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

Question

Quizplus · Accepted Answer

As the cloud shrank, its gravitational potential energy was converted to kinetic energy and then into thermal energy. This process is known as gravitational contraction, which caused the solar nebula to heat up as it collapsed.  Nuclear fusion did not occur until much later when the pressure and temperature in the protosun's core reached the necessary conditions. Radiation from nearby stars or a nearby supernova shock wave are not likely explanations, as the solar nebula would have been too isolated at the time of its formation. Collisions among planetesimals also played a role in the evolution of the solar system, but they were not the primary cause of the solar nebula heating up.

Why Did the Solar Nebula Heat Up as It Collapsed