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Kepler-9c

Coordinates: Sky map 19h 2m 17.76s, +38° 24′ 3.2″
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Kepler-9c is one of the first 7 exoplanets discovered by NASA's Kepler Mission, and one of at least two planets orbiting the star Kepler-9. Kepler-9c and Kepler-9b were the first exoplanets confirmed to be transiting their star.[1][2] The planet's discovery was announced by the Kepler Mission team on August 26, 2010 after its initial discovery by Kepler. At the time, it was one of 700 planetary candidates noted by Kepler. Observations of the planet have suggested that it is a hydrogen-helium gas giant that is slightly smaller than Saturn, and that it orbits nearby its star at .225 AU. Kepler-9c and b are notable in that the planets share a pattern of orbital resonance, in which the orbit of each planet stabilizes the orbit of the other. The planet's orbit, which lasts approximately 38 days, shortens by 39 minutes every "year" because of this effect.


Nomenclature and history

As with most exoplanets, the name "Kepler-9c" denotes that it is the second planet discovered in the orbit of the star Kepler-9. Kepler-9 itself was named after the Kepler Mission, a NASA project oriented towards discovering planets that are transiting their home stars.[3]

The planet was one of 700 planetary candidates considered by Kepler in its first 43 days of operation. It was highlighted as a part of one of five star systems that seemed to hold multiple transiting planets. Kepler-9c and Kepler-9b were confirmed as the first planets discovered to transit the same star.[4]

Initial estimates concerning Kepler-9c's mass were refined by follow-up observations made by the Keck 1 Telescope at the W.M. Keck Observatory at Mauna Kea, Hawaii. Keck was able to confirm that Kepler-9c and Kepler-9b were planets that were slightly smaller than planet Saturn.[4]

Characteristics

Kepler-9c is a gas giant that is smaller and slightly less massive than planet Saturn. It is approximately .171 MJ, or 17% the mass of planet Jupiter. It also has a radius of .147 RJ, which is some 15% of Jupiter's. The planet is, on average, situated .225 AU from the star.[5]

It is probable that the planet is composed of hydrogen and helium. The planet orbits on the same plan as Kepler-9b, a second and larger gas giant located in the Kepler-9 system. While observing the planet, the Kepler team noticed that Kepler-9b and c orbited in a 1:2 ratio, where Kepler-9b orbits its star every 19 days and Kepler-9c orbits every 38 days. The gravitational pull that each planet has on the other, known as orbital resonance, keeps the planets in a stable orbit. This phenomenon is the first of its kind seen outside the Solar System. Every time Kepler-9c completes an orbit, its orbit grows 39 minutes shorter.[6]

See also

References

  1. ^ "Summary Table of Kepler Discoveries". NASA. 2010-08-26. Retrieved 2010-09-01.
  2. ^ Matthew J. Holman, Daniel C. Fabrycky, Darin Ragozzine, Eric B. Ford, Jason H. Steffen, William F. Welsh, Jack J. Lissauer, David W. Latham, Geoffrey W. Marcy, Lucianne M. Walkowicz, Natalie M. Batalha, Jon M. Jenkins, Jason F. Rowe, William D. Cochran, Francois Fressin, Guillermo Torres, Lars A. Buchhave, Dimitar D. Sasselov, William J. Borucki, David G. Koch, Gibor Basri, Timothy M. Brown, Douglas A. Caldwell, David Charbonneau, Edward W. Dunham, Thomas N. Gautier III, John C. Geary, Ronald L. Gilliland, Michael R. Haas, Steve B. Howell, David R. Ciardi, Michael Endl, Debra Fischer, Gabor Furész, Joel D. Hartman, Howard Isaacson, John A. Johnson, Phillip J. MacQueen, Althea V. Moorhead, Robert C. Morehead, Jerome A. Orosz (2010-08-26). "Kepler-9: A System of Multiple Planets Transiting a Sun-Like Star, Confirmed by Timing Variations". Science. 330: 51. doi:10.1126/science.1195778. {{cite journal}}: |access-date= requires |url= (help)CS1 maint: date and year (link) CS1 maint: multiple names: authors list (link)
  3. ^ "Kepler: About the Mission". NASA. 2011. Retrieved 14 February 2011.
  4. ^ a b "NASA's Kepler Mission Discovers Two Planets Transiting the Same Star". NASA. 26 August 2010. Retrieved 16 February 2011.
  5. ^ "Notes for star Kepler-9". Extrasolar Planets Encyclopaedia. 2010. Retrieved 13 February 2011.
  6. ^ Alan Boyle (26 August 2010). "Planets spotted in changing orbits". Cosmic Log. MSNBC. Retrieved 13 February 2011.
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