planetary formation

8/18/2019 Planetary Formation

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Planetary Formation

The whole process of Planetary Formation begins with a chance interaction between a supernovae

explosion and a cloud of molecular dust, when the explosion hits the cloud it can cause some partsof the cloud to collapse and compress; these parts of the cloud now have the potential to become a

new star. As the collapsing regions of the cloud become more dense their temperature will

increase, as the density and temperature increase the forces of gravity, acting towards the centre

of the region, and pressure, acting outwards from the centre, become balanced and the collapsing

stops, this is when the star has reached a temperature of approximately 1,, !elvin, the

core is now call a "Protostar#. $owever due to the fact there might be more than one collapsing

core, two cores could mean that a binary system is made. %1&

As this is happening most of the cloud starts rotating in the same direction and there becomes a

slight separation between the materials close to the Protostar that do not have a great enough

angular velocity to avoid falling into the star's( and the materials that have a angular velocity thatis. The dis) that has a greater angular velocity is now called the "Protoplanetary dis)#.

The formation of this Protoplanetary dis) ta)es a few million years, its initial mass and composition

are solely due to the "*tar Formation +nvironment#, the *tar Formation +nvironment is the left over

molecules in the dust cloud that didn#t collapse into the star, 'or one of the stars if a binary system

is made(, the closer towards the centre of the Protoplanetary dis) you get the less gas there will be

as the new star's( pull in most of the gas surrounding it, but then as you move further towards the

edge of the dis) the materials mostly consist of ices and gases. ow the Protoplanetary dis) has

begun to ta)e shape its evolution can be easily altered by a number of things such as the other

stars in the cluster, a cluster normally consists of approximately 1 stars. The Protoplanetarydis)#s evolution is affected by stellar flybys; these are when stars in the cluster pass close to the

newly formed Protoplanetary dis), it can also be affected by the radiation emitted by the closest

stars in the cluster, especially if the radiation is in the -ltra iolet region. The other main factor that

affects how Protoplanetary dis)s evolve is called "/as Accretion# this is where the Protoplanetary

dis) has a strong enough gravitational pull to draw in molecules floating round in free space to

increase its mass and alter its composition. %0&

The Protoplanetary dis) is now rotating in one direction, due to the matter in the dis) being of

different masses their angular velocities will be different so in time there will be collisions between

dust particles which may lead to them stic)ing together to ma)e a larger particle, these particles

carry on colliding with the other dust particles in the dis) until they are approximately 0 metres indiameter the rate of collisions starts to decrease from then, when the clumps are around 1

)ilometres in diameter they are classified as "Planetesimals#. hen the clumps become the si2e

re3uired to be a Planetesimal their growth rate is around a few centimetres every year and it will

remain at this rate for a few million years. The composition of the Planetesimals depends on how

close to the centre of the system they are, the closer Planetesimals will be at too higher

temperature for molecules such as water to condense therefore will be largely made up of roc)y

substances or metals with high melting points, these Planetesimals will be similar to the 4ercury5

4ars section of our *olar *ystem and will be classified as terrestrial planets. 6ue to the rarity of

the compounds that ma)e up terrestrial planets they tend to be the smaller planets in a system.

Although terrestrial planets tend to be the smallest in a system there is usually a lot of themorbiting the central star's( and because of this they will interact with each other gravitationally and


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possibly even collide with each other to form new planets, asteroids or other smaller planetary

masses such as moons.%7& %8& %9&

Planetesimals further than 8Au away from the central star's( will consist of more icy compounds

and gases; this is where you are more li)ely to find gas giants such as :upiter and *aturn.%0& The

ore Accretion theory does state that giant planets ':upiter and *aturn( form differently toterrestrial planets. The theory suggests that if a core undergoes enough collisions in a short space

of time so that its mass will exceed a specific critical mass, this mass is estimated to be

approximately 1 4⊕ 'ten times the mass of the +arth( it has the potential to become a giant

planet. At this point the "core# is able to hold a substantial gaseous atmosphere, the next stage of

growth occurs when the atmosphere is in $ydrostatic e3uilibrium, this is when the force of gravity

from the core is balanced out by the pressure exerted by the atmosphere on the surface of the

core. *maller Planetesimals will start being drawn towards the core and upon collision will slightly

increase the mass of both the core and the atmosphere, this continues until the mass of the core

exceeds a different critical mass, this mass however has not been given a value as it will vary from

core to core. hen the mass becomes greater than the critical mass the core begins pulling in allthe surrounding gases it can, during this phase the growth of the core and atmosphere is only

limited by the availability of the surrounding gases. This phase will only last around ten thousand

years. After the planet has ta)en in as much as is available it begins to cool down and contract. %


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i[1] http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/starform.htm[2] Astrophsics of!lanet "ormation #!a$es %& ' %()* !hilip +. Armita$e* 2010[%] http://en.,i-ipedia.or$/,i-i/"ormationandeolutionoftheSolarSstem* Section 2.2*ie,ed 09/11/201&[&] http://en.,i-ipedia.or$/,i-i/"ormationandeolutionoftheSolarSstem* Section %.1*ie,ed 09/11/201&[(] http://hulesite.or$/hulediscoeries/discoerin$planetseond/ho,doplanetsform*

ie,ed 09/11/201&[] Astrophsics of !lanet "ormation #3hapter .1)* !hilip +. Armita$e* 2010[4] http://en.,i-ipedia.or$/,i-i/Self$raitation* ie,ed 09/11/201&[5] Astrophsics of !lanet "ormation #!a$e 20%)* !hilip +. Armita$e* 2010[9] http://,,,.mpiahd.mp$.de/homes/ppi/tal-s/helled.pdf #!a$es 22 ' 2%)[10] http://,,,.cfa.harard.edu/eents/collo6uia/fall99/15%.pdf
http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/starform.htmhttp://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/starform.htmhttp://en.wikipedia.org/wiki/Formation_and_evolution_of_the_Solar_Systemhttp://en.wikipedia.org/wiki/Formation_and_evolution_of_the_Solar_Systemhttp://hubblesite.org/hubble_discoveries/discovering_planets_beyond/how-do-planets-formhttp://en.wikipedia.org/wiki/Self-gravitationhttp://www.mpia-hd.mpg.de/homes/ppvi/talks/helled.pdfhttp://www.mpia-hd.mpg.de/homes/ppvi/talks/helled.pdfhttp://www.cfa.harvard.edu/events/colloquia/fall99/1836.pdfhttp://www.cfa.harvard.edu/events/colloquia/fall99/1836.pdfhttp://en.wikipedia.org/wiki/Formation_and_evolution_of_the_Solar_Systemhttp://en.wikipedia.org/wiki/Formation_and_evolution_of_the_Solar_Systemhttp://hubblesite.org/hubble_discoveries/discovering_planets_beyond/how-do-planets-formhttp://en.wikipedia.org/wiki/Self-gravitationhttp://www.mpia-hd.mpg.de/homes/ppvi/talks/helled.pdfhttp://www.cfa.harvard.edu/events/colloquia/fall99/1836.pdfhttp://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/starform.htm

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