2014-04-04

Why the Norwegian "Skydiving Meteorite" came from Earth, not from Space

This was one of those mornings when instead of getting to my work I got ghastly distracted by some incredible news: A Norwegian skydiver has filmed how he almost got hit by a meteorite! Really sensational, if true. My first thought: Is this a joke, a hoax? It didn't look that way. The video came via a respected Norwegian broadcasting corporation (which in itself does not mean much these days) and looks professionally made. Look for yourself, if you haven't already. (The meteorite claim has been retracted by the Norwegians, scroll down for updates!)

Here's the interesting part in slow motion:


 This collage was taken from the video and is used here with permission:

Is this a meteorite in Dark Flight? Photo: Anders Helstrup / Dark Flight, photomontage: Hans Erik Foss Amundsen
Later I found a blog of a Norwegian Meteoritic Society explaining the incident in detail: It therefore happened almost two years ago, on 17th June 2012 near Østre Æra airstrip close to the town Rena in Norway. There have been extensive searches for the supposed meteorite on the ground, all without success. The case was kept secret (to keep professional and amateur meteorite hunters away, I guess) and is assured to be definitely no hoax. Ok, let's believe that.    
 
Looks like a real conundrum. Well, not really.

At first glance, it could actually be true. The hollywoodesque believe that meteorites fall burning and glowing to the ground is wrong - the visible meteor (the shooting star, that's what you see) terminates in the high atmosphere. For the last kilometers, meteorites fall like simple rocks to the ground. This is called "Dark Flight" and is very well explained in the Norwegian blog. No one has ever seen a meteorite in Dark Flight - and neither has the skydiver.

Why I'm so sure about that?

Because there are missing all of the essentials of a meteorite fall: no reports of a fireball, no sound, no seismic recordings. A meteorite of the size of the object in the video (which is unknown but can be assumed to be some centimeters perhaps) would not fall completely unnoticed.

More doubts swashed in. A respected meteorite expert informed that the object in the video looks much too bright to be a meteorite. Real meteorites usually have a deep black crust, a result of the initial fireball. This crust reflects very few light (it has a very low albedo) and thus should look much darker than the stone in the video, which reminded more like a mundane granite rock from Earth.

But how could a rock from Earth get up there falling onto the skydiver? Assuming there was no one else playing bad tricks, and the Norwegians tell the truth (which I believe that they do) the explanation is surprisingly simple: It was carried up there by themselves, unintentionally, in their own parachutes. I'm not a skydiver (and will never be) but others are, and one of them told that this scenario is far from being unlikely.

So how can we decide which story is true? How can one say with certainty that it was a meteorite or a mundane rock? Some smart people may now go into their math, calculate, triangulate, estimate descent angles and speeds. I'm not that smart and a bit lazy, too. I will employ some simple Logic instead, and put together those thoughts some clever people in my Twitter timeline and other social media deliver me.

We have two contradicting hypotheses: H1: The rock in the video is a meteorite from space, entering the atmosphere with several dozens kilometers per second. H2: The rock in the video is a common stone from Earth, that was entangled in the skydiver's canopy or parachute and just fell out when it opened. Lets see what speaks for each hypothesis.

H1: The rock was a meteorite.

1) If the rock was a meteorite, then there must have been a great fireball shortly before the event. If there was no bright flash visible shortly before the event, it can't have been a meteorite. Was there a bright fireball? NO

2) If the rock was a meteorite, then there must have been a loud sonic boom. If there was no audible roar or thunder shortly before the event, it's very unlikely to have been a meteorite. Was there a loud roar or thunder? NO

3) If the rock was a meteorite, then there should have been a fresh meteorite find in the area. A thorough search should have encountered it. Has there been a meteorite find? NO - after almost two years of searching.

4) If the rock was a meteorite, then it should look similar to typical meteorites, e.g. it's albedo should be very low, reflecting almost no light. Does it look like it had a very low albedo? NO
 
5) The plausibility of this hypothesis would rise significantly if there had been any similar incidents of meteors visible in dark flight (by other parachutists, aircraft pilots, etc.) in the past. Are there reports of similar incidents? NO - not to my knowledge.

That's five NOs, doesn't look too good for our meteorite, does it? Ok - a meteorite on the ground can be overlooked, a sonic boom overheard, a flash could have been obscured by clouds and invisible in daylight. The meteorite might have looked different on the tape than typical ones in a museum. But at least one of the NOs should be a Yes, to put any believe in this hypothesis, don't you think?

So let's look at H2: The rock was a mundane stone entangled in the parachute.

1) A normal rock lifted up by the skydiver himself would not have entered the atmosphere with speeds of kilometers per second, hence requires no bright meteor fireball. CHECK

2) A normal rock lifted up by the skydiver himself would not have entered the atmosphere with speeds of kilometers per second, hence requires no loud roar, thunder or boom. CHECK

3) A normal rock would not yield any positive find of a fresh meteorite in the area, no matter how thorough the search - because it would in no way differ from all the other rocks on Earth. CHECK

4) A normal rock would look like a normal rock on the video, e.g. show some shiny surfaces if it was a common piece of granite. CHECK

5) The plausibility of the object being a normal rock would rise significantly if there were reports of similar incidents of rocks falling out of parachutes or canopies. Are there reports of similar incidents? CHECK

Do with this whatever you like. I'll take Ockham's Razor and slice through it like a hot knife through butter: This rock came from Earth, not from Space. 

I am well aware that these considerations do not prove anything nor rule out the possibility that it indeed was a meteorite. But for me they do suffice. If you do think that I'm wrong, then go out there and find the meteorite. Turn any of the red "NOs" into a green "CHECK". As long as you can't, the case is closed for me.

Really, do it. I like to be proven wrong.  But remember: Extraordinary claims require extraordinary evidence. So far I haven't seen any evidence at all that supports the meteorite hypothesis!

It's not wise to discard a story just because it is very unlikely, but it would be foolish to prefer the unlikely explanation to a very much more probable one. With the thoughts outlined here, I wouldn't even have bothered to search for that stone.

***UPDATE: Marco Langbroek informed me of a second object, falling almost parallel to the first, somewhat more distant. Now what is that supposed to mean? Meteorites fall in groups if the initial body disintegrated in the fireball, but since there was no fireball (to our knowledge) is it best to assume the parachutes carried more than one stone?

A second object (arrow) is visible in the video shortly before the alleged "meteorite". Click to embiggen. Hat tip to Marco Langbroek.
UPDATE 2: Phil Plait leans more towards the meteorite hypothesis.

UPDATE 3: Alessandro Patruno in turn tends more to the stone-from-parachute-version. If you still don't believe a small stone can be entangled in a parachute canopy, read his blog and the comments to it, or watch this!

UPDATE 4: Philip Metzger has performed another analysis of the stone's trajectory:

"Here is my conclusion: the ballistics are consistent with it being a small piece of gravel that came out of his parachute pack and flew past at close distance. The ballistics are also consistent with it being a large meteorite that flew past at about 12 to 18 meters distance. It could be either one, but IMO not anything in between. Based on the odds of parachute packing debris (common) versus meteorite personal flybys (extremely rare), and based on the timing (right after he opened his parachute), I vote for the parachute debris as the more likely."

Just what I think...

UPDATE 5: After taking into account more detailed analyses, Phil Plait reconsiders and no longer dismisses the rock-in-parachute theory. In fact, he says that it's the more probable explanation.

At the end of the day, it becomes clear that we'll probably never really know what the stone in the video was. But given the fact that nothing really supports the meteorite-hypothesis except our desire to have witnessed something extraordinary, the stone-in-parachute is the explanation we should settle with for now. Anything else would be unsound at this time.

UPDATE 6: Finally, the Norwegians have retracted the claim of a meteorite - and thank the international community for helping to solve this mystery!

(Disclaimer: I do not think at all that the video was faked, but this interpretation is too funny to spare...)



****

In retrospect, keeping the video a secret for two years before disclosing it to the public maybe wasn't such a good idea after all.

11 comments:

  1. Hi Jan. Couldnt quite figure out the "Comment as:" option. My name is Hans Amundsen. One of the two geologists figuring in the meteorite/skydiver story. First of all, thanks for posting this. We are thrilled about all the response we are getting. And we welcome any debate around the story. Thought I was going to sleep when you kindly asked permission to use the image (I´m in Berlin). But changed my mind. Much more fun to follow up on some of the threads on www :). I am also a big fan of Occam with the razor.

    First some basics about meteorite velocities, shapes and colors. Meteorites enter Earths atmosphere at hypervelocities (km´s/sec). Visible as glowing fireballs. Smaller ones burn up. Larger ones fragment and end up as debri on the ground. Like Chelyabinsk which was the size of a large truck. Fragmentation occurs at high altitude (> 20 km) and single pieces gradually enter a vertical trajectory and terminal velocity (ca 300 km/h - 60 m/s) long before they hit the ground (way above skydiver altitude). They also quickly stop glowing. Hence the term "Dark Flight".

    Some meteorites are rounded and totally covered by fusion crust (acquired at hypervelocities). Others go through svereal fragmentation events and show a mix of fusioned and freshly fractured surfaces. The fracture surface of an ordinary Chondrite has a color (and albedo) similar to concrete.

    All the above does not prove that the rock passing the skydiver is a meteorite. But there is nothing in the observations (apparent velocity, shape, color, size) that precludes the hypothesis.

    We have pondered the possibility that the rock is a piece of gravel released from the parachute. Anders was heading forward/downwards at >> 100 km during the incident. Imagine standing in a 150 km/h blaze and someone dropping a small rock 2 m above you. You would never see it. And it certainly wouldnt rush down below your feet. Perspective/film footage indicates that the rock is at least potato-sized (> 5 cm). And it has a near vertical trajectory with significant speed. Difficult to reconcile with something falling out of the parachute. There are no other skydivers above or nearby. The airplane is about to land far away.

    Most meteorites (meteors) are visible as high altitude fireballs and some explode with a "boom". Hollywood will happily make this happen at low altitude close to Bruce Willis ;). But these are the ones we notice. There are lots of cases where freshly fallen meteorites are found with no witness accounts of fireballs and booms. A fairly large space rock disintegrated over Oslo in March 2012. Nobody saw or heard anything. Apart from a couple of houseowners finding meteorites tucked in holes in their roof.

    There are no reported firballs or sonic booms reported in connection with the skydiver incidence. Seismic stations operated by NORSAR were unfortunately down for maintenance. But more importantly - the area is home to one of the largest army test ranges in Norway. Local people stopped noticing booms long ago...

    We are happy to provide original film footage/single frames to anyone interested in finding the truth. Personally - I´m trying to find the meteorite ;)

    Best regards, Hans

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    1. Dear Hans,

      thanks for sharing your thoughts. I think finding the meteorite will be the only way to finally prove it was one. Good luck for that! Do you have any hope to find it almost two years later now? Are there areas you haven't searched yet? What's the area like? If there are large lakes or rivers, the stone might be lost forever...

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    2. The area I saw in the video seems to have a lot of trees, water and grass so I could imagine it would be very difficult to search the stone.

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  2. Jan,

    Very interesting theory! Can you give any details about those incidents of rocks falling out of parachutes or canopies?

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    1. Dear Paolo,

      I was referring to the link given above: http://slashdot.org/comments.pl?sid=4985557&cid=46660923

      We know there are meteorite falls, and we know there are incidents where small stones might fall out of parachutes. Now we have this video. Which scenario is more likely? I strongly favor the second one (stone from parachute), especially since there are no other indications of a meteorite fall.

      That's my whole argumentation, very simple ;-)

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  3. On the composite image the stone moves along a parabola, not a straight line. This is most notable near the top. It is consistent with launch during parachute deployment. - Marco Langbroek

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    1. Before analyzing the video frames one has to understand the optical distortions of the wide-angle lens used: these helmet-mounted cameras often come with fish-eye-like optics that do weird things. I reckon such an analysis *has* been done in an attempt to narrow the impact zone of the rock but it doesn't seem to be published yet. Waiting for the announced website with *all* that was done in the past two years.

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  4. Here's their website with their impressive analysis:

    http://norskmeteornettverk.no/wordpress/?p=1399

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  5. Phil Plait's opinion that this may be legit is based mainly on the assertion that this object must have been moving at a high relative speed. If so, that would have been inconsistent with a small piece of gravel that fell out of the canopy.

    But that is precisely something we can't say for sure. A small piece of gravel passing by at very short distance and a larger rock passing by a correspondingly larger distance would appear to pass at the same angular velocity as seen in the movie. However, the actual velocity of a larger rock passing by at a distance of a few meters must exceed that of a small piece of gravel passing by at a distance of a few tens of centimetres by a factor of ten.

    Given the large field of view of this type of camera, either would appear to be in focus, apart from a slight blurring due to its relative speed and its rotation. The point is, you just tell the distance with nothing nearby to gauge it. That's a well-know phenomenon.

    Therefore, one cannot make any assertions based on the apparent velocity, because this relative velocity is unknown. We don't see it in the movie. All we see its the angular velocity. To deduce the actual velocity, we need to know the distance, and we don't know that.

    So we just can't tell.

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  6. My first reaction when I heard about this is "Did this really happen or is it a hoax?" Then I thought about how such a hoax would have been perpetrated. No possible explanation sounded right. Phil Plait has also gone into this, and I agree with him. Someone throwing a rock from higher above? Come on. Skydivers don't do such things to each other. they just don't, because they know how dangerous that it. And they would have to do it numerous times until it looked right on video. This doesn't hold water.

    So then, naturally perhaps, after exhausting the potential for this being a hoax, my conclusion was that it must be real. If it's not a hoax, it must be real, right? That's the thinking the digital age instils.

    But I was missing something there. It might well be an honest mistake. An error in judgement. I think there is a real chance that this is real, but it also appears very plausible that this may be no more than a misinterpretation of a video of a smallish piece of gravel that fell out of the wildly swinging canopy.

    There is no way to tell, and perhaps there never will be. Even if they do find a meteorite, how could anyone tell for sure that it was the same one as in the movie?

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  7. So, surprise, surprise, the Very Bad Astronomer (Phil Plait) was wrong once again.

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