Quiz 3: Formation and early evolution of planets & terrestrial planets
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10 Terms
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Which force counteracts the gravitational force of the Sun in the protoplanetary disc?
gas pressure
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What is the effective radius of a planetesimal? Explain in words.
It is the radius at which it attracts material through gravitational focussing.
The effective radius and the Hill sphere are two different concepts, check equations. The effective radius describes the space along its path from which a planetesimal mops up material through gravitational focussing. The equation takes into account the escape velocity of the planetesimal (and thus its mass) and the velocity of the particles being accreted. The Hill sphere describes the space in which a body is gravitationally dominant. It takes into account its own mass and the mass of the dominant gravitational body. So these are two different ways to approach a similar question.
The effective radius and the Hill sphere are two different concepts, check equations. The effective radius describes the space along its path from which a planetesimal mops up material through gravitational focussing. The equation takes into account the escape velocity of the planetesimal (and thus its mass) and the velocity of the particles being accreted. The Hill sphere describes the space in which a body is gravitationally dominant. It takes into account its own mass and the mass of the dominant gravitational body. So these are two different ways to approach a similar question.
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The rich get richer and the poor, well they crash into the Sun. To become a planet, an oligarch of the sky, you must grow in size quickly. At what point can you commence oligarchic growth?
when R > 1000s of km
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Subcentimeter-sized particles can accrete onto a planetesimal, or, if their velocities are very high, can erode the planetesimal through a process dubbed
sandblasting
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A planetary embryo accretes material from a region
4 times the size of its Hill sphere
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What must happen for a planetary embryo to experience runaway gas accretion?
It must have a comparable mass of solids and gas
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What did the migration of Jupiter and Saturn accomplish in the Grand Tack model, and what monumental ensuing event did this allow for?
The migration of Jupiter and Saturn cleared the protoplanetary disc of gas, allowing the terrestrial planets to form.
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Why might Neptune and Uranus be smaller than Jupiter and Saturn?
They formed later when there was less material in their Hill spheres
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What did the Grand Tack model explain that no previous model could?
The relative sizes of Earth and Mars, It suggests that the migration of Jupiter disrupted the formation of planets in the inner regions, leading to variations in the composition and sizes of the terrestrial planets.
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Where can massive planetary embryos form?
at regular intervals of the semimajor axis of the disc
Note 
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