Did That Skydiver Almost Get Hit by a Meteorite, or Just a Plain Old Rock?

The entire universe in blog form
April 7 2014 11:00 AM

Follow-Up: The Meteorite and the Skydiver

rock or meteorite?
Composite image showing the trajectory of the object that flew past the skydiver.

Photo by Anders Helstrup, from the video

Last week, a video went viral that purports to show a skydiver narrowly missed by a meteoroid falling past him. A lot of people have been speculating over the video, of course. I watched it many times, and after giving it some thought I wrote up my own opinion. Basically, the video doesn’t looked faked to me, and while I remained skeptical, I leaned toward it being real, and open to the idea that it really is a meteoroid.

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death from the Skies!  

Note: If this rock came from space then technically it was a meteoroid; they’re called meteorites after they hit the ground. I took great pains in my first article to call it a rock or an object, since its pedigree is still <puts on sunglasses> up in the air. I will do so again here. However, most of the articles I saw called it a meteorite, so I used that term in the titles so people would know what video I’m talking about.

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Here's the footage again; you can see the object fly past at about the 1:50 mark.

Over the weekend I received lots of comments on Twitter, Facebook, and via email about the video and my post. Some of them were from people convinced the object is a meteoroid, while others poo-pooed the whole idea. But some of the discussion went into details of the video and what it could be, and I want to follow-up on what I wrote because of that.

To be clear and concise: While I initially dismissed this idea after some thought, it is entirely possible that what the video shows is a smaller rock that fell out of the skydiver’s parachute. I don’t think this can be ruled out, and indeed, is more parsimonious than the idea that the video captures an extraordinarily rare event like the dark flight of a meteoroid. So the video is almost certainly real, in that I mean it wasn’t hoaxed, but as things stand now we cannot know for sure what the object is or isn’t. But it being a rock trapped in the ‘chute is a far more likely explanation.

Well, ‘Chute

In my first post, I brought up the idea that the object was a bit of debris caught in the parachute, and then fell out when the parachute opened. However, given the size and speed of the object, that seemed unlikely to me, so I discounted it.

I may have been too speedy in that assessment. First, many skydivers have said falling debris is a relatively common event; all manners of small objects can get caught in the parachute when it is packed on the ground before the dive. So it’s not impossible, and there’s plenty of precedent.

Second, I discounted the idea of this being such an object due to its size. An analysis of the video by Steinar Midtskogen indicated the rock was between 8-20 cm (3-8 inches) across. Surely something that size (and weighing 1-20 kilos) would not get missed when the ‘chute was being packed!

But Midtskogen was assuming the object was a meteoroid, and falling several hundred kilometers per hour, terminal velocity for such an object. The speed it falls is critical for getting its distance from the camera (the object moves rapidly across the camera field of view, so if you know how fast it is moving then you can calculate how far it falls between video frames, and that can be used to determine its distance from the camera). He finds it was between 2.5 and 6.5 meters (8-21 feet) away when it passed.

But that assumes the object really is moving rapidly. If it fell from his ‘chute, then it could easily be moving much less quickly, and that would mean it was actually much closer to the camera, and therefore smaller. I didn’t initially think this would be the case because the object is well-focused in the video, and if it were really close it wouldn’t be.

That was an error on my part. The camera used is wide-angle and has a very large depth-of-field, the technical term used to mean the range of distance over which an object is focused. As you can see in the frame grabs from the video, the hand straps and tethers in the parachute are well-focused, and are less than a meter away from the camera! That means the object too could have been less than a meter away, which means it could have been much smaller, as small as just a couple of centimeters.

My friend and astrophotographer André van der Hoeven also analyzed the video, and determined the object was not accelerating when it flew past; in other words it was at terminal velocity. He reasoned that a rock falling from the parachute would be expected to accelerate due to gravity, so he concluded it must have fallen from far, far above the diver. [Update (Apr. 7, 2014 at 16:00 UTC): van der Hoeven recently updated his analysis to note that he can't rule out the rock coming from the parachute, only that it was unlikely.]

However, there are a lot of variables to this. At the speed at which the skydiver was falling, air resistance would be quite high and could slow a small rock very rapidly. There could also be quite a bit of turbulence from the parachute itself, creating eddies in the air that could change the velocity of a small falling rock. I don’t think we can rule out the possibility of it being debris initially stuck in the ‘chute due to the speed and/or acceleration at which it falls.

And I have to admit that it bugged me right away that we see the object just seconds after the parachute deployed. That’s another big coincidence in a big series of them. At first the evidence seemed to weigh against it coming from the parachute, but now it’s clear that’s not the case.

meteor by Mark Gee
The hot, glowing phase of a meteor's fall only lasts for a few seconds and occurs high in the atmosphere; after that the rock cools and falls at terminal velocity, a few hundred kph.

Photo by Mark Gee, used by permission

[Update 2 (Apr. 7, 2014 at 17:30 UTC): Dr. Philip Metzger a physicist and planetary scientist at NASA, analyzed the video using some sophisticated computer modeling and determined that the object was most likely either a small piece of rock very close to the camera, or a far larger one between 12-18 meters away. Given how big the object must have been if it were really that far away, this again lends more weight to the idea that this was actually a small bit of debris caught up in the parachute.]

Earth Diving

In my first article, I was more concerned over whether this was a hoax than a case of mistaken identity. That gave me a certain angle, a certain point of view, while looking over the video. I should have been more concerned over the possibility that while the video was authentic, the conclusion was mistaken.

After more thought, I not only cannot rule out that it was a smaller rock caught in the parachute that fell once the ‘chute deployed, I have to admit that it is a more likely explanation. That does not mean it’s the right one, of course. But bear in mind that meteoroids big enough to see are extremely rare, and are so uncommon that none—not one—has ever been positively caught on video, despite all the cameras we use all the time. That means this object is even more unlikely to be one, since it also fell very close to the camera (and coincidentally right after the parachute opened). That’s a whole lot of unlikely events happening in a row, which triggered my skeptical sense right away but makes it tingle even more strongly now.

I’ll note that Midtskogen emailed me over the weekend and was quite open about this possibility, and is eager to have others analyze the video to see what they can find; they put all the original footage on YouTube (though the original raw footage off the camera is not available yet; it’s too big for YouTube, but Midtskogen assured me they’re working on a home for it). That is precisely the right attitude, and I hope that other people can find clever ways to figure out more about this.

And finally, another observation: As usual, with a claim on the Internet, the reactions to it have been diverse, fascinating, and frustrating. From the comments I received, I found a lot of people didn’t really read what I wrote. Some people thought I was saying it is definitely a meteorite—but that’s not the case. I tried very hard not to say that in my post (though my concluding paragraphs are based on the idea that it was). Others were dismissive of the idea, saying that a meteoroid would still be hot and moving at hypersonic speeds, a misconception I specifically debunked in my article!

It was nice to see much of the commentary being calm and rational, with different people picking up various threads and analyzing them for their merit or lack thereof. Of course that wasn’t always the case, and some folks got pretty hot under the collar about this. But that is less than useless; it turns people off and can close avenues of discussion that might otherwise be useful. In a case like this, simple, reasoned discussion is the best way to go.

I’m still willing to be swayed further either way on the topic. I am not saying it was or was not a meteoroid, but it seems far more likely to have a far more mundane explanation. And either way, any conclusion will have to rely on better evidence and better, more detailed analysis than we have seen so far.

But if I had to bet, based on what we’ve seen? I’d put my money on it being a plain ol’ rock.