Pluto and Other Dwarf Planets

Module 7: Pluto and Other Dwarf Planets

Pluto’s Discovery

  • Background:
  • Irregularities observed in the orbits of Uranus and Neptune suggested the presence of another planet.
  • Percival Lowell (P.L.):
    • Dedication to finding this theorized planet based on calculated predictions.
  • Clyde Tombaugh:
    • Discovered Pluto 6 degrees away from Lowell's predicted position.
    • Discovery attributed to luck rather than calculation, as the expected irregularities did not exist.
    • Pluto's mass is too small to affect the orbits of Uranus and Neptune significantly.

Pluto Images

  • Challenges:
  • Pluto is approximately 40 Astronomical Units (AU) from the Sun, making it difficult to observe.
  • Imaging of Pluto has improved over time, enhancing clarity.

Images from New Horizons Flyby

  • Notable Images:
  • Captured by New Horizons from June 29 to June 2, 2015.
  • Data Points:
    • Distances ranged from 50,500,000 km to 55,000,000 km during imaging.
    • Observations taken over consecutive days leading up to arrival.

Moons of Pluto - Charon

  • Charon:
  • Primary moon of Pluto with a mass of 0.0021 times that of Earth.
  • Demonstrated mutual eclipses, enhancing observational analysis.
  • Charon's size is significant; it has a radius of 600 km and is 0.12 times the mass of Pluto, leading to the largest moon-to-planet mass ratio in the solar system.
  • Physical Dimensions:
  • Pluto's radius is about 1/5 that of Earth's.

Moons of Pluto - Hydra and Nix

  • Additional Moons:
  • Hydra and Nix are smaller moons with diameters ranging from 100 to 200 km.
  • These moons orbit at approximately twice the distance of Charon.

Kuiper Belt

  • Composition:
  • Over 1,200 objects have been identified within the Kuiper Belt, located beyond Neptune.
  • The majority of objects are approximately 40-50 AU from the Sun, indicating a limited sample of the total population.
  • Estimates suggest there may be around 100,000 objects larger than 100 km across, creating a mass significantly greater than that of the asteroid belt.
  • Observational Techniques:
  • Observing the Kuiper Belt is challenging, but techniques continue to improve.
  • Pluto is considered one of the more accessible objects for observation, with about 25% of known Kuiper Belt Objects (KBOs) sharing the same orbital plane as Pluto.

Dwarf Planets

  • Definition and Classification:
  • Dwarf planets represent a new classification category, resulting in Pluto being reclassified from planet to dwarf planet.
  • Other notable dwarf planets include Eris, Ceres, Haumea, and Makemake.
  • Plutoids:
    • These are icy dwarf planets situated beyond Neptune.
  • Historical Classification:
    • Illustrates similarities with the reclassification of asteroids in the 1800s when many were discovered, leading to changes in astronomy texts.

Discoveries of Plutoids/Dwarf Planets

  • Notable Discoveries:
  • Quoar, with a diameter of 1,200 km, surpasses Ceres in size.
  • Haumea and Makemake are also significant, with diameters between 1,500 to 2,000 km.
  • Eris:
    • Larger than Pluto and crucial to understanding the diversity of dwarf planets.
  • Sedna:
    • Noted for its distance as the furthest known object in the solar system, featuring a highly elliptical orbit approximately 1,000 AU long, marking the potential inner boundary of the Oort Cloud.
  • Potential for the discovery of more dwarf planets remains open, indicating a rich area of ongoing research.