Lecture 9: Small Solar System Bodies Flashcards
1
Q
Asteroids
A
- 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
2
Q
Distribution of asteroids
A
- mainly 2-3.5 A.U (main asteroid belt)
- Trojan asteroids with oprbital resonance +/- 60º
3
Q
Size and Shape of Asteroids
A
- 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
4
Q
Asteroid Compositions
A
- C type is carbonaceous
- S type is stony, made of silicates
- M type is metallic
- No major asteroid class matches the most common meteorites
5
Q
Asteroid Sample Return Missions
A
- 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
6
Q
Meteors and Meteorites
A
- 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
7
Q
Interstellar Asteroids
A
- Oumuamua was discovered by PanSTARRS in 2017 and has eccentricity of 1.199
8
Q
Comets
A
- 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)
9
Q
Comet Structure
A
- 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
10
Q
Halley’s Comet
A
- Period of 76 years
- Giotto was one of five missions to Halley’s Comet
- Returned samples from a comet back to the Earth
11
Q
Results of Missions to Comets
A
- 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
12
Q
Comet Orbits
A
- 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
13
Q
Orbit Patterns
A
- 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
14
Q
Major orbit families
A
- Kuiper Belt (30-50 A.U)
- Oort Cloud, extends to 50,000 A.U
15
Q
Borisov
A
- First Interstellar Comet
- Discovered in 2019
44º inclination and perihelion at 2.007 A.U - Spectra showed identical to Oort cloud comets
