Of the Extrasolar Planets That Have Been Found, Many Have

Multiple Choice

Of the extrasolar planets that have been found, many have masses comparable to that of Jupiter but orbits smaller than Earth's. What is believed to be the most likely explanation for this surprising combination?

A) The protoplanetary disk was much denser than that of the Sun, and larger planets formed. Collisions between these planets then sent some of them into much smaller orbits.
B) Friction with the protoplanetary disk caused planets formed farther from the Sun to lose energy and migrate inward.
C) "Planets" are, in fact, low-mass objects that formed separately in the same manner as stars, and were later captured into the orbits in which we now see them.
D) The protoplanetary disk was much denser than that of the Sun, allowing large planets to form very close to the star.