UKC

As opposed to purely random shapes?

In reply to Trangia:

Gravity pulls them into that shape as they form.

In reply to DaveHK:

Beat me to it.

I guess the ones that are initially hot liquids form to spheres.

Asteroids formed later out of impacts are solid and jagged.

In reply to Trangia:

Some helpful info here
http://hubblesite.org/hubble_discoveries/discovering_planets_beyond/how-do-...

In reply to Trangia:

Lowest energy state I guess.

In reply to Rick Graham:

Thanks to you and David.

The reason I asked is because there was a bit on the telly this morning which said that the Earth was formed by two planets colliding and fusing together. A large chunk broke off and became the moon. The simulation depicted this Moon chunk as being solid and jagged. If this is correct I wondered how it formed into the sphere we see now?

In reply to Trangia:

Perhaps the impact generated sufficient heat to cause melting of the rock although much of the material ejected from within the Earth would have been molten anyway as it still is today and so would form a shere under the influence of grivity.
There is certainly plenty of evidence that the moon has had active volcanic activity in the past showing to have had some molten rock within it.

In reply to Trangia:

Not all moons are spheres - Phobos and Deimos (Mars) are like giant potatoes and are most likely captured asteroids. They are too small for gravity to have pulled them into spheroid shapes. All solar system objects like planets, moons, comets and asteroids are somewhere on a continuous scale. Somewhere along that scale gravity will be sufficient to pull the body into a spherical shape. There are objects which sit near dividing lines eg Ceres which is the largest object in the asteroid belt between Mars and Jupiter and is large enough to be spherical and so is now classed as a dwarf planet (like Pluto). Vesta, the second-largest asteroid definitely isn't a sphere. Actually, the planets are mostly 'oblate spheroids' (ie slightly bigger equatorial circumference than polar equivalent) due to rotational effects, but you'd never know just by looking from space at them.

In reply to Trangia:

That's a theory not a fact. In any case the same gravity influence on form applies.

In reply to Trangia:

Thanks everyone. Some interesting responses.

Large bodies such as planets do not always have to be fluids/gases originally to form spheres. The mantle beneath the Earths crust is a solid (it transmits shear waves), but when observed over large time scales it behaves like a fluid. Consequently, the theory that the moon was broken off of the Earth allows them both to return to spheres (approximately) under gravity without melting, but any melt would help the process along

In reply to Trangia:

On of the main definitions of a planet (as opposed to a dwarf planet) is that its own gravity is strong enough to pull it into a sphere. The 'sphere' part is roughly defined as a ratio of the highest mountain (or other feature) to the diameter of the planet. Hence one of the reasons Pluto was demoted; it wasn't 'round enough' (along with not being the dominant body in it's orbital path - something taken by Neptune who's path it crosses).

In reply to crayefish:

Being pedantic the Earth and most planets are Oblate Spheroids, ellipses rotated about their minor axis, in the Earth's case the radius at the equator is roughly 1/273 more than at the poles.

Or put another way its a squashed sphere, it bulges at the equator or middle (because it spins round) and since its roughly half way through its life it can be looked on as middle age spread. Thus proving the immutable fact intrinsic to the fabric of the universe that as you get older you spread out and it has absolutely nothing to do with cream cakes or beer.

In reply to Trangia:

Climbing related Trivia - Chimborazo in Equador is further from the centre of the Earth than any other point on Earth due to its position close to the equator and the equitorial bulge. It use to be thought to be the highest mountain on Earth (from sea-level) before accurate measurements showed this not to be true

In reply to James Moyle:
And it would be ever so slightly easier to climb there, because the gravitational force is weaker as you 1. Increase distance from the centre of the Earth, and 2. Reduce latitude which increases centripetal acceleration from the Earth's rotation

In reply to Trangia:

They aren't!

<irony>
It's all a conspiracy by NASA and the globe/map manufacturers to cover up the existence of a flat Earth!

http://www.theflatearthsociety.org/tiki/tiki-index.php?page=The%20Conspirac...

They even killed Henry Worsley to stop him from showing that it's all a lie!

http://www.theflatearthsociety.org/forum/index.php?topic=65592.0#.Vq9GQ9WLR...

Besides, he wouldn't have managed to get past the ice wall anyway ...

http://www.theflatearthsociety.org/tiki/tiki-index.php?page=Ice%20Wall
</irony>

(There are actual people who believe this stuff).

In reply to zebidee:

Bizarre when I click on one of the flat earth society links it takes a long time to load and the Internet Explorer icon shows the timer arrow circulling round and round.

Surely the arrow should just go backwards and forwards.

In reply to zebidee:
Hahaha, that website's brilliant!


The moon is a sphere. It has a diameter of 32 miles and is located approximately 3000 miles above the surface of the earth.

In reply to Liamhutch89:

And 3) The atmosphere is somewhat denser at any given altitude at the equator compared with the poles. (e.g. Denali 'feels' higher than 6100m)

In reply to Cardi:


Is that true? I would have thought with the spin the atmosphere would be more attenuated with altitude over the equator?


Chris

In reply to Trangia:


http://www.theguardian.com/notesandqueries/query/0,5753,-48866,00.html

In reply to zebidee:

The ice wall sounds amazing for new route potential, definitely one for next years trip