A story surfaced over the last few days about a Norwegian skydiver who captured on film a rock flying by just after he deployed his parachute. Actually this happened about two years ago during which time some experts have been examining the evidence and have concluded that what he recorded was a falling meteoroid (it becomes a meteorite once it hits the ground) I was very skeptical about this story and was waiting for the bad astronomer to debunk it but he failed to do so, so I will have to do it for myself. Update 7-4-2013: Phil Plait has now posted a more skeptical followup suggesting similar ideas as written here (and by others elsewhere) which I fully agree with.
The first thing to think about is what are the chances of this happening? Records indicate that only one person has ever been hit by a meteorite. The person was a German boy who was hit by a pea sized meteorite. He was fine. There is also a story of a dog that was hit and vaporized but that story seems to be fake. In addition there are also a handful of cases where cars have been hit by sizable meteorties. At least one, the Peeksill meteorite was verified.
It could be that there are more unrecorded cases but we dont need precise numbers so let’s assume that as many as one car a year is actually hit by a sizable meteorite. There are about a billion cars in the world and most of them are outside exposed to the sky for most of the time. That is a lot of target space. On the other hand there are not too many active skydivers, maybe a hundred thousand at most doing on average a few jumps a year. Let’s be very optimistic and call it a million jumps where an event might have been recorded. A typical descent lasts about 5 minutes which is about a hundred thousandths of a year. You can work it our yourself, with these generous figures and the assumption that a car hit has a similar cross-section to the claimed event, then we expect about one event like this every 100 million years. Yes, coincidences happen, but not something like that.
So what are the alternative theories. One possibility is a planned hoax. It would not be hard to put such a hoax together and there are plenty of hoaxes around, but the motivation to do an elaborate science hoax like this seems lacking. This is much more likely to be a hoax than a meteoroid but I dont think that is the best solution.
The most plausible explanation is the first thing that came into my mind and which others on slashdot have also suggested. It was a small stone that fell out of the parachute. Some people have disputed this because they say it was going too fast. In fact the estimated speed of the falling stone depends on its size or distance from the camera. The meteor experts estimated a large rock of a few kilograms travelling at 300 km/hr, but that is really based on the assumption that it is a meteoroid falling at terminal velocity. If it was a stone that fell out of a parachute it would have to be much smaller and slower and therefore nearer to the camera. This is equally consistent with what was recorded.
The object fell past about four seconds after the canopy opened. This is perfectly in line with expectations if it was on top of the parachute and bounced off. Is it possible for a skydiver to pack a stone in his parachute? Yes certainly as this video shows. A testimony from a skydiver on slashdot confirms that this happens. It is not common but it is common enough to expect someone to capture it on video sooner or later.
Update 8-4-2014: There is now an official explanation along the lines that the stone fell out as the parachute began to open and then passed the camera as the skydiver turned back a few seconds later. This is possible, as is my own similar explanation that it bounced off the top of the parachute and fell back a few seconds later.
Now everybody is saying that it is all fine and they knew all along that it might not have been a meteorite etc. Funny that the video and all the news reports made a very strong case for it being a meteorite and very few of us immediately noticed that this was very unlikely. That is the power of wishful thinking, confirmation bias and the persuasiveness of the authority of a qualified expert . If you were fooled, you will know to be more skeptical next time. In fact if you watch the video again you will see that they considered the possibility that it fell from the chute and that this was the one other possibility that they could not easily dismiss, but they did not say that outright. They just conveniently skipped over it and talked about other theories that could be more easily dismissed. The expert is also reported to have said that the chances of this happening are like winning the lottery three times in a row. That is about right and it is something that never happens but he did not seem to get that. Sometimes people’s desire to be involved in something special are just so strong that their powers of reason are put on hold.
Of course this does not mean that everything a scientist says can be dismissed. It means you have to listen to the reasoning rather than just the claim. It is not always possible to estimate the approximate probability for something being true as it was in this case and not everyone has the right kind of sense to make the right judgement. If that is you then you might want to take note of who quickly saw the truth in this story and who didn’t so you have a better idea of who to trust next time :-)