How Many Planets Could Be in the Kuiper Belt?

A recent study published in The Astrophysical Journal Letters investigates the potential existence of Mars-sized free-floating planets (FFPs)—also known as rogue planets, starless planets, and wandering planets—that could have been captured by our Sun’s gravity long ago and orbit in the outer solar system approximately 1,400 astronomical units (AU) from the Sun. For context, the…