Lecture 9: Small Solar System Bodies

Question 1

Asteroids

Answer 1

• Small rocky bodies
• No atmosphere
• orbit the sun
• discovered as a result of searches for the missing planet between Mars and jupiter
• First asteroid, Ceres (now a dwarf planet), found in 1801
• Asteroid Pallas found soon after
• Over 30,000 asteroids now catalogued
• most are in the asteroid belt with a=2-3.3 A.U and have low eccentricities
• Orbital resonances with Jupiter alter asteroid orbits
• Trojan asteroids are in Jupiter’s orbit
• A few have “Earth-crossing” orbits with perihelion less than 1 A.U
• Carbonaceous asteroids are very dark and carbon, 75% of all asteroids
• Siliceous, 15% of all asteroids
• Metallic, iron and rarest type

Question 2

Distribution of asteroids

Answer 2

• mainly 2-3.5 A.U (main asteroid belt)
• Trojan asteroids with oprbital resonance +/- 60º

Question 3

Size and Shape of Asteroids

Answer 3

• Reflected sunlight depends on size
• Infrared emission depends on total cross-sectional area
• These things give estimate to size and albedo
• Rotating asteroids often vary in brightness and this sets limits on shapes
• Hubble Space Telescope imaging
• radar ranging data

Question 4

Asteroid Compositions

Answer 4

• C type is carbonaceous
• S type is stony, made of silicates
• M type is metallic
• No major asteroid class matches the most common meteorites

Question 5

Asteroid Sample Return Missions

Answer 5

• Hayabusa 2 was launched in 2014 to Ryugu
• Returned to Earth in 2020 with 200 carbon-rich millimeter-size grains and some finer materials
• Origins Spectral Interpretation Resource Identification Security Regolith Explorer (OSIRIS-Rex) launched to Bennu in 2016
• Carbonaceous and water rich
• Highest risk to earth

Question 6

Meteors and Meteorites

Answer 6

• A meteor falls toward Earth
• A meteorite falls and hits the surface of the Earth
• Meteors mostly the same as asteroid types
• Largest meteorite is 2000 kg
• Organic materials found in some meteorites
• Meteor showers are due to Earth passing through debris left behind from a passing comet
• Yucatan crater timing coincides with death of dinosaurs
• thousands hurt from Chelyabinsk meteor 2013
• Crater size correlates with impactor size, bigger the impactor size, less likely it is to happen

Question 7

Interstellar Asteroids

Answer 7

• Oumuamua was discovered by PanSTARRS in 2017 and has eccentricity of 1.199

Question 8

Comets

Answer 8

• Distinguished by their appearance, coma, tail
• bright ones are not very common
• virtually all have very eccentric orbits
• complicated structure that changes with time
• relatively low mass
• most of mass is in form of ices (water and carbon dioxide)

Question 9

Comet Structure

Answer 9

• Nucleus is the “dirty snowball”, frozen with dust and small rocks mixed in, 10’s of km in length, much more fragile than large rock
• A coma is formed as the comet approaches the Sun as ices begin to vaporize
• Two or more tails form as the material in the Coma is accelerated by solar wind and light pressure form the sun

Question 10

Halley’s Comet

Answer 10

• Period of 76 years
• Giotto was one of five missions to Halley’s Comet
• Returned samples from a comet back to the Earth

Question 11

Results of Missions to Comets

Answer 11

• Nuclei are very dark and very small compared to size of coma and tail, potato-shaped
• Dust is not just silicate but contains many CHON particles
• Particle grains condense at high temperatures
• Heavy water abundances unexpected
• Comet appearance changes with distance from the Sun

Question 12

Comet Orbits

Answer 12

• Several classes of comets, just from properties of their orbits
• Main difference is that some repeat and some don’t
• parameters used to differentiate are semi-major axis, period, inclination, eccentricity, perihelion distance

Question 13

Orbit Patterns

Answer 13

• Periodic comets have two types, small inclination with full range of eccentricity, and full range of inclination with high eccentricity
• Non-repeating comets have full range of inclination and are completely random, come form very large distances and form all directions

Question 14

Major orbit families

Answer 14

• Kuiper Belt (30-50 A.U)
• Oort Cloud, extends to 50,000 A.U

Question 15

Borisov

Answer 15

• First Interstellar Comet
• Discovered in 2019
  44º inclination and perihelion at 2.007 A.U
• Spectra showed identical to Oort cloud comets

Question 16

Dwarf Planets

Answer 16

• massive enough to be spherical
• is not a satellite
• ha snot cleared its neighborhood
• Examples are ceres, Pluto, Eris, Sedna, Makemake, Haumea
• Densities are in between terrestrial planets and giant planets
• Moons are common

Question 17

Pluto

Answer 17

• Much more elliptical and inclined than any major planet
• closer to sun than Neptune for 20 years of its 248 year orbit
• Orbital resonance keeps them from colliding
• Charon is one of Pluto’s 5 moons and orbits Pluto every 6.4 days
• Charon less dense than Pluto
• Charon could be formed form large impact
• Small amount of nitrogen in atmosphere but will freeze out in next 100 years