reply to post by eriktheawful
The strange moon appears to be pitted by numerous lightening-bolt strikes and arcing as if a giant arc welder's device was held close to the moon's
surface. The pitting looks like the pitting of our moon . Could both the moon and this strange moon be hollow?
Hollow inside, as in the outer part we see is just a rocky shell with large chambers or a single large chamber inside?
I doubt it seriously based up on the physics involved:
We know our moon has a mass of 7.3477 × 10^22 kg (or 73,477,000,000,000,000,000,000 kg) and a density of 3.3464 g/cm^3 (which is an average density
of many types of rocks).
We are able to tell this based upon some other things: the size of the moon, and it's gravity.
When we have space craft flyby or orbit another body in space, the way the space craft behaves shows us how that object's gravity is affecting it.
This in turn allows us to figure out an object's mass much more accurately because any object with mass has gravitation, and the more mass it has,
the more gravitation it has.
A very good example of how this helps us is when Voyager 2 flew by Neptune. For a very long time, Neptune's mass was something hard for us to figure
out. However, the effect it's gravity had on Voyager 2 as it flew by Neptune allowed us to calculate Neptune's mass with a high degree of
It works the same for Mimas as Cassini has flown by it and we are able to measure the effect it's gravity had on the Cassini probe, and of course all
the different space craft that we have had fly to the moon and especially those that have orbited it.
Another way to infer an object's mass, is by knowing it's density and size. An object that is filled with air is going to be less dense than a solid
object. The denser it is, the more mass it has.
You can observe this using a 2 liter bottle of soda. A 2 liter bottle of soda is filled with a liquid that consists mostly of water, ingredients like
sugar and coloring that has a density just a little bit more than water. Then the plastic of the bottle itself also has a specific density. Measuring
the bottle gives us it's size and of course it's volume.
Now pour out all the soda from the bottle. It's density is now drastically different as the bottle is filled with air now and not a more dense
material (the liquid soda). You can tell it's mass has changed without even having to measure it simply by how the empty bottle full of air feels in
your hand compared to a full bottle.
With our moon (and Mimas) we can measure their size (which also gives us their volume using basic geometry). Spectral analysis of it's surface tells
us what they are made of (at least on the surface, since that is the area that is reflecting the sun's light). However what we see and what the
spectroanalysis tells us can be highly suggestive of what is below that center.
What helps us know better is that space craft traveling near it. When it flies by it, gravity pulls on the space craft, changing it's course. The
amount of pull is known by how much we have to tell the craft to correct it's flight path to compensate for that pull.
Now we are armed with really good information: Size, Volume and Gravitational Strength.
By knowing those 3 things, you can find an object's mass using physics. When you know the object's mass, you can then calculate it's density
because knowing the mass of an object, and it's size is going to tell you how dense something is.
Density tells us a lot of what an object is made up of. Objects with densities that are close to 1.0 g/cm^3 tells us there is a LOT of water there
because that is the density of water. Having a density of 3.0 g/cm^3 or more tells us the object is made up mostly of rock.
For example, the average density of Earth is 5.515 g/cm^3.
If our moon (or Mimas) were hollow, then their density would be a LOT lower. For example, our air at sea level and 0 deg C has a density of only
You can physically feel the difference when you walk through the air (least dense), walking through deep water (more dense) and try to walk through a
large rock (most dense, and will hurt if you try to do that).
Another example is my 30 gallon fish tank. when it's empty, I can pick it up. When it's full of water, there is no way I can pick it up as it is
much to heavy, and if it were full of a denser material than water, say sand, it would be equally impossible for me to pick up or move.
Using a simple equation, F=mg, where F = force measured in Newtons, m = mass of object and g = gravitational acceleration of that object, we can find
out what an object's mass is if we know the force and the gravitational acceleration of that object. If we use it for the moon (because we know how
space craft act trying to navigate around the moon) we are able to use that formula to find the moon's mass.
Now, if the moons were hollow all those numbers would be different, because the mass of the moons would be a LOT lower, because their density would be
a LOT lower. As this makes their mass a LOT lower, then their gravitational attraction would also be a LOT lower.
Having such a low gravitational attraction, we would not get the tides we get here on Earth either.
It IS possible for there to be "voids" inside both our moon and other moons, smaller areas that have no mater in them. But the basic physics for how
these moons behave show that they are not hollow.
The math just does not work out for it.