Final answer:
The correct answer is b) angular momentum, which is responsible for the spinning disc shape of our solar system due to the conservation of angular momentum, an important concept in the physics of rotational systems.
Step-by-step explanation:
Everything in the solar system is spinning in a disc shape because the angular momentum from their formation keeps things moving. The correct answer is b) angular momentum. This rotational motion is a result of the conservation of angular momentum which states that if no external torque acts on a system, the total angular momentum of the system remains constant. During the formation of our solar system, a massive cloud of gas and dust began to collapse under its own gravity. As it shrank, this protoplanetary disk spun faster due to the conservation of angular momentum — analogous to a figure skater pulling in their arms to spin faster on the ice.
As a result, the solar system we observe today, with planets, moons, and other bodies orbiting in a relatively flat, disk-like plane, retains this initial angular momentum. Earth itself showcases this conservation; as a rotating body, it acts like a gyroscope, with its rotational axis pointing towards Polaris, the North Star. However, Earth is also subject to precession, slowly changing the direction of its axis due to gravitational interactions with the Sun and the Moon, over a period of approximately 26,000 years.