INCOMING!, Detection and observation of Earth-approaching asteroids. Options

[dilo]

I suspect it's a hoax, they didn't find any meteorite on the ground and, probably, the rock was released from the other falling guy...
A good proof could be the eventual meteor echo radar registered in that region...

[Paolo]

I think it is much more likely that the rock had been trapped in the canopy of the parachute when it was folded

[Explorer1]

Wouldn't it have fallen out as soon as the chute opened if it was trapped like that?

The main article is here:
http://www.nrk.no/viten/skydiver-nearly-st...rite-1.11646757
Apparently it happened in 2012 and they only released the footage now so that the public could possibly help in finding it (assuming it exists).

[Gerald]

This is a preliminary site (in Norwegian) with a link to the (yet unavailable) website they are preparing for public help. It provides some more detail.

As long as the (presumed) meteorite isn't found, it will remain much more likely, that some of their assumptions or conclusions turn out to be wrong, than an exceedingly unlikely close encounter of a meteorite with a skydiver.
The weird thing is, that - based on the available information - all possible explanations are unlikely.

[john_s]

Given the number of humans on the ground compared to the number in mid-air (and not inside planes) at any given time, you'd expect millions of cases of meteorite near-misses on the ground for every mid-air near-miss. We do have examples of near-misses on the ground, but not millions of them. So I'm highly skeptical, even though I don't have a better explanation (unless it's a hoax).

John

[Explorer1]

Phil Plait weighs in; he's leaning towards it being real...
http://www.slate.com/blogs/bad_astronomy/2..._meteoroid.html

[alan]

Seems more likely that the other skydiver dropped it.

[dilo]

The asteroid 2007 VK184, which was the only known NEO with a non-zero Torino Scale rating for a while, has been re-discovered by Dr. David Tholen of the University of Hawaii and the new improved orbit calculation exclude the potential impact in 2048, with no closer encounters predicted for the foreseeable future. So we have now all zeroes in the Torino Impact Hazard Scale (excluding Bennu and 1950DA with potential impacts in the deep future):
http://neo.jpl.nasa.gov/news/news183.html

[Paolo]

the rock had been trapped in the canopy of the parachute when it was folded

It looks like I was right: http://norskmeteornettverk.no/wordpress/?p=1497

[ElkGroveDan]

I suppose the pebble argument is compelling and it fits along the center of the probability curves, still I wouldn't call it "settled."

[JohnVV]

we could speculate all we want but i am going with Phil Plait on this
-- update --
http://www.slate.com/blogs/bad_astronomy/2...was_a_rock.html
-- older ---
http://www.slate.com/blogs/bad_astronomy/2...ust_a_rock.html
-- even a bit more older --
http://www.slate.com/blogs/bad_astronomy/2..._meteoroid.html

[Gerald]

This sounds about a dozen orders of magnitude more likely than the meteorite hypotheses.

[Mongo]

It seems to me that we already have enough information to deduce the size of the object. If it's small, it is most likely a rock falling from the parachute, while if it's large, it almost certainly has to be a meteoroid.

We do know several things about it. One, it's falling at terminal velocity. Even if it was dislodged from the parachute, there was enough time for it to have reached terminal velocity. There would have been a surprisingly long time between the object detaching from the parachute and it falling past the camera, according to the relevant video. This is especially so because it would have been fairly small to have escaped notice, and hence would have had a lower terminal velocity. Two, its density is probably around 3, which is typical of Earth crustal material and also of the type of meteoric material it would likely be, assuming that it is a meteoroid.

So step one, calculate terminal velocity for a range of diameters assuming a density of 3, from 1 cm to 10 cm.

Step two, calculate the distance of closest approach, using the images from the video and the (known) field of view of the video camera.

Step three, adjust for the (estimated) velocity and direction of the skydiver to get the relative velocity of the object, assuming the various sizes.

Step four, calculate the apparent angular velocity at closest approach for each of the sizes, using the calculated relative velocity and calculated closest approach.

Step five, using the frames from the video, calculate the observed angular velocity and compare with the calculuted angular velocities.

A smaller object would have a closer approach, but also a lower relative terminal velocity, so these two effects would partially cancel each other out. However, terminal velocity is not linear with diameter for an object of given density, so there would always be a significant difference between the calculated maximum angular velocities.

[Mongo]

I did some quick calculations. The terminal velocity for a 1 cm rock is around 90 m/s at sea level. This is roughly the same as the terminal velocity of a human skydiver before the parachute opens (about 100 m/s -- the reason that the skydiver's terminal velocity is barely greater than that of the 1 cm rock is that the skydiver has a much lower density). Since the skydiver was using a wingsuit after jumping from the plane, his terminal velocity would be somewhat lower than this, probably lower than that of the rock.

In the video, the initial drogue parachute deploys, then about 2 seconds later the main parachute opens, then about 6 seconds after that the rock is caught on video falling past. If the rock was dislodged from the parachute, the rock would immediately start accelerating downwards, always with a downward velocity greater than that of the skydiver. If it were dislodged as soon as the main parachute opened, it would have been far below the skydiver at the time the rock was captured on video. In order for it to have been seen when it was, it would have to have dropped from the parachute around one second before being captured on video (since by that time, the skydiver's downward velocity had been fairly low for around 4 or 5 seconds), and at that time, its velocity relative to the camera would be about 10 m/s (if the parachute is 5m above the camera).

Looking at the video, the rock appears to move by about 10-12 rock widths per frame, or 300-360 widths per second at 30 frames per second. This translates to the following:

3.0-3.6 m/s for 1 cm rock (~3.7% of the terminal velocity of 90 m/s)
6.0-7.2 m/s for 2 cm rock (~5.1% of the terminal velocity of 130 m/s)
9.0-10.8 m/s for 3 cm rock (~6.3% of the terminal velocity of 156 m/s)
12.0-14.4 m/s for 4 cm rock (~7.3% of the terminal velocity of 180 m/s)
24.0-28.8 m/s for 8 cm rock (~10.2% of the terminal velocity of 260 m/s)
48.0-57.6 m/s for 16 cm rock (~14.7% of the terminal velocity of 360 m's)

So the rock is definitely not moving at terminal velocity, but is moving at about the expected speed to have been dislodged from the parachute about 1 second earlier and 5 seconds after the parachute deployed, if it were about 2-3 cm across.

[Mongo]

Meteorite smashes into Nicaraguan capital

Nicaragua's government said Sunday that a loud boom heard overnight by residents of the capital was made by a small meteorite that left a crater in a wooded area near the city's airport.

Government spokeswoman Rosario Murillo said a committee formed by the government to study the event confirmed it was a "relatively small" meteorite that "appears to have come off an asteroid that was passing close to Earth."

Murillo said Nicaragua will ask international experts to help local scientists in understanding what happened.

The crater left by the meteorite had a radius of 12 meters (39 feet) and a depth of 5 meters (16 feet), said Humberto Saballos, a volcanologist with the Nicaraguan Institute of Territorial Studies who was on the committee. He said it is still not clear if the meteorite disintegrated or was buried.

Humberto Garcia, of the Astronomy Center at the National Autonomous University of Nicaragua, said the meteorite could be related to an asteroid that was forecast to pass by the planet Saturday night.