S14 - Formation of planetary systems Flashcards
What are terrestrial planets?
Planets with rocky cores and rocky exteriors.
What are gas-giant planets?
Planets with metallic, rocky cores and huge gaseous atmospheres.
What is the asteroid belt?
A collection of thousands of asteroids near the ecliptic plane of the Sun at distances 2-3.5au from the Sun.
What is the Kuiper belt?
A collection of cometary nuclei located roughly in the plane of the ecliptic, beyond the orbit of Neptune (>30au).
What is the Oort cloud?
An approximately spherically symmetric cloud of cometary nuclei surrounding the solar system spreading from 3,000-10,000au.
What is the snow line (for water)?
The radius of a protoplanetary disk beyond which, water condenses and dust grains become coated by an icy mantle of water. The ice coatings make dust grains sticky and significantly increase the mass that solids can grow into having.
Where is most of the mass in a stellar system located?
The equatorial plane (a.k.a. midplane) of the star.
Why do agglomorates of dust grains move towards the equatorial plane of the disk?
When grains agglomorate, they become heavier masses and the vertical component of the star’s gravity causes the dust to sediment out towards the equatorial plane of the disk.
How are macroscopic solids formed sufficiently fast to not be accreted by the star which they orbit?
If the nebula is quiescent (inactive/dormant), the dust and small particles settle into a layer thin enough to be gravitationally unstable to clumping (allowing clumping), and ∼1km planetesimals are formed.
If the nebula is turbulent, growth continues via simple two-body collisions. Attractive molecular forces can lead to ∼km sized planetesimals by coagulation. Then when size >1km, gravity becomes the dominant attractive force and mutual gravitational perturbations become important.
Describe the evolution of the protoplanetary disk.
At the beginning, there are lots of planetesimals, but as time goes on, they interact and agglomorate, causing the number of individual planetesimals to decrease until all available material is depleted. Any remaining gas is slowly accreted.
Where do Jovian planets form? Describe Jovian planet formation.
They form in the outer disk, where there are lower temperatures and thus slower moving grains. More rapid core growth due to higher solid mass availability and stickiness as past snow line. When core mass > 10 Earth masses, gravitational accretion of gasesous envelope creates a gas giant planet. Accretion stops when there is no more material available. Combination of accretion and tidal forces produced by gas giant creates a gap in the disk, removing material from the area, halting gas giant growth.
What are the most common indirect planet detection techniques?
Radial velocity technique and transit photometry.
Describe the radial velocity technique.
Doppler shifting of spectral lines due to orbital motion about a shared centre of mass with a star.
Planets can be detected by looking at the radial velocity of the star and planet around their shared centre of gravity. The presence of a planet causes the centre of mass of the solar system to shift away from the star’s centre so it starts to orbit around the stellar system’s new centre of mass. Light from star will redshift and blueshift as it orbits the centre of mass of the stellar system.
What is transit photometry?
Observing dips in brightness/luminosity from a star as a planet obscures some of its light as it passes during its orbit.
How can some young planets be seen via direct imaging with current technology?
The light reflected by planets is very faint. However, some young planets can be seen via direct imaging as their gravitational contraction causes their lost G.P.E. to be released as light that is much brighter than reflected light alone.
