Read the given passage and answer the questions that follow.

Pluto was first found nearly a century ago in 1930. In 2006, Pluto, scientists told us, should no longer be called a planet, but instead a dwarf planet. Is Pluto a planet or not? In 2006, the International Astronomical Union considered the controversial question, ‘what is a planet?’ Some moons, like Jupiter's moon, Ganymede, are larger than the planet Mercury. And some objects, like Eris, have never been known as planets, despite being very nearly as large as Pluto. So, what makes a planet a planet? The IAU came to a decision that would annoy Pluto's fans even a decade later. They agreed on updated criteria. To classify as a planet, an object must orbit the sun and not another planet. And it must be massive enough for its gravity to have pulled it into a roughly spherical shape-- no problem for Pluto there. Unfortunately, there is another qualification for planet status. To be a planet, an object must be large enough to have cleared the path of its orbit of other debris orbiting the sun. Unlike the eight planets the IAU now recognizes, Pluto hasn't managed that. Checking every box except one means that Pluto can't be considered a true planet. Instead, it's classified as a dwarf planet, along with Eris and other large objects, like Ceres, Haumea, and Makemake. The ranks of the dwarf planets may grow over time, too. Since they are relatively small and usually very distant, scientists believe we haven't found all of them yet. But don't feel too bad for Pluto. In 2015, the New Horizons Spacecraft sent us the most detailed pictures and data about Pluto we've received yet. We found that the dwarf planet has geological features we hadn't imagined-- towering mountains, ice ridges, vast, smooth areas of carbon monoxide ice.