Moons of moons

[Pingu]

About the same size as Mercury iirc.


Titan is the biggest in the solar system (hence the name) and Gannymed around Jupiter next.


[edit] Sorry, Gannymede > Titan >Io >Callisto > Our moon > the rest.

According to wikinaccurate only Ganymede & Titan are bigger than Mercury. Our moon is a fair bit smaller.

[caerau]

Yeah, that was from memory.  Something like the Mercury is about 2400 km wide, the moon is about 1700 km wide.  Same ball park.  So about 1.4ish times in volume less.


An interesting factoid is that Mercury is however MUCH more massive - about 4 times (again iirc) which lends weight to the hypothesis that the Moon is a scion of Earth, made up largely of ocean floor basalts ripped off from Earth during some cataclysmic collision with something many moons (see what I did there  ) ago.


Since planets formed as molten globules during their earliest times, their liquified nature allowed more dense elements and rocks to sink into them and form the cores.  So the moon may lack the dense iron core of the Earth - hence its lower density compared to a 'proper' planet like Mercury or Earth.


Woohoo -    [geek] -time.

[Mr Larrington]

I did have a book by Carl Sagan - I think it was "Broca's Brain" - which went into considerable detail about the various moons dotted around the solar system but it disappeared during a house move chiz.

[ian]

It's all well and good, but it's all wasted cheese until we build spaceships to bring it back.

[jsabine]

Yeah, that was from memory.  Something like the Mercury is about 2400 km wide, the moon is about 1700 km wide.  Same ball park.  So about 1.4ish times in volume less.

Closer to a third of the volume, isn't it? (v=4/3(pi*r³), so a sphere of r1200 is about 2.8x the volume of one of r850.)

That difference is then a lot closer to the difference in mass you mention.

[trekker12]

It's all well and good, but it's all wasted cheese until we build spaceships to bring it back.

Elon Musk can help you there. You will just need an ice cream scoop on a long stick

http://www.bbc.co.uk/news/science-environment-39111030

[caerau]

Yeah, that was from memory.  Something like the Mercury is about 2400 km wide, the moon is about 1700 km wide.  Same ball park.  So about 1.4ish times in volume less.

Closer to a third of the volume, isn't it? (v=4/3(pi*r³), so a sphere of r1200 is about 2.8x the volume of one of r850.)

That difference is then a lot closer to the difference in mass you mention.

They are very different in density - but yeah I should have said 1.4 ish times in diameter (or radius) less, sorry.  Certainly it does bring the figures closer together as you say.

[T42]

The Apollo CMs can more accurately be considered as temporary artificial satellites of Luna, which in turn is a natural satellite of Earth.

Yebbut I was talking about orbital mechanics, not terminology.   In orbit, the Apollo CMs obeyed Newton/Einstein just like every other body in space.

[Cudzoziemiec]

That's mentioned in the Cornell site. Given time, their orbits would have decayed and/or tidal influences would have pulled them apart.

[Brucey]

given enough time, all orbits of all objects will change or fail somehow or other; there is no such thing as 'permanent'.

IIRC the definition of 'moon' occasionally changes, as does our state of knowledge about celestial objects. Hence the Earth has been (supposedly accurately) said to have had one, two or many moons at various times in the recent past.

cheers