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Extrasolar planet List of extrasolar planets 300pxSize comparison of HR 8799 d (gray) with Jupiter. HD 218396 d[8]
Database references

HR 8799 d is an extrasolar planet located approximately 129 light-years away in the constellation of Pegasus, orbiting the 6th magnitude Lambda Boötis star HR 8799. It has a mass between 5 and 10 Jupiter masses and a radius from 20 to 30% larger than Jupiter's. The planet orbits at 24 AU from HR 8799 with an eccentricity greater than 0.04 and a period of 100 years. Upon initial discovery, it was the innermost known planet in the HR 8799 system, but e, discovered later, is now known to be closer to their parent star. Along with two other planets orbiting HR 8799, this planet was discovered on November 13, 2008 by Marois et al., using the Keck and Gemini observatories in Hawaii. These planets were discovered using the direct imaging technique.[5][9][10][11]

Near infrared spectroscopy from 995 to 1769 nanometers made with the Palomar Observatory show evidence of Acetylene, Methane, and Carbon Dioxide, but Ammonia is not definitively detected.[12]

## NotesEdit

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 −0.216 and −0.582 arcseconds respectively.
3. 3.0 3.1 Value given assuming the planet's orbit is circular and is being observed face-on.
4. The lower limit on the eccentricity is given for the case that the planet is in a 2:1 resonance with HR 8799 c, as suggested by stability constraints.

## ReferencesEdit

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 5.7 Marois, Christian (November 2008). Direct Imaging of Multiple Planets Orbiting the Star HR 8799. Science 322 (5906): 1348–1352.
6. Fabrycky (1 December 2008). Stability of the directly imaged multiplanet system HR 8799: resonance and masses. Astrophys.J. 710 (2): 1408–1421.
7. Template:Cite arxiv
8. HD 218396d -- Extra-solar Planet Candidate, entry, SIMBAD. Accessed on line December 6, 2008.
9. Script error
10. Script error
11. Template:Cite news
12. B. R. Oppenheimer. Reconnaissance of the HR 8799 Exosolar System I: Near IR Spectroscopy.