A rare, ethereal lightning flash was captured by astronauts aboard the International Space Station on March 25th. The ISS was passing over the north-eastern United States when astronaut Don Pettit noticed a bright pulse of light in the distance below. I saw this huge burst of light off to my right, says Pettit, who has taken photos from orbit before but never seen anything like this. It’s so bright it just completely fills up your whole field of view. After taking several more shots and examining them later, he determined that what he had witnessed was likely a natural phenomenon called ball lightning. While nothing like this has ever been reported before by astronauts, the phenomenon is often discussed in scientific circles, says Pettit.
Ball lightning is virtually impossible to study on Earth, because mere seconds after forming it either explodes or evaporates. Lightning strikes create charged plasma spheres that hover for milliseconds before either disappearing with a pop or exploding like firecrackers. Pettit’s photos appear to depict very stable spheres that could persist long enough to be studied in detail, says physicist and ball lightning expert Oleg Prezhdo of the University of Michigan. However, finding out more will still require a microgravity platform such as the ISS. There is no chance whatsoever I would see this on Earth, says Pettit.
I just happened to be at the right place, at the right time, for this rare phenomenon but I also had a camera ready.
Ball lightning has been reported throughout history, but only recently have scientists entertained the notion that it might be physically real. Lightning itself is difficult to study because the temperatures are high and discharges happen very quickly. These spheres of plasma could resolve some of the questions surrounding ball lightning, says Prezhdo. The ISS orbits around 400 kilometers above Earth’s surface and its crew performs around three space walks a week, so it is likely that astronauts will be able to catch more of these unusual phenomena in the future.
Figure 1. The International Space Station on March 25th, 2011 at 18:25 UTC, moments before the appearance of ball lightning.
Figure 2. The ISS was passing over an area that is prone to tornadoes when Don Pettit saw what appeared to be a plasma sphere forming in the distance below the station’s horizon.
Figure 3. A closeup of the ball lightning captured by Don Pettit in his original photograph. The ISS was moving at around 7 km/s when this photo was taken, meaning that the exposure lasted for only five milliseconds. At this moment in its flight path, it would have been separated from the anomaly by about 5.5 kilometers in the fore-to-aft direction east-west.
Figure 4. The ball lightning appears only in the original, uncropped photo taken by Don Pettit; it is not present in any of his frame grabs or crops shown here. This means that the anomaly was within five meters of the camera and persisted for at least 10 milliseconds, probably much longer.
Figure 5. When Don Pettit examined his photos later, he noticed a bright pulse of light in the distance below the ISS. The photo was taken through a 400 mm lens with an exposure time of 1/6th of a second, meaning that the features in the image are about 1/30th of an arc-minute in size. The ISS was at this point between 350 km and 400 km, well beyond any sensible atmosphere.
Figure 6. This map shows the flight path for that day’s activities, showing the location of Don Pettit when he took his photograph (red cross), as well as the location of a possible origin for his anomaly red plus.