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    Default How Powerful And Big Can An Asteroid Destroy A Planet?

    I actually read a yahoo news articles saying that an asteroid size of the Empire State Building passes by planet Earth. I even made a comment it's a good thing that asteroid didn't hit the planet Earth because it'll be doomsday for Planet Earth. Then someone else says the asteroid with the sizing of the Empire State Building can only destroy the size of London, England and people with survive. And another comment saying the asteroid with the size of Long Island, New York can destroy the entire planet. So I just want to ask the science experts how big and powerful can an asteroid destroy a planet?

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    Default Re: How Powerful And Big Can An Asteroid Destroy A Planet?

    I think a big part of your question is how you're defining it. Does "destroy the planet" mean cracking it into pieces or throwing it far enough out of a stable orbit that it eventually crashes into another planet or sun? Or does "destroy the planet" mean creating enough of an environmental impact that it a large percentage of creatures living on the planet die off, and then what percentage? The latter would also depend not only on size but exactly where it hit.
    Also of great importance is mass and density, not just size. A very large asteroid that breaks into many smaller pieces is going to have to be of a different size than a very solid high metal containing asteroid that hits with most of it's impact in a single spot.

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    Default Re: How Powerful And Big Can An Asteroid Destroy A Planet?

    Well, the asteroid (actually a comet) that killed the dinos wast estimated to be somewhere between 11 and 81 kilometres in diameter, which is way bigger than this asteroid. And even that impact didn't destroy the earth. To actually destroy the earth (as in, crack the crust, melt the surface, and generally render the place sterile), you'd probably need something the size of a small moon. There are no such objects in the solar system that we wouldn't see coming a long time in advance.
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    Default Re: How Powerful And Big Can An Asteroid Destroy A Planet?

    The problem is, the mass of the asteroid isn't the most important factor--its speed is. You could entirely destroy the Earth (e.g. exceed its gravitational binding energy) with a golf ball if you could make it go fast enough.

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    Default Re: How Powerful And Big Can An Asteroid Destroy A Planet?

    Quote Originally Posted by DeTess View Post
    Well, the asteroid (actually a comet) that killed the dinos wast estimated to be somewhere between 11 and 81 kilometres in diameter, which is way bigger than this asteroid. And even that impact didn't destroy the earth. To actually destroy the earth (as in, crack the crust, melt the surface, and generally render the place sterile), you'd probably need something the size of a small moon. There are no such objects in the solar system that we wouldn't see coming a long time in advance.
    This. There's a big difference between causing major ecological damage and mass extinctions, and going all death star on a whole planet. BMH might want to look at the wikipedia page for earth's crust, to see what a tiny fraction of the earth's volume is occupied by everything that we know.

    We'd know if something like the dinosaur killer was coming at us. Whether we'd be able to effectively do anything about it is another matter.

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    Default Re: How Powerful And Big Can An Asteroid Destroy A Planet?

    The one that hit the Yucatán wasn't that big (relatively) so just in terms of destroying most of life on Earth, the answer is not that big.

    If we're talking about severe alteration of the planet's surface, Theia was about the size of Mars. Presumably it would take something on that order again, since the Earth's mass hasn't changed so much since that impact (it lost what became the moon, but also absorbed part of Theia). Should such an event occur, however, no planet would be destroyed. Shortly before the impact, the Earth would be demoted to a dwarf planet on account of having failed to clear its neighborhood.

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    Default Re: How Powerful And Big Can An Asteroid Destroy A Planet?

    Quote Originally Posted by JCarter426 View Post
    If we're talking about severe alteration of the planet's surface, Theia was about the size of Mars. Presumably it would take something on that order again, since the Earth's mass hasn't changed so much since that impact (it lost what became the moon, but also absorbed part of Theia). Should such an event occur, however, no planet would be destroyed. Shortly before the impact, the Earth would be demoted to a dwarf planet on account of having failed to clear its neighborhood.
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    Default Re: How Powerful And Big Can An Asteroid Destroy A Planet?

    Quote Originally Posted by factotum View Post
    The problem is, the mass of the asteroid isn't the most important factor--its speed is. You could entirely destroy the Earth (e.g. exceed its gravitational binding energy) with a golf ball if you could make it go fast enough.
    Considering speed is capped at the speed of light of roughly 3x10^8 m/s, no you couldn't. The Earth's gravitational binding energy is a whooping 2x10^32 joules, and so even a 1 kg golfball would at best reach 4.5 x 10^16 joules kinetic energy (which is still about a order of magnitude stronger than a megaton nuke so not soo shabby).

    Thus you would need something in the order of 10^16 kg going at the speed of light to completely destroy the Earth.
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    Default Re: How Powerful And Big Can An Asteroid Destroy A Planet?

    Quote Originally Posted by deuterio12 View Post
    Considering speed is capped at the speed of light of roughly 3x10^8 m/s, no you couldn't. The Earth's gravitational binding energy is a whooping 2x10^32 joules, and so even a 1 kg golfball would at best reach 4.5 x 10^16 joules kinetic energy (which is still about a order of magnitude stronger than a megaton nuke so not soo shabby).

    Thus you would need something in the order of 10^16 kg going at the speed of light to completely destroy the Earth.
    You're forgetting relativity. Mass dilation means that the golfball gets heavier as seen from Earth as it approaches lightspeed--there is absolutely no limit to how much kinetic energy it can have. See also: the "Oh My God particle", a single proton which entered the Earth's atmosphere above Utah in 1991 and which had the equivalent kinetic energy of a typical baseball pitch.

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    Default Re: How Powerful And Big Can An Asteroid Destroy A Planet?

    Quote Originally Posted by deuterio12 View Post
    Considering speed is capped at the speed of light of roughly 3x10^8 m/s, no you couldn't. The Earth's gravitational binding energy is a whooping 2x10^32 joules, and so even a 1 kg golfball would at best reach 4.5 x 10^16 joules kinetic energy (which is still about a order of magnitude stronger than a megaton nuke so not soo shabby).

    Thus you would need something in the order of 10^16 kg going at the speed of light to completely destroy the Earth.
    The energy kinetic of a moving object is (mass/2) x v^2 x 1/((1-(v^2)/(c^2))^.5)
    If v = c then this is a 1/0 equation, as velocity approaches the speed of light the kinetic energy approaches infinity. For example a a 1 kg golfball moving at 99.9999999999999999% would have more kinetic energy than the earth's gravitational binding energy (by I think 10x times or thereabout)
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    Default Re: How Powerful And Big Can An Asteroid Destroy A Planet?

    There is no limit to the amount of kinetic energy an object can hold, but there is a limit to how much speed an asteroid or comet can have, assuming it's not an interstellar object. I figure the speed limit on our collision is roughly solar escape velocity from Earth orbit, which is 42.1km/s~152,000km/h~0.00014C (140uC). So I propose that's the speed we use to calculate maximum kinetic energy. And that speed is low enough that relativity can be pretty safely ignored.

    Any asteroid from the main belt will be going much slower than that both relative to the sun and relative to Earth, even if a slingshot around Jupiter reverses its orbit.
    Last edited by Lvl 2 Expert; 2019-09-16 at 01:58 PM.

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    Default Re: How Powerful And Big Can An Asteroid Destroy A Planet?

    Quote Originally Posted by Lvl 2 Expert View Post
    There is no limit to the amount of kinetic energy an object can hold, but there is a limit to how much speed an asteroid or comet can have, assuming it's not an interstellar object. I figure the speed limit on our collision is roughly solar escape velocity from Eartg orbit, roughly 42.1km/s~152,000km/h~0.00014C (140uC). So I propose that's the speed we use to calculate kinetic energy. And that speed is low enough that relativity can be pretty safely ignored.
    That's a fair proposition, I suppose, but it rules out objects from outside our solar system (of which we've now detected two!) which can have higher velocities. The object cited in the linked article is currently doing 41 km/s, and is still 420 million km out from the sun. For that matter, Jupiter can accelerate objects to greater speeds as well.

    This link might be helpful: Asteroid Impact Crater Calculator.
    If your browser runs Flash, then Perdue's Impact: Earth! is good, too.

    Here's another Impact Calculator: Impact Earth. No flash required for this one.
    Last edited by Lord Torath; 2019-09-16 at 03:29 PM.
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    Default Re: How Powerful And Big Can An Asteroid Destroy A Planet?

    Quote Originally Posted by factotum View Post
    You're forgetting relativity. Mass dilation means that the golfball gets heavier as seen from Earth as it approaches lightspeed--there is absolutely no limit to how much kinetic energy it can have. See also: the "Oh My God particle", a single proton which entered the Earth's atmosphere above Utah in 1991 and which had the equivalent kinetic energy of a typical baseball pitch.
    Readin your response, my first thought would be that the golf ball would completely disintegrate when it hit Earth's atmosphere, but that doesn't really matter when traveling at such speeds. Instead of being impacted by a really hot and fast golf ball, the Earth would instead be hit by a ~45g glob of near-light plasma, which likely doesn't make it any better.

    There are a couple of XKCD What Ifs (including the very first one) that are somewhat relevant:
    Throwing a baseball at 0.9C would cause an nuclear-like explosion, leveling buildings in a ~1-mile radius

    A 100ft radius diamond impacting earth doesn't seem to do much at solar system speeds. At 72 km/s, the impact would cause an explosion similar to a large fusion bomb (Tsar Bomba maybe?). Unfortunately, he doesn't really dig into the effects of a 3000 km/s impact, and jumps from there straight to 0.99c, which would puncture the crust possibly end all life on the planet. 0.999999c is where the energy is destroying huge parts of the planet, killing everything, but not cracking it apart into pieces. At the oh-my-god particle speed (0.9999999999999999999999951c) is where the Earth is blown into smithereens, though I imagine that would happen at a lower fraction of c as well..

    Dropping Denali (Mt. McKinley) from arbitrary height to impact at 10 km/s would be a possibly civilization ending event, but not earth shattering. The article didn't state the mass of Denali that was used, but a quick google someone else estimated 6x10^13 kg (this is from Yahoo Answers and I didn't check the math, but their height was on the low side, so ). In comparison, the Chicxulub impactor, which also didn't destroy the planet but likely caused mass-extinctions, had a mass of between 1x10^15 kg and 4.6x10^17 kg (pdf), which is between 15x to 750x the guesstimated mass of Denali, and was traveling at 20 km/s.

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    Default Re: How Powerful And Big Can An Asteroid Destroy A Planet?

    It depends on what you mean by "destroy".

    The current most scientifically accepted hypothesis as to the origin of the moon posits that it was initially a dwarf planet with an orbit intersecting the orbit of Earth, and that several billion years ago the two bodies collided. This produced enough heat and energy to melt significant parts of both planets but ultimately resulted in the Earth getting larger, as most of the heavy elements from the moon were left behind on the earth

    EDIT:
    Quote Originally Posted by deuterio12 View Post
    Considering speed is capped at the speed of light of roughly 3x10^8 m/s, no you couldn't. The Earth's gravitational binding energy is a whooping 2x10^32 joules, and so even a 1 kg golfball would at best reach 4.5 x 10^16 joules kinetic energy (which is still about a order of magnitude stronger than a megaton nuke so not soo shabby).
    Momentum can increase arbitrarily though. As speed approaches c mass approaches infinity; that's a big part of the reason why you can't accelerate past the speed of light.

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    Default Re: How Powerful And Big Can An Asteroid Destroy A Planet?

    Quote Originally Posted by factotum View Post
    The problem is, the mass of the asteroid isn't the most important factor--its speed is. You could entirely destroy the Earth (e.g. exceed its gravitational binding energy) with a golf ball if you could make it go fast enough.
    Wouldn't it get converted to energy depending on how close it got to the speed of light?

    This is also bringing up a related question: what are the dividing lines between an asteroid being an asteroid, a planetoid (if those exist), a moon, or a planet? If a moon got flung out of orbit for some reason is it still considered a moon based on its size anyway, or is there another term for this? I never actually studied much astronomy.
    Last edited by Arcane_Secrets; Yesterday at 11:29 AM.

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    Default Re: How Powerful And Big Can An Asteroid Destroy A Planet?

    Quote Originally Posted by Arcane_Secrets View Post
    This is also bringing up a related question: what are the dividing lines between an asteroid being an asteroid, a planetoid (if those exist), a moon, or a planet? If a moon got flung out of orbit for some reason is it still considered a moon based on its size anyway, or is there another term for this? I never actually studied much astronomy.
    Moons are defined purely by the fact that they orbit bigger bodies - some planets, like Mars and the gas giants, have tiny moons.

    "Dwarf planet" is used when the thing is big enough that its own gravity is beginning to play a major part in its shape - "rounding it". Ceres is both an asteroid and a dwarf planet.

    "Asteroid" tends to be used for things that haven't "cleared out" all other objects of comparable size. If they're by far the biggest object in their zone, due to having absorbed most of the small objects, "planet" is used.
    Last edited by hamishspence; Yesterday at 11:32 AM.
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    Default Re: How Powerful And Big Can An Asteroid Destroy A Planet?

    Quote Originally Posted by Arcane_Secrets View Post
    Wouldn't it get converted to energy depending on how close it got to the speed of light?
    No. I'm not sure where you got that information, but nothing of the sort happens.
    The relationship between mass and energy, especially as it relates to the speed of light, isn't really intuitive or something that I fully understand, nor could I properly make you fully understand in this setting if I did. However, mass increases as the speed of light is approached.
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    Mass is energy. It's hugely energy-dense, but anywhere you have energy, you have mass. Nuclear reactions, for example, are so powerful because they're transforming a very small percentage of that mass back into free energy. As speed approaches c, energy approaches infinity. As a result, the object appears heavier to an outside frame of reference, meaning it is exponentially harder to speed it up more.
    As far as I know. There could be (read: likely are) some fundamental mistakes in my understanding, so don't take me at my word on this. At the very least, I'm sure it's much more complicated and dependent on technical laws of physics.
    That's all I can think of, at any rate.

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    Default Re: How Powerful And Big Can An Asteroid Destroy A Planet?

    Quote Originally Posted by monomer View Post
    Readin your response, my first thought would be that the golf ball would completely disintegrate when it hit Earth's atmosphere, but that doesn't really matter when traveling at such speeds. Instead of being impacted by a really hot and fast golf ball, the Earth would instead be hit by a ~45g glob of near-light plasma, which likely doesn't make it any better.
    The odds are very, very strongly against this happening, anywhere, since the universe isn't actually infinite.

    However, theoretically, the golf ball, if going fast enough, could get a long way through the Earth before turning to plasma, because that takes time and time dilates as speed approches that of light (since speed is relative, and the speed of the Earth relative to the golf ball is the same as the speed of the golf ball relative to Earth, I don't understand why Earth's time isn't also dilated).
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