On 2012 in the New Horizons' The PI's Perspective Alan Stern wrote The Kuiper Belt at 20: Paradigm Changes in Our Knowledge of the Solar System (more also archived) which includes:
Most of the known KBOs are just 100 to 300 kilometers across, about one-tenth of Pluto’s diameter. But some are smaller than 100 kilometers across, and some are larger than 300 kilometers across. In fact, there is great diversity among KBOs:
- Some are red and some are gray;
- The surfaces of some are covered in water ice, but others (like Pluto) have exotic volatile ices like methane and nitrogen;
- Many have moons, though none with more known moons than Pluto;
- Some are highly reflective (like Pluto), others have much darker surfaces;
- Some have much lower densities than Pluto, meaning they are primarily made of ice. Pluto’s density is so high that we know its interior is about 70% rock in its interior; a few known KBOs are more dense than Pluto, and even rockier!
Question: How many Kuiper Belt objects have moons? How do we know this? What observational techniques have revealed moons of KBOs?