Why did the solar nebula heat up as it collapsed? A) As the ...

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Why did the solar nebula heat up as it collapsed?
 
  A) As the cloud shrank, its gravitational potential energy was converted to thermal energy.
  B) Collisions among planetesimals generated friction and heat.
  C) Radiation from other nearby stars that had formed earlier heated the nebula.
  D) Nuclear fusion occurring in the core of the protosun produced energy that heated the nebula.
  E) The shock wave from a nearby supernova heated the gas.

Question 2

Contrast the densities and compositions of the four Galilean moons.
 
  What will be an ideal response?

[nyrave]

Answer to Question 1

A

Answer to Question 2

Closer to Jupiter and dried out by its tides and radiation, Io and Europa are about as dense as our own Moon and made chiefly of rock. But larger Ganymede and Callisto are less stressed, less dense, and have extensive mantles of water and ice above their rock cores.

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TYSM

[bigcheese9]

Gracias!