<p>Horizontal atmospheric entries are unlikely because the object would have to almost miss the Earth and brush against it rather than impact it (and probably would disintegrate in the atmosphere if it's a small one, due to the long flight through it in such case).</p>
<p>Vertical entries are unlikely for the opposite reason: the object would have to fly at precisely 90 degrees relative to the Earth, meaning the Earth is in the very center of the object's orbital path.</p>
<p>But if an asteroid or comet comes at another angle its path may be changed by the Earth's gravity towards about 45 degrees. This is an approximation, it is about 40-50 degrees, but 45 degrees is the most likely one out of <em>specific</em> angles.</p>

CC BY-SA 4.0
2020-07-20T08:42:45.920Z
So if an meteor fell on a hypothetical body with no mass, its incidence angle would follow a uniform law. But since the gravity of the impacted body changes the trajectory of the meteoroid, the incidence angle distribution is changed too.
usernumber
CC BY-SA 4.0
2020-07-20T09:14:13.997Z
@usernumber Right, gravity changes a meteoroid's path so that it goes towards the planet's center. Therefore, a horizontal entry is the least likely. For that, it would have to be a very fast comet.
Ioannes
CC BY-SA 4.0
2020-07-16T17:05:49.860Z
2020-07-16T17:05:49.860Z
Ioannes
<p>I've been reading the book <a href="https://www.springer.com/gp/book/9783319651774#" rel="nofollow noreferrer"><em>Planetary Geology</em></a>. In chapter 7, section 7.6, the author states that</p>
<blockquote>
<p>The angle of incidence at which asteroids or comets encounter the surface of
a planetary body follows a Gaussian probability distribution with vertical and
horizontal collisions being extremely unlikely and the highest probability existing
for 45°</p>
</blockquote>
<p>Why is this the case? Why doesn't the angle of incidence for meteoroids follow a uniform law? Isn't there just as much chance for an asteroid or a comet to arrive from any direction?</p>

<impact><meteoroid>
Incidence angles of meteoroids
usernumber
# Incidence angles of meteoroids

(Asked by: username_0 on 2020-07-16)

I've been reading the book [*Planetary Geology*](https://www.springer.com/gp/book/9783319651774#). In chapter 7, section 7.6, the author states that

> The angle of incidence at which asteroids or comets encounter the surface of
> a planetary body follows a Gaussian probability distribution with vertical and
> horizontal collisions being extremely unlikely and the highest probability existing
> for 45°

Why is this the case? Why doesn't the angle of incidence for meteoroids follow a uniform law? Isn't there just as much chance for an asteroid or a comet to arrive from any direction?

**Tags:** impact, meteoroid


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## 1 answers

### Answer by username_1 on 2020-07-16. Score: 1 | Accepted answer

Horizontal atmospheric entries are unlikely because the object would have to almost miss the Earth and brush against it rather than impact it (and probably would disintegrate in the atmosphere if it's a small one, due to the long flight through it in such case).

Vertical entries are unlikely for the opposite reason: the object would have to fly at precisely 90 degrees relative to the Earth, meaning the Earth is in the very center of the object's orbital path.

But if an asteroid or comet comes at another angle its path may be changed by the Earth's gravity towards about 45 degrees. This is an approximation, it is about 40-50 degrees, but 45 degrees is the most likely one out of *specific* angles.

> **Comments:**
> **username_0**: So if an meteor fell on a hypothetical body with no mass, its incidence angle would follow a uniform law. But since the gravity of the impacted body changes the trajectory of the meteoroid, the incidence angle distribution is changed too.  
> **username_1**: @username_0 Right, gravity changes a meteoroid's path so that it goes towards the planet's center. Therefore, a horizontal entry is the least likely. For that, it would have to be a very fast comet.  

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