Question

The image below shows a protoplanetary disk, which is a spinning disk made up of the gases and dust that surround a recently-formed star.


Image courtesy of NASA

What does a protoplanetary disk most likely have in common with Earth's Solar System?
A.
They both have well-defined planets that orbit due to gravity.
B.
They both decrease in gravity as they accumulate more mass.
C.
They both have planets that have formed without gravity.
D.
They both are in motion and are held together by gravity.

Answer 1

D

Both the protoplanetary disk and the Solar System are rotating systems that are gravitationally bound (held together by the central star's gravity), even though the disk has not yet formed clearly defined planets.