portion[%]: 42.2
IR portion[%]: 51.5
Metalicity : 0.2
Absolute Magnitude: 5.9
Apparent Magnitude: 12.2
Right Ascension(RA) 348.9490
Declination (DEC) -10.8497
Hubble Space Telescope Guide Star Catalog (GSC) ID
Discovered by
Discovery Paper - Authors
Discovery Paper - Title
Discovery Paper - Journal
Discovery Paper - URL
SIMBAD LINK http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=K2-138+&submit=SIMBAD+search
Open Exoplanet Database Link
K2-138 b
K2-138 b

  • K2-138 b is an exoplanet orbiting the star K2-138, located about 596.9 light-years (183.0 pc) away from Solar System. Its discovery was publicly announced on 2017.
  • The host star K2-138 has apparent magnitude of 12.2, with absolute magnitude of 5.9.
  • It is 0.9 times more massive and 0.9 times bigger compared with our Sun. The surface temperature is 5378 with its spectral types of K1 V
  • In this planetary system, the extrasolar planet K2-138 b orbits around the star K2-138 every 2.4 days with its orbital distance of 0.03 AU ( 5056408.0 km)
  • (Projected orbit of K2-138 b around its host star K2-138)


  • The Star K2-138 's habitable zone is located at the following distance
  • Inner Boundary (the orbital distance at Venus's Equivalent Radiation ) : 0.539 AU ( 80611714.8 km)
  • Earth Boundary (the orbital distance at Earth's Equivalent Radiation) : 0.745 AU ( 111426456.2 km)
  • Outer Boundary (the orbital distance at Mars's Equivalent Radiation) : 1.135 AU ( 169789260.6 km)
  • Snow Line (the orbital distance at Snow Line Equivalent Radiation) : 1.670 AU ( 249852334.9 km)
  • Radiation at Planetary Boundary of K2-138 b : 664127.56 W/m2

    (Habitable zone calculated based on SEAU(Solar Equivalent Astronomical Unit) around the star K2-138)



  • Kopparapu Recent Venus for Star K2-138 distance : 0.572 AU
  • Kopparapu Runaway Greenhouse for Earth-sized planet for Star K2-138 distance : 0.724 AU
  • Kopparapu Runaway Greenhouse for Super-Earth-sized planet for Star K2-138 distance : 0.699 AU
  • Kopparapu Runaway Greenhouse for Mars-sized planet for Star K2-138 distance : 0.767 AU
  • Kopparapu Outer Boundary for Maximum Greenhouse for Star K2-138 distance : 1.294 AU
  • Kopparapu Outer Boundary for Early Mars for Star K2-138 distance : 1.365 AU

    (Habitable zone calculated based on Kopparapu et al.(2013) around the star K2-138)



  • Original Kopparapu Recent Venus for Star K2-138 distance : 0.568 AU
  • Original Kopparapu Runaway Greenhouse for Star K2-138 distance : 0.745 AU
  • Original Kopparapu Moist Greenhouse for Star K2-138 distance : 0.752 AU
  • Original Kopparapu Outer Boundary for Maximum Greenhouse for Star K2-138 distance : 1.316 AU
  • Original Kopparapu Outer Boundary for Early Mars for Star K2-138 distance : 1.369 AU

    (Habitable zone calculated based on Kopparapu et al.(Original) around the star K2-138)



    (Position in Stellar Map of star K2-138 and its Exoplanet K2-138 b)



    (Zoomed position in Stellar Map of star K2-138 and its Exoplanet K2-138 b (zoom level 3))

    (Synthetic Spectrum of star K2-138*)
    *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