[ngcles]

Hi Gary & All,

Marvellous technical feat to detect these very tiny bodies -- kudos to all those involved but leads to another question.

How big/massive does a body have to be to be designated a "Moon".

I believe we need to think about writing a definition in the same way we did with the planet/dwarf planet ... thing.

When I was a young lad just starting as an amateur astronomer, my How and Why Wonder Book "Stars" (published 1968) had the (known) moon count:

Mercury & Venus: 0
Earth: 1
Mars: 2
Jupiter: 12
Saturn: 9
Uranus: 5
Neptune: 2

During my lifetime, the count of natural satellites for major planets in our solar-system has blown out from 31 to 205 -- over 660%. In my mid-fifties and assuming I am about 2/3rds of the way through my life-span it would be reasonable to assume that on my demise, the number of "moons" in our solar-system would be somewhere between five hundred and one thousand -- an absurd number and really, meaningless.

I think we should introduce a division between moons and moonlets.

I know it's a somewhat arbitrary line I'm drawing here, but I'd suggest that for it to be classed as a "moon" it must be a body (a) in a closed orbit around a major planet (any one of the eight) and either (b) have a major axis radius greater than 50km and/or (b) have an estimated mass greater than 10^18kg. Any body that does not meet a+b or a+c would be classed as a "moonlet". Unlike the planet/dwarf planet test, hydrostatic equilibrium is not required nor is clearing its orbit.

In the above scheme (a) the IAU retains jurisdiction over naming moons, (b) no existing moons with names would be "un-named" (merely re-classified) while newly discovered moonlets are instead numbered.

Under that definition, Jupiter would therefore have 7 moons, Saturn 10, Uranus 8, Neptune 6, Earth 1 making a grand total of 32 and a combined count of 173 known moonlets in the rest of the solar-system.

Yes I know this would mean re-classifying Phobos and Deimos, but they wouldn't become "un-named", merely re-classified. I know that might upset one or few people but you can't make an omelette without breaking a few eggs.

It's an arbitrary line, but I think we have to draw a line somewhere before this gets out of control.

Thoughts?

Best,

L.