On 17th June 2012 Anders Helstrup was skydiving using his wingsuit. In one of the jumps something very unexpected happened, and his two helmet mounted camera confirmed it: A rock fell from the sky, just past Anders towards the ground. There was no one or nothing above him that could have dropped it. He contacted some geologists and meteorite experts, and an investigation was under way. The videos were analysed and the area was searched, but the only conclusive proof for a meteorite, the meteorite itself, was not found. We know that a few meteorites fall over populated areas on Earth every day, often unnoticed. Relatively slow fireballs may be fainter than the full moon and still drop meteorites, and they may be very hard to see in the glare of the sun or behind clouds. A sonic boom could be mistaken for thunder or human activity. Considered the many million cameras now in use worldwide, one is occasionally bound to capture something extremely unlikely. So however unlikely a near hit of a meteorite is, it is certainly a possibility. Due to its extreme low probability, it’s naturally the last pick of all the thinkable actual possibilities. A number of scenarios were considered, but all apparently failed to explain what is seen in the video. We were left with scenarios that we were unable to find possible solutions for against something that fits but is extremely improbable, though possible. We seemed to get no further, and we decided to go public with what we had and at the same time invite anyone to have a go at the puzzle. The story was announced here on the web pages of the Norwegian Meteor Network, where we expressed our hope that it would go viral and scrutinised for something that we might have missed, and the result was beyond our expectations.
Let’s get straight to the conclusion. The good news: The crowdsourcing was a success. The bad news: There is no meteorite. It was a rock accidentally packed into the parachute. But how? It was a scenario considered from the beginning and it kept haunting us until the time we went public, as Anders told in the TV interview. Despite much effort, we saw no way to reconcile this scenario with the videos. The rock was clearly falling from well above the parachute. It did not seem to accelerate as if released from the parachute. It fell several seconds after the parachute had fully deployed. So what did we miss? The riddle quickly cracked under the pressure of the numerous fresh eyes now looking at the problem. Several people were able to point out the important clue that made the pieces fall into place.
We think we can reconstruct what happened: A pebble, a few cm in size at most, was accidentally caught inside the parachute at the landing site after the previous jump. Then the parachute was packed on a clean floor and the pebble was not noticed. Then Anders made the jump with the stowaway. This is a wingsuit dive and he’s travelling fast northwards at an downward angle of approximately 40 degrees. When he releases the parachute, the wind catches it and it shoots out to the south of him. The parachute is held back by the cords, but the pebble is not. The pebble is now increasingly getting further south and further above Anders. However, the parachute then slows Anders down, he makes a 250 degree clockwise rotation and at this moment the pebble happens overtake him. It had now been falling for a few seconds and was no longer accelerating much.
The exact details are somewhat unclear, but it doesn’t matter. It has been demonstrated that a pebble brought by the parachute can appear falling rapidly, not accelerating much, above the parachute a few seconds later. It doesn’t matter that a long chain of events that usually don’t happen is required when the alternative hypothesis is a passing meteorite. All of these events were orders of magnitude more probable and the presence of Occam is quickly felt. The pebble was shot out and then Anders was overtaken by it. This is the possibility that we had completely missed all this time. An adaptation of Linus’s law, after the creator of Linux, applies: Given enough eyeballs, all mysteries are shallow.
Are we disappointed? The ultimate prize would be a meteorite, but frankly, we had been faced with a mystery for nearly two years, we went public, and thanks to an incredible crowdsourcing effort the mystery was solved beyond reasonable doubt in just a few days. That’s amazing.
We are tremendously thankful for all those who engaged in this. The creativity has been outstanding and much appreciated. Special thanks go to Dr. Phil Metzger for his ballistics analysis.
It turns out that during the many hours of calculating the path of the object we were closer to the answer than we were aware of. Ironically, «calculus» is the Latin word for «pebble».