: how are comets , meteorites and asteroids so powerful that they are able to completely annihilate their target in a matter of seconds?
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They’re going very, very fast.
An object that hits Earth from deep space can’t be going slower than Earth’s escape velocity. Orbits are reversible, so any outward trajectory that could take a rocket to deep space (and necessarily starts with reaching escape velocity) has a corresponding inward trajectory with an object coming in and *reaching* escape velocity.
Earth’s escape velocity is, by human standards, incredibly fast. It’s about 11 km/s or, if you prefer, about 40,000 kilometers per hour (or, if you prefer, more than 20,000 miles per hour). That’s much faster than any object you see in everyday life. Even a bullet typically leaves a gun barrel at something like 1 km/s, about ten times slower. Even anti-tank weapons usually don’t break 2 km/s. And because kinetic energy goes with the *square* of speed, ten times faster means 10^2 = 100 times more energy per mass than a bullet.
So what we’re talking about here is an object much bigger than a bullet, striking at a speed that makes it hit 100 times harder per mass. Bullets weigh a few grams – let’s say about 4 for the sake of argument – but even a baseball-sized meteor weighs ~600 grams (using 3 g/cm^3 for a density, which is a reasonable number for a rocky meteor; iron meteors are much heavier).
So in sum, a baseball-sized meteor is like getting hit by (600/4) = 150 bullets, each of which is hitting 100 times harder than a normal bullet. Or, if you prefer, being hit by 15,000 bullets at once. In energy terms, a 600 gram meteor going at 11 km/s has a kinetic energy of 36 MJ, or about 100 times the energy of a speeding car.
Their energy comes from speed. Energy scales with the square of speed. A car at 100 mph has 100 times the energy of a car at 10 mph.
Now imagine a ‘car’ at 20,000 mph. That’s about the speed that something reaches falling into Earth’s gravity if it started with no speed at all. 40,000 times the energy of the same car moving at 100 mph.
But that’s just a little car. Cars are mostly hollow. A hunk of rock the size of a car would weigh something like 10 times as much. 400,000 times the energy of a car moving at 100 mph.
And these things can easily be bigger than cars.
Because they’re extremely massive and they’re moving extremely fast. Even a meteor only a few dozen meters in diameter can have a mass of thousands of tons, and are moving at at minimum of a 40,000 kilometers per hour.
Think about how much damage a car crashing into a building causes, and now imagine a rock millions of time more massive than a car *and* moving thousands of times faster.
They are not powerful, they are just fast.
Imagine dropping a baseball on your foot from waist height and compare that with getting hit by a baseball by a professional player.
The ball is the same but the latter can really hurt you because it goes faster.
Or getting bumped by a car as it slowly tried to park versus getting hit by the same car at highway speeds.
It is not really the object that matters but the speed.
Technically both the mass and the speed matter, but it is a simple linear correlation for the mass and the square for the velocity.
So if you want to have an impact that is 100n times as powerful you can either increase the mass of the object a 100-fold or the velocity just tenfold.
Objects in our solar system tend to be going very fast in respect to one another when they cross paths and gravity helps accelerate them towards one another even more as they get closer.
Our atmosphere helps a lot dealing with smaller stuff, but any big space rock that makes it to near the ground relatively intact is going to be a huge problem.
Thankfully those impacts are rare at least on human timescales.
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