SUMMARY: A whole new class of mini-moons have been discovered lurking inside Saturn's rings. These tiny moons are about 100 metres (300 feet) across, and there could be as many as 10 million in total in the ring system. Scientists have wondered for many years if Saturn's rings are the result of a larger object that was shredded by Saturn gravity millions of years ago, and these moonlets could help provide the answer. They would be remnants of the former object, and could give insights into what its structure was.

View full article
What do you think about this story? post your comments below.

We've been thinking a lot about what can be called a planet. Now we have to seriously consider what we can call a moon. Does Saturn have 10 million moons? If we discover a 100 meter pile of rocks orbiting the Earth, is that a moon?

It will be several decades before we have any hope of getting a lander to any of these moonlets, but it'll be interesting to see what we can learn from such a mission.

__________________
Forming opinions as we speak

I think that the same bottom limit for size would apply... If, for example, gravitational rounding is used then anything smaller would be an asteroid (orbiting a star) or a moonlet (orbiting a non-star)

__________________
"Barbarism is the natural state of mankind. Civilization is unnatural. It is a whim of circumstance. And barbarism must always ultimately triumph" -- Conan

I want to be sure I understand you here. By this measure Deimos and Phobos would be moonlets, and Jupiter has only four moons.

__________________
Forming opinions as we speak

I was wondering that too - at the extreme, would you call each ring particle a moon? I wouldn't, but I have a name for them - nanomoons .

I suspect you would not so much "land" on a 100 meter moonlet as you would dock with it.

__________________
At night the stars put on a show for free (Carole King)

One Earth, One Sky - IYA 2009

That's correct.

__________________
"Barbarism is the natural state of mankind. Civilization is unnatural. It is a whim of circumstance. And barbarism must always ultimately triumph" -- Conan

Any criteria for dominating an orbit? No problem for Jupiter, but some of Saturn's moons might have trouble with this.

__________________
Forming opinions as we speak

Hi,

everything that orbits a planet is a moon. Everything that orbits a sun and is to cold to shine by its own light, is a planet. Everything that shines by its own light is a star. If a star orbits another star, we have a double star system. And if there are more stars orbiting each other, we have a multiple star system. Such systems are common.

It is amazing to read of a larger moon that was shredded by the gravity field of Saturn. I think this is not feasible. Why?

A moon which orbits Saturn in the rotational direction of Saturn will gradually move away from Saturn, due to tidal interaction. As such moons move away from the planet, the gravity field of Saturn becomes weaker for these moons and thus it cannot harm them. Such close to Saturn as the rings are, a moon cannot develop because this area lies within the Roche limit of Saturn, which prevents any larger body to develop there. In the realm of the rings, no large moon was able to develop.

A moon which orbits Saturn in a direction against the rotational direction of Saturn will gradually move closer to Saturn, will desintegrate as it transits the Roche limit and the pieces will finally crash into Saturn, or keep orbiting Saturn in their direction against the rotational direction of Saturn.

So far as I know, the material of the rings orbits Saturn in the rotational direction of Saturn...

Further, the material in the rings is orbiting Saturn exactly in the equatorial plane of Saturn. I think this is a clear indication that they are a relict from the formation of that planet.

We have not yet come close enough to the rings to precisely know their composition and the spectrum of sizes of the bodies which make up these rings. I read that this spectrum ranges from dust grain size to the size of houses. These are well-founded guesses. If we now look closer to these "houses", it might not be unlikely that we find that some may be larger than than expected. To find things like this, Cassini was sent to the Saturn system. Let us use it to look.

Regards,

Günther