# How much heat would a 1km asteroid release into earth's atmosphere?

I am writing a theory for a game that is in an apocalypse. An asteroid is heading for earth and will crash into the earth regardless in this theory. It is 1km in size but due to the YORP effect it has broken apart (it has a fragile composition because it's carrying something dangerous within it). It is now a group of rocks with the largest being 300m in diameter.

I've read that as a meteor reaches earth and either hits or burns up, it releases a lot of energy. This obviously means that it gives off heat into earth's atmosphere. If a 1km asteroid that has broken up into pieces were to hit earths surface, they would probably release a lot of heat too.

Considering that an asteroid of 300m size has never been recorded to hit earth in our time, it could be assumed that a lot of heat is released by its impact. It may also trigger events like volcanic eruptions and a kick up of lots of dirt to block out the sun in the area that it hits.

Oh yeah, I forgot to add that the velocity of this asteroid is supposed to be 31 km/s. Super fast to punch through atmosphere.

Would an impact of an asteroid of 1km (that breaks up) be enough to change the normal temperature of earth when taking into consideration all the side effects that the asteroid would cause?

• The amount of energy released is exactly the same (in this case, about 1,000 to 10,000 very big thermonuclear bombs), regardless whether the asteroid comes in one piece or in multiple pieces, and whether it hits the ground or it doesn't. The major difference between the scenarios is that if the pieces burn up high above the ground then much less dust and debris is ejected into the atmosphere, which very greatly reduces the resulting global cooling. So, what is it? How many pieces? How many hit the ground? How wide is the impact area? – AlexP Jan 9 at 2:54
• Am I correct that Astronomy or Physics or Science SE will have better answers than here? – Mr.J Jan 9 at 5:10

First you need to learn about kinetic energy, the amount of energy a moving body possesses. This is given by the formula $$E = \frac{m v^2}{2}$$ where m is expressed in kilograms, v in meters/second, and E is joules.

In your case, calculate the volume of a 1 km sphere and multiply by the density of the asteroid (choose between, lets say, ice, stone and iron) to get the mass. Pick a velocity v. For instance, the velocity of earth in its orbit is 30 km/s. Use a calculator to figure out the energy, all of which will be converted to other forms when the asteroid comes to a complete stop (velocity goes to zero). This is your base number.

Now comes the complicated part. Not all of that energy will be converted to heat, although a lot will. Some of it will produce ejecta which actually escape earth. Some of it will produce an enormous flash of light, and much of that light will also escape earth. Take stab at how much is left over, and 50% might be a good starting point.

Now that you have an energy, what does it mean? Well, here's a handy number: one megaton of TNT will release just about $$4 \cdot 10^{15} J$$

So a 1 km asteroid is going to produce a lot of heat.

• L.Dutch - I have overridden much of your edit, specifically expanding units to full names. Neither you nor I are certain of how much physics the OP knows, so going with standard abbreviations may not work. Better safe than sorry. – WhatRoughBeast Jan 9 at 4:07
• Your answer I grant is more rigerous than mine. We still make assumptions though, when we should demand clarification from the OP. +1 – Agrajag Jan 9 at 4:52

When an asteroid or comet impacts the Earth, the energy released mainly depends on the mass and velocity of the impactor.

• Using your figure of 100m diameter, an angle of 90 degrees (ie. coming straight down) and a density approximating iron @ 2.6grams per cubic centimetre, an impact velocity of a modest 20km per second - using this tool (convertalot):

• The basic energy (thermal plus sonic) released on impact is: 7.4*10^18 joules or 7.4 Exa joules.

• About 900,000 times the energy of Nagasaki's "Fat Man" at 88 Tera joules.

It would cause a flattening of the local landscape over tens of kilometers, wildfires over more.

People 500 Km away might see a flash and a glow in the sky, a few seconds later later there would be a shaking of the ground, a tremour of a distant earthquake.

A cloud of dust would gently dispurse around an oblivious world.

• Unless it hit a supervolcano calderra like Yellowstone, then you'd expect this swelling mass that's been building up to an eruption for 640,000 years to spill it's searing guts.