Overview
This lecture covers the basic characteristics, orbit, moons, and atmosphere of Pluto, as well as its similarities to other solar system bodies.
Pluto's Size and Classification
- Pluto is a dwarf planet that, along with its largest moon Charon, can fit within the United States.
- Pluto is located in the Kuiper Belt, a region beyond Neptune filled with icy bodies.
Pluto's Orbit and Motion
- Pluto's orbit is highly elongated (eccentric) and tilted compared to the other planets.
- For part of its orbit (e.g., 1979–1999), Pluto is closer to the Sun than Neptune.
- Pluto's orbital period is 240 years.
- Despite apparent orbital crossings, Pluto and Neptune will not collide due to their orbital tilt.
Pluto's Moons
- Pluto has five known moons, likely formed by a massive collision.
- Charon, the largest moon, was discovered in 1979 and named after the mythological ferryman of the underworld.
- Nix and Hydra were discovered in 2005, followed by Kerberos and Styx.
- Pluto's system is oriented at about a 90° tilt, causing its moons to orbit in a vertical plane.
Observations and Exploration
- As of 2014, imaging of Pluto and its moons was limited to Hubble and ground-based observations.
- The New Horizons spacecraft was scheduled to fly by Pluto in summer 2015 for close-up observations.
Pluto's Composition and Atmosphere
- Pluto's mass and size allow calculation of its density, indicating a mix of rock and ice.
- Pluto shares its composition with comets and large moons of the outer planets.
- When far from the Sun, Pluto’s atmosphere is frozen; when closer, some ices vaporize, creating a thin, temporary atmosphere.
- Atmospheric pressure on Pluto is about one ten-thousandth of Earth's, making it extremely tenuous.
Key Terms & Definitions
- Dwarf planet — a celestial body resembling a small planet but lacking certain criteria to be classified as a full planet.
- Kuiper Belt — a region beyond Neptune filled with small icy bodies and source of short-period comets.
- Eccentric orbit — an elongated orbital path.
- Charon — Pluto’s largest moon, named after the mythological boatman of the underworld.
- Tenuous atmosphere — an extremely thin and sparse atmosphere.
Action Items / Next Steps
- Review images and information from the New Horizons flyby of Pluto (summer 2015).
- Prepare for upcoming discussion on the characteristics of dwarf planets.