Dwarf Planets Flashcards

Dwarf Planets

• The International Astronomical Union (IAU) redefined the criteria for classifying planets in 2006.
  • Criteria for a celestial object to be considered a planet:
  1. Must orbit the Sun.
  2. Must possess sufficient mass for self-gravity to pull it into a spherical shape.
  3. Must have cleared its orbital zone of debris (like asteroids or comets).
• Pluto was reclassified as a dwarf planet because it met the first two criteria but not the third.

Dwarf Planets Overview

• Currently, five objects are classified as dwarf planets, with many more potentially existing in the outer reaches of the solar system.

Eris

• Discovered in 2005.
• Size and mass similar to Pluto.
• Orbits the Sun at a distance of 68 AU (over twice that of Neptune).
• Highly elliptical orbit with an eccentricity of 0.44.
• Axial tilt of 78°, indicating a likely past collision with a large impactor.
• Has a moon named Dysnomia, with a diameter of 50 km (30 mi).
• Surface is highly reflective due to methane ice, with an albedo higher than Saturn's Enceladus.

Pluto

• Orbit characteristics:
  • Average radius: 39.5 AU.
  • Eccentric orbit takes it inside Neptune's orbital path; eccentricity slightly greater than Mercury's (0.25 vs 0.21).
  • Orbital inclination of 17° and a significant axial tilt of 113° (spins retrograde).
• Physical characteristics:
  • Approximately 2/3 the size of the Moon, with 18% of the Moon's mass, making it less dense than the Moon.
  • Average surface temperature: 40 K (-390 °F), much colder than Antarctica.
  • Surface composition includes frozen H₂O, CO₂, N₂, CH₄, and CO.
  • Thin atmosphere consists of sublimated N₂, CH₄, C₂H₆ (ethane), and CO.
  • Icy mountains up to 3.5 km (2 mi) high, likely formed in the last 100 million years based on a lack of craters.
• Pluto features one of the youngest surfaces in the solar system, with an unexplained internal energy source, potentially linked to radioactive decay of long half-life nuclei.

Ceres

• Discovered on January 1, 1801, by Giuseppe Piazzi.
• First asteroid discovered and largest body in the asteroid belt.
• Size and Mass:
  • Diameter of about 940 km, roughly 30% the size of the Moon.
  • Contains about 25% of the asteroid mass in the belt, with a specific gravity of 2.2, between Mars (3.93) and Jupiter (1.33).
• Hypothesized to have a differentiated structure with a rocky core, icy mantle, and a surface rich in hydrated minerals (clays and carbonates).
• Detection of water vapor plumes suggests the possibility of subsurface oceans.
• Evidence of organic material found in a crater (Urnutet, 52 km in diameter) by NASA’s Dawn mission, linking to the basis of life and carbon chemistry.