HAT-P-11b

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 122 light-years (37 pc) away in the constellation of Cygnus, orbiting the 10th apparent magnitude K-type star HAT-P-11. This planet was the smallest transiting planet known when first discovered, with a radius about 5 times that of Earth; but is more massive than Gliese 436 b at a true mass of 26 times that of Earth. 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.

The HAT-P-11 system was within the field of view of the Kepler spacecraft.

Its radial velocity is drifting and this may be a result of an as-yet-undiscovered planet in the system.

The planet fits models for 90% heavy elements. Expected temperature is 878 ± 15K. 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. 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 lighting 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 thunder storms on Earth or Saturn would have produced <1% of the strength of the signal coming from the planet.