Astronomy: Pluto

2. One of Pluto's small dark moons named after the three-headed dog of Greek mythology.
3. Describes Pluto's orbit which is tilted at an angle of 17 degrees relative to the plane of the other planets.
5. Pluto's stable 2 3 relationship with Neptune where Pluto completes two orbits for every three Neptune orbits.
6. A dwarf planet in the Kuiper Belt once considered the ninth planet from the Sun.
8. The NASA space probe that performed a flyby of Pluto and its moons in 2015.
11. Describes Pluto's highly elliptical path around the Sun which sometimes brings it closer than Neptune.
13. The American astronomer who discovered Pluto in 1930 at the Lowell Observatory.
16. The smooth icy western lobe of Tombaugh Regio which is a vast glacier of frozen nitrogen.
18. The disc-shaped region of icy bodies beyond the orbit of Neptune where Pluto resides.
19. The large bright heart-shaped feature on the surface of Pluto made of nitrogen and methane ice.

1. A specific term for a dwarf planet that orbits the Sun at a distance greater than Neptune.
4. Pluto's largest moon so large that the two are sometimes considered a binary system.
7. The primary component of the glaciers and bright plains on Pluto's surface.
9. The classification for a celestial body that orbits the Sun is nearly round but has not cleared its orbital neighborhood.
10. A type of frozen gas found on Pluto's surface that contributes to its reddish-brown areas.
12. The astronomical observatory in Flagstaff Arizona where Pluto was discovered.
14. One of Pluto's five known moons the outermost one discovered by the Hubble Space Telescope.
15. The smallest and innermost of Pluto's moons named after the mythological river.
17. One of Pluto's small inner moons discovered along with Hydra in 2005.