  The discovery of Pluto in 1930 presaged the discoveries of both the Kuiper
Belt and ice dwarf planets, which are the third class of planets in our solar
system. From the 1970s to the 19990s numerous fascinating attributes of the
Pluto system were discovered, including multiple surface volatile species,
Pluto's large satellite Charon, and its atmosphere. These attributes, and the
1990s discovery of the Kuiper Belt and Pluto's cohort of small Kuiper Belt
planets, motivated the exploration of Pluto. That mission, called New Horizons
(NH), revolutionized knowledge of Pluto and its system of satellites in 2015.
Beyond providing rich geological, compositional, and atmospheric data sets, New
Horizons demonstrated that Pluto itself has been surprisingly geologically
active throughout the past 4 billion years, and that the planet exhibits a
surprisingly complex range of atmospheric phenomenology and geologic expression
that rival Mars in their richness.
