When Pluto was downgraded from planet status in 2006, our solar system was reduced to eight planets. But now new evidence suggests that we may have a ninth planet after all, one that is 5,000 times bigger than Pluto — which is now considered a dwarf planet — and billions of miles further away. Two California Institute of Technology scientists presented what they described as “good evidence” yesterday for “Planet 9,” a huge gas giant that may have its own rings and moons and is so far away it would take 10,000 to 20,000 years to circle the Sun. The planet hasn’t actually been seen, but the researchers’ evidence is based on mathematical and computer modeling, and they believe it will be discovered using a telescope within five years. They said they were reporting on their research because they want people to help them look for the planet.