Kepler Planet Lightning Storms Detected: “Millions Times More Powerful Than Those on Earth –The Source of Otherworldly Radio Signals”

 

Lightning-optical

Lightning storms millions of times more powerful than those on Earth could be responsible for unexplained radio signals from planets orbiting other stars. In 2009, radio telescopes picked up faint emissions from the HAT-P-11 star system, about 122 light years away. The signal stopped when HAT-P-11b, a “hot Neptune” discovered by NASA’s Kepler Mission in 2009 orbiting HAT-P-11, passed behind the star, so astronomers decided the radio waves must have come from the planet – if they were ever really there, that is. The signal didn’t reappear in 2010, when HAT-P11b transited its star again, and astronomers still aren’t sure it was real.


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 kilometer per hour would explain the observed radio signal on HAT-P-11b. This storm would have been so enormous that the largest electrical storms on Earth or Saturn would have produced <1% of the strength of the signal coming from the planet.

(In 2009 lightning the longest-lasting storm in our solar system some 3,000 kilometers wide was detected on Saturn shown below. The lightning flashes are 10,000 times stronger than those on Earth).

 

Saturn-storm

Assuming the exoplanet’s lightning is similar to Earth’s, it would take over 3 million lightning flashes per square kilometer every hour to produce the radio waves that reached Earth in 2009. Then again, if the lightning on HAT-P-11b is as powerful as the lightning on Saturn, for instance, the storm would only need 53 flashes per square kilometer every hour.

“We assumed that this signal was real and was coming from the planet,” said Gabriella Hodosán, with the Life, Electricity, Atmosphere, Planets (LEAP) Project. “Then we asked the question: could such a radio signal be produced by lightning in the planet’s atmosphere, and if yes, how many lightning flashes would be needed for it?”

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 53 lightning flashes of Saturnian lightning-strength in a km2 per hour would explain the observed radio signal on HAT-P-11b.

“Imagine the biggest lightning storm you’ve ever been caught in,” said Paul Rimmer, LEAP researcher and co-author of the paper. “Now imagine that this storm is happening everywhere over the surface of the planet. A storm like that would produce a radio signal approaching 1% the strength of the signal that was observed in 2009 on the exoplanet HAT-P-11b.”

Miss Hodosán continued: “Studies conducted by our group have also shown that exoplanets orbiting really close to their host star have very dynamic atmospheres, meaning that they change continuously, producing clouds of different sizes, even whole cloud systems, all over the planet’s surface. HAT-P-11b, being so close to the star, is likely to have such a dynamic, cloudy atmosphere, which would allow the formations of huge thunderclouds, focusing the lightning activity to a certain regime of the planetary surface, such as the face of the planet, which was observed in 2009.”

The team hoped that this intensity of lightning could be observed with optical telescopes but were thwarted by the powerful light emissions from the star around which HAT-P-11b orbits.

The process of lightning discharges involves plasma processes at very high temperatures and the release of a large amount of energy. This results in chemical reactions in the atmosphere that otherwise would not occur. These reactions produce molecules that can be used as lighting tracers.

The team considered whether such enormous thunderstorm clouds produce these tracer molecules, which then could be observed by Earth-telescopes, and suggested hydrogen cyanide (HCN) to be such a potential fingerprint of lightning. This molecule could be observable in the infrared spectral band, even years after the huge storm on HAT-P-11b would have occurred.

“With all necessary caution, linking extraterrestrial lightning and radio emissions will open a new window to prove the presence of atmospheres and of clouds on extrasolar planets, both being essential for the existence of life as we know it,” said Christiane Helling, the LEAP Project principal investigator, said:

The Daily Galaxy via University of St Andrews School of Physics and Astronomy

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