Lecture 10: Formation of Solar System / Extrasolar Planets Flashcards
1
Q
The Formation of the Solar System
A
- A nebula is a gas cloud of mostly hydrogen
- It contracts due to gravity and changes the cloud into a disk
- planets form from accretion of gas and solids
- leftover material makes asteroids and comets
2
Q
Four major characteristics of the solar system that must be explained by a formation model
A
- large solar system bodies have orderly motions
- there are two types of major planets, rocky terrestrial inner planets, and gas giant outer planets
- Asteroids, comets and dwarf planets exist in various regions of the solar system
- Exceptions to these patterns
3
Q
Gravitational Collapse
A
- Solar nebula initially somewhat spherical and a few parsecs in diameter, very cold and rotating slowly
- begins to contract perhaps due to a shockwave from a nearby supernova
4
Q
Flattening of Solar Nebula
A
- As the nebula collapses, clumps of gas collide and merge
- spinning nebula assumes shape of a disk
5
Q
Solar System Motions vs Nebular Model Predictions
A
- Sun formed in the centre of the nebula
- Nuclear fusion reactions began once temperature and density were high enough
- planets form in rest of disk
6
Q
The Protoplanetary disk
A
- Star surface heats up as material accretes onto it
- Inner parts of disc get much hotter than outer parts
- Disc gets denser, particles settle to midplane, stick together when they collide, and grow into larger planetesimals
- Eventually star begins stellar wind which pushes away all gas, but solids and large bodies are left behind in debris disc
7
Q
Why are there two kinds of major planets
A
- Planet composition and size depends on temperature and materials available
- condensation temperature
8
Q
Building the Planets
A
- only rocks and metals condensed within 3.5 A.U of the sun (frost line)
- some planetesimals get massive enough to attract smaller planetesimals
- Beyond frost line, there is more mass also icy, so gas giants are created
9
Q
Solar Wind
A
- Charged particles streaming out from the sun cleared away the leftover gas
- most mass of solar nebula was in form of gas
- solar wind cannot move objects larger than small grain of dust
10
Q
Origin of the Asteroids
A
- Solar wind did not clear leftover planetesimals
- rocky planetesimals are present day asteroids
11
Q
Origins of the Comets
A
- Leftover icy planetesimals are present-day comets
12
Q
“Heavy Bombardment”
A
- many leftover planetesimals collided with newly formed planets and moons during the first 100 million years of the solar system
- This was the heavy bombardment period
13
Q
Exceptions to the Rules
A
- Some moons orbit opposite direction to their planet’s rotation if they were captured like Triton
- rotation axes are tilted because impacts “knock them over”
- some planets rotate more quickly than others because impacts “split them up”
- Earth is the only terrestrial planet with a large moon because of a giant impact
14
Q
Extrasolar Planets
A
- Haven’t been observable until recently
- Many have been found through indirect methods such as detailed study of the doppler shift of stars
- transit studies
- observation of orbits
15
Q
First discoveries
A
- 1988 discovered planet around gamma Cephei
- 1992 discovered planet around pulsar
- 1995 discovered Pegasi, first official exoplanet in orbit around a normal star
16
Q
Indirect Detection of Extrasolar Planets: Doppler Shift
A
- Stars “wobble” due to gravity form planets
- Plot of radial velocity shifts forms a wave
- wavelength tells you period size of planet’s orbit can be determine using mass of star
- amplitude tells you mass of planet
- extrasolar planets are often very eccentric, have small orbits, and large masses
17
Q
Limits of doppler technique
A
- 1-2 m/s
- velocity has to change periodically
- can detect planet at 1 A.U form 1.0 solar mass star if it has a mass greater than 33 Earth masses
18
Q
Measuring Radius of Extrasolar Planet
A
- Use of transits
- Size of planet estimated from the amount of starlight it blocks
- Only thing measurable is total brightness form the star
- transits are relatively rare
- can also calculate density of planet
- most extrasolar planets have Jovian-like densities
19
Q
Kepler - NASA mission
A
- 1235 “candidate” terrestrial exoplanets discovered by 2011
- Kepler-10b is the first rocky exoplanet ever found
- Kepler-22b is the first planet in the habitable zone of a sun-like star
- As of now, over 9185 planet candidates and 5243 confirmed planets, most discovered by transit
20
Q
Infrared emission from extrasolar planet
A
- Stars are fainter at infrared wavelengths while emission from planets is strongest in the infrared
