Final answer:
Pluto is a dwarf planet that differs from terrestrial planets in orbit, size, and composition. It was reclassified by the IAU in 2006 because it hasn't cleared its orbit of other debris. The New Horizons mission provided detailed images of its surface, including the bright Sputnik Planitia.
Step-by-step explanation:
The status of Pluto has been the subject of much debate in the astronomical community and among the public. In 2006, the International Astronomical Union (IAU) established three criteria for a celestial body to be classified as a planet. Pluto met only two of these criteria, which led to its reclassification as a dwarf planet. The criterion it did not meet is that it has not cleared its orbit of other debris — meaning it shares its orbital zone with other objects of similar size.
Moreover, Pluto's characteristics differ significantly from the terrestrial planets. Its orbit is more elliptical and tilted compared to the planets, and it is much smaller in size. The Hubble Space Telescope initially revealed bright and dark regions on Pluto, which the New Horizons mission later identified as a large bright area known as Sputnik Planitia, surrounded by darker regions composed of differing terrains and complex geographical and atmospheric features.