Dwarf Planets Flashcards

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.

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

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.

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.

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.