Planet 9
.png?lang=simple)
Planet Nine, also called Planet X, is a hypothetical planet orbiting beyond Neptune. This theory would explain the anomalies in the Kuiper Belt. Planet 9 could have a weight (mass) about 5 to 10 times the weight of Earth. Since this planet should orbit far away, it would take between 10000 to 20000 Earth years to orbit the Sun. The brightness (Magnitude) of Planet 9 could be around 21, which means that it is very dim.