A composite of some of the best images obtained during the approach of New Horizons to Pluto (NASA)
NASA unofficially declared 2015 the year of the dwarf planet, a class of planetary bodies defined in 2006 by the International Astronomical Union. Both Pluto and the asteroid Ceres are members of the class, and while some may see Pluto’s reclassification from a planet as a demotion, Jim Zimbelman, a geologist at the Air and Space Museum, finds that clarification was definitely needed because so many new objects have been discovered in the outer solar system.
He reviews the background behind the decision to create the designation of dwarf planet, and summarizes the latest results obtained from studying these unique objects. According to Zimbelman, there is much to interest scientists and the public in those findings. For example, early in 2015 the Dawn spacecraft went into orbit around Ceres, detecting on its battered surface several “bright patches” where water ice-rich materials and salts are exposed.
Later that year, the New Horizons spacecraft made a spectacular encounter with the Pluto system after a journey of more than 9 years. Pluto and its large moon Charon dazzled with an array of unexpected landforms: glaciers of frozen nitrogen on Pluto that have moved between mile-high mountains of water ice, and on Charon, a canyon several times deeper than the Grand Canyon.
Zimbelman offers a guide to our first up-close views of both bodies, and a glimpse into what other surprises may await future discovery in the Kuiper Belt, a zone of the solar system beyond the orbit of Neptune.
