HR 8799 c
Extrasolar planet List of extrasolar planets
Size comparison of HR 8799 c (gray) with Jupiter.
Parent star

<tr> <td colspan="2">Star</td> <td>HR 8799</td></tr><tr> <td colspan="2">Constellation</td> <td>Pegasus</td></tr><tr> <td>Right ascension</td> <td style="text-align: center">(α)</td> <td>23h 07m 28.7150s[1]</td></tr><tr> <td>Declination</td> <td style="text-align: center">(δ)</td> <td>+21° 08′ 03.302″[1]</td></tr><tr> <td>Apparent magnitude</td> <td style="text-align: center">(mV)</td> <td>5.964[1]</td></tr><tr><td colspan="2">Distance</td><td>129 ± 4[2][note 1] ly
(39 ± 1[2][note 1] pc)</td></tr><tr><td colspan="2">Spectral type</td> <td>kA5 hF0 mA5 V; λ Boo[3][4]</td></tr> <tr style="background-color: #A0B0FF;"><td colspan="3" align=center>Observed separation
Observation epoch 2008-09-18</td></tr><tr> <td>Angular separation</td> <td style="text-align: center">(ρ)</td> <td>964[5][note 2] mas</td></tr><tr> <td>Position angle</td> <td style="text-align: center">(θ)</td> <td>317.06[5][note 2]°</td></tr><tr> <td>Projected separation</td> <td style="text-align: center">(d)</td> <td>38[5] AU</td></tr>

Orbital elements

<tr><td>Semimajor axis</td><td style="text-align: center">(a)</td> <td>~ 38[5][note 3] AU
(~ 5600 Gm)</td></tr><tr><td>Orbital period</td><td style="text-align: center">(P)</td> <td>~ 190[5][note 3] y</td></tr>

Physical characteristics

<tr><td>Mass</td><td style="text-align: center">(m)</td><td>7+3
[6] MJ</td></tr><tr><td>Radius</td><td style="text-align: center">(r)</td><td>1.3[7] Template:Jupiter radius</td></tr><tr><td>Density</td><td style="text-align: center">(ρ)</td><td>3.2+1.3
kg m-3</td></tr><tr> <td>Temperature</td> <td style="text-align: center">(T)</td> <td>1090+10
[5] K</td></tr>

Discovery information

<tr> <td colspan="2">Discovery date</td> <td>November 13, 2008</td></tr><tr> <td colspan="2">Discoverer(s)</td> <td>Marois et al.</td></tr><tr> <td colspan="2">Discovery method</td> <td>Direct imaging</td></tr><tr> <td colspan="2">Discovery site</td> <td>Keck and Gemini
in Hawaii</td></tr><tr> <td colspan="2">Discovery status</td> <td>Published</td></tr>

Other designations
HD 218396 c[8]

<tr style="background-color: #A0B0FF;"><td align=center colspan=3>Database references</td></tr><tr valign=baseline><td colspan=2>Extrasolar Planets
</td><td>data</td></tr><tr><td colspan=2>SIMBAD</td><td>data</td></tr>

HR 8799 c is an extrasolar planet located approximately 129 light-years away in the constellation of Pegasus, orbiting the 6th magnitude Lambda Boötis star HR 8799. This planet has a mass between 5 and 10 Jupiter masses and a radius from 20 to 30% larger than Jupiter's. It orbits at 38 AU from HR 8799 with an unknown eccentricity and a period of 190 years; it is the 2nd planet discovered in the HR 8799 system. Along with two other planets orbiting HR 8799, this planet was discovered on November 13, 2008 by Marois et al., using the Keck and the Gemini observatories in Hawaii. These planets were discovered using the direct imaging technique.[5][9][10][11][12] In January 2010, HR 8799 c became the 3rd exoplanet to have a portion of its spectrum directly observed (following 2M1207b and 1RXS J1609b), confirming the feasibility of direct spectrographic studies of exoplanets.[7][13]


File:Spectrum of planet around HR 8799 (annotated).jpg

Near infrared spectroscopy from 995 to 1769 nanometers made with the Palomar Observatory show evidence of Ammonia, perhaps some Acetylene but neither Carbon Dioxide nor substantial Methane.[14] High resolution spectroscopy with the OSIRIS instrument on the Keck Observatory show numerous well resolved lines of molecular absorption in the planet's atmosphere in the K band. Although methane is absent, the planet's atmosphere contains both water and carbon monoxide; the carbon-to-oxygen ratio of HR 8799 c is higher than that of its star, suggesting that the planet formed through the core accretion process.[15][16]


  1. 1.0 1.1 Computed from parallax: \scriptstyle \mathrm{distance\ in\ parsecs}=\frac{1000}{\mathrm{parallax\ in\ milliarcseconds}}
  2. 2.0 2.1 Calculated from the separations in the East and North directions which are −0.657 and 0.706 arcseconds respectively.
  3. 3.0 3.1 Value given assuming the planet's orbit is circular and is being observed face-on.

See alsoEdit


  1. 1.0 1.1 1.2 V* V342 Peg -- Variable Star of gamma Dor type, entry, SIMBAD. Accessed on line November 14, 2008.
  2. 2.0 2.1 van Leeuwen, F. (2007). HIP 114189. Hipparcos, the New Reduction. Retrieved 2008-10-13.
  3. Gray, R.O. and Kaye, A.B. (1999). HR 8799: A Link between γ Doradus Variables and λ Bootis Stars. The Astronomical Journal 118 (6): 2993–2996.
  4. Kaye, A.B. (1999). Gamma Doradus Stars: Defining a New Class of Pulsating Variables. PASP 111 (761): 840–844.
  5. 5.0 5.1 5.2 5.3 5.4 5.5 5.6 Marois, Christian (November 2008). Direct Imaging of Multiple Planets Orbiting the Star HR 8799. Science 322 (5906): 1348–1352.
  6. Template:Cite arxiv
  7. 7.0 7.1 Jason, M. (2010). Spatially resolved spectroscopy of the exoplanet HR 8799 c. The Astrophysical Journal.
  8. HD 218396c -- Extra-solar Planet Candidate, entry, SIMBAD. Accessed on line December 6, 2008.
  9. Script error
  10. Script error
  11. Template:Cite news
  12. Fabrycky (1 December 2008). Stability of the directly imaged multiplanet system HR 8799: resonance and masses. Astrophys.J. 710 (2): 1408–1421.
  13. Janson, M. (13 January 2010). VLT Captures First Direct Spectrum of an Exoplanet. ESO.
  14. B. R. Oppenheimer. Reconnaissance of the HR 8799 Exosolar System I: Near IR Spectroscopy.
  15. Alien planet’s atmosphere contains water and carbon monoxide
  16. Giant Alien Planet in Supersized Solar System May Solve Mystery

External linksEdit

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Template:HR 8799 Coordinates: Sky map 23h 07m 28.7150s, +21° 08′ 03.302″

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