# Smallest Body Possible to Have Rings

• 3point14rat
In summary, there is no minimum size for an object to support rings, as long as it can meet the conditions required for ring formation. The Roche Limit is the closest an object can orbit without breaking up, but it is not a minimum size requirement for ring support. The discovery of Centaur Chariklo having rings is scientifically plausible and has been demonstrated through data. Astronomers are still looking for the mechanism by which these rings were formed, as the centaur's weak gravity makes the usual method of tidal forces tearing a satellite apart unlikely. The radius of the object may also be a limiting factor, depending on the density ratio between the primary object and the rings.
3point14rat
What is the lower mass limit for a body to have rings?

I'm thinking that Chariklo, at 155 miles in diameter is pretty small. Gravity would be so weak you'd have to hold on just to not 'jump' off with every step.

Cheers,
3point14rat

Astronomy news on Phys.org
Awesome link Simon, very easy to understand. Thank you.

So, there is no minimum size an object can have, below which it cannot support rings? The Roche Limit sounds like it's the closest an object can orbit without breaking up, not the minimum size the primary object must be to have the gravity necessary to support rings.

I'm asking because the discovery of Centaur Chariklo doesn't seem to have raised much skepticism over the fact that such a tiny object has rings. I'm just a guy who read an article on it and immediately thought that there's no way something that small could hold onto anything, let alone a couple of rings.

Is my ignorance showing?

So, there is no minimum size an object can have, below which it cannot support rings?
"Support" is always a matter of time for rings, but there is no fundamental limit that says "this object is too small, it cannot have a ring".
The Roche Limit sounds like it's the closest an object can orbit without breaking up, not the minimum size the primary object must be to have the gravity necessary to support rings.
Right - as long as internal stiffness of the objects is negligible. This is a good assumptions for large objects, it can be wrong for small objects.
I'm just a guy who read an article on it and immediately thought that there's no way something that small could hold onto anything, let alone a couple of rings.
You can make two billard balls orbit each other in space if you like. Why not? They just have to move very slowly (and don't be too close to other massive objects).

1 person
What he said.
I'd add that the radius of the small object may be a limiting factor.
Though I haven't done the math for a body whose radius is bigger than it's Roche limit.

When you hear "rings" you tend to think "Saturn" ... but there is no need for rings to be so spectacular or even visible. Rings are generally be difficult to detect unless very big and/or they have lots of ice in them.
These ones were detected by stellar occultation with spectrographic data in support.

There's a decent reference:
http://www.nature.com/nature/journal/vaop/ncurrent/full/nature13155.html
... there's plenty there but the bulk is (sadly) behind a paywall.

Phil Plait (aka Bad Astronomy) has a nice discussion on the findings:

But basically you have not seen skepticism concerning rings about such a small object because it is scientifically plausible with well known mechanisms. The main iffy bit is that there are two well-defined rings and Phil talks about that (link above).

Last edited by a moderator:
1 person
I read Phil's article and the data really does demonstrate rings. That's awesome.

I'm still very suprised that there are rings on such a small object and that it may even have a tiny moon that's herding the rings. These situations must have a very limited life span, so we're very fortunate to be around when it's discovered.

So glad I came on here to see what smart people had to say on the subject. Thanks a heapCheers,
3point14rat

Last I heard, astronomers were still looking for the mechanism by which these rings might have been formed. This centaur's gravity is too weak for the usual method of tidal forces tearing a satellite apart. I have been thinking that this centaur orbits at a distance from the Sun at which ice (water ice) does not sublimate. But what about ammonia or methane or CO2?

Simon Bridge said:
What he said.
I'd add that the radius of the small object may be a limiting factor.
Though I haven't done the math for a body whose radius is bigger than it's Roche limit.
This just depends on the density ratio, as
$$d = 1.26\; R\left( \frac {\rho_M} {\rho_m} \right)^{\frac{1}{3}}$$
where d is the Roche limit and R is the radius of the primary object and the densities are the averages over the whole objects. Roche limit and radius scale in the same way.

## What is the smallest body known to have rings?

The smallest body known to have rings is the asteroid Chariklo, with a diameter of only 250 kilometers.

## How do rings form around small bodies?

Rings around small bodies are believed to form through a process called tidal disruption, where a passing object or moon exerts strong enough gravitational forces to break apart the surface of the body and create a ring system.

## Why are rings around small bodies rare?

Rings around small bodies are rare because most small bodies do not have enough mass or gravitational pull to form and maintain a ring system. Additionally, other factors such as the presence of moons or the body's distance from the sun can also affect the formation of rings.

## Can rings around small bodies provide information about their composition?

Yes, the composition of a small body's rings can provide valuable information about the body itself. For example, the color and reflectivity of the rings can indicate the presence of certain materials, and the thickness and density of the rings can give insights into the body's internal structure.

## Could there be smaller bodies with rings that we have not discovered yet?

It is possible that there are smaller bodies with rings that we have not discovered yet. As technology and observational techniques improve, we may be able to detect smaller and more distant bodies with rings. Additionally, some small bodies may have very faint or thin rings that are difficult to detect with current methods.

Replies
30
Views
2K
Replies
9
Views
2K
Replies
11
Views
2K
Replies
8
Views
3K
Replies
96
Views
7K
Replies
2
Views
2K
Replies
52
Views
5K
Replies
42
Views
2K
Replies
22
Views
2K
Replies
3
Views
782