Researchers simulate lightning formation on an exoplanet for the first time

Lightning is well known on Earth and also occurs elsewhere in our Solar System. But could there also be lightning on planets orbiting entirely different stars?

Researchers from DTU Space and partners have come a step closer to answering that question. For the first time, they have used computer models to simulate how the initial stages of lightning could develop in the atmosphere of an exoplanet.

Using data from the James Webb Space Telescope, they studied K2-18b, which is located around 124 light-years from Earth. It is an exoplanet, meaning a planet that orbits a star other than the Sun.

”Of course, we cannot see a lightning flash on a planet 124 light-years away. But observations from James Webb can provide us with information about the atmosphere and allow us to simulate whether the physical processes that can lead to lightning can take place. And our results show that the process can indeed occur in the atmospheres we have studied,” says Elloise Fangel-Lloyd, who is a scientist at the Danish Meteorological Institute (DMI) and carried out the work as a PhD student at DTU Space.

She is the first author of an article presenting the results, which has just been published in the Nature journal Scientific Reports .

Small electrical discharges could be the beginnings of lightning

The researchers simulated so-called streamers. 

These are small electrical discharges that are typically among the first stages in the development of lightning. The researchers have therefore not simulated an entire lightning flash, but rather the process that can help initiate one.

The simulations show that the discharges that can initiate lightning can occur in all three possible compositions of the exoplanet’s atmosphere investigated by the researchers.

Lightning may form more easily there than on Earth

The calculations also show that electrical breakdown in the modelled atmospheres requires only around half the electric field strength needed on Earth.

The results therefore suggest that the atmosphere of K2-18b may be more conducive to lightning formation than Earth’s atmosphere.

”An electric field exerts a force on electrically charged particles. If the field becomes sufficiently strong, the gas in the atmosphere can become ionised, allowing the electrical discharges that can lead to lightning to begin developing,” says Christoph Köhn, Senior Researcher in the Astrophysics and Atmospheric Physics Division at DTU Space and co-author of the study.

”What is particularly interesting here is that we can use our knowledge of electrical discharges on Earth to investigate what may be happening in the atmosphere of a planet many light-years away”.

The researchers’ simulations also show that the amount of water vapour in an atmosphere affects how easily the process leading to lightning can begin.

Once lightning has formed, it can affect the chemistry of an atmosphere and may therefore have implications for potential life and habitability, both on a planet such as K2-18b and on other exoplanets.