Earth-bound asteroids

I remember hearing recently somewhere that if an asteroid a few miles in diameter hit the earth, it would wreak all sorts of havoc and basically kill us off. What I don’t understand is, that doesn’t seem too big of a lump of rock to cause that much trouble. I was looking out an airplane window yesterday and in the scheme of things, it just doesn’t seem that large. I mean, is it really gonna kick up that much dust? Put this in perspective for me. I want to understand why this is so, because it seems every scientist agrees on this. And what is the minimal size that would cause cataclysmic changes?

It’s not like God is just going to set it quietly in the middle of the Atlantic, barely setting off a ripple.

Interplanetary objects move many miles a second. (The Earth itself is moving 30 miles/sec in its orbit, IIRC.) Even allowing for braking as it enters the atmosphere, it’s going to hit pretty @!#?@! fast!

Of the damaging effects:
[li]The pressure wave as it goes through the atmosphere will be pretty intense, many times more destructive than any atom bomb explosion.[/li][li]If it hits an ocean, it’ll generated tsunami that’ll wreck havoc on the coasts many times more than earthquake/landslide-generated tsunami would. (I won’t hazard a guess at the range inland they’ll go.)[/li][li]If impact is either on land or sea, it’ll kick up more dust than any volcano has ever. Volcano’s dust clouds have been known to start “mini” ice ages, lasting a few years. An meteor of that size would probably cause at least 200 years of climatic changes.[/li][li]The impact may rupture the crust at the impact site, creating a new mega volcano.[/li][li]The impact will also create a huge earthquake that’ll be felt worldwide. Again, I don’t hazard a guess as to its Richter Scale measurement, but it’d be a great deal more than what mankind has ever experienced.[/li][/ul]

Well here’s what could happen:

• Asteroid/meteor plunges into the ocean, causing a huge hunker-toad tsunami which subsequently wipes out costal cities on multiple continents.

• A comet (not a meteor) smacks into the earth as is believed to have happened in Tunguska in 1908. Such a cometary impact simulates an atomic blast, there would even be a mushroom cloud. The only thing missing would be the radiation. I would not be surprised if some nuclear-capable nation believed it to be an attack & promptly started launching retaliatory nukes towards whichever country they suspected was responsible.

I have not followed up on the event since about 10 years ago, but at that time the object in question was thought to be only about a few hundred feet in diameter, and it hit with a force of approximately 40 megatons (more than 1000 times as powerful as the Hiroshima bomb). By contrast, according to my link, the resulting blast that created the great crater in Arizona about 50,000 years ago was only 3.5 megatons. Anybody know how big that crater is?

The physical size of the asteroid is somewhat insignificant - it’s the velocity which does all the damage.

Objects in motion possess kinetic energy, which can be defined thus:

kinetic energy = 1/2 mass multipled by the velocity squared

From this equation, it is obvious that while doubling the mass (size) of the object really doesn’t make that much difference, doubling the velocity quadruples the amount of energy produced. In other words, speed kills.

Just think of the speed needed by the space shuttle on lift-off - it’s on the thick end of 25000 miles an hour - and that is just to get into Earth orbit. So a celestial body which is orbiting around the sun would also require an immense velocity to stay in orbit.

Now, if the Earth and this hypothetical asteroid were to collide, the equation above would be calculated using the combined speeds of both bodies, as well as the combined mass. You don’t need to be Einstein to realise the kinetic energy released would be immense.

Now do you understand?

On the Bad Astronomy page, I found a calculator for finding the energy released by imcoming meteors.

A rock meteor that’s 2 km in radius (4 km diameter, 2.4 miles) and hitting at a barely-above-minimum 15 km/sec would generate 1.884954 million megatons. For comparison, the BA says that the biggest nuclear bomb tested had a yield of 57 megatons.

Even a small impact is pretty big. A rock meteor 1 meter in diameter coming in at the bare minimum 11 km/sec would generate an energy yield of 15.8 tons of TNT. And that’s a tiny pebble in the scheme of things.

BTW, a pebble 2 mm in diameter would have a yield of about 110 mg of TNT. :D:D

I recall reading somewhere (Scientific American?) that it is conjectured that the impact off the coast of the Yucatan Peninsula in Mexico, which took out the dinosaurs 65 million years ago, resulted from an asteroid that came in at a very shallow angle from the South. This brings to mind not just tsunamis, but a continent-scouring blast of superheated steam that may have instantly sterilized much of N. America.

The large species on other continents, of course, were doomed to much slower deaths as dust blocked out the Sun and altered the climate.

I’m sure AWB knows this, but I’m compelled to point out that the 2mm pebble would have to hit the surface at orbital velocity. In practice, smaller asteriods (i.e. meteorites)
are burned up by friction with the Earth’s atmosphere. Larger meteorites (say, fist-sized) are slowed down to terminal velocity, so they hit with the same speed they’d have if they were just dropped from a tall building or an airplane.

robby, the Chixulub impact actually threw debris into orbit. Vaporized rock from the asteroid and from the Earth’s crust was thrown up onto ballistic trajectories, and then rained down over the entire surface of the globe.
The heat of those little bits of rock burning up in the atmosphere raised the surface temperature to that of an oven, causing massive forest fires which filled the atmosphere with soot. The ashes from the forest fires changed the acidity of the ocean, killing off many aquatic species as well.

Makes Noah’s flood sound pretty tame by comparison, eh?

Don’t tempt fate:

Heres a website that talks about when the comet Shoemaker-Levy collided with Jupiter in 1994.

This quote describes the effect of just one of the fragments that struck Jupiter.

If that fragment had hit the Earth instead, it would have definitely messed some shit up.

The reason meteors cause so much damage is that they don’t just land with a dull “thud” and stick out of the ground like a shotput. The heat and kinetic energy from their mass velocity (squared) are so high, it vaporizes the ground, water, and everything around it. I believe it also creates a vacuum in its wake as well.

That vaporized material has to go somewhere so from there you just get the normal giant explosion effects. ie: Supersonic pressure wave, heat, flying fragments, dust, etc.

My personal favorite is the 2 mile high tsunami like in “Deep Impact”.

I have a little trouble comprehending that one, though. Could someone who actually remembers their fluid dynamics class verify that a wave that big could actually be transmitted through the ocean?

To get an idea of the size of the impact of an asteroid, check out the Sandia National Laboratory page on the subjects.

3D Comet Impact Simulation has a series of pictures and movies of a simulated impact run on the Intel Terraflop computer of a 1 km comet imact on the ocean, with the skyline of New York as a scale comparison.

Impact of an Asteroid off the New York Coast has views of a simulated impact of an asteroid created by the same Intel Terraflops computer. There is also a series of views from a virtual reality simulation of the same impact. Considering I could probably watch the impact from my attic window (at least until the blast front blew the house apart) it’s an arresting image, at least to me.

Whoa, dude, careful with that technical terminology, or you’re going to confuse people.

Thanks! This is brilliant stuff, and I now understand it all. I didn’t really just how freakin’ fast space debris would be coming through the atmosphere. I somehow figured the air would slow it down more, but I suppose there’s really not much time for it to slow down if it’s going that fast to begin with.