HAT-P-11b

HAT-P-11b / Kepler-3b

Size comparison of Neptune with HAT-P-11b (gray).
Discovery[1]
Discovered by	Bakos et al.
Discovery site	Cambridge, Massachusetts
Discovery date	2 January 2009
Detection method	Transit (HATNet)
Orbital characteristics
Apastron	0.0637+0.0020 −0.0019 AU
Periastron	0.0413+0.0018 −0.0019 AU
Semi-major axis	0.05254+0.00064 −0.00066 AU
Eccentricity	0.218+0.034 −0.031[2]
Orbital period (sidereal)	4.887802443+0.000000034 −0.000000030[3] d
Inclination	89.05+0.15 −0.09[3]
Time of periastron	2454957.15+0.17 −0.20[2]
Argument of periastron	19+14 −16[2]
Semi-amplitude	10.42+0.64 −0.66[2]
Star	HAT-P-11
Physical characteristics
Mean radius	4.36±0.06[3] REarth
Mass	23.4±1.5[2] MEarth
Mean density	1,440 kg/m3 (2,430 lb/cu yd)
Surface gravity	1.20 g

HAT-P-11b (or Kepler-3b) is an extrasolar planet orbiting the star HAT-P-11. It was discovered by the HATNet Project team in 2009 using the transit method, and submitted for publication on 2 January 2009.

This planet is located approximately 123 light-years (38 pc) distant from Earth.^[4]

Discovery[]

The HATNet Project team initially detected the transits of HAT-P-11b from analysis of 11470 images, taken in 2004 and 2005, by the HAT-6 and HAT-9 telescopes. The planet was confirmed using 50 radial velocity measurements taken with the HIRES radial velocity spectrometer at W. M. Keck Observatory.^[1]

At the time of its discovery HAT-P-11b was the smallest radius transiting extrasolar planet discovered by a ground based transit search and was also one of three previously known transiting planets within the initial field of view of the Kepler spacecraft.^[1]

There was a linear trend in the radial velocities indicating the possibility of another planet in the system.^[1] This planet, HAT-P-11c, was confirmed in 2018.^[2]

Characteristics[]

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 103⁺²⁶
₋₁₀°.^[5] degrees relative to its star's rotation.^[6][7]

The planet fits models for 90% heavy elements^{[clarification needed]}. Expected temperature is 878 ± 15K.^[1] 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]

In December 2021 a magnetosphere was discovered in HAT-P-11b, the first ever in any exoplanet.^[11][12]

See also[]

• Gliese 436 b
• HATNet Project
• HAT-P-7b
• Kepler Mission

References[]

External links[]

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

• "HAT-P-11 b". Exoplanets. Archived from the original on 11 May 2012. Retrieved 1 February 2009.

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