HD 38858
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Orion
Right ascension 05h 48m 34.93996s[1]
Declination −04° 05′ 40.7153″[1]
Apparent magnitude (V) +5.97[2]
Spectral type G4V[3]
U−B color index +0.10[2]
B−V color index +0.64[2]
Radial velocity (Rv)+31.2[4] km/s
Proper motion (μ) RA: 60.84 ± 0.41[1] mas/yr
Dec.: –228.35 ± 0.33[1] mas/yr
Parallax (π)65.89 ± 0.41[1] mas
Distance49.5 ± 0.3 ly
(15.18 ± 0.09 pc)
Mass0.886[5] M
Radius0.9331 ± 0.0162[5] R
Luminosity0.7943 ± 0.0101[5] L
Surface gravity (log g)4.36 ± 0.06[3] cgs
Temperature5,660 ± 20[3] K
Metallicity [Fe/H]–0.27 ± 0.03[3] dex
Rotational velocity (v sin i)2.61[6] km/s
Age6.2[7] Gyr
Other designations
BD–04 1244, FK5 1155, GJ 1085, HD 38858, HIP 27435, LTT 2380, SAO 132554, 2MASS .
Database references
Exoplanet Archivedata
Extrasolar Planets

HD 38858 is a G-type star,[3] much like The Sun, with one detected planet. The planet, designated HD 38858 b, is about twice the mass of Uranus and orbits in the star's habitable zone.[8]

The last observation of this system for a dust disc or comet belt was in 2009 by the Spitzer Space Telescope; a belt was inferred at 102 AU.[7] It has an inclination of 48◦.[9]

The star exhibit a magnetic activity cycle remarkably similar to that of Sun, with the period of 10.8 years.[10]

Planetary system

The exoplanet HD 38858 b was discovered in 2011 in orbit in its host star's habitable zone, a zone in which Earth-like conditions (namely the presence of liquid water) on a planet's surface are possible.[11][12] The planet is likely a gas giant, a type of planet which astronomers believe is unlikely to support life as it is currently understood. However, the planet could have a rocky natural satellite capable of sustaining an Earth-like environment.[13] In 2020, the issue of habitability was explored by the popular YouTube channel "Fire of Learning", in which the planet was referred to as "Kynigos", and its hypothetical satellite was compared to the Jovian Moons of Europa and Io. Potential obstacles to habitability of any natural satellite, including the eccentricity of the planet's orbit, likelihood of the moon being tidally locked, and probable prevalence of geothermic activity owed to its orbit around the gas giant, were highlighted.[14][15][16]

The existence of planet was disputed since 2015 though, attributing the planetary signal to the frequency-domain alias of the star magnetic activity cycle, although another planet on the 198-day orbit is suspected.[10]

The HD 38858 planetary system[17]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b (disputed[10]) 32[18] M🜨 1.0376 ± 0.0189 407.15 ± 4.2857 0.27 ± 0.17
Disk 102–102 AU


  1. ^ a b c d e van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600. Vizier catalog entry
  2. ^ a b c Johnson, H. L.; Iriarte, B.; Mitchell, R. I.; Wisniewskj, W. Z. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory. 4 (99): 99. Bibcode:1966CoLPL...4...99J.
  3. ^ a b c d e J. Maldonado, C. Eiroa, E. Villaver, B. Montesinos and A. Mora (2012). "Metallicity of solar-type stars with debris discs and planets". Astronomy & Astrophysics. 541: A40. arXiv:1202.5884. Bibcode:2012A&A...541A..40M. doi:10.1051/0004-6361/201218800. S2CID 46328823.CS1 maint: uses authors parameter (link)
  4. ^ Nordström, B.; et al. (May 2004). "The Geneva-Copenhagen survey of the Solar neighbourhood: Ages, metallicities, and kinematic properties of 14,000 F and G dwarfs". Astronomy and Astrophysics. 418 (3): 989–1019. arXiv:astro-ph/0405198. Bibcode:2004A&A...418..989N. doi:10.1051/0004-6361:20035959. S2CID 11027621.
  5. ^ a b c Boyajian, Tabetha S.; et al. (July 2013), "Stellar Diameters and Temperatures. III. Main-sequence A, F, G, and K Stars: Additional High-precision Measurements and Empirical Relations", The Astrophysical Journal, 771 (1): 40, arXiv:1306.2974, Bibcode:2013ApJ...771...40B, doi:10.1088/0004-637X/771/1/40, S2CID 14911430.
  6. ^ Martínez-Arnáiz, R.; et al. (September 2010). "Chromospheric activity and rotation of FGK stars in the solar vicinity. An estimation of the radial velocity jitter" (PDF). Astronomy and Astrophysics. 520: A79. arXiv:1002.4391. Bibcode:2010A&A...520A..79M. doi:10.1051/0004-6361/200913725. S2CID 43455849.
  7. ^ a b Wyatt, M. C.; et al. (2012). "Herschel imaging of 61 Vir: implications for the prevalence of debris in low-mass planetary systems". Monthly Notices of the Royal Astronomical Society. 424 (2): 1206. arXiv:1206.2370. Bibcode:2012MNRAS.tmp.3237W. doi:10.1111/j.1365-2966.2012.21298.x. S2CID 54056835. citing Lawler et al. 2009, and recalculating its distance.
  8. ^ LTT 2380 -- High proper-motion Star, SIMBAD Astronomical Database, accessed 11 October 2012.
  9. ^ Bryden et al., promised in John E. Krist; Karl R. Stapelfeldt; Geoffrey Bryden; Peter Plavchan (2012), "Hubble Space Telescope Observations of the HD 202628 Debris Disk", Astronomical Journal, 144 (2): 45, arXiv:1206.2078, Bibcode:2012AJ....144...45K, doi:10.1088/0004-6256/144/2/45, S2CID 40040285
  10. ^ a b c HD 38858: a solar type star with a ∼10.8 yr activity cycle Searching for Balmer and metallic line variations, 2018, arXiv:1809.05581
  11. ^ "The Extrasolar Planet Encyclopaedia — HD 38858 b". exoplanet.eu. Retrieved 2020-03-06.
  12. ^ Cain, Fraser (2015-06-29). "What is the Habitable Zone?". Universe Today. Retrieved 2020-03-06.
  13. ^ "Should We Look For Life on Gas-Giants?". Futurism. Retrieved 2020-03-06.
  14. ^ "HD 38858". exoplanetarchive.ipac.caltech.edu. Retrieved 2020-03-06.
  15. ^ "Io's Alien Volcanoes | Science Mission Directorate". science.nasa.gov. Retrieved 2020-03-06.
  16. ^ March 2018, Elizabeth Howell 22. "Europa: Facts About Jupiter's Icy Moon and Its Ocean". Space.com. Retrieved 2020-03-06.
  17. ^ "hd_38858_b".
  18. ^ Wyatt; m sin i is 0.0961 ± 0.012 MJ / 30.55 ± 4.11 (which Wyatt knew from most current cited paper Mayor, "HARPS XXXIV", 2011). Wyatt has likely factored in the inclination but did not state this outright in the arXiv version of the paper.