New moon for Uranus

[AstroMike]

http://www.jpl.nasa.gov/releases/200...e_2002_197.cfm

Total of Uranian satellites now 21.

[GrapesOfWrath]

I forget, who's ahead now?

I thought I found the perfect webpage to answer that, but it seems to be broken.

[Superstring]

Jupiter has 27 confirmed, plus 11 more recently discovered that have not been confirmed. Saturn has 18, and then 12 that have not yet been confirmed. Uranus has 21, Neptune 8.

So as of right now, Jupiter is in the lead.

[Laser Jock]

How small can an object be and still be considered a moon? Seems to me that these 'moons' are getting rather small.

[Superstring]

On 2002-10-28 15:05, Laser Jock wrote:
How small can an object be and still be considered a moon? Seems to me that these 'moons' are getting rather small.

Well, a moon is afterall a celestial body that orbits a planet/asteroid. So technically, you don't have a limit as to the size of it. I seriously think though, anything smaller than 1km should be dubbed as nothing more than a space grain (which there are probably tons of these orbiting the planets anyways; no use in naming 100 moons the size of your head).

[GrapesOfWrath]

On 2002-10-28 15:05, Laser Jock wrote:
How small can an object be and still be considered a moon? Seems to me that these 'moons' are getting rather small.

Yeah, but what about the object formerly known as J002E3, the "new moon" of Earth which turned out to be an Apollo booster. That was pretty small. We discussed it in this thread.

[Laser Jock]

On 2002-10-28 15:41, GrapesOfWrath wrote:

Yeah, but what about the object formerly known as J002E3, the "new moon" of Earth which turned out to be an Apollo booster. That was pretty small. We discussed it in this thread.

My point exactly. Like a planet, what makes up a moon should also be well defined (ie. spherical, a certian size and/or mass, etc.).

[CJSF]

On 2002-10-28 16:39, Laser Jock wrote:
My point exactly. Like a planet, what makes up a moon should also be well defined (ie. spherical, a certian size and/or mass, etc.).

I disagree. I think having a perhaps deliberately UNdefined terminology is actually a good thing. It stimulates debate and intellectual discourse. If everything gets defined, what then do we have to talk about?

CJSF

[GrapesOfWrath]

I don't think we need any more stimulation. [img]/phpBB/images/smiles/icon_smile.gif[/img]

[Atko]

On 2002-10-28 16:39, Laser Jock wrote:
My point exactly. Like a planet, what makes up a moon should also be well defined (ie. spherical, a certian size and/or mass, etc.).

Better ditch "spherical" if you want to keep Phobos and Deimos in the fold.
[img]/phpBB/images/smiles/icon_smile.gif[/img]

[AstroMike]

On 2002-10-28 16:59, Atko wrote:

On 2002-10-28 16:39, Laser Jock wrote:
My point exactly. Like a planet, what makes up a moon should also be well defined (ie. spherical, a certian size and/or mass, etc.).

Better ditch "spherical" if you want to keep Phobos and Deimos in the fold.
[img]/phpBB/images/smiles/icon_smile.gif[/img]

And Hyperion too (longest dimension about 360 km).

[Superstring]

Yeah don't worry about whether its spherical or not. Hyperion was probably larger anyways, it just suffered badly from a catstrophic impact. The largest non-spherical moon in the solar system is Neptune's Proteus which has a diameter of about 418 km. Usually any body larger than 400km has enough material to develop spherically (again, Proteus is the exception).

[GrapesOfWrath]

On 2002-10-28 19:24, Superstring wrote:
The largest non-spherical moon in the solar system is Neptune's Proteus which has a diameter of about 418 km. Usually any body larger than 400km has enough material to develop spherically (again, Proteus is the exception).

I don't know if you can say that. It doesn't appear to be the exception at all--instead it seems to be the rule. We discussed this in regards to asteroids in this thread--all the asteroids up to and including Ceres seem to have a distinctly non-spheroidal shape. Ceres has a diameter of more than twice Proteus's.

[Superstring]

On 2002-10-28 19:57, GrapesOfWrath wrote:
I don't know if you can say that. It doesn't appear to be the exception at all--instead it seems to be the rule. We discussed this in regards to asteroids in this thread--all the asteroids up to and including Ceres seem to have a distinctly non-spheroidal shape. Ceres has a diameter of more than twice Proteus's.

That's true. However, and correct me if I'm wrong, but don't bodies with an icy composition develop spherically easier than those composed of rock? I remember hearing this somewhere, and it sounds pretty logical. So Ceres and other large asteroids being irregular-shaped is not surprising considering they are made up of mostly rock rather than ice.

[GrapesOfWrath]

On 2002-10-28 21:20, Superstring wrote:
That's true. However, and correct me if I'm wrong, but don't bodies with an icy composition develop spherically easier than those composed of rock? I remember hearing this somewhere, and it sounds pretty logical. So Ceres and other large asteroids being irregular-shaped is not surprising considering they are made up of mostly rock rather than ice.

Isn't Proteus rock also?

I looked up Proteus at Nine Planets, and it repeats what you say about it being about as big as it can be without being pulled into a spherical shape by gravity, but it would seem that those asteroid examples are even bigger ones.

[Superstring]

On 2002-10-29 05:54, GrapesOfWrath wrote:

On 2002-10-28 21:20, Superstring wrote:
That's true. However, and correct me if I'm wrong, but don't bodies with an icy composition develop spherically easier than those composed of rock? I remember hearing this somewhere, and it sounds pretty logical. So Ceres and other large asteroids being irregular-shaped is not surprising considering they are made up of mostly rock rather than ice.

Isn't Proteus rock also?

I looked up Proteus at Nine Planets, and it repeats what you say about it being about as big as it can be without being pulled into a spherical shape by gravity, but it would seem that those asteroid examples are even bigger ones.

Well the composition of Proteus is pretty much unknown (especially without density estimates). So I'm not sure if it composed of more rock or ice. I'm wondering if some sort of mechanism in the early solar system formation prevented the asteroids from gravity pulling themselves into a spherical shape (maybe a bloated Jupiter???) Hmmmmmm.

[The Shade]

On 2002-10-28 15:05, Laser Jock wrote:
How small can an object be and still be considered a moon? Seems to me that these 'moons' are getting rather small.

Laser Jock (love the name BTW) has a point. If we count every object revolving around a planet as a moon, then the gas giants would have trillions of them if you count the ring particles orbiting each planet.

(Added a correction: originally stated that gas giants would have millions, not trillions of moons if all ring particles were counted.)

<font size=-1>[ This Message was edited by: The Shade on 2002-10-30 08:35 ]</font>

[GrapesOfWrath]

On 2002-10-29 06:57, Superstring wrote:
I'm wondering if some sort of mechanism in the early solar system formation prevented the asteroids from gravity pulling themselves into a spherical shape

When they talk about gravity pulling the object into a spherical shape, the reference is to its current gravity--that is, the strength of its gravity would tend to make the object spherical now, meaning plus or minus a million years. [img]/phpBB/images/smiles/icon_smile.gif[/img]

[Superstring]

On 2002-11-05 06:26, GrapesOfWrath wrote:

On 2002-10-29 06:57, Superstring wrote:
I'm wondering if some sort of mechanism in the early solar system formation prevented the asteroids from gravity pulling themselves into a spherical shape

When they talk about gravity pulling the object into a spherical shape, the reference is to its current gravity--that is, the strength of its gravity would tend to make the object spherical now, meaning plus or minus a million years. [img]/phpBB/images/smiles/icon_smile.gif[/img]

Ah, I see. [img]/phpBB/images/smiles/icon_smile.gif[/img] Well I still ponder as to why the outer moons had an easier time become spherical more than the asteroids. Freak coincedence? Yeah maybe. But I still think a hot Jupiter had something to do with it, as well as their chemical compositions.