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HAT-P-11b / Kepler-3b
Exoplanet List of exoplanets
Exoplanet Comparison HAT-P-11 b.png
Size comparison of Neptune with HAT-P-11b (gray).
Parent star
Star HAT-P-11
Constellation Cygnus[1]
Right ascension (α) 19h 50m 50.2475s[2]
Declination (δ) +48° 04′ 51.0973″[2]
Apparent magnitude (mV) 9.59[3]
Distance123.3±0.1[2] ly
(37.81±0.03[2] pc)
Spectral type K4[3]
Orbital elements
Semi-major axis(a) 0.05254+0.00064
[4] AU
Periastron (q) 0.0413+0.0018
[4] AU
Apastron (Q) 0.0637+0.0020
[4] AU
Eccentricity (e) 0.218+0.034
Orbital period(P) 4.887802443+0.000000034
[5] d
Inclination (i) 89.05+0.15
Argument of
(ω) 19+14
Time of periastron (T0) 2454957.15+0.17
[4] JD
Time of transit (Tt) 2454957.8132067+0.0000053
[5] JD
Semi-amplitude (K) 10.42+0.64
[4] m/s
Physical characteristics
Mass(m)23.4±1.5[4] M
Radius(r)4.36±0.06[5] R
Density(ρ)1440 kg m−3
Surface gravity(g)1.20 g
Discovery information
Discovery date 2 January 2009
Discoverer(s) Bakos et al.
Discovery method Transit (HATNet)
Other detection methods Radial velocity
Discovery site Cambridge, Massachusetts
Discovery status Published
Database references
Extrasolar Planets
Exoplanet Archivedata
Open Exoplanet Cataloguedata

HAT-P-11b (or Kepler-3b) is an extrasolar planet. Its discovery was based on the transit method, and submitted for publication on 2 January 2009.

This planet is located approximately 123 light-years (38 pc) away[2] in the constellation of Cygnus, orbiting the 10th apparent magnitude K-type star HAT-P-11. At the time of its discovery this planet was the smallest radius transiting extrasolar planet discovered with a ground based telescope, with a radius about 5 times that of Earth;[3] but is more massive than Gliese 436 b at a true mass of 26 times that of Earth.


HAT-P-11b was discovered by the HATNet Project team lead by Gáspár Bakos in 2009 and is within the field of view of the Kepler spacecraft.[3]

There was a linear trend in the radial velocities indicating the possibility of another planet in the system.[3] This planet, HAT-P-11c, was confirmed in 2018.[4]


This planet orbits about the same distance from the star as 51 Pegasi b is from 51 Pegasi, typical of transiting planets. However, the orbit of this planet is eccentric, at around 0.198, unusually high for hot Neptunes. HAT-P-11b's orbit is also highly inclined, with a tilt of approximately 103 degrees relative to its star's rotation.[6][7]

The planet fits models for 90% heavy elements[clarification needed]. Expected temperature is 878 ± 15K.[3] Actual temperature must await calculations of secondary transit.

On 24 September 2014, NASA reported that HAT-P-11b is the first Neptune-sized exoplanet known to have a relatively cloud-free atmosphere and, as well, the first time molecules, namely water vapor, of any kind have been found on such a relatively small exoplanet.[8] In 2009 French astronomers observed what was thought to be a weak radio signal coming from the exoplanet. In 2016 scientists from the University of St Andrews set out to solve the mystery. They assumed that the signal was real and was coming from the planet and investigated whether it can be produced by lightning on HAT-P-11b. Assuming that the underlying physics of lightning is the same for all Solar System planets, like Earth and Saturn, as well as on HAT-P-11b, the researchers found that 3.8 × 10^6 lightning flashes of Saturnian lightning-strength in a square kilometre per hour would explain the observed radio signal on HAT-P-11b. This storm would have been so enormous that the largest thunderstorms on Earth or Saturn would have produced <1% of the strength of the signal coming from the planet.[9][10]

See also[edit]


  1. ^ Roman, Nancy G. (1987). "Identification of a Constellation From a Position". Publications of the Astronomical Society of the Pacific. 99 (617): 695–699. Bibcode:1987PASP...99..695R. doi:10.1086/132034. Vizier query form
  2. ^ a b c d e Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  3. ^ a b c d e f Bakos, G. Á.; et al. (2010). "HAT-P-11b: A Super-Neptune Planet Transiting a Bright K Star in the Kepler Field". The Astrophysical Journal. 710 (2): 1724–1745. arXiv:0901.0282. Bibcode:2010ApJ...710.1724B. doi:10.1088/0004-637X/710/2/1724.
  4. ^ a b c d e f g h i Yee, Samuel W.; et al. (2018). "HAT-P-11: Discovery of a Second Planet and a Clue to Understanding Exoplanet Obliquities". The Astronomical Journal. 155 (6). 255. arXiv:1805.09352. Bibcode:2018AJ....155..255Y. doi:10.3847/1538-3881/aabfec.
  5. ^ a b c d Huber, K. F.; Czesla, S.; Schmitt, J. H. M. M. (2017). "Discovery of the secondary eclipse of HAT-P-11 b". Astronomy and Astrophysics. 597. A113. arXiv:1611.00153. Bibcode:2017A&A...597A.113H. doi:10.1051/0004-6361/201629699.
  6. ^ "Inclined Orbits Prevail in Exoplanetary Systems". 12 January 2011.
  7. ^ Roberto Sanchis-Ojeda; Josh N. Winn; Daniel C. Fabrycky (2012). "Starspots and spin-orbit alignment for Kepler cool host stars". Astronomische Nachrichten. 334: 180–183. arXiv:1211.2002. Bibcode:2013AN....334..180S. doi:10.1002/asna.201211765.
  8. ^ Clavin, Whitney; Chou, Felicia; Weaver, Donna; Villard; Johnson, Michele (24 September 2014). "NASA Telescopes Find Clear Skies and Water Vapor on Exoplanet". NASA. Retrieved 24 September 2014.
  9. ^ "Could ferocious lightning storms beam radio signals to Earth?". 26 April 2016.
  10. ^ "Lightning as a possible source of the radio emission on HAT-P-11b". ADS. arXiv:1604.07406. Bibcode:2016MNRAS.461.1222H. doi:10.1093/mnras/stw977.

External links[edit]

Media related to HAT-P-11b at Wikimedia Commons

Coordinates: Sky map 19h 50m 50.2469s, +48° 04′ 51.085″