Oh, well, phew then

Residents of a city in southern Argentina got a scare when a series of powerful explosions shook homes and buildings, but the cause turned out to be a natural wonder: a meteor disintegrating overhead.
It was an ordinary Wednesday afternoon in General Roca, a city of 85,000 people, when suddenly a series of loud blasts caused buildings to shake and windows to rattle.
“Everything trembled,” said Martin Soria, the local mayor.
Police, firefighters and emergency workers rushed to the scene, but found no evidence of a bomb, earthquake or calamity.

And?

Finally, scientists pieced together the reason: A meteor had entered the Earth’s atmosphere some 10,000 metres (33,000 feet) overhead, traveling at 1,500 miles per hour.
“It took everyone by surprise because it entered the atmosphere over an inhabited area. If it had fallen over the desert, the sea, Antarctica, we would never have known,” said astronomer Roberto Figueroa, head of the nearby Neuquen observatory.

He estimated Wednesday’s meteor measured about 12 metres in diameter before breaking into three fragments.

I do sorta doubt that it was 12 metres in diameter. But, to take them at their word.

It was just 900 tonnes of rock moving at 1,500 mph. Phew, nowt to worry about then.

13 thoughts on “Oh, well, phew then”

  1. “A meteor had entered the Earth’s atmosphere some 10,000 metres (33,000 feet) overhead”

    That’s below the altitude of a cruising airliner. Who knew? Easyjet operates in space! Where do I get my mission patches?

  2. That’s a very slow meteor. They are usually 20 times that fast.

    And not very dense – rock is usually 2 to 3 times as dense as water and there is often a lot of iron in meteors.

  3. Speeds are normally 25,000 mph to 160,000 mph.

    But I might give them a pass on where the atmosphere starts. Really, the atmosphere just goes up and up, getting thinner and thinner, until it merges with the solar wind. It never reaches zero density, so where you set the boundary is one of those arbitrary, ‘for all practical purposes’ things.

    About 80% of the atmosphere (by mass) is below 10 km, so stuff re-entering doesn’t meet serious resistance until it gets quite close. I’m guessing this is what was meant.

    As for size, I think the Chelyabinsk meteorite was estimated at 17-20 metres, and Tunguska at 60-190 metres. So 12 metres doesn’t sound totally implausible to me.

  4. That’s a much more likely size I think…..12 metres is something the size of a (small) house.

  5. “That’s a much more likely size I think…..

    More likely as a meteorite size, or more likely to cause “a series of powerful explosions [that] shook homes and buildings” leading “Police, firefighters and emergency workers [to rush] to the scene”?

    12 metres is something the size of a (small) house.”

    So?

  6. Bloke in Costa Rica

    Meteor facts listicle:
    • Carbonaceous chondrites are the lowest density types; nickel-iron are the highest. Their densities range from ~2000 to ~8000 kg·m⁻³
    • Velocities at the point at which they encounter the Earth range from a low of 11 km·s⁻¹ (Earth’s escape velocity) to 72 km·s⁻¹ (the sum of solar system escape velocity at the Earth-Moon system—42 km·s⁻¹— and Earth’s orbital velocity—30 km·s⁻¹)
    • Most meteors below a certain size (~50–70 m diameter) are incapable of reaching the surface. They are destroyed by aerodynamic forces in the atmosphere. Nonetheless, they are still capable of causing destruction by air blast. A nickel-iron meteor of 50m diameter can reach the surface; such a body is believed to have created the Barringer meteor crater. If the Chelyabinsk impactor had come in at a steeper angle and slightly earlier it would have devastated the city, with a large number of fatal casualties.
    • Meteors bigger than ~70m can reach the surface, and this is very bad news for anyone in the vicinity. The definition of ‘vicinity’ varies according to size of the impactor. Kilometre-sized bodies will cause massive casualties out to 300 km or so from air blast, thermal exposure to the fireball, and seismic effects.

    The numbers in the Mail article don’t make any sense. A 12m body is going to blow up from aerodynamic stresses at 25 or 30 km altitude. The impact energy will be in the hundreds of kT range, but no-one on the surface will be in the least bit of danger. It will make a loud bang, though, exactly as described. The funny thing is, just a bit bigger (20m instead of 12) and there could have been casualties.

  7. “Most meteors below a certain size (~50–70 m diameter) are incapable of reaching the surface. They are destroyed by aerodynamic forces in the atmosphere.”

    I’m not sure about that. I think very small ones and very big ones can make it to the surface, but there’s a range in between that can’t.

    It’s to do with the area-to-mass-ratio, I think. The force slowing them is proportional to cross-sectional area, and the deceleration this produces is inversely proportional to mass. Small meteorites have a very big surface area compared to their mass, and so decelerate much more quickly. The less time they spend going fast, the less time there is for them to melt and fall apart.

    A small meteorite will be slowed rapidly to terminal velocity (when air resistance equals gravity) and becomes simply a falling rock. The air friction isn’t enough to melt it any more, and it falls intact. A big enough rock is still decelerating when it hits the ground.

    I’m not sure, though.

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