Fifth moon found around Pluto!:

Originally posted by Soothfast
As with the term "planet," I think a more rigorous definition for what constitutes a "moon" is in order. Once we get down to the size of a double-wide trailer it's not a moon.

There is one already. I don't know the details, or even the official terms; I just know that the distinction is made by real astronomers who understand these matters better than I.
However, AIUI a proper moon is a body orbiting anothing body which was formed from that larger body, or from the same accretion disc (as our moon is believed to be, and I think Charon as well, for Pluto). A pseudo-moon is any heap of rock which happens to circle any (dwarf?) planet. The Earth has a number of these as well, all of them small (smallish, anyway). Obviously, this distinction would be important if Pluto's moons are to be used to draw conclusions about Pluto's origin.

Richard

Originally posted by Shallow Blue
There is one already. I don't know the details, or even the official terms; I just know that the distinction is made by real astronomers who understand these matters better than I.
However, AIUI a proper moon is a body orbiting anothing body which was formed from that larger body, or from the same accretion disc (as our moon is believed to be, and I th ...[text shortened]... mportant if Pluto's moons are to be used to draw conclusions about Pluto's origin.

Richard

Where are you getting this? Astronomy sites I've gone to say (if they say anything at all) only that there is no "hard" definition. The definition you give is reasonable, but try to find the astronomy textbook that says Mars has no moons, or that Jupiter has only four moons.

Originally posted by Soothfast
Where are you getting this? Astronomy sites I've gone to say (if they say anything at all) only that there is no "hard" definition. The definition you give is reasonable, but try to find the astronomy textbook that says Mars has no moons, or that Jupiter has only four moons.

I got this idea from a (popularising but not braindead) television program on astronomy, but to be honest I can't recall which one.

In any case, however they want to call it, the distinction would be relevant in this case.

Richard

Originally posted by Shallow Blue
In any case, however they want to call it, the distinction would be relevant in this case.

I have no problem with distinguishing moons based on thier origin, but I see no reason to use the term pseudo for the distinction. The word 'moon' as far as I know in no way suggests a common origin with the planet and just refers to the fact that it is an orbiting body. The Wikipedia page even says that man made satellites have at times been referred to as 'moons' and for this reason titles the page on the subject 'Natural Satellites' instead of 'Moons'.
So I would prefer something like 'common origin natural satellite' and 'foreign object natural satellite' or the equivalent with 'moon'. I don't think pseudo-moon gives the right impression at all. To me, it suggests the object does not really orbit the planet or something along those lines.

I also see no problem with creating a size distinction. Wikipedia mentions that very small objects have at times been called 'moonlets'.

Originally posted by twhitehead
I have no problem with distinguishing moons based on thier origin, but I see no reason to use the term pseudo for the distinction. The word 'moon' as far as I know in no way suggests a common origin with the planet and just refers to the fact that it is an orbiting body. The Wikipedia page even says that man made satellites have at times been referred to ...[text shortened]... ikipedia mentions that very small objects have at times been called 'moonlets'.

To me, pseudo moons would be those with temporary orbits, that are unstable orbitwise and may revolve around a larger body for some time but the inherent instability will come in to play and it will be flung out of the system, maybe by interaction with larger moons in the same area.

Originally posted by sonhouse
To me, pseudo moons would be those with temporary orbits, that are unstable orbitwise and may revolve around a larger body for some time but the inherent instability will come in to play and it will be flung out of the system, maybe by interaction with larger moons in the same area.

What's your time frame? Both Phobos and Triton are scheduled for a crash landing eventually.

Originally posted by twhitehead
I have no problem with distinguishing moons based on thier origin, but I see no reason to use the term pseudo for the distinction.

Well, as I said all along, I am not at all sure about the terminology, I'm just interested in the scientific significance of this object.

Richard

Originally posted by Soothfast
What's your time frame? Both Phobos and Triton are scheduled for a crash landing eventually.

Not if we can help it🙂