destroy of Earth by asteroid

[mersecske]

Which is the asteroid size or mass
which can destroy the Earth totally
(I mean, breaking apart)?

[Ryan_m_b]

I doubt one could, the earth is ~6 billion trillion tonnes of matter. To completely break the Earth apart would require you to overcome the Gravitational Binding Energy (http://en.wikipedia.org/wiki/Gravitational_binding_energy) of all the mass of the Earth, that would require 2.23E32 joules of energy. An asteroid, even a titanic sized one could only ever hope to vaporize the biosphere and perhaps break some fragments of the Earth off.

[mersecske]

What is the time scale of the fusion (hydrogen into helium) in the Sun.
And what is the event rate?

[Ryan_m_b]

I'm not sure what you mean by "event rate". In 5 billion years the sun will convert into a red giant, I believe that by this stage hydrogen fusion will be over and helium fusion will be dominant, you might want to google that though because I'm not 100% sure

[mersecske]

Back to the asteroids and Earth.
My question is not about real world.
So lets see an imagenary planet, maybe smaller than Earth.
Asteroids usually cause only small demage on the surface,
but a real big one can brake the planet apart.
Maybe the size of the asteroid is comparable to the planet,
but my question is that it can be order of magnitude smaller or not?

[Nabeshin]

Back to the asteroids and Earth.
My question is not about real world.
So lets see an imagenary planet, maybe smaller than Earth.
Asteroids usually cause only small demage on the surface,
but a real big one can brake the planet apart.
Maybe the size of the asteroid is comparable to the planet,
but my question is that it can be order of magnitude smaller or not?

Well, the current theory about how the moon was generated suggests a mars-sized object had an off-centre collision with the Earth, and obviously the Earth survived that.

To take ryan_m_b's binding energy of 2.23e32 J, and typical collision velocities for objects in the solar system are on the order of 10km/s, so that means you need a mass of about 4e24 kg to provide that much energy, or roughly an object the size of Venus.

[mersecske]

What is
"ryan_m_b's binding energy of 2.23e32 J"
?

[Vagn]

What is
"ryan_m_b's binding energy of 2.23e32 J"
?

The binding energy that ryan_m_b talked about before.
The potential energy keeping Earth together is 2.23x1032 joules, which means you fully break Earth apart, you would need to supply that amount of energy to the Earth.

[Janus]

The binding energy that ryan_m_b talked about before.
The potential energy keeping Earth together is 2.23x1032 joules, which means you fully break Earth apart, you would need to supply that amount of energy to the Earth.

To be more accurate, you could shatter the Earth with less energy. The binding energy is the energy you need to impart to the Earth to prevent the resulting pieces from rejoining due to mutual gravitational attraction.