Section 6 - Dwarf Planets and small Solar system bodies

Question 1

• What are asteroids, where are they found, and what is their composition like?
• What is the composition of Kuiper-belt objects?
• What are dwarf planets?
• What are comets?

Answer 1

• Small solar system bodies in the inner solar system, mainly found in the asteroid belt between Mars and Jupiter. Volatile poor.
• Volatile rich.
• Largest examples of each including Ceres (asteroid belt) and Pluto (Kuiper-Belt).
• Volatile rich often with highly eccentric orbits, originating much further out in the hypothetical Oort Cloud.

Question 2

• What prevented the formation of a planet in the asteroid belt?
• What are the 3 main types of asteroids?

Answer 2

• Probably strong orbital resonances with Jupiter.
• C-type - Dark carbonaceous surface composition, the most common type
  S-type - Bright silicaceous surface composition, about 17%
  M-type - mainly metallic composition.

Question 3

Ceres:

• Ceres is the largest _______ and the only _____ ______ in the asteroid belt. The surface composition of Ceres makes it a ______ ______. Has an icy interior with fresh ice deposited from below. Ice is short-lived on the surface due to _______.
• Density is ________, placing it between the rocky composition of the ________ _____ and the icy moons of the ____ _____.

Answer 3

• Asteroid, dwarf planet, C-type asteroid, sublimation.

- Intermediate, terrestrial planets, gas giants.

Question 4

• Why are C-type asteroids a priority for collecting material from?
  Meteorites:
• Most meteorites are ______ which contain spheres of minerals and metals called _______. They are associated with ______ asteroids. These have not remelted so must be from small undifferentiated bodies. They are therefore primitive material that dates from….
• Some rocky meteorites lack chondrules, suggesting later melting are called _______ . Associated with _____ asteroids. Where are these thought to be from?
• There are also some pure iron meteorites from the _____ of differentiated bodies. These are associated with _______ asteroids.

Answer 4

• They are expected to contain unprocessed material from the formation of the Solar system.
• Chondrites, chondrules, C-type, formation of the Solar system.
• Achondrites, S-type, From the mantle or crust of a differentiated body since they are deficient in iron.
• Cores, M-type

Question 5

Describe the composition of chronditic meterorites.

Answer 5

• Composition similar to Earth, dominated by Fe, O, Si, Mg. Abundances of most elements match those in the Sun apart from Lithium which is overabundant since it is burnt in the Sun. Deficient in volatiles, consistent with formation in the warm environment of the inner solar system.

Question 6

• Describe the interior of Pluto.
• Has a stable orbit at the edge of the Kuiper belt despite crossing with ______ because of a _______ resonance that keeps them apart at perihelion.
• What does the Kuiper belt contain? The Kuiper belt is aligned with the ecliptic plane of the solar system.

Answer 6

• Density of Pluto suggests interior dominated by water ice, with a rocky core and a water ice mantle. Similar composition to that of the icy moons of the ice giants.
• Neptune, 3:2
• At least 3 other dwarf plants, debris from outer protoplanetary disc, origin of short-period comets.

Question 7

• Comets have two tails; what are they?

- Where do long-period comets originate from?

Answer 7

• Ion tail: Consists of ionised gas that is swept directly away from the Sun by the solar wind.
  Dust tail: Consists of solid particles in Keplerian orbits around the Sun that are modified by outward radiation pressure.
• The Oort cloud

Question 8

Origin of water on Earth:

• See a gradient in D/H ratio in the outer Solar system, with comets having _____ D/H. Where and why did this gradient arise?
• Why is water not thought to have been delivered to Earth by comets?
• How is water thought to have been delivered to Earth? What is the evidence for this?

Answer 8

• Enhanced. Arose in the protoplanetary disc because at low temperatures water ice forms preferentially with D, and D/H ratio in ice is enhanced. In warmer regions, water is in the gas phase and exchanged D with hydrogen gas, maintaining an equilibrium.
• Earth has enhanced D/H ratio but it is lower than that of comets.
• By asteroids. Calculations of the mass of H2O on large asteroids such as Ceres, and the mass of H2O on Earth have shown that the accretion of seven Ceres-like asteroids would be sufficient to deliver the Earth’s water.