In 2013, Corrado Cimarelli, a volcanologist at the LMU University of Munich, re-created volcanic lightning in his lab by pushing dust into a small glass tube at extremely high pressure. He took slow-motion footage, elucidating the small physics of the lab-made lightning. What flashed on the screen was a spray of black grains, released from a pressurized tube like water from a fire hose, with little bursts of electricity — veins of white just centimeters long.
Adding laboratory data like this to Drift, Helling found that lightning could happen on both gaseous exoplanets and brown dwarfs — in bolts as large as the Empire State Building. Cimarelli’s lab-made lightning, using the same kinds of materials as the gemstone clouds, suggests that streamers are most likely to occur when dust is pelted together quickly. This suggests that lightning might be most likely on planets with plenty of light and radiation from a host star to create wind.
Atmospheres of Electricity
With gemstone clouds — and their attendant lightning — more common than she could have imagined, Helling knew for certain that alien lightning could flash in atmospheres all across our universe. But how could she ever tell? These worlds are too far away to see directly. It’s not simply a matter of sending a space probe or pointing Hubble toward the nearest exoplanet.
To figure out how to look for actual proof of extrasolar lightning, Helling combined Drift’s code with another atmospheric model called Phoenix, created by astrophysicists at the University of Hamburg. Phoenix placed the individual clouds that Drift could model into the context of a whole planet. Using results from Drift-Phoenix, Helling made the first steps toward figuring out exactly what telltale elements lightning would leave behind in a world’s atmosphere. It turns out that where there is lightning — whether on Earth or worlds away — there is slightly more methane and carbon monoxide.
Today’s observatories capture just the big features of an atmosphere; they aren’t yet sensitive enough to pick up the trace amounts of the chemicals lightning would leave behind on other worlds. Fortunately, more powerful views of exoplanets are on the horizon when the James Webb Space Telescope launches in 2018. The unparalleled view it will provide to astronomers could include a glimpse of a stormy world. But that’s not all that finding lightning’s signature would mean.
More strikingly, lightning may also be a key catalyst for spawning life. An experiment by biochemists Stanley Miller and Harold Urey over 60 years ago established that, if you take the wet, disorganized ingredients found on early Earth — water, ammonia, methane, hydrogen — and add an electric spark, you get amino acids, the building blocks of all known life.
That doesn’t mean that lightning equals life. Far from it. Liquids are rare, and astrobiologists think that gaseous planets, the kind that Helling has studied so far, aren’t as likely to harbor life as Earth-like rocky ones. But habitable planets are a tantalizing prospect, one that Helling references in the very name of her LEAP project. In the search for life, lightning could be a key clue.
We might not ever be able to see extraterrestrial lightning firsthand. But how electrifying to know that where there’s lightning, there just might be something to stare back up at it.