question about planets

[Alphy420]

well to begin i got my idea yesterday i was sick and wasnt able to fall alseep for hours so i hade nothin to do but think the whole time since u know it was pitch black in my room anyways anyways i was thinkin and i have always been interested in science the human body space and planets stars well anyways i was thinkin why are all the plants almost perfectly round if not perfectly round werent planets made basicly the same way as astroids mass just collecting agaisnt each other as a result of gravity and yet astriod are not perfectly round... they are pretty lumpy yes some are round but most arent quite as round as planets so why why are planets round when astroids are not..

 

i also hade another question but i currently cant remember so i gues i'll post some other time when i do

[mezarashi]

I believe that the nature of things is to be round. Planets are supposedly formed as left-overs of the sun. Hydrogen and other heavier gases coming together. Gravitational forces will ensure that they it will become round.

 

The main question therefore is, what makes asteroids bumpy. As far as I know, asteroids are probably former planets, parts of planets, planetary debris that has broken off. They were not formed like planets, but I'm no asteroid formation expert. I believe there is still disagreement as to the origins of our very own asteroid belt.

[swansont]

Gravity has spherical symmetry. In a large body, gravity is stronger than the residual stresses or other internal forces, and removes the "bumpiness" to a large degree, but in a small body they are not.

[Alphy420]

you guys are great lots of smart in this forums hmmm maby i should think of lots of question everyday b4 i got to sleep to post here cuz you guys succesfully cured my curiosity lol

[Mayflower]

Is part of the reason why planets are so round because they were very much liquid and then gradually froze (liquid being much easier to be rounded by gravity)? I always figured that is how it went with the Earth.

[Severian]

It is interesting that most problems in physics can be answered by simple symmetry arguments....

[JonM]

Also earth isn't a perfect sphere, and I would imagine most other planets arent either

[swansont]

Also earth isn't a perfect sphere, and I would imagine most other planets arent either

 

The earth is oblate because it is spinning, but that deviation can be accounted for. Other non-regular, non-spherical features are very small deviations - mountain height and ocean depth are km-scale on a planet of radius 6400 km. So spherical is a very good approximation.

[swansont]

Is part of the reason why planets are so round because they were very much liquid and then gradually froze (liquid being much easier to be rounded by gravity)? I always figured that is how it went with the Earth.

 

Actually, the earth still behaves like a liquid on the appropriate time scale. Even though we have a solid crust, it still deforms, even on a daily basis - the solid earth has tidal deformations of several tens of cm.

[tony873004]

Imagine if the Earth were a cube. The only places where you could feel like you were on level ground is in the middle of each face of the cube. The farther you travelled from the center of the face, the steeper your ground seemed. The corners would be very tall mountains. Things would want to erode downhill, with the center of the faces as the bottoms of valleys. Basically, the Earth would be eroding into a sphere.

 

Asteroids don't have enough gravity to make this happen, at least not in reasonable timescales, and probably never.

[Ophiolite]

I like the description of the Earth's shape as being a geoid i.e. Earth shaped. So very precise, seemingly erudite, yet containing absolutely no information.

[swansont]

I like the description of the Earth's shape as being a geoid i.e. Earth shaped. So very precise, seemingly erudite, yet containing absolutely no information.

 

Kind of like having the glossary entry of recursive be "see recursive"