Lecture 30: Pluto and the Kuiper belt

Overview of Pluto and the Kuiper Belt

• Pluto is classified as a Kuiper Belt object (KBO).

• The Kuiper Belt contains many small celestial bodies beyond Neptune, mostly seen as faint specks of light.

Discovery of Pluto

• Neptune's mass was originally thought too small to account for Uranus' orbit deviations.

• In 1906, Percival Lowell initiated the search for a theoretical "Planet X".

• Clyde Tombaugh discovered Pluto in 1930 by comparing thousands of photographic plates for movement.

• The search for Pluto was based on false assumptions.

Characteristics of Pluto

• Size:

  • Pluto's radius: $1153 ext{ km}$

  • Triton's radius: $1353 ext{ km}$

• Density:

  • Pluto: $ext{~2.0 g/cm}^3$

  • Triton: $2.06 ext{ g/cm}^3$

• Composition:

  • Similarities to Triton, thought to be captured from Kuiper Belt.

Measurement of Pluto's Mass

• The mass of Pluto was first measured after the discovery of its moon, Charon, in 1978.

• Knowing the mass of a celestial body is crucial for understanding its structure and evolution.

• By 2005, Hubble discovered two additional moons: Nix and Hydra.

Research Limitations and New Insights

• Prior to the New Horizons mission, limited information about Pluto's surface was available.

• Observations showed that Pluto's surface varies in brightness and color, suggesting distinct terrains.

• Pluto's reddish color likely results from organic molecules formed from UV exposure to methane and ammonia ice.

Internal Structure of Pluto

• Notable composition: approximately 50-70% rocky and 30-50% icy materials.

  • Ice types present: water ice, $ext{CO}<em>2$ ice, $ext{CO}$ ice, and $ext{N}</em>2$ ice.

• Layers of Pluto:

  • Layer 1: Frozen nitrogen

  • Layer 2: Water ice

  • Layer 3: Rock and iron

Heat Generation within Pluto

• Radioactive decay of elements like potassium, uranium, and thorium generates internal heat.

• Heat may cause melting in a potential subsurface ocean beneath Pluto's icy mantle.

Interpreting Geological Features

• Predictions based on the presence or absence of a subsurface ocean:

  • If no ocean exists:

  • Should have an equatorial bulge and extensile features on the surface.

  • If an ocean exists:

  • No bulge and compressional features evident (e.g., wrinkle ridges).

New Horizons Mission

• Launched in 2006 and flew past Pluto in 2015, providing significant new data.

• The spacecraft's journey to Pluto involves a nearly 4.5-hour light travel time for communication.

• New Horizons has redefined our understanding of Pluto and its environment.

Pluto's Atmosphere

• Analysis of atmospheric thickness through sunlight refraction was conducted during the New Horizons flyby.

• Pluto's atmosphere primarily consists of nitrogen and is more complex than initially expected.

Sputnik Planum

• A large area of Pluto's surface showing vast nitrogen ice with interesting geological structures.

• Observations suggest soft ice behavior with convective down welling.

Geology of Charon

• Charon exhibits canyons resembling grabens, indicating historical crustal stresses.

• Surface features suggest that if Charon had liquid water, Pluto possibly did too.

Shape Implications

• Pluto's nearly spherical shape (like a basketball) suggests a potential subsurface ocean versus an onion-like layered structure.

• The absence of a historical tidal bulge suggests that Pluto may be soft or liquid internally, allowing it to reform into a sphere.

Resolution of Pluto's Status

• The discovery of numerous similarly sized KBOs led to Pluto's demotion from "planet" to "dwarf planet" status.

  • Eris, a significant KBO, has a diameter of approximately $2300 - 2400 ext{ km}$.

Gravitational Influences in the Kuiper Belt

• Predictions of further celestial bodies ("Planet Nine") influencing KBO orbits have emerged as scientists explore unexplained orbital patterns.

• An undiscovered planet could have a mass exceeding ten times that of Earth, influencing these distant objects.

Upcoming Topics

• Future discussions will focus on extrasolar planets and related phenomena.

• Additional reading: http://en.wikipedia.org/wiki/Extrasolar_planet