<p>For such a body (if it exists) the axis of rotation would not intersect with the surface of the body, so there is no &quot;pole&quot; on the surface.</p>
<p>This might cause a few issues for cartography software, but apart from that there's no particular requirement to define &quot;extreme ends&quot; of an asteroid.  For cartography, a simple &quot;longitude&quot; and &quot;Latitude&quot; grid would not be appropriate, and some kind of custom solution.</p>
<p>As a further practical issue, a highly concave body, such as comet 67P, would have a high chance of having a &quot;tumbling&quot; motion, and so the axis of rotation would not be fixed and the &quot;poles&quot; of rotation would not be fixed.</p>
<p>For Comet 67P there is <a href="https://3d-asteroids.space/comets/67P-Churyumov-Gerasimenko" rel="nofollow noreferrer">a &quot;custom solution&quot;</a></p>

CC BY-SA 4.0
2023-06-14T03:59:58.707Z
2023-06-14T03:59:58.707Z
James K
<p>Continuation of: <a href="https://astronomy.stackexchange.com/questions/40214/what-is-the-definition-of-a-pole-of-a-celestial-body">What is the definition of a &quot;pole&quot; of a celestial body?</a></p>
<hr />
<p><a href="https://astronomy.stackexchange.com/questions/40214/what-is-the-definition-of-a-pole-of-a-celestial-body/40220#40220">uhoh's answer</a> says that distinct bodies should have a center of mass. If the body is spherical, then the COM will be near the middle of the body. By definition, the body's rotational axis should pass though COM and the extreme ends of this rotational axis should be considered &quot;poles&quot;.</p>
<p>But what about bodies whose COM lies outside the body itself? For instance, crazy C-shaped objects. In this cases, the COM lies outside the body, the axis of rotation does not intersect the body's surface and so technically, there are no &quot;poles&quot; for such bodies. So, how should we describe the &quot;extreme ends&quot; of the body?</p>
<p><sub>Note: There are a few bodies where there are no stable poles but they have their reasons. Saturn's moon Hyperion and the asteroid 4179 Toutatis lack a stable north pole. They rotate chaotically because of their irregular shape and gravitational influences from nearby planets and moons, and as a result the instantaneous pole wanders over their surface, and may momentarily vanish altogether.</sub></p>

CC BY-SA 4.0
2020-12-06T09:31:38.260Z
I would say that in absence of an inner magnetic field or a more or less stable rotation vs a defined plane or axes then there aren't poles of sort. Instantaneous rotational poles do obviously exist.
Alchimista
CC BY-SA 4.0
2020-12-06T15:19:08.507Z
Hard to prove the negative, but I don't think there are any C-shaped asteroids.  Such a body would need to be rigid enough to support its mass against its own gravity (so not a rubble pile). There are some asteroids with significant concavities, but I can't find any for which the COM would be outside the body. Even if it did exist, and doesn't have a "pole"... so what...  What do we need "poles" for anyway?
James K
CC BY-SA 4.0
2020-12-06T21:35:21.877Z
@uhoh mentioned https://en.wikipedia.org/wiki/67P/Churyumov%E2%80%93Gerasimenko which to my mind is more "r" shaped than "c" shaped, but still seems to have a decent chance of the axis of rotation intersecting the object in other-than-exactly-two-evenly-spaced places.
Jack Schmidt
CC BY-SA 4.0
2020-12-07T02:53:57.597Z
@JamesK poles can be helpful in describing the extreme ends of the body just like north pole and south pole; incidentally [433 eros](https://en.wikipedia.org/wiki/433_Eros?wprov=sfla1)   is kind of elongated peanut or shoe shaped asteroid.
Nilay Ghosh
<orbit><astrophysics><rotation><pole>
What should be the "poles" for irregular shaped bodies?
Nilay Ghosh
# What should be the "poles" for irregular shaped bodies?

(Asked by: username_0 on 2020-12-06)

Continuation of: [What is the definition of a "pole" of a celestial body?](https://astronomy.stackexchange.com/questions/40214/what-is-the-definition-of-a-pole-of-a-celestial-body)

---

[uhoh's answer](https://astronomy.stackexchange.com/questions/40214/what-is-the-definition-of-a-pole-of-a-celestial-body/40220#40220) says that distinct bodies should have a center of mass. If the body is spherical, then the COM will be near the middle of the body. By definition, the body's rotational axis should pass though COM and the extreme ends of this rotational axis should be considered "poles".

But what about bodies whose COM lies outside the body itself? For instance, crazy C-shaped objects. In this cases, the COM lies outside the body, the axis of rotation does not intersect the body's surface and so technically, there are no "poles" for such bodies. So, how should we describe the "extreme ends" of the body?

Note: There are a few bodies where there are no stable poles but they have their reasons. Saturn's moon Hyperion and the asteroid 4179 Toutatis lack a stable north pole. They rotate chaotically because of their irregular shape and gravitational influences from nearby planets and moons, and as a result the instantaneous pole wanders over their surface, and may momentarily vanish altogether.

**Tags:** orbit, astrophysics, rotation, pole

> **Comments:**
> **username_1**: I would say that in absence of an inner magnetic field or a more or less stable rotation vs a defined plane or axes then there aren't poles of sort. Instantaneous rotational poles do obviously exist.  
> **username_2**: Hard to prove the negative, but I don't think there are any C-shaped asteroids.  Such a body would need to be rigid enough to support its mass against its own gravity (so not a rubble pile). There are some asteroids with significant concavities, but I can't find any for which the COM would be outside the body. Even if it did exist, and doesn't have a "pole"... so what...  What do we need "poles" for anyway?  
> **username_3**: @uhoh mentioned https://en.wikipedia.org/wiki/67P/Churyumov%E2%80%93Gerasimenko which to my mind is more "r" shaped than "c" shaped, but still seems to have a decent chance of the axis of rotation intersecting the object in other-than-exactly-two-evenly-spaced places.  
> **username_0**: @username_2 poles can be helpful in describing the extreme ends of the body just like north pole and south pole; incidentally [433 eros](https://en.wikipedia.org/wiki/433_Eros?wprov=sfla1)   is kind of elongated peanut or shoe shaped asteroid.  

---

## 1 answers

### Answer by username_2 on 2023-06-14. Score: 3 | Accepted answer

For such a body (if it exists) the axis of rotation would not intersect with the surface of the body, so there is no "pole" on the surface.

This might cause a few issues for cartography software, but apart from that there's no particular requirement to define "extreme ends" of an asteroid. For cartography, a simple "longitude" and "Latitude" grid would not be appropriate, and some kind of custom solution.

As a further practical issue, a highly concave body, such as comet 67P, would have a high chance of having a "tumbling" motion, and so the axis of rotation would not be fixed and the "poles" of rotation would not be fixed.

For Comet 67P there is [a "custom solution"](https://3d-asteroids.space/comets/67P-Churyumov-Gerasimenko)


---

