by neufer » Mon Sep 21, 2009 1:49 am
orin stepanek wrote:I take it that the rayed craters are the younger ones.
That sounds about right.
orin stepanek wrote:Some of the craters look as though they be bulged upwards; rather than indented. Could this be a possibility?
Certainly not
the floor of a crater if that's what you mean.
(E.g., our own moon:)
orin stepanek wrote:Planet sized-- 8)
Two moons in our solar system are larger than Mercury; Ganymede and Titan.
How big does a moon have to be to be called planet sized?
Actually a planet is more defined by
its mass than its volume:
- A planet must have sufficient mass:
1) for self-gravity to overcome rigid body forces such that
it assumes a hydrostatic equilibrium (nearly round) shape, and
2) that it is able to clear the neighborhood around its orbit.
If it were my decision I would make the cutoff at
10^23 kilograms
such that
Ganymede, Titan & Callisto are "planet sized"
Code: Select all
Mass in
10^22 kilograms
33.022 Mercury
--------------------
14.82 Ganymede
13.45 Titan
10.76 Callisto
..................
8.932 Io
7.348 Moon
4.80 Europa
2.14 Triton
--------------------
1.67 Eris
[/b]
[quote="orin stepanek"]I take it that the rayed craters are the younger ones. :?: [/quote]
That sounds about right.
[quote="orin stepanek"]Some of the craters look as though they be bulged upwards; rather than indented. Could this be a possibility?[/quote]
Certainly not [b]the floor[/b] of a crater if that's what you mean. [b](E.g., our own moon:)[/b]
[img]http://www.lpi.usra.edu/lunar/missions/clementine/images/img2_lg.gif[/img]
[quote="orin stepanek"]Planet sized-- 8)
Two moons in our solar system are larger than Mercury; Ganymede and Titan.
How big does a moon have to be to be called planet sized? :roll:[/quote]
Actually a planet is more defined by [b]its mass[/b] than its volume:
[list]A planet must have sufficient [b]mass[/b]:
1) for self-gravity to overcome rigid body forces such that
it assumes a hydrostatic equilibrium (nearly round) shape, and
2) that it is able to clear the neighborhood around its orbit.[/list]
If it were my decision I would make the cutoff at [b]10^23 kilograms[/b]
such that [b]Ganymede, Titan & Callisto are "planet sized"
[code]Mass in
10^22 kilograms
33.022 Mercury
--------------------
14.82 Ganymede
13.45 Titan
10.76 Callisto
..................
8.932 Io
7.348 Moon
4.80 Europa
2.14 Triton
--------------------
1.67 Eris [/code][/b]