Planet formation DOES happen in slow motion

[pnjabiloafer]

Okay, this is a general question.. i just read this thread (https://www.physicsforums.com/showthread.php?t=28343) and started wondering about it. THis planet is considered "young", and it is a million years old. SO, my question was why does planet formation take so long? i think a 100 years would do, its not like everything is happening in slow motion, it is happening in normal space-time?

 

[niranjan]

well, to answer this question i guess one needs to understand as to what goes into "forming" a planet? my guess is that any celestial body of considerable mass which revolves around a star can be called a planet of the star...and again planets are beleived to be the debris of the star formation...or a result of some cosmic collision of the star with some other body...and all this can happen in a matter of days/months. i think the 1 million year time period just gives the time period since its formation...other planets might have been formed a some point really back in time(as if 1 million is not back in time )
aneways this is what i think...don't know whether it is right or wrong!
niranjan

 

[chroot]

Planet formation DOES happen in slow motion. Keep in mind that objects 1 AU from the Sun (like the Earth) require a year to complete an orbit. The Earth was formed from chunks of matter that were initially strewn about randomly all along its orbit. Each of these chunks had only a very small velocity relative to all the other, on the order of a few meters per second, and the Earth's orbit is a billion kilometers in circumference. All of those chunks had to accumulate to form the Earth, and it took a very, very long time. In fact, the inner solar system is still full of small bits of matter even after 4.6 billion years.

- Warren

 

[Chronos]

Like chroot said. The rings of saturn offer an image similar to the formation of planetary systems. The central star is surrounded by an accretion disc [ring]. Denser regions in this disc gravitationally collasce into planetoids. These larger mass bodies orbit more rapidly than the small particles making up the disc, hence they 'vacuum' up the debris in their orbital paths.

 

[niranjan]

ok! but any idea after how much mass can a mass be called as planet?ya if it is made by the accumulation of smaller chunks of matter then it might take a really long time! but can't planets be formed by some massive collision ...or some star's loss of mass due to some passing star? i which case it might not take days/months but say some years..
please some info on this...thx
niranjan

 

[ElectroPhysics]

Stars and planets are formed due to angular momentum and gravitational pull on the light gaseous material. Plate tectonics is the main cause of the todays shape of earth. Earth is still moving 1-2 cm/year.

 

[Chronos]

That is why it was surprising a planetary body could form in a 'mere' million years after the central star. The process of local density fluctuations evolving into a planet size mass was thought to take much longer.

 

[Nereid]

You've probably heard of the 'snow line', as in mountains; did you know there is also a 'snow line' for planetary systems? As the proto-star gets hotter, clumps of stuff (planetismals) that form early in the gas cloud collapse and early disk phases evaporate if they are too close to the nascent sun - just like comets do when they enter the inner solar system. As most of solid phase stuff is ices (water, methane, ammonia, CO2, etc), a 'snow line' forms, at a distance from the star where these ices evaporate; outside the snow line planetismals rapidly form planets - and the big ones, like Jupiter and Saturn, can capture lots of H and He too - through planetismal collisions; inside the snow line, there's much less mass, and it's mostly 'rock' and 'iron'.

As chroot says, there's lots of these clumps left over from the early days of the solar system - the asteroids, small outer satellites of the giant planets, the Edgeworth-Kuiper Belt objects, Sedna, and the Oort cloud. A question currently being actively studied is, to what extent are these objects 'primordial'? It's certainly true there are far, far fewer of them than in the early days of the solar system ... the Oort cloud excepted, of course.

 

[pnjabiloafer]

i unterstand what you guys a saying, but comon, a 1,000,000 YEARS! when i think of all this time, its like a second in the life of the universe, and to us, it so much.. i feel so small compared to the universe.. w0w, really hope there IS INTELIgent life somewhere else.