Study Notes on Pluto and the Solar System

Overview of Solar System Discoveries

  • Pre-Pluto Discoveries:
    • Saturn: Most distant known planet to ancient astronomers.
    • Uranus: Discovered in 1781 by accident.
    • Neptune: Discovered in 1846 via predicted position search.

Search for Planet X

  • Uranus & Neptune's unexpected orbits led to speculation of an additional planet, termed "Planet X" by Percival Lowell.
  • Lowell sought to locate Planet X, but died in 1916 without success.
  • Clyde Tombaugh discovered Pluto in 1930, close to Lowell's predicted location.

Pluto's Characteristics

  • Size & Orbit:
    • Smaller than all known planets, more eccentric and inclined orbit.
    • Sometimes closer to the Sun than Neptune.
  • Orbital Dynamics:
    • Pluto and Neptune have a 3:2 orbital resonance preventing collisions.

Pluto and Charon

  • Discovery of Charon: Southsea in 1978, largest moon relative to its planet.
  • Orbital Dynamics: Charon's orbit is aligned with Pluto's equator; both show captured rotation.
  • Eclipsing Events: Charon's orbit allowed for unique observational opportunities from Earth.

Pluto's Surface and Atmospheric Conditions

  • Surface Temp: Ranges from 33 to 55 K.
  • Atmosphere: Present near perihelion, primarily nitrogen, with carbon monoxide and methane. Potentially cryovolcanic.

Pluto's Interior Composition

  • Density: 1.86 g/cc; about 70% rock, 30% ices.
  • Surface: Contains nitrogen ice, water ice mountains.
  • Possible subsurface ocean and differentiated structure.

Trans-Neptunian Objects (TNOs)

  • The concept proposed in 1943, later verified with discoveries from 1992 onward.
  • Over 2500 TNOs discovered, mostly within the Kuiper Belt, which extends 42-50 AU.
  • Types of Kuiper Belt Objects:
    • Classical KBOs: Low eccentricity, majority found near Pluto's orbit.
    • Scattered KBOs: Higher eccentricity, some extend hundreds of AU from the Sun.
    • Plutinos: ¼ of TNOs in a 3:2 resonance with Neptune; similar dynamics as Pluto.

Recent Discoveries and Classification

  • Eris: Discovered in 2005, larger than Pluto; redefined classification of celestial bodies.
  • Dwarf Planets (IAU 2006 definition): Objects meeting criteria for planetary status including Eris, Haumea, Makemake, and Ceres. Pluto is classified here due to not meeting the "cleared the neighborhood" criterion.

Discussion on Pluto's Status

  • The debate on Pluto's classification as a planet continues post-2006; raises questions on definition and classification of celestial objects in our Solar System.