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OT but can anyone explain to me why the planets all have the same orbit plane? I've never read a succesful explanation.

by brc 16y ago

Nick_C 16y ago
Because they formed (conglomerated) from an accretion disk around the Sun. Being a disk, it is in one plane. Why a disk? The sphere of dust surrounding the Sun is drawn inwards and conservation of angular momentum flattens it out to eventually form a disk. Simple explanation: Accretion disk: http://www.daviddarling.info/encyclopedia/A/accretiond.html http://www.daviddarling.info/encyclopedia/A/accretiond.html Planetary formation: http://www.daviddarling.info/encyclopedia/P/plansysform.html http://www.daviddarling.info/encyclopedia/P/plansysform.html Wikipedia (detailed maths): http://en.wikipedia.org/wiki/Accretion_disc http://en.wikipedia.org/wiki/Accretion_disc
InclinedPlane 16y ago
Take a proto-stellar nebula, it's a big mass of gas and dust thousands of AU in diameter. Each particular bit will generally be moving very slowly in a random direction relative to the whole but the whole thing has some particular net angular momentum. As the nebula collapses to form a star this angular momentum gets concentrated (insert standard ice-skater pulling in their arms description here), which is why stars tend to have some particular spin. The same mechanism of concentration works to help form a protoplanetary disc. Objects in eccentric orbits or orbits tilted to the average plane of the forming disc will be more prone to collisions, causing them to be absorbed or captured by larger bodies or to form a debris cloud of generally lower eccentricity and lower inclination. Over time these effects add up to cause most of the mass in the inner Solar System to be concentrated in a small number of planets in circular orbits within a narrow range of inclinations. Note that in the far outer Solar System of the kuiper belt and oort cloud these effects are much diminished (orbital periods are much longer, distances are much larger, overall volumetric mass densities are lower, etc.) so objects are more likely to have eccentric and inclined orbits relative to the inner solar system consensus.
- brc 16y ago
  I get most of that, just not how it ends up in a flat disc. as opposed to an array of discs or something similar. Is the idea that if you took the nebula, and measured across in 1 deg increments, the plane that had the largest percentage of largest objects is the highest probability of becoming the eventual plane? This seems like the sort of concept that could do with a nicely done animation to explain.

OT but can anyone explain to me why the planets all have the same orbit plane? I've never read a succesful explanation.

by brc 16y ago

OT but can anyone explain to me why the planets all have the same orbit plane? I've never read a succesful explanation.

Because they formed (conglomerated) from an accretion disk around the Sun. Being a disk, it is in one plane. Why a disk? The sphere of dust surrounding the Sun is drawn inwards and conservation of angular momentum flattens it out to eventually form a disk. Simple explanation: Accretion disk: http://www.daviddarling.info/encyclopedia/A/accretiond.html http://www.daviddarling.info/encyclopedia/A/accretiond.html Planetary formation: http://www.daviddarling.info/encyclopedia/P/plansysform.html http://www.daviddarling.info/encyclopedia/P/plansysform.html Wikipedia (detailed maths): http://en.wikipedia.org/wiki/Accretion_disc http://en.wikipedia.org/wiki/Accretion_disc

InclinedPlane 16y ago

Take a proto-stellar nebula, it's a big mass of gas and dust thousands of AU in diameter. Each particular bit will generally be moving very slowly in a random direction relative to the whole but the whole thing has some particular net angular momentum. As the nebula collapses to form a star this angular momentum gets concentrated (insert standard ice-skater pulling in their arms description here), which is why stars tend to have some particular spin. The same mechanism of concentration works to help form a protoplanetary disc. Objects in eccentric orbits or orbits tilted to the average plane of the forming disc will be more prone to collisions, causing them to be absorbed or captured by larger bodies or to form a debris cloud of generally lower eccentricity and lower inclination. Over time these effects add up to cause most of the mass in the inner Solar System to be concentrated in a small number of planets in circular orbits within a narrow range of inclinations. Note that in the far outer Solar System of the kuiper belt and oort cloud these effects are much diminished (orbital periods are much longer, distances are much larger, overall volumetric mass densities are lower, etc.) so objects are more likely to have eccentric and inclined orbits relative to the inner solar system consensus.

brc 16y ago
I get most of that, just not how it ends up in a flat disc. as opposed to an array of discs or something similar. Is the idea that if you took the nebula, and measured across in 1 deg increments, the plane that had the largest percentage of largest objects is the highest probability of becoming the eventual plane? This seems like the sort of concept that could do with a nicely done animation to explain.