Kepler-22b
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Kepler-22b is the first confirmed extrasolar planet found by NASA's Kepler Space Telescope to orbit within the habitable zone of a Sun-like star.[1][2] Kepler-22b, a possible super-Earth, is 587 light years away from Earth, in orbit around the G-type star Kepler-22.[1][2]
Discovery
The discovery was announced December 5, 2011.[2] The planet was originally discovered on Kepler's third day of science operations in mid-2009. The third transit was detected in late 2010. Additional confirmation data was provided by the Spitzer Space Telescope and ground-based observations.
Composition and structure
Kepler-22b's radius is roughly 2.4 times the radius of Earth, or about half that of Neptune. Its mass and surface composition remain unknown,[2][1] with only some very rough estimates established: It has less than 124 Earth masses at the 3 sigma confidence limit, and less than 36 Earth masses at 1 sigma confidence.[3]
It has been estimated that it is probably a "Neptunian" (i.e. mass similar to Neptune[4]) planet with a mass of ~35 Earth masses, but in the "best case" it could be an ocean world with only some 10 Earth masses.[5]
Depending on its actual mass, the planet could be rocky, liquid, or gaseous.[2]
Since it is substantially larger than Earth, it is likely to have a different composition than Earth. If it is mostly ocean with a small rocky core, Natalie Batalha, one of the scientists on the project, speculated "it's not beyond the realm of possibility that life could exist in such an ocean."[6] This possibility of life has spurred SETI to perform research on top candidates for extraterrestrial intelligence.[7]
Orbit
The only parameters of the planet's orbit that are currently available are its period which is about two hundred and ninety days, and its inclination, which is such that it transits the disk of its star as seen from Earth.
No information is available about the shape of the planet's orbit. Many extrasolar planets are known to move in highly elliptical orbits. We only know that the semi-major axis of its orbit is within the habitable zone of an Earth mass planet. If Kepler-22b has a highly elongated orbit it may well only spend a small fraction of its time within this habitable zone.
Surface temperature and composition
| Temperature comparisons |
Venus | Earth | Kepler 22b | Mars |
| Global Equilibrium Temperature |
307 K 34 °C 93 °F |
255 K −18 °C −0.4 °F |
262 K −11 °C 22.2 °F |
206 K −67 °C −88.6 °F |
| + Venus' GHG effect |
737 K 464 °C 867 °F |
|||
| + Earth's GHG effect |
288 K 15 °C 59 °F |
295 K 22 °C 71.6 °F |
||
| + Mars' GHG effect |
210 K −63 °C −81 °F | |||
| Tidally locked |
Almost | No | ?? | No |
| Global Bond Albedo |
0.9 | 0.29 | ?? | 0.25 |
| Refs.[8] [9][10] | ||||
The average distance from Kepler-22b to its host star Kepler-22 is about 15% less than the distance from Earth to the Sun[11] but the luminosity (light output) of Kepler-22 is about 25% less than that of the Sun.[2] This combination of a shorter average distance from the star and a lower stellar luminosity are consistent with a moderate surface temperature at that distance.
If the planet is found to move in an elliptical orbit, its surface temperature will vary from a higher temperature when close to Kepler-22 to lower when further away. If the orbit is indeed highly elliptical, then the temperature variance range will be extreme.
Scientists estimate that in the absence of an atmosphere, the equilibrium temperature would be approximately -11°C. If the atmosphere provides a greenhouse effect similar in magnitude to the one on Earth, the planet would have an average surface temperature of 22 °C (72°F).[2][1]
Scientists may estimate better with temperature and surface composition when the Cygnus constellation is in better view in the summer transits.
See also
References
- ^ a b c d "NASA - NASA's Kepler Confirms Its First Planet in Habitable Zone of Sun-like Star". NASA Press Release. Retrieved 6 December 2011.
- ^ a b c d e f g "BBC News - Kepler 22-b: Earth-like planet confirmed". BBC Online. 5 December 2011. Retrieved 6 December 2011.
- ^ http://arxiv.org/abs/1112.1640
- ^ http://phl.upr.edu/projects/habitable-exoplanets-catalog/methods gives the defintion of "Neptunian", among others.
- ^ Abel Mendez Torres (2011-12-08). "Updates on Exoplanets during the First Kepler Science Conference". Planetary Habitability Laboratory at UPR Arecibo.
- ^ Borenstein, Seth (5 December 2011). "Planet in sweet spot of Goldilocks zone for life". Associated Press. Retrieved 6 December 2011.
- ^ Ian O'Neill (2011-12-05). "SETI to Hunt for Aliens on Kepler's Worlds". Discovery News.
- ^ "NASA, Mars: Facts & Figures". Retrieved 2010-01-28.
- ^ Mallama, A.; Wang, D.; Howard, R.A. (2006). "Venus phase function and forward scattering from H2SO4". Icarus. 182 (1): 10–22. Bibcode:2006Icar..182...10M. doi:10.1016/j.icarus.2005.12.014.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Mallama, A. (2007). "The magnitude and albedo of Mars". Icarus. 192 (2): 404–416. Bibcode:2007Icar..192..404M. doi:10.1016/j.icarus.2007.07.011.
- ^ Cite error: The named reference
ExtrasolardatabaseKepler-22bwas invoked but never defined (see the help page).
External links
- "NASA Telescope Confirms Alien Planet in Habitable Zone" (Space.com)
- "Kepler 22-b: Earth-like planet confirmed" (BBC)
- "NASA's Kepler Confirms Its First Planet In Habitable Zone" (NASA)
- "Kepler discoveries: Kepler-22b: 'a yearly orbit of 289 days'" (NASA)
- "View of Kepler 22-b Sky Location" (Worldwide Telescope)
- "The Habitable Exoplanets Catalog" (PHL/UPR Arecibo)
- Preprint of discovery paper - Accepted to Astrophysical Journal
