How Much Energy Would be Required For...

[GWestphal]

Say a 1km spherical astroid is heading towards Earth. Assuming a density about equivalent to say granite, how much velocity would it need to punch completely through Earth?

[lakedude]

If I recall correctly, the faster an object is going (after a certain point) the more it tends to explode rather than penetrate.

Also are you asking for Energy or velocity?

[lakedude]

http://impact.ese.ic.ac.uk/ImpactEffects/

[DSF]

So you're asking for the asteroid to punch through the crust, mantle, outer core, nickel/iron inner core, and then back through all those layers again on the other side? That seems unlikely.

If we assume a human is roughly 300 mm (1 ft) thick, that's about 33 times as thick as a 9 mm bullet. Bullets deform significantly as they travel through the flesh. (I know many of them are engineered to, but flesh is still a much softer medium than rock.)

A 1 km asteroid would be trying to penetrate an object over 12,000 times as thick as it is. It's just hard to imagine that happening at any speed without the complete destruction of the asteroid.

[Paul98]

Not going to happen no matter how fast it's moving.

[Biftheunderstudy]

http://what-if.xkcd.com/20/

The more relevant stuff near the end.

[GWestphal]

Well I was thinking along the lines of rail gun projectiles can penetrate metal because they are moving several kilometers/sec, so if you ramped up something to say 10c would it have the requisite energy to just plow through?

1 km, lets say generously a density of 20 g/cm3 (uranium astroid), moving at 10c,
that nets us ~3.25e20 joules. Which really doesn't seem like that much...hmm.

So, according to D=L * A/B we're talking about needing a 4500km long projectile, but I'm fairly certain that doesn't hold up at relativistic velocities.

Actually, if a material were able to travel at multiples of c would it even have material properties any longer? Or would it just be light/energy for all intents?

[dave_the_nerd]

10c? Dude, that's Warp Factor 2.

Let's obey physics here.

[lakedude]

Originally Posted by Biftheunderstudy

http://what-if.xkcd.com/20/

The more relevant stuff near the end.

That is a great website! Thanks for the link.

[Eureka]

Originally Posted by lakedude

That is a great website! Thanks for the link.

xkcd in general is a great comic, if you haven't seen it before.

Coming off that link, here's an interesting thought: if that meteor was traveling near the speed of light and coming directly towards us, we'd never see it before it hits! Radar would be just as useless too!

[pw38]

Originally Posted by GWestphal

Well I was thinking along the lines of rail gun projectiles can penetrate metal because they are moving several kilometers/sec, so if you ramped up something to say 10c would it have the requisite energy to just plow through?

1 km, lets say generously a density of 20 g/cm3 (uranium astroid), moving at 10c,
that nets us ~3.25e20 joules. Which really doesn't seem like that much...hmm.

So, according to D=L * A/B we're talking about needing a 4500km long projectile, but I'm fairly certain that doesn't hold up at relativistic velocities.

Actually, if a material were able to travel at multiples of c would it even have material properties any longer? Or would it just be light/energy for all intents?

lol not sure if serious...

[Braznor]

You can theoretically use a 1 km radius quark/neutron degenerate matter asteroid at relativistic speeds to make the punch through effort. But beware, the gravity of the damn things will suck up large amounts of matter before it punch through the other side. Perhaps even deforming Earth into a more oval shape like a doughnut. Of course, all of this is after considering whether Earth survives such a collision instead of simply evaporating. You can use a smaller diameter for such an exotic star. A few very meter one across size should do the trick. You can get away saying the collision drilled a hundred km round doughnut through our planet's radius. Of course, the asteroid will take a severe hit in velocity too.

Otherwise just make it out of normal matter, but give it a shield or invent some kind of extremely dense material. The above was just stretching that.

[Kyanzes]

Almost completely irrelevant, but I'm wondering if it would be possible for an asteroid to flawlessly touch down on the surface of the Earth.

What I mean is a scenario where the Earth catches up with an asteroid (the right time and place, velocities being right etc.) in a way that in the end the asteroid simply touches the surface and becomes a rock sitting on it.

[tommo123]

wouldn't the earths gravity pull the rock towards it no matter what?

[Tuna-Fish]

Originally Posted by Kyanzes

Almost completely irrelevant, but I'm wondering if it would be possible for an asteroid to flawlessly touch down on the surface of the Earth.

What I mean is a scenario where the Earth catches up with an asteroid (the right time and place, velocities being right etc.) in a way that in the end the asteroid simply touches the surface and becomes a rock sitting on it.

Nope.

Earth's gravity pulls things harder as they approach. This means that for any object traveling at any speed there is a "line", beyond which they miss us completely, and within which they will hit us very hard.

[DrPizza]

Originally Posted by Kyanzes

Almost completely irrelevant, but I'm wondering if it would be possible for an asteroid to flawlessly touch down on the surface of the Earth.

What I mean is a scenario where the Earth catches up with an asteroid (the right time and place, velocities being right etc.) in a way that in the end the asteroid simply touches the surface and becomes a rock sitting on it.

Minimum impact velocity = escape velocity of the Earth = 11.2 km/s

[tynopik]

Originally Posted by DrPizza

Minimum impact velocity = escape velocity of the Earth = 11.2 km/s

You're forgetting air resistance.

Yes, asteroids can slow significantly in the air and there was even a report of someone surviving a hit by one.

They would still be travelling at least at terminal velocity, but depending on size, shape and density, that might not be terribly high.

http://www.telegraph.co.uk/news/ukne...meteorite.html
http://en.wikipedia.org/wiki/Sylacauga_%28meteorite%29

[Sunny129]

Originally Posted by tynopik

You're forgetting air resistance.

Yes, asteroids can slow significantly in the air and there was even a report of someone surviving a hit by one.

They would still be travelling at least at terminal velocity, but depending on size, shape and density, that might not be terribly high.

http://www.telegraph.co.uk/news/ukne...meteorite.html
http://en.wikipedia.org/wiki/Sylacauga_%28meteorite%29

only meteors and meteorites are affected substantially by air resistance...not whole asteroids. and in the highly unlikely event that an asteroid-sized object was going to impact the earth at only the minimum possible velocity (earth's escape velocity of 11.2 km/s), wind resistance isn't going to slow it down substantially anyways during the 10 or so seconds between atmospheric entry and ground impact.

[tynopik]

Originally Posted by Sunny129

only meteors and meteorites are affected substantially by air resistance...not whole asteroids.

A meteorite is an asteroid that makes it to the ground.

[William Gaatjes]

Originally Posted by GWestphal

Say a 1km spherical astroid is heading towards Earth. Assuming a density about equivalent to say granite, how much velocity would it need to punch completely through Earth?

When thinking of railguns, you really need very hard projectiles for such a mass and speed.
It is not for a reason these bullets are made of material with a very high density.
I think some are made of depleted uranium.
But what does density mean ?
Is it the binding energy that keeps atoms together ?

You need a very high density to perform such actions.
Thinking of an asteroid build up to perform as a single atom.
You can calculate it by finding out how much energy is needed before the atoms fall apart of the asteroid when seen as a projectile.
It will be very unrealistic however. You can perform the calculation while assuming no temperature increase. Atoms are hold together by forces. If you do several calculations, with keeping some variables ideal. You will get the picture.

Think of the startrek series. In the series, a lot of energy from that warp core reactor is used to keep the ships together while in warp. To maintain structural integrity. Why do materials fall apart ?

[Sunny129]

Originally Posted by tynopik

A meteorite is an asteroid that makes it to the ground.

no - a meteorite is a meteor that makes it to the ground. while both asteroids and meteors are solid bodies in space, the former is generally used to refer to those objects that are large enough to be seen in orbit about the sun. a meteor on the other hand is too small to bee seen while in orbit, and is discovered only if it is seen burning up in the atmosphere or found on the ground afterward. the reason i made the distinction is b/c the atmospheric entry speed of a solid object large enough to qualify as an asteroid would hardly be slowed down by wind resistance in the handful of seconds before it hit the ground, unlike much smaller meteors.