Today I watched an astonishing video on the web about a meteorite that has almost hit a skydiver who was launching from an airplane in Norway back in 2012. This post is off-topic here but I could not resist to comment on it. To summarize what is seen in the video, a skydiver opens his parachute and just a few seconds after that, a small rock grazes him. In the following, the video shows an interview to a geologist and a 'meteorite expert' who confirm that indeed the most (and apparently only) plausible explanation for what is seen in the video is that the rock was indeed a meteorite. This story rapidly spread across the web and on the press. I am rather skeptical about what is shown in this video for several reasons.
1. Statistical probability of the event.
There are about 20.000-80.000 estimated meteorites with mass > 10 g reaching the Earth’s surface every year. Let’s be generous and use 80.000 meteorites per year. Since land covers 30% of Earth, the skydivers can cross the path of about 24.000 meteorites every year. Since the total land surface is about 150.000.000 sq-km (square kilometers), there is 1 meteorite falling every year over an area of 6.250 sq-km. Now, this meteorite fell within 2 meters of the skydiver (that’s what the geologist says in the video), which means a probability of 1 in 1.6 billions for the two objects to fall within that distance. There are about 3 million launches from skydivers every year and we need that the meteorite and the skydiver fall at almost the same time otherwise they won’t cross. Since the skydiver falls in say, 5 minutes, the probability that any of the skydivers launching every year crosses any of the meteorites within the 5 minutes of the launch is 1 in 2 millions (thanks Phil Uttley for the addition of the time matching probability). Since this can happen any year since skydiving has begun then the probability of this to happen in say, 100 years, is about 1 in 20.000. This is not ridiculously small, but it’s quite small.
Update (06-Apr): some video analysis has shown that the rock must have been about 8-20 cm across and weigh between 1 and 20 kg. It is also proposed that the "meteorite" has passed at about 2.5-6.5 m from the skydiver. A meteorite of a few kg is rather massive and indeed the known mass distribution of meteorites is a power-law. For masses > 1 Kg, as it seems to be suggested, the relation is N proportional to M to the power -1.7. So there are many more small (few grams) meteorites than massive ones.Therefore, the probability calculated above is a tremendously generous one, and a more realistic one can be obtained by using the mass distribution. Considering all this, the final probability that I calculate for the event is between 1 in 5.000.000 and 1 in 10.000.000.000. Now this looks really small to me...
There are however, alternate scenarios which to me appear much more mundane and quite more likely than the meteorite hypothesis. The “stone” falls after about 4-5 seconds since the parachute has fully opened (at least this is my calculation). Say that the 'stone' was hidden in the parachute bag and it is released right before the parachute opens (it seems that this is a common situation that happens to skydivers, provided the stone is a small one. How small? I do not know). The terminal velocity of the stone and the skydiver should be different. Say the stone is a 5*5*5 cm^3 with a mass of about 100 g. Say the skydiver is an 80 kg man. Then the terminal velocity of the skydiver is 55 m/s and the stone is 35 m/s (assuming same drag coefficient). Once the parachute is open and the skydiver is substantially slowed down in its descent, then the stone is about 100 meters behind the skydiver (or more if it hasn’t reached its terminal velocity yet). Therefore in a few seconds the stone reaches and crosses the path of the skydiver who is now gently falling with the open parachute. One can of course change the coefficient/weight/volume used, but the order of magnitude is similar and the result should hold: the small stone and the human body have a small velocity difference. This is compatible with what is observed in the video. Why is this less plausible than the meteorite? Or why can’t it be that the rock is released by one of the companions of the skydivers (by accident or intentionally)? (thanks Tim van Kempen for noticing).
Update (06-Apr): I've read that some people have dismissed the 'rock in the parachute' hypothesis because the falling object had a speed which is too high relative to the skydiver. However, the video clearly shows that the parachute has already unfolded when the stone is seen in the video, so the skydiver was flying at a substantially lower velocity relative to the stone.
2. Suspicious choice of technical experts.
In the video there are two technical experts. One is the geologist Hans Erik Foss Amundsen, whereas the other is the “meteorite expert” Morten Bilet. Since I am not a geologist neither a meteorite expert, I tried to gather more information about them. First, I checked for whom do they work. The video says that the former works for Vestvonna Geophysical, a private company that provides geophysical consultancy and training, whereas the latter works for Geoservice. And what does Geoservice do? Well, I admit I had to translate the page from Norwegian with google but I understand that they trade minerals, meteorites and precious stones. Now, I might have absolutely no doubt about the excellent level of preparation of both experts. I might have also no doubt about their analysis. However, it sounds a bit suspicious to me that such interesting fact is handled by a geologist of a private company and someone who sells meteorites. To be clear: why is there no involvement from a third party institution to give an independent opinion about the robustness of this hypothesis? I also understand that they released the video after two years because they could not find the meteorite and therefore are asking now for help. But some legitimate suspicion can arise, are we sure this rock does really exist and it is not an artifact made to create a big advertisement (of the two companies) gone viral? I’m sorry for being so evil minded but we do remember the 2009 Latvia meteorite hoax, don’t we?
3. Lack of video-editing analysis
Also, the video has not been analyzed by any video-editing expert to my knowledge, and it could well be that inconsistencies might emerge (the trajectory of the stone looks a bit weird to me, too bent like a nice parabola made more for display rather than to match reality) but again, this is speculation and I could easily be wrong but I’ve heard from some experts that at least the rock in the image is suspiciously well defined.
If one wants to be quite extreme it is also possible to imagine a fraud behind all this. Now that we’ve made such an amazing advertisement of this meteorite, we 'find one' and we sell it for an amazing price. I do realize this is rather unlikely (but is the probability of this event to be true really less than 1 in 20.000?), but again when faced with weird hypothesis like a meteorite falling a few meters from a skydiver one should consider all alternative scenarios. Whatever the truth is I feel the press and some scientists at least should be more careful in their approach. Again, maybe I’m wrong and this is really a meteorite (no way! :D) so I will be the one who has resisted the truth at the end. However, this is the typical situation we are all used to nowadays, where the more incredible the story being proposed is, the faster it gets published. It is said that a big claim requires a big proof. But I have the feeling that this is changing rapidly with internet and it’s rather becoming: a big claim requires a big headline, regardless of the proof.
Alessandro Patruno is a researcher at the Leiden University working in the field of compact objects (neutron stars, black holes and white dwarfs) and high energy astrophysics. In his blog Astrosplash Alessandro discusses news in his research field and posts updates on his work.