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Comment by dclowd9901 | Hacker News Reader

I'm... skeptical. If you look at the frames of the meteorite falling, it looks like each frame has the fragment at about 3 feet from its last position. If that's a 60fps camera (I think it is?), that's 180 f/s speed or 122mph. That seems really slow for a rock flying into the atmosphere from space, and far slower than a rock would have to be going for it to "cut him in half."

My guess: a rock that fell off the undercarriage panel of an airliner, and was carried by strong winds. Or a particularly slow meteorite.

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These rocks slow down considerably when they move through the atmosphere (Unless they are massive and this one was not). What is also interesting is most the time they are cold to the touch immediately after impact.[1][2]

[1]http://misconceptions.us/are-meteorites-hot-or-cold-when-the... [2] http://curious.astro.cornell.edu/question.php?number=215

>> it looks like each frame has the fragment at about 3 feet from its last position

How did you arrive at this number? What distance do you estimate between the camera and the falling rock?

> If that's a 60fps camera (I think it is?), that's 180 f/s speed or 122mph.

Are you assuming the skydiver is stationary?

Terminal velocity for a small flat rock is not all that fast. 200-400mph: http://www.amsmeteors.org/fireballs/faqf/#8

Considering the skydiver also has a significant speed, that corresponds reasonably well with your estimate.

The rock also looks very much like fragment of a meteorite with classic "fusion crust".

And probably they would have known if an airliner was in the area, considering they were essentially right above a general aviation airport. And probably airliners would not choose to fly over that area.

I think the meteorite identification is much more plausible than anything else.

By the time it has reached the kind of altitude that skydivers would be operating it, a meteor would have lost most of its speed to atmospheric compression and friction. According to this faq [1] the terminal velocity for a small meteorite is 200-400 miles/hour, which is not far from your estimate.

[1] http://www.amsmeteors.org/fireballs/faqf/#12

> If that's a 60fps camera (I think it is?) ...

The camera appears to be recording at a rate of about 10 frames per second. This is a way to reduce memory consumption in a portable device in which recording duration has a higher priority than recording frame rate.

AT 10 FPS, the rock's sequential positions seem consistent with a falling rock.

And, lo and behold:

http://gopro.com/cameras/hd-hero3-silver-edition

Quote: "Features video resolutions up to 1080p60, 10MP photos up to 10 frames per second, enhanced low-light performance and built-in Wi-Fi. Waterproof to 131’/40m."

According to the above, ten frames per second is the highest available frame rate.

> Or a particularly slow meteorite.

Not a meteorite until it gets to the ground.

So even slower. At 20 mph, it could've simply come out of his parachute.

> So even slower. At 20 mph, it could've simply come out of his parachute.

It seems you're missing the point that the rock passed him by at a fairly high horizontal speed, while descending past him. That's not consistent with the rock coming out of his canopy.

The 1080p60 means 1080p video at 60 frames per second. I would guess they are taking videos and not capturing stills, but who knows.

That's 1080p (~2MP) at 60fps, or stills at 10MP at 10fps.

Camera isn't stationary.

Even if it's not, the relative speed is what's the issue here. The thing I take most issue with is his statement that this rock would've killed him. If it's only moving 120 or so mph in relation to his speed, it probably wouldn't kill him, let alone cut him in two.

Let's say that meteorite is about the size of a baseball. 120mph is faster than a fastball baseball pitch, and getting hit by a fastball? That can do damage, which is why baseball players wear protective gear (the catcher's padding is not for show). An iron nickel meteorite is maybe five-six times denser than water; a baseball? Well baseballs float - they're about 2/3 as dense as water. So the meteorite is maybe 3-4 times as dense as a baseball, going 20% faster than the fastest fastball ever recorded; so it's carrying more than 4 times the kinetic energy of a fastball. If that hit you, it could certainly be immediately fatal, or at least cause severe injuries; I would imagine that becoming severely injured while skydiving comes with a significantly increased risk of death.

But maybe he's just being a drama queen.

$ If that's a 60fps camera (I think it is?), that's 180 f/s speed or 122mph. That seems really slow for a rock flying into the atmosphere from space, and far slower than a rock would have to be going for it to "cut him in half."

A slushie travelling at 120mph into a windshield: http://www.discovery.com/tv-shows/mythbusters/videos/soda-cu...

Regarding the speed, the atmosphere will slow the rock down considerably, aerodynamic drag is proportional to the square of the speed.

The high speed/slowmow internal shot of the slushie at 120mph:

http://www.discovery.com/tv-shows/mythbusters/videos/soda-cu...

Er, the actual direct link: http://www.discovery.com/tv-shows/mythbusters/videos/soda-cu...

GoPros have high frame-rate modes.

Agreed. When is the last time you saw a bullet videotaped on a normal camera? This is moving 10x faster than a bullet?

Did you actually read the article? The stone/object they filmed was within the atmosphere, thus going around terminal velocity, depending a little on the size of it, which varies a little on the estimations.

All: please don't say testy things like "Did you actually read the article?" on HN.

This is one of those phrases that can always be deleted with instant improvement in comment quality. Check out how much more substantive and neutral this comment is without it.

Re-read what you've posted and, if you notice phrases that add nothing but testiness to your comment, edit them out. That's what I do.

> Did you actually read the article? The stone/object they filmed was within the atmosphere

OH! They were parachuting inside the atmosphere!

I read the article, watched the video, and read other content related to it, so the answer is yes. Somewhere i ran into that crazy speed estimate.

I am very skeptical. Although quite stupid, it wouldn't be hard for the other guy to have thrown some kind of junk and get it on camera, then claim it was a meteorite.

I bet nobody ever finds any evidence of said "space rock".

So they wasted the time and money of a few geologists, and spent a day or more with a group of friends/family searching around the forests for a meteorite.. because of a stunt for fame?

HN skeptics. The shit they say, I swear.

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