<p>This is a nice little Fermi problem, and can be answered if we don't take it too seriously. The Chicxulub impact was 20km/s and about 10 kilometers in diameter (with a density of about 3g/cm³). Mass is proportional to volume and so is proportional to the cube of the diameter.</p>
<p>Energy = ½mv² so energy is proportional to the cube of the diameter and to the square of the velocity.</p>
<p>One mile is about ⅙ of 10km  so the mass decreases by a factor of 1/216, and so to keep the same energy the velocity must be increased by a factor of √216, which is 6√6 or about 15.</p>
<p>So the velocity of the one-mile impactor would have to be about 300 km/s to impact with the same energy. This is considerably higher than the maximum theoretical velocity that a solar orbiting asteroid could have with Earth (anything going that fast won't be orbiting the Sun).</p>
<p>There are lots of uncertainties here, which is why this is only a Fermi estimate.</p>

CC BY-SA 4.0
2023-02-16T20:52:14.370Z
yes. However, it could be in an elliptical-type orbit around the sun (and I mean REALLY elliptical.) and the earth is at the periapsis of this orbit (where it will be going fastest) not only will this high velocity from the gravity assist type thing the elliptical orbit has, but the Earth's gravitational pull may also accelerate it. Still, like you said, we shouldn't take this too seriously. Especially not this theory.
Deko Revinio
CC BY-SA 4.0
2023-02-16T21:20:42.833Z
Even if you put this thing on a parabolic orbit, it will have a velocity relative to the sun of less than 45km/s at perihelion (that is escape velocity from the sun),  if it is moving retrograde around the sun and colliding head on, that is 75km/s, adding 11km/s for the Earths gravity brings us to 86km/s. So that is the limit for any asteroid, The practical limit is less, more like 50km/s. Anything faster must be on a hyperbolic orbit.
James K
CC BY-SA 4.0
2023-02-16T21:23:02.477Z
That's going on the list of one of my absolute biggest miscalculations.
Deko Revinio
CC BY-SA 4.0
2023-02-17T03:19:57.470Z
So the asteroid would have to come from outside the solar system.  That's not completely impossible, is it?
Mark Ransom
CC BY-SA 4.0
2023-02-17T05:31:44.473Z
@MarkRansom An interstellar asteroid impacted the earth in 2014, although it was only 1m in size. A much bigger one is improbable, but not impossible.
Nuclear Hoagie
CC BY-SA 4.0
2023-02-17T06:28:59.993Z
@NuclearHoagie potential intersteller asteroid.  There is quite a lot of scepticism about these claims
James K
CC BY-SA 4.0
2023-02-17T08:06:39.197Z
A flaw in this calculation is the assumption that the density would be the same. You can have highly metalic asteroid with 5 times the density. Then the speed wouldn't be that drastic.
Negdo
CC BY-SA 4.0
2023-02-17T08:12:16.783Z
@Negdo The upper limit is about 7 times the density (pure osmium) but even in that case speed is still 100 km/s, so it doesn't actually change much.
Zizy Archer
CC BY-SA 4.0
2023-02-17T17:22:03.790Z
@ZizyArcher Of course, a pure osmium asteroid of that size would be positively terrifying for entirely different reasons, even if you ignore the question of how it exists in the first place.
Austin Hemmelgarn
CC BY-SA 4.0
2023-02-18T03:28:36.123Z
Not only must the object be from outside the solar system but I'm not seeing an orbit that allows it to be part of our galaxy--too fast for something orbiting with us, too slow for something retrograde.
Loren Pechtel
CC BY-SA 4.0
2023-02-18T19:10:34.747Z
Also because the mass is smaller and the impact velocity higher, the initial velocity needs to be much higher. These factors cause air friction to be more significant. I'm not sure how big of a role air friction plays on these scales but I can imagine that it would be significant
AccidentalTaylorExpansion
CC BY-SA 4.0
2023-02-19T21:18:18.127Z
@AccidentalTaylorExpansion atmospheric effects become less significant the larger an object is because the amount of air they interact with relative to their own mass decreases.  For a planet killer class object I don't believe it would have any effect beyond setting things in line of sight on fire a few seconds prior to impact.
Dan Is Fiddling By Firelight
CC BY-SA 4.0
2023-02-16T17:12:03.577Z
2023-02-17T07:15:45.843Z
2023-02-17T07:15:45.843Z
James K
<p>I was playing a silly asteroid game and had a question in my head: how fast would a mile long meteor have to go to match the impact of the Chicxulub impact? (The impact that killed the dinosaurs.)</p>

CC BY-SA 4.0
2023-02-18T08:27:53.053Z
Our question is poorly phrased.   A meteoroid is is defined as a space object larger than a grain of space dust and smaller than one meter in diameter; a larger object is defined as an asteroid.  A meteor is defined as the trail of glowing gases left by the passage of a solid object like a meteoroid or asteroid though the atmosphere of Earth.  Thus calling a solid object a meteor is inaccurate.  Saying your asteroid is one mile long implies that it is rather cylindrical in shape and thus its volume is undefined by you, though James K assumed it was spherical.
M. A. Golding
<asteroids><meteor>
How fast would a one mile asteroid have to go for it to match the impact that killed the dinosaurs?
Student man boy
# How fast would a one mile asteroid have to go for it to match the impact that killed the dinosaurs?

(Asked by: username_0 on 2023-02-16)

I was playing a silly asteroid game and had a question in my head: how fast would a mile long meteor have to go to match the impact of the Chicxulub impact? (The impact that killed the dinosaurs.)

**Tags:** asteroids, meteor

> **Comments:**
> **username_1**: Our question is poorly phrased.   A meteoroid is is defined as a space object larger than a grain of space dust and smaller than one meter in diameter; a larger object is defined as an asteroid.  A meteor is defined as the trail of glowing gases left by the passage of a solid object like a meteoroid or asteroid though the atmosphere of Earth.  Thus calling a solid object a meteor is inaccurate.  Saying your asteroid is one mile long implies that it is rather cylindrical in shape and thus its volume is undefined by you, though username_2 assumed it was spherical.  

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## 1 answers

### Answer by username_2 on 2023-02-16. Score: 27 | Accepted answer

This is a nice little Fermi problem, and can be answered if we don't take it too seriously. The Chicxulub impact was 20km/s and about 10 kilometers in diameter (with a density of about 3g/cm³). Mass is proportional to volume and so is proportional to the cube of the diameter.

Energy = ½mv² so energy is proportional to the cube of the diameter and to the square of the velocity.

One mile is about ⅙ of 10km so the mass decreases by a factor of 1/216, and so to keep the same energy the velocity must be increased by a factor of √216, which is 6√6 or about 15.

So the velocity of the one-mile impactor would have to be about 300 km/s to impact with the same energy. This is considerably higher than the maximum theoretical velocity that a solar orbiting asteroid could have with Earth (anything going that fast won't be orbiting the Sun).

There are lots of uncertainties here, which is why this is only a Fermi estimate.

> **Comments:**
> **username_3**: yes. However, it could be in an elliptical-type orbit around the sun (and I mean REALLY elliptical.) and the earth is at the periapsis of this orbit (where it will be going fastest) not only will this high velocity from the gravity assist type thing the elliptical orbit has, but the Earth's gravitational pull may also accelerate it. Still, like you said, we shouldn't take this too seriously. Especially not this theory.  
> **username_2**: Even if you put this thing on a parabolic orbit, it will have a velocity relative to the sun of less than 45km/s at perihelion (that is escape velocity from the sun),  if it is moving retrograde around the sun and colliding head on, that is 75km/s, adding 11km/s for the Earths gravity brings us to 86km/s. So that is the limit for any asteroid, The practical limit is less, more like 50km/s. Anything faster must be on a hyperbolic orbit.  
> **username_3**: That's going on the list of one of my absolute biggest miscalculations.  
> **username_4**: So the asteroid would have to come from outside the solar system.  That's not completely impossible, is it?  
> **username_5**: @username_4 An interstellar asteroid impacted the earth in 2014, although it was only 1m in size. A much bigger one is improbable, but not impossible.  
> **username_2**: @username_5 potential intersteller asteroid.  There is quite a lot of scepticism about these claims  
> **username_6**: A flaw in this calculation is the assumption that the density would be the same. You can have highly metalic asteroid with 5 times the density. Then the speed wouldn't be that drastic.  
> **username_7**: @username_6 The upper limit is about 7 times the density (pure osmium) but even in that case speed is still 100 km/s, so it doesn't actually change much.  
> **username_8**: @username_7 Of course, a pure osmium asteroid of that size would be positively terrifying for entirely different reasons, even if you ignore the question of how it exists in the first place.  
> **username_9**: Not only must the object be from outside the solar system but I'm not seeing an orbit that allows it to be part of our galaxy--too fast for something orbiting with us, too slow for something retrograde.  
> **username_10**: Also because the mass is smaller and the impact velocity higher, the initial velocity needs to be much higher. These factors cause air friction to be more significant. I'm not sure how big of a role air friction plays on these scales but I can imagine that it would be significant  
> **username_11**: @username_10 atmospheric effects become less significant the larger an object is because the amount of air they interact with relative to their own mass decreases.  For a planet killer class object I don't believe it would have any effect beyond setting things in line of sight on fire a few seconds prior to impact.  

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