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Old 08-10-2019, 10:03 AM
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Saturn overtakes Jupiter as planet with most moons - 20 new ones discovered

Originally Posted by Paul Rincon, Science Editor, BBC, 8 Oct 2019
Saturn has overtaken Jupiter as the planet with the most moons, according to US researchers.

A team discovered a haul of 20 new moons orbiting the ringed planet, bringing its total to 82; Jupiter, by contrast, has 79 natural satellites.

The moons were discovered using the Subaru telescope on Maunakea, Hawaii.

Each of the newly discovered objects in orbit around Saturn is about 5km (three miles) in diameter; 17 of them orbit the planet "backwards".

This is known as a retrograde direction. The other three moons orbit in a prograde direction - the same direction as Saturn rotates.
Originally Posted by Paul Rincon, Science Editor, BBC, 8 Oct 2019
The finds were made by applying new computing algorithms to data gathered between 2004 and 2007 with the Subaru telescope. These algorithms were able to fit orbits to potential moons identified in the old data.
Story here -
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Old 08-10-2019, 08:01 PM
Dazzled by the Cosmos.

Dennis is offline
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Oh No - I thought I was doing well to record 9 of them with my old C9.25...


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Old 08-10-2019, 09:44 PM
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Moon or Moonlet?

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.



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Old 08-10-2019, 10:53 PM
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billdan (Bill)
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You would be upset to learn that Professional Astronomers believe there could be another 100 smaller moons orbiting Saturn.

I don't know if we need to reclassify them, by definition if they orbit a planet they are called a moon, size is irrelevant.

( I also think Pluto should retain its planet status)
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