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..<br /><br />i also hade another question but i currently cant remember so i gues i'll post some other time when i do

 

[newtonian]

alphy420 - Well rounded questions!<br /><br />One answer has to do with size. The larger the mass the more likely it will be nearly a perfect sphere.<br /><br />Note that earth is not a perfect sphere - almost, but not quite.<br /><br />A higher mass object has greater gravity which pulls equally in all directions and is a force tending to cause a spherical shape.<br /><br />If the object was fluid or was shattered repeatedly by impacts it would tend to come back together as a spherical shape.<br /><br />Rapid rotation on earth causes a slight bulging at the equator, where rotation speed is fastest, btw.

 

[jatslo]

Our solar system in its infant stages is thought to have been molten or liquid rock. Well the planets were anyways, so throw in a little spin in space with internal gravity on liquid planets, and you can bet the farm on spherical shapes. The faster they spin the more elongated they are like Earth. Try researching gravity maps of the Earth: Very bumpy, and Everest looks cool, with a big spike. That Pluto sized object they found recently is not a sphere, which is an odd one.<br /><br />What would something spinning at -(.75c) look like?

 

[CalliArcale]

Lying in bed sick is a great time for contemplation. In fact, some great insights were made while scientists were bedridden; I think boredom is a major factor. <img src="/images/icons/wink.gif" /> One famous example is the periodic table of the elements; look up the story sometime.<br /><br />The more massive an object, the more it's gravity will pull it into a sphere.<br /><br />The more rigid an object, the more it will resist this effect.<br /><br />The more rapidly an object spins, the more force will be applied to flatten it out (exactly like a hand-tossed pizza crust).<br /><br />Consider various celestial objects to think out how this works. Saturn behaves in a very fluid way (the gas giants are massive, but not very dense), so much so that it is visibly oblate; even if you took away the optical illusion of the rings, Saturn is obviously not a sphere. There are some extreme cases; astronomers recently deduced from various observations that they'd found a star that was shaped like a pancake! It rotates <i>very</i> fast.<br /><br />A few interesting things:<br /><br />* The Moon has moutains taller than Mount Everest; Earth's gravity prevents mountains from getting much taller than that under ordinary circumstances (or at least from staying tall), so the lower gravity on the Moon means that mountains can get taller<br /><br />* The moon Io (innermost of the "Galilean" moons of Jupiter) is deformed by the tidal influence of Jupiter and the other Galilean moons, especially Europa. You know how the tides on Earth cause the ocean to rise and fall; the tides on Io are so severe they cause the *land* to rise and fall. There are mountains on Io that are purely the result of Io's crust cracking and buckling under the strain.<br /><br />* Large irregular objects might be fragments of larger bodies; it would take a long time for such a fragment to gradually collapse down into a sphere due to gravitational erosion.<br /><br />* Very few asteroids are noticeably spherical; they seem <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[vogon13]

Science News just had a blurb about Ceres being quite spherical. As the largest asteroid, perhaps not so surprising. But degree of sphericity may imply a geological active past and quite a bit of water.<br /><br />NASA is planning to launch a probe there next year. Arrival is quite a ways out though.<br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[jatslo]

Yeah, pizza shaped. hehehehe <img src="/images/icons/wink.gif" /><br /><br />The Earth is flat.

 

[newtonian]

jatslo & you all - Consider the rapidly rotating galaxies - often not spherical as in ellipticals and spirals.<br /><br />Is there any correlation between rotational speed and shape in galaxies - or does original magnetic fields at accretion play a more important role than gravity initially?

 

[alokmohan]

From planet to punctuation.